Proceedings of the Geological Society of South Africa, 40, xxiii-li

Johannesburg, the Golden City of Africa, has just completed the celebration of its 50th anniversary or Golden Jubilee. The Empire Exhibition, with all its splendour and magnificence, undoubtedly was the crowning achievement of these celebrations. Among the numerous exhibits of the latter the mineral industry took up a very prominent place. The golden column in front of the Chamber of Mines pavilion symbolised in a very impressive way the dominating influence of gold not only in the astounding growth of the city, but also in the Union as a whole. Johannesburg, in the literal sense of the word, has been built on a foundation of gold. And this foundation has been carried down to such depths that in time it has come to support the entire economic structure of the Union. The truly amazing growth of Johannesburg and the Rand within a period of 50 years from bare veld, supporting less than a hundred people, to a great industrial centre, sustaining a population of over half a million, represents one of the most astounding episodes not only in mining development, but also in the political and economic expansion of a whole sub-continent. Whether one wishes to credit the capacity for organisation of the financiers and great captains of industry, the enterprise of large numbers of brilliant engineers, or the foresight of politicians, alive to the need for great industries in developing a new country, for the co-ordination of the factors that have accomplished the result, one cannot conceive of such a consummation without the existence of truly large ore-bodies, of the pioneer prospectors, whose perseverance led to their discovery, and of the miners who bring the ore to the surface from a maximum depth of more than 9,000 feet. And in recent years, when the exhaustion of the mines at least in certain portions of the Rand, while by no means imminent, yet became a factor to be reckoned with in the not distant future, modern prospecting parties, aided by geophysics and the diamond drill, have extended the boundaries of the Rand to the west far beyond its original limits, and have also helped considerably to increase mining activity on tile Ear East Rand. At the same time, guided by the research of brilliant engineers the mining houses are expending vast sums of money on ventilation and air cooling, and already now ore-recovery has been rendered possible at depths hitherto unheard of in the history of mining.

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Transactions of the Geological Society of South Africa, 41, 1-36

A description is given of a coastal area north of Durban. New data are presented on the pre-Quaternary formations. The possibility of there being two old Granites in the Umhloti valley, the transition between the Dwyka tillite and the Lower Ecca shales, and the differentiation of certain of the Karroo dolerites on the basis of their lithology and metamorphic effects are discussed. Evidence is presented which indicates that the calcareous coastal sandstones at Umhloti Beach, the presumed equivalent of the Durban Bluff beds, are aeolian in origin; criteria being given which enable consolidated sand dunes to be specifically recognised. The mechanism of the pigmentation of the coastal red and brown sands is considered and the results of heavy mineral separations tabulated. Evidence is discussed which suggests that the eastern coast of South Africa is a fault-line coast. Raised beaches and other evidence of Pleistocene sea level oscillations and a peculiar type of dune ridge are described. An account is given of the Talc and Kaolin deposits at Ndwedwe.

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Transactions of the Geological Society of South Africa, 41, 103-108

A twenty-foot thick dolerite sill at Aliwal North is described. The direction of emplacement has been deduced from distortions preserved in the sandstone floor and from the shape of a detached sandstone block. Sub-surface alteration of the dolerite is discussed, and analytical data given. Volumetric determinations of olivine percentages indicate differentiation in place. Colloidal structures in quartz veins traversing the sandstone floor are described.

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Transactions of the Geological Society of South Africa, 41, 109-111

Molengraaffite from the Pilansberg is shown to be identical, chemically and optically, with lamprophyllite, the name of which has priority. Attention is drawn to the presence of a mineral agreeing with lovchorrite in specimens of foyaite from the Pilansberg, and also to the geochemical and petrographical similarity of the alkali complexes of the Kola Peninsula and the Pilansberg.

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Transactions of the Geological Society of South Africa, 41, 113-172

In central Africa the peneplanation, uplift, fracturing and erosion of the Tertiary period were preceded by comparable events in the later Jurassic and Cretaceous which still influence to a greater or less extent the topography of the present day, and it is accordingly possible to distinguish in this region the following features: -
(1) A high-level late Jurassic peneplain, which cuts across the post-Karroo boundary faults;
(2) a low-level surface of erosion, usually peneplained, overlain by early Cretaceous sediments and re-exposed in part in the later Tertiary and post-Tertiary;
(3) a great post-Cretaceous peneplain uplifted in the Miocene and subjected to extensive rift-faulting in the east and warping in the west, and
4) a lower end-Tertiary peneplain developed on the softer rocks.
A review of the main physiographical features of southern Africa suggests that the above conclusions are applicable to an appreciable extent to this region also. The presence of high-level post-Karroo but pre-Miocene peneplain remnants shows that the production of the great plateau of southern Africa took place in not one but two main stages and there is evidence for deep marginal erosion and for the formation of great inland valleys in the early Cretaceous prior to the peneplanation and uplift of the Tertiary.
The following features are discussed in the light of these observations: the Cape Ranges, the Great Escarpment, the scarp of the Southern Rhodesia plateau, the Limpopo, Sabi and Orange River valleys, the De Kaap valley, the Barberton Mountain Land, and the Lebombo flats. The main post-Karroo boundary faults are older than the late Jurassic peneplanation, and they were succeeded by new systems of faults in, probably, the early Cretaceous and in the mid-Cretaceous. The disposition of the late Jurassic peneplain remnants on the rim of the upraised Tertiary peneplain, and the deep marginal erosion of the early Cretaceous, suggest that the uplift of the older peneplain was accentuated around the margins; if so, this movement is contrasted with the irregular up-doming of the younger peneplain, which was accompanied by seaward tilt of the exposed margins. The physiographical development of southern Africa and of other parts of Gondwanaland is discussed in relation to the Theory of Continental Drift.

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Transactions of the Geological Society of South Africa, 41, 173-174

A sodalite-rich syenite from the Pilansberg is described for the first time. Attention is drawn to its attractive ultra-violet fluorescence and the properties of some of the constituent minerals are given.

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Transactions of the Geological Society of South Africa, 41, 175

We have heard a good deal recently of the sands occurring on the Natal coast, and members may be interested to know something of their actual composition. Many years ago two samples were examined and more recently very careful estimations were made of the constituent minerals. As sands are well known to change much in composition especially in relation to the heavier and lighter constituents, and the samples of these sands handled are no different in this respect, no details will be given of the proportion of light and heavy minerals. It has been found to vary between 5 and 90%. There is, in the samples examined, little variation in the proportions of the heavier minerals present and as these alone are of economic interest details will be confined to them. Ilmenite is by far the most important constituent, and values varying between 79% and 85% have been obtained. The average composition of three samples is given in column I and the most accurate analysis made in column II.

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Transactions of the Geological Society of South Africa, 41, 177-191

The paper describes the general characters of the Black Reef Series in the Klerksdorp and Randfontein areas and gives an account of the petrographic characters of the various rock types present. The conglomerates are described in detail with regard to both their primary and secondary constituents and the possible hydrothermal origin of the pyrite and gold in well mineralised localities is stressed.

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Transactions of the Geological Society of South Africa, 41, 193-198

A rapid traverse in a little-known area in the south-eastern part of S. Rhodesia resulted in the discovery of rhyolites of the Lebombo type and a sandstone probably of Cretaceous age. Chemical analyses of the interesting rock types met with are appended.

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Transactions of the Geological Society of South Africa, 41, 199-204

The paper supplies additional information on matters dealt with in the author's previous paper under the same title, viz.: - (i) A new rock analysis; that the red Granite described before by the author as "post-Pongola Granite", and also some further observations on its tectonics; (ii) a description of a basal conglomerate, and (iii) an account of a lepidolite-rubellite-pegmatite.

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Transactions of the Geological Society of South Africa, 41, 205-210

Six fragments of a meteorite which fell in Zululand on September 23rd, 1936, have been examined and an analysis made. The material proves to be an achondrite rather poor in magnesium and rich in calcium, resembling most closely eucrite in mineralogical and chemical composition.

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Transactions of the Geological Society of South Africa, 41, 211-224

Clear sections of the beds between the Karroo basalts and the Kalahari sand at the Victoria Falls are described. It is shown that the silicification of the basal limestone was completed before the deposition of the overlying beds, contrary to the prevailing view of the date of this process. After a break following the period of intense silicification, deposition under more humid conditions was resumed. A rubble bed then indicates a land surface with disintegration and some erosion of the bed beneath. The rubble contains some chippings which may be of human workmanship. Undisturbed Kalahari sand up to 40 feet thick caps the section. The beds can be correlated with Passarge's stratigraphy in the Kalahari, and a broad correlation can be established with the succession of events described by A. C. Veatch in the Belgian Congo and Angola.

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Transactions of the Geological Society of South Africa, 41, 225-248

A detailed description of the Upper Witwatersrand System at Randfontein is presented, and attention drawn to the presence of a dolomitic horizon in the Kimberley shales. It is pointed out that possibly as many as 300 separate conglomerate bands are represented, of which 15 have been mined for gold. The importance of recognising groups of quartzites is stressed, and two important markers, viz.: the Square Pebble Zone, and the Boulder Marker are described. These latter have been used at Randfontein for many years with great success. The recognition of these markers in other mines leads the authors to believe that they may be applicable from the Central Rand westwards, and are likely to be of value even as far afield as the Free State. Owing to the well known difficulty of recognising shale horizons in the Witwatersrand System, it is emphasised that the discovery of these markers immediately above a shale horizon renders the determination of Jeppestown Shales certain. Some experimental stream table work is also described, and following certain significant observations made at Randfontein, some suggestions are offered as to the conditions of deposition of the Upper Witwatersrand System.

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Transactions of the Geological Society of South Africa, 41, 249-272

The paper gives an account of the gold deposits of the Central Murchison Range. The structural features in the area and their origin are discussed. Three different types of ore bodies are recognised and described. They are regarded as having been formed during a single period of mineralisation, under conditions of slowly decreasing temperatures.

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Transactions of the Geological Society of South Africa, 41, 37-40

Around the Molen River, 23 miles from Camfer station in the Cape Province, about 72 square miles of country were mapped. Topographically the area may be divided into a southern half or the Long Kloof and a northern half or the Kammanassie Valley.
Long Kloof is bounded on the south by the Outeniqua Mountains and a range of hills about 500 feet high separates it from the Kammanassie Valley. The floor of the Long Kloof is fairly level except where it is interrupted by occasional rows of flat-topped eminences 120-250 feet high which are aligned in a N. 40 deg. E. direction. At the same height level strips of ground bevel the sides of the Kloof.
The Kloof has no river of its own. Streams drain instead across it to pass through deep gorges in the fairly even-crested hill range between the Kloof and the Kammanassie Valley.
In the Kammanassie Valley, which the Kammanassie Mountains bound on the north, there are also a few isolated flat-topped hills and traces of level stretches or terraces at the same height along the valley sides. In other respects this valley differs topographically from Long Kloof. A characteristic feature is an extensive flat south of the Kammanassie river into which the river and its tributaries have cut deep down to about 300 feet and more. This flat, which may be termed an asymmetric erosion terrace, lies at the same altitude as the floor of Long Kloof.
From the north bank of the river the ground rises steeply to, a level terrace 600 feet above the river bed. This terrace, rising slightly towards the foot of the Kammanassie Mountains, corresponds in altitude and character with the terrace on the hill slopes along the south of the valley. The Cape system, represented in the area under consideration by the Table Mountain series and the lower shales of the Bokkeveld series, is intensely folded. Overfolding to the north along the southern flanks of the Long Kloof and Kammanassie Valley, respectively, is responsible for the Bokkeveld shales dipping southwards under the older Table Mountain series, whereas in the northern flanks of both valleys the succession is normal with the Table Mountain series dipping southwards at fairly steep angles underneath the Bokkeveld beds. This general structure is complicated locally by sharp minor folding.
A puzzling feature at first was the apparently great thickness of the Bokkeveld shales compared with that of the lowest shale band of the series elsewhere. The effect of dragfolds, the presence of which is suspected, could account for such a thickening of the shales. The Bokkeveld series as an incompetent mass probably yielded to differential movement between the competent sandstone masses of the Table Mountain and the Witteberg series during the major folding of the Cape system. From the evidence it would appear that the beds of the Cape system were folded by pressure from the south. The development of the physical features were largely controlled by the structure of the area and the lithological character of its rocks. The resistant Table Mountain Series build the mountains and hills while remnants of the Bokkeveld beds are preserved in the synclinal valleys. A striking feature of the area is the high-level gravels. They cap the flat-topped hills rising from the valley floors, and are also on the terraces along the slopes of the hills which border Long Kloof and Kammanassie Valley. The high-level gravels on Long Kloof and those in Kammanassie Valley lie at 200 to 300 feet above the valley floors and are considered to be of the same age. The gravels consist of well-rounded boulders and pebbles of quartzites derived from the Table Mountain series and cemented together by secondary silica. They are of fluviatile origin. In the Kammanassie Valley it was found that besides sloping inwards to the centre of the valley they also have a definite slope to the west. Several interesting features, as, for example, the absence of rivers running down and not across Long Kloof, the absence of the gravels in one deep gorge but the presence of their remnants in another gorge, that of the Ganzekraal River, through the same divide of Table Mountain series between Long Kloof and Kammanassie Valley, make it possible to reconstruct the former river system. From this reconstruction it appears that in the Long Kloof, including Little Long Kloof, some rise in the ground existed which acted as a watershed, that west of this watershed the ground was drained by the Ganzekraal River with a southern tributary in Little Long Kloof; that east of this watershed there was an east-flowing river, forming the head of the Keurbooms River, and having, as a consequent tributary, the Huis River with its source in the divide between Long Kloof and Little Long Kloof, and another tributary tapping the latter. Greater corrasive power by the Kammanassie River and its tributaries, such as the Molen River, aided by an elevation of the land, resulted in piracy on the above-mentioned streams. The Molen River, a consequent antecedent stream, cutting through the T.M.S. divide captured the head-waters of the Keurbooms River. The present Diep River entering the Molen River thus represents a former portion of the Keurbooms River with the direction of flow reversed. Similarly the Huis River cut through to the Little Long Kloof and beheaded the tributary there of the Ganzekraal River. The elevation of the land is regarded as having occurred during post-Pleistocene times.

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Transactions of the Geological Society of South Africa, 41, 41-82

The paper is a study in regional geology of virgin ground. A representative area of approximately 90 square miles is mapped and described in some detail. The paper postulates (a) the existence of two granites of widely different age, a pre-Pongola body (the "older granite and gneiss") and a post-Pongola massive red granite with "Bushveld granite" similarities; (b) the non-intrusive character of the "older granite" into the Upper Pongola Beds; (c) the probability of a correlation of the Upper Pongola Beds with those of the Witwatersrand System. An isolated patch of Dwyka tillite is described and occurrences of "Karroo Dolerites" are given petrographic attention.

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Transactions of the Geological Society of South Africa, 41, 83-102

The Gwanda gold belt in Matabeleland, Southern Rhodesia, comprises ancient metamorphic rocks exposed over an area some 45 miles long in an east and west direction by, roughly, 10 miles wide, though considerably broader in the western than in the eastern half. It is surrounded by granitic rocks, largely foliated, forming portions of vast batholithic masses. Near its eastern end, where the width notably decreases, an interesting igneous complex, here named the Colleen Bawn complex, has intruded the metamorphics, apparently by forcing them aside and causing much disturbance. In close proximity to this complex there is a mass of crystalline limestone displaying field relations that are hardly compatible with an aqueous origin such as is normally assumed for this type of material. Rather do they point to a magmatic origin.
The Colleen Bawn complex includes as its major members an adamellite, a quartz-bearing monzonite, and an olivine-monzonite, to a large extent unfoliated. While these rocks were probably emplaced after the major deformation of the rocks of the schist belt consequent on their invasion by the batholithic magma, it is believed, on petrographic and chemical grounds, that the interval was not great and that the rocks of the complex are comagmatic with those of the batholiths. The petrographic evidence also suggests that a good deal of contamination has taken place in the production of some of the rock types observed.

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Proceedings of the Geological Society of South Africa, 41, xxv-xliii

It would not be true to say that mining development in South Africa has always followed or has been dependent on the results of geological work. There is, however, increasing evidence that the importance, or from a Geologist's point of view, indispensability, of the science of geology to mining development is realized. This is perhaps because mining development is done today on a truly scientific basis.
In South Africa the history of mining development is so largely bound up with that of gold and diamonds and, perhaps, coal, that the attention being paid to deposits of other minerals and metals is apt to be forgotten. Even in the earliest unrecorded period of mining development represented by the many ancient workings in the Northern Transvaal and adjoining territories further north, there is evidence that not only gold but also the base metals, copper, tin and iron were excavated and smelted at a large number of localities. In the present period of European occupation of what is today the Union of South Africa attempts at the exploitation of base metals ores antedated the discovery and mining of gold and diamonds by many years.

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Transactions of the Geological Society of South Africa, 42, 1-14

Faults in the Pretoria Series can be determined in the usual manner by observation of displacements of certain distinctive horizons. The absence of such markers in the Dolomite Series necessitates the application of more indirect methods for the mapping of faults in areas underlain by this formation. Such methods include interruptions of outcrops, detailed observation of bends and drags, and, in the absence of outcrops, the distribution of quartz veins (parallelisms of quartz veins to faults and also the difference in the number of quartz veins in separated fault blocks). The trend of a fault can also be determined by careful mapping of the frequency of joints accompanying the fault. These various methods are explained and their application illustrated by examples.

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Transactions of the Geological Society of South Africa, 42, 123-219

New data are presented on the Stinkfontein, Kaigas and Numees Series in Namaqualand. The former is divided into three groups. The above-named three series were invaded by the Kuboos granite and the metamorphic effect is described. The Kuboos Batholith, with an approximate area of 200 square miles rises to a great height and reveals a serial change vertically in: (a) Texture, (b) Chemical composition, (c) Composition of perthite phenocrysts, and (d) Anorthite content of the plagioclase in the matrix. Some of the primary and platy flow structures in the granite were mapped together with fracture systems like shears and cross-joints.
The strike directions of quartz veins, aplite and lamprophyre dykes associated with the batholith were also mapped together with cross-joints in the adjoining sediments. The direction of orogenic thrust was deduced. A detailed petrography of the granite and dyke-rocks is given. The original height of the batholith and the volume of granite intruded above a certain level are calculated from textural, chemical and horizontal-sectional variations. Evidence is discussed which suggests that, (a) the variation of composition in the batholith was not caused by gravitative influence on phenocrysts; (b) sloping was at least one of the methods of emplacement. Average compositions of the Kuboos, Cape and Bushveld granites are compared. Finally, a discussion on the mode of intrusion of the batholith is presented.

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Transactions of the Geological Society of South Africa, 42, 15-18

The green colour of the quartzites is shown to be due to a chromiferous hydro-muscovite in which the chromium has been derived from chromite grains in the rock. The properties and chemical composition of the mica are given.

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Transactions of the Geological Society of South Africa, 42, 19-22

During an excursion last June (1938), I found what at first glance appeared to be the well-known ventifacts or "kanters". They were encountered, however, under peculiar conditions, namely, in the bed of the Breede River, just upstream of the bridge on the road between Worcester and Villiersdorp. I thought at first that they were ventifacts which had been gradually added to the bed-load of the stream during periods of flood. After a thorough search on both banks, which, at intervals have wind-blown levees, none were found, and seeing that these facetted stones were obviously derived from a spread of unconsolidated stream-gravels, which flank the main channel for a considerable distance upstream, special attention was given to their location with regard to stream-flow with the following results:-
(a) Throughout the entire length of the Breede River no other locality yielded similar products.
(b) The facetted pebble-type is restricted to the flanks of the main current where infrequent hollows or none occur, and where the depth of water does not exceed 8 inches.
(c) Large boulders showing crude facetting on upstream faces are found at greater depths, but only where they directly face an unhampered floor- or bed-current, and are, in addition, encircled by sand.
(d) The smaller and better-shaped pebbles are obviously restricted to a tenacious bottom (sand, covered with a thin spread of after-flood silt), or where wedging holds the pebbles in place.
I had the opportunity of watching the peculiar facetting process in action. In a depth not exceeding eight inches, sand grains of one mm. (approx.) size were driven at considerable speed to a height of two inches suspension, and where these encountered obstacles of a height greater than the suspension level they were driven, firstly against, and then around these obstacles. The lee surfaces of the pebbles form natural eddies and the sand grains shift by rolling over the downstream surfaces.

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Transactions of the Geological Society of South Africa, 42, 23-34

The copper-bearing pegmatite at the Khan mine, South-West Africa, is one of the few known pegmatites that contain enough of the base metal to warrant extraction on a commercial scale. The dyke cuts through quartz syenite-gneiss, the parent body, and is mineralized over a length of 1,100 feet by pyrite, sphalerite, chalcopyrite, bornite and chalcocite. Except for the zeolites, some calcite, quartz, gypsum and kaolin, these sulphides were the last minerals to be introduced, replacing the preceding silicates in strikingly clear fashion.
The pegmatite is also remarkable for its content of lime silicates, suggesting assimilation of limestone from the roof region which is now removed by denudation. The pegmatitic liquid dissolved enough lime to deposit diopsidic pyroxene (sahlite), sphene and apatite towards the end of crystallization of simple pegmatite; then followed high-temperature replacement by sahlite, hornblende, apatite and phlogopite, accompanied by albitization. At moderate temperature sericitization and propylitization began before the introduction of copper sulphides. Some pegmatites of the same minerogenetic province show a lateral gradation from igneous rock to hydrothermal quartz-sulphide veins, at the Khan mine the entire hydrothermal cycle is super-imposed upon the pegmatite body itself.

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Transactions of the Geological Society of South Africa, 42, 35-46

This paper deals mainly with the microscopic characteristics of the gold, carbon and metallic sulphides in the Black Reef. The association of carbon and gold is contrasted with that of pyrite and gold. The hydrothermal origin of at least a portion of the gold is stressed.

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Transactions of the Geological Society of South Africa, 42, 47-56

A general description is given of the stratigraphic succession in the southern Zoutpansberg and the geology of Bosch is treated in some detail. On this farm copper occurs both as primary chalcopyrite in altered andesitic lavas and as chalcocite-covellite-cuprite-malachite-azurite replacements in quartzitic grits. These latter deposits occur sporadically in fracture zones int eh quartzite immediately adjacent to one of a number of W.N.W.-E.S.E. striking faults and the microscopic and other data presented suggest that they are low temperature replacements formed by ascending solutions. The economic possibilities are also discussed.

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Transactions of the Geological Society of South Africa, 42, 57-82

The paper deals chiefly with the petrography and variation in the composition of the rhombic pyroxenes of the Critical zone. The new data are used in discussing the origin of the pyroxenites and seams of chromitite.

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Transactions of the Geological Society of South Africa, 42, 83-122

This paper discusses the sub-surface exploration of the Far East Rand which was carried out during the period from 1933 to the end of 1936. To general area under discussion lies between Springs and Bethal, in the Transvaal, and particularly centres around and to the south-east of the village of Leslie, some thirty miles east of Springs. This area is on the watershed between the Limpopo and Vaal rivers, at an average elevation well above 5,000 feet. It consists of the rolling grass-land so characteristic of to South African high veld, where underlain by Karroo rocks.
The paper is designed to describe the methods employed in organizing and conducting the investigation, and to correlate and describe the sub-surface geology revealed. It must be understood in this connection that the provisional summary of the geology given in Part IV is by no means conclusive. Constantly during the course of the investigation geological ideas were revised as new facts came to light. This summary gives the correlation that satisfied most of the facts at the time active exploration stopped. It is also true, however, particularly as regards local correlation between boreholes, that many of the conclusions are confirmed by sufficient evidence to be wholly acceptable. Part III indicates to what extent this is true.
The paper assumes familiarity on the part of the reader with the general geology and stratigraphy of the Witwatersrand area. The following introductory review of the distribution and structure of the major geological systems is given as a general statement of the original problem.

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Proceedings of the Geological Society of South Africa, 42, xxvii-xlv

Having selected the dykes of the Transvaal for my address, I realize that I do not possess sufficient information to deal adequately with so large a mass of subject matter. I can only honour the existing custom by describing as many examples as possible from all the types of dykes at present known in the Transvaal. In grouping these dykes one could do so in one of several ways, e.g., on a geographical, geological, petrographical or chronological basis, but with our present knowledge it is either impossible or inadvisable to use the same criterion throughout. It is proposed to group the dykes of the Transvaal as follows:-
I. Basic dykes in the gabbroidal rocks of the Bushveld Complex.
II. Basic dykes in the Old Granite, Pietersburg District.
III. Dykes in the Eastern Transvaal.
IV. Post-Karroo dykes.
V. Dykes of the Pilansberg and East Rand Systems.
Contents:
Basic dykes in the gabbroidal rocks of the Bushveld Complex.
Basic dykes in the Old Granite, Pietersburg district.
Basic dykes in the Eastern Transvaal.
Dykes of the Pilansberg and East Rand Systems.
Discussion of data pertaining to the dykes of the Pilansberg and East Rand Systems.

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Transactions of the Geological Society of South Africa, 43, 1-8

Data on the nature and mode of occurrence of the carbon, sphalerite and gold are given and properties of the pyrite are described. Silicification is briefly discussed. A modified placer theory of the origin of the gold is supported.

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Transactions of the Geological Society of South Africa, 43, 109-126

In the introductory chapters the tectonic alignment of the Virunga volcanoes, their age and the nature of their lavas are briefly discussed. Then follows an account of a visit to the Sake lava flow and an ascent of Nyamlagira volcano in July, 1939. A detailed description of the interior of the crater and the new centre of eruption outside the crater is given, supplemented by a summary of changes within the crater since 1929 and the various initial phases of the recent eruption as observed by an eye-witness, R. Hoier, Chief Conservator of the Parc-National Albert, within which the volcano is situated.

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Transactions of the Geological Society of South Africa, 43, 127-142

This paper deals with an intrusion of altered dolerite, which differs from many in its shape and its origin. Its shape is a stepped dome, which never reached the ground surface, and the space occupied by the intrusion is that left by the sinking of the rocks inside the dome. On the dyke phases of the intrusion the strata show a normal vertical displacement, down-thrown within the dome, equal to the thickness of the sill phase. Owing to its unusual shape, the reef displacement on it, and its toughness, it has embarrassed mining. This paper describes the intrusion, offers a theory of its origin, and suggest its age.

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Transactions of the Geological Society of South Africa, 43, 143-152

Gravimetric and earth-magnetic measurements were carried out by the writer's organisation for discovering the hitherto unknown geological structure of the Great Dyke of Southern Rhodesia. The gravity anomalies are the largest ever published over similarly narrow widths on any continent, their maximum being 46.7 and 54.0 milligals on the two respective traverses. The interpretation of the gravity anomalies proves the existence of a heavy, slowly tapering, and very deep linear core below the exposed rocks of the Great Dyke. The average density of this core is about 3.3, and it is considered to be peridotite or possibly pyroxenite. It is suggested that the name " Dyke " is not quite correct, and that the term " Abyssolith " would more accurately describe this bottomless mass of injected rocks. The magnetic results show that the contact between the granite and the Dyke can be located with the magnetometer. The absence of major magnetic anomalies from deep-seated sources proves that the heavy eye contains little or no magnetic minerals, and therefore the iron content of the core must be in the form of silicate and not magnetite. The weak magnetic anomalies support the idea that serpentinization has not penetrated into the core of the Dyke, and that the hydration was caused by waters of meteoric origin.

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Transactions of the Geological Society of South Africa, 43, 153-158

Utilizing the flexure known as the Natal Monocline, an attempt is made to estimate average rates of erosion in Natal over long periods of time. The results are compared with estimates obtained by other means.

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Transactions of the Geological Society of South Africa, 43, 159-174

A dolerite sill 200 feet in thickness is exposed on the slopes of Downes Mountain near Calvinia. Rheomorphic and syntectic phenomena with the adjacent Karroo sediments are visible at both contacts and are described. A mineralogical investigation of the sill yields information as to the course of crystallisation of tholeiitic magma under hypabyssal conditions.

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Transactions of the Geological Society of South Africa, 43, 17-22

A review is made of all the structures known to occur in the Dolomite Series of South Africa of the kind generally referred to the activities of algae. They are classified according to the different phases of sedimentation which they characterise. The structure placed in the second of the two groups adopted are regarded by the author as being of uncertain origin.

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Transactions of the Geological Society of South Africa, 43, 175-203

Detailed mineralogical data of the old granite and granite-gneiss of Namaqualand, the granite on the farm Aggenys, and the Paarl and Cape Peninsula granites are recorded. The old granite is correlated with the basement granite of South Africa. It frequently shows the effects of either metasomatism or contamination by Kheis sediments. The Namaqualand granite-gneiss is correlated with the Cape granite and exhibits a more acid marginal phase on the farm Aggenys.

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Transactions of the Geological Society of South Africa, 43, 23-26

A description is given of occurrences in the Dolomite Series of concretionary structures of conical shape. They are supposed to have been formed after consolidation of the limestones in which they are found.

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Transactions of the Geological Society of South Africa, 43, 27-36

The geological information gained from a study of recent workings, and of the core yielded by the borehole for water on the virgin manganese-bearing farm Aucampsrust, is the chief subject matter. Furthermore, the nature and origin of the ore deposits and the possibilities of geophysical investigations are discussed, and references are made to the manganese fields in general.

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Transactions of the Geological Society of South Africa, 43, 37-68

A detailed mineralogical and petrographical description is given of the diabase which overlies the Magaliesberg quartzites north of Pretoria. The diabase, which may also be called a fine grained hypersthene gabbro, is considered to occur in the form of a composite sill and its probable mode of emplacement is discussed. In addition a brief description is given of the gabbro immediately overlying the diabase, with special reference to the variations in its mineralogical composition. An explanation is offered to account for the absence of the Merensky Reef and Chromitite horizons due north of Pretoria.

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Transactions of the Geological Society of South Africa, 43, 69-84

This paper gives a general description of a kimberlite occurrence with special reference to the inclusions. An attempt is made to establish a definite relationship between kimberlite and melilite-basalt by means of Niggli values.

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Transactions of the Geological Society of South Africa, 43, 85-108

The stratigraphical position of the Ventersdorp Contact Reef between the Witwatersrand and Ventersdorp Systems is defined and the relationship between the two Systems discussed. The origin and mode of occurrence of the V.C.R. is described in detail, and the mineralogy and petrography of the reef is dealt with. The latter part of the paper deals fairly exhaustively with the various economic aspects of the reef and includes a note on the bearing that this reef has on the origin of the gold in the Witwatersrand System. The information was largely obtained form the exploration of this horizon on West Witwatersrand Areas and Venterspost.

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Transactions of the Geological Society of South Africa, 43, 9-16

The occurrence is recorded of a graphitic limestone with concretionary structure believed to be of algal origin. The rock occurs at an horizon low down in the "Basement Schists" of the Bembesi gold belt. The principal structures observed are briefly described and illustrated.

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Proceedings of the Geological Society of South Africa, 43, xxvii-xliii, 11 pl, 1 tab.

In taking this unique body of rock as my subject I am treading on dangerous ground, for many geologists have worked on it, but no finality has been reached as to its origin. I can at least claim to have done a large amount of pioneer work on it myself, and no harm will be done in collecting together what has been found out about it up to the present time. It may also help to draw attention to this body as a field for petrological research, which is beyond the scope of geological surveyors compelled to devote their attention to gold mining. Many years ago I had the privilege of showing some exposures to that distinguished American geologist, Professor A. C. Lawson, who remarked at the end of the trip: " I expect that geologists will be working on this in a 100 years time but, whatever it is, it isn't a dyke".
However, the name Great Dyke is firmly established, and the rocks composing it bear so close resemblance to the basic portion of the remarkable Bushveld Igneous Complex that it is assumed to be of the same age.

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Transactions of the Geological Society of South Africa, 44, 1-18

The paper reviews some earlier theories of the Vredefort "dome,'' and the question of centrifugal or centripetal pressure in arching up the central circular region with its flanking ring of overturned sediments. The structure has an inner and an outer ring, and it is shown that the enormous central uplift and deformation under radial pressures tangential to the geoid could not have arisen from the driving inward of the outer ring, nor from the collapse of a flat arch. The deformation appears to have developed outwards from the centre, in two stages: First, by the irruption of a magma into the buckled centre of an original shallow basin, and secondly by the horizontal resolution of the vertical magmatic forces as the opposing flanks of the syncline were lifted upwards and brought together. It is considered that the 531 square mile area of the Vredefort granite plug could never have been covered by sediments as it exists today, since this would demand the presence of more material than was ever in the original structure; and that the ragged upturned edges of the Witwatersrand sediments have never been carried very far into the realm of denudation. The old granite subjected to plastic flow through the " toggle-action" of the structure acted as a buffer over which the sediments were overturned, and finally bulged out at the surface.

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Transactions of the Geological Society of South Africa, 44, 113-120

Veins of pseudo-coal occurring near Riversdale are described, and a colloidal origin is suggested for them.

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Transactions of the Geological Society of South Africa, 44, 121-126

This paper records the occurrence of an unusual suite of minerals from a vug in a quartz vein on the Kimberley Level, Daggafontein Mines. The following minerals were identified: - Quartz, chlorite, dickite, hydrocarbon, galena, sphalerite, chalcopyrite, pyrrhotite and pyrite. Some of these proved to be gold-bearing.

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Transactions of the Geological Society of South Africa, 44, 127-150, 2 pl

A suite of basic sills intrusive into Karroo strata in the neighbourhood of Calvinia is described. They consist without exception of dolerite or tholeiite and very often carry a small proportion of olivine. Orthopyroxene, which is prominent in some of the thicker sills, is antipathetic towards olivine and its relationship to the various clinopyroxenes is discussed. Acid material associated with several of the sills proves to be a reaction product of dolerite with argillaceous siltstone of Ecca or Beaufort age. The adjacent shales have generally escaped reaction. Rheomorphic veining of the dolerite by shale or siltstone is frequent but crystallisation differentiation is relatively unimportant, being confined to the production of a few small veins or schlieren of dolerite-pegmatite. Some of the types of dolerite described appear to have a widespread distribution in the Karroo.

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Transactions of the Geological Society of South Africa, 44, 151-160, 4 pl

The folding and faulting in the Baviaans Kloof are briefly described, and the following three points emerge from the discussion: - 1. An alternative theory to Schwarz's "fault-pits" is suggested to explain the occurrence of the Enon beds in detached basins. 2. The continuity of the Cango, Baviaans Kloof and Uitenhage faults is claimed. 3. A northward tilt during the Tertiary elevation is proved.

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Transactions of the Geological Society of South Africa, 44, 161-166, 1 pl

The rocks underlying the Pniel lavas in the vicinity of Taungs are described and structural and lithological evidence is produced to the effect that they consist of two entirely distinct major formations, of which the upper is correlated with the Pniel series of the Ventersdorp system, while the lower is correlated with the Zoetlief or Dominion Reef series. The existence of a pre-Pniel dolomite is established.

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Transactions of the Geological Society of South Africa, 44, 167-206, 6 pl

An area of 570 sq. miles between Goodhouse and Pella in Namaqualand S.A., is mapped on a scale 1:150,000. It comprises three intrusive granites which carry a profusion of sedimentary xenoliths of the Kheis Series. Mineralogical and petrographical data are amplified by volumetric analyses, which together with other available modal percentages are represented graphically. Seven new chemical analyses are appended and data pertaining to assimilation, granitisation, foliation and correlation are discussed. Six new analyses of the younger Cape granites render possible the construction of reliable variation diagrams, and a relationship is deduced between the quantity of normative corundum and the potash-soda ratio. The compositions of the granites of South Africa are discussed in the light of normative variation diagrams of the bilinear co-ordinates, and a rigid chemical distinction seems applicable to some of these provinces.

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Transactions of the Geological Society of South Africa, 44, 19-34, 5 pl

Evidence of glaciation has for the first time been discovered in the Nama system, South West Africa. The nature of the glacial grooves and the mode of occurrence of the related deposits strongly suggest a contemporaneous glaciation during the deposition of the Schwarzkalk series. Although variable within restricted areas, the main direction of ice movement was from north to south.

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Transactions of the Geological Society of South Africa, 44, 207-218, 3 pl

A hitherto unknown tillite horizon has been discovered in the Otavi Mountains, S.W.A., and it may prove to be of considerable value in correlating the Otavi suite of rocks with other systems.

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Transactions of the Geological Society of South Africa, 44, 219-232, 1 pl

The topography of Eastern Natal, though largely influenced by the monoclinal structure of the region, is shown to have been developed during three distinct cycles of erosion. Seaward tilting is suggested and the features of certain critical localities examined.

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Transactions of the Geological Society of South Africa, 44, 233-301

In the vicinity of Port St. Johns and on the banks of the Umtamvuna River east of Bizana, there occur a number of highly mineralised springs issuing from Dwyka Tillite along lines of tectonic disturbance. Cones of travertine of varying extent have been built up around their orifices. Analyses of waters from these springs are compared with analyses of ordinary Dwyka groundwaters. The conclusion is reached that the springs represent highly concentrated Dwyka groundwater and do not rise from great depths. The process of cone building is described and two new analyses of travertine from the Umtamvuna Springs are provided.
While the Port St. Johns springs are rich in H2S, the origin of which is discussed, the Umtamvuna Springs emit abundant CO2, but no H2S. The Umtamvuna Springs rise from a prominent fault fissure, from which higher up on the plateau, in the area round Bongwan, CO2 issues at several localities. These exhalations represent the only commercially exploited occurrence of natural gas in South Africa.
The composition of the gas and the wall-rock alterations along the fault are described in detail, analyses of the fresh and altered tillite being compared. The origin of the gas is discussed, and the conclusion reached that it is not of volcanic origin, but probably due to the action of groundwater containing free sulphuric acid, derived from the oxidation of pyrite in pyritiferous zones of the lower Karroo beds, on crystalline limestones in depth. Xenoliths of the latter in the underlying Old Granite occur some distance to the east (Marble Delta). The Bongwan Gas fault is shown to be one of the longest faults in the whole area affected by the great monoclinal coastal flexure of Zululand, Natal and Pondoland. The mechanism of faulting is discussed in relation to flexuring and a connection indicated between extensive faulting and curvature of the monoclinal axis.

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Transactions of the Geological Society of South Africa, 44, 35-38, 2 pl

Pyrite from the Leeuwpoort Tin Mine was found to contain small amounts of nickel and showed unusual zoning after etching with HCl + Zn. This etch-test gives interesting results with pyrite from various localities and is advocated in studying this mineral. The paragenesis of the tin ore is described.

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Transactions of the Geological Society of South Africa, 44, 39-50, 1 pl

On the basis of new observations in the Victoria Falls area, and elsewhere, and a re-examination of earlier records, the conclusion is reached that the fossiliferous chalcedony, silicified sandstone, and related deposits known in Northern Rhodesia Angola, and the Belgian Congo rest, in many cases, not on the Miocene peneplain, but on valley-floor extensions of the end-Tertiary peneplain. From this it follows that these silicified beds represent surface deposits of the younger peneplain, and that the silicification, which, in some cases, affected also similar deposits resting on the Miocene and possibly older surfaces, dates from the intense and widespread period of aridity that prevailed in the end-Tertiary and early Pleistocene and culminated in the deposition of the Kalahari sand.

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Transactions of the Geological Society of South Africa, 44, 51-60, 2 pl

About 15 miles north-west of Kuruman the Black Rock forms a conspicuous landmark in the flat sand-covered landscape. It is a low hogsback of banded ironstones in which bodies of manganese ore are present. The geology of the occurrence is described, and the possibility that a thrust fault lies hidden east of the Rock beneath the sand is suggested, but the evidence available is scanty and indirect. The nature and possible origin of the manganese ore bodies is discussed, and the probability of hidden ore reserves being present is mentioned. In conclusion, a rough summary is given of the types and quality of the ore found at the outcrops.

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Transactions of the Geological Society of South Africa, 44, 61-78

Obituary - List of papers - Geological Maps issued by the survey in which Dr. Mellor's work is included.
Dr. Mellor was born at Manchester in 1868, and was educated at the Manchester Grammar School and the Victoria University, where he studied geology under Sir William Boyd Dawkins and was awarded the Dalton Prize for Natural History. In 1893 he was in the valley of the Macleay River in Australia when the greatest flood within living memory in that neighbourhood came down during a rainfall of twenty-five inches in three days. He kept the effects he saw in mind when, eighteen years later, he was forming a mental picture of the conditions during the deposition of certain wide spread conglomerates on the Rand, for he believed that the gravels, as they must have been then, were the result of exceptional flooding.
He graduated B.Sc. with Honours at the University of London, and in 1909 he was given the degree of D.Sc. at the same University. He joined the Geological Society of London in 1901 and our Society in 1903, became a Member of the Institution of Mining and Metallurgy in 1912, and was awarded the Goldfield Premium of the Institution in 1916. He was elected Fellow of the Royal Society of South Africa in 1909. In 1922 he gave a sectional address to the S.A. Association for tile Advancement of Science, and was President of the Association in 1926, on each occasion taking directly economic work for the subject of his address. From 1906 onwards he served on our Council, was President in 1911 and received the Draper Memorial Medal in 1939. (See Journal for the complete article).

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Transactions of the Geological Society of South Africa, 44, 79-112

The paper deals with the Chrome ores of the critical zone of the Bushveld Igneous Complex in the Rustenburg area. Firstly the scheme of chemical analysis of the ore used in this investigation is given. The results of the chemical analyses are tabulated, and curves showing a relation between the Chromites and Pyroxenes are supplied. Variations in the composition of the Chromites are also shown, and lastly, the relationship between the Chromites in the Chromitite bands and the Chromites in the silicate bands is illustrated.

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Proceedings of the Geological Society of South Africa, 44, xxv-lxx, 3 pl

In this address I shall endeavour to give an outline of the principal mineral resources of South Africa, including South-West Africa, and Northern and Southern Rhodesia, their present and future importance, particularly in regard to the mineral economy of the British Empire as a whole. It will be useful to obtain, at the outset, a broad conception of the importance of the mineral resources of these territories and I propose to introduce my subject by statistics of Empire mineral production. For purposes of comparison I shall use production figures for the year 1935, which was a year of relative prosperity - the first since 1929 - and for which Empire and World statistics have been compiled by the Imperial Institute as set out in the tabulation overleaf.

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Transactions of the Geological Society of South Africa, 45, 1-25, 2 pl

Thin dykes intrusive into typical Karroo dolerite dykes in the southern part of the Rouxville District, O.F.S., are found to be more basic in composition than the latter. Attempts were made to isolate the constituent minerals. The results of detailed chemical, mineralogical and petrographical investigations are given. The chemical compositions and mineralogical make-up suggest affinities with the olivine-basalt magma type of Stormberg basalts rather than with average (tholeiite) Karroo dolerite, but it appears more likely that they are derived from the latter.

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Transactions of the Geological Society of South Africa, 45, 109-150, 6 pl, 1 tab.

A short résumé is given of the existing literature concerning the Namaqualand copper deposits, as well as the various hypotheses advanced to account for their origin. The petrographical characteristics of the ore bearers are briefly discussed. Hypersthene and plagioclase are the two most important minerals. Monomineralic rocks are unusually common. Nine new rock analyses are included. Petrographical investigation seems to indicate that the various ore bearers are consanguineous.
The microscopy of the opaque minerals constitute the principal subject of research. The principal ore minerals in order of abundance are: bornite, chalcopyrite, pyrrhotite, pyrite, magnetite, and ilmenite. The less common and rarer minerals are blende, millerite, molybdenite, linnaeite, vallerite, melonite, etc. The micro-structure and interrelation of the opaque minerals and its bearing on the genesis of the ore, is discussed.
Attempts were made to reproduce natural micro-textures by heating experiments conducted on Namaqualand copper ores, and in this respect the production of unmixing phenomena at relatively low temperatures is significant. Twenty-three photomicrographs of polished sections are included to illustrate the mutual relations of the opaque minerals. The sulphides appear to be preferentially associated with hypersthene. The sulphides are believed to be of magmatic origin and there is little evidence of supergene replacement. Differentiation of the parent magma appears to have been accomplished in depth, prior to injection. Hydrothermal action is of secondary importance and the silicates, even though associated with large concentrations of sulphides, are remarkably fresh.

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Transactions of the Geological Society of South Africa, 45, 151-181

Some features in the geomorphology of central Africa are reviewed, and evidence is given to show that the main watersheds and river systems were determined, not by the Miocene uplift, but by much earlier events most of which date back to the movements of early post-Karroo times (early to middle Jurassic). In an earlier paper it was suggested that the late Jurassic peneplain of central Africa was represented in the upper erosion surfaces of the Basuto Highlands and the Cape Ranges, and in South-West Africa, and that the early Cretaceous and end-Tertiary surfaces were also represented in southern Africa.
In this paper is traced a new peneplain, intermediate between the late Jurassic and Miocene surfaces, and comparable with the Vipya peneplain of Nyasaland and Northern Rhodesia, which is possibly of late Cretaceous or early Tertiary age. This new surface, which is present in the highlands extending around the margins of the Miocene peneplain, cuts across a wide range of pre-Karroo formations and all stages of the Karroo.
It is suggested that the end-Tertiary and post-Tertiary surfaces are extensively developed in southern Africa, both inland along the main valleys and in the coastal belt, and the relation of these surfaces to the Miocene peneplain is discussed. A review of the erosion surfaces suggests that over very large areas no appreciable warping accompanied the uplifts that terminated the early Tertiary and Miocene peneplains, but that the end-Tertiary uplift was followed by widespread gentle warping, which was, perhaps, contemporaneous with the main period of Rift Valley movements farther north.

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Transactions of the Geological Society of South Africa, 45, 183-214

The ‘old granites' of Southern Natal and Northern Pondoland comprise hypersthene-bearing types first noted by A. L. du Toit. In the region of Port Edward and the lower Umtamvuna River there is a body of considerable size comprising hypersthene quartz-diorite, granodiorite, quartz-monzonite and granite (charnockite). Chemical analyses and a considerable number of modes are provided and compared with those of similar rocks from India and elsewhere. The hypersthene content is found to vary from almost 23 % in the more basic quartz-diorites to a minimum of 2.75 % in the acid charnockites. Accompanying femic minerals are hornblende and biotite, in a few types also very subordinate diopside. Occasionally hornblende predominates over hypersthene in quartz-dioritic varieties. Titaniferous magnetite is abundant in practically all types; apatite and zircon are common accessories. Pink garnet (almandine) is often conspicuous not only in the acid charnockites, but also in the normal granites of the area. Interspersed with normal granites and charnockitic rocks to the north of the Port Edward massif there occur leptynitic garnet-granulites comprising also hypersthene-bearing types. An analysis of one of the latter is provided and does not correspond with any known type of igneous rock. Field relationships and the presence of migmatitic charnockitic rocks suggest the latter to have largely resulted from anatexis, palingenesis and granitisation by the 'old granites' of an ancient group of granulites and schistose rocks. Further work is in progress.

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Transactions of the Geological Society of South Africa, 45, 27-35, 3 pl

The following ore minerals are recorded: zinc blende, pyrrhotite, pyrite, marcasite, arsenopyrite, gudmundite, galena, chalcopyrite, boulangerite, bournonite and tetrahedrite. Zonary and intergrowth structures are described and the paragenesis of the ore minerals is discussed.

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Transactions of the Geological Society of South Africa, 45, 37-53, 1 a3 map

This paper deals with the coastal terraces of Eastern Pondoland in relation to warping and tilting of the coast line. Various cycles of erosion, which were initiated prior to the cutting of the coastal terraces, are also considered. The marginal movements and deposition along the coast are examined in connection with their effect upon the continental shelf.

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Transactions of the Geological Society of South Africa, 45, 55-64

The Karroo dolerites between Sutherland and Middelburg are very similar to those of the adjacent Calvinia district. Exceptions are a dolerite with porphyritic orthopyroxene from Hanover, C.P., a picrite near Middelburg and an unusual olivine-dolerite from a thick inclined sheet north of Graaff Reinet.

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Transactions of the Geological Society of South Africa, 45, 65-74

The hot springs described are situated on the floor of the Tugela gorge, ˜3,100 feet below the closely adjacent Table Mountain Sandstone Plateau around Kranskop. They rise from a well-marked crush-breccia, indicating a fault intersecting amphibolites and biotite-hornblende gneiss of the Tugela Series. The crush-breccia is impregnated with abundant pyrite, infilled and veined by calcite and cemented by silica. The greater part of the fault-fissure is occupied by a massive calcite-silica rock, consisting of narrow lamellae of calcite alternating with thin layers of cryptocrystalline silica. The mineral content of the water is 99 parts per 100,000, the most abundant cations being Na and Ca, and the characteristic anions SO4", Cl' and HCO3'. The silica content is appreciable. Small quantities of CO2 bubble through the water, which also contains small amounts of H2S. The temperature of the springs is 52-53°C. Calculations based on the normal geothermal temperature gradient indicate that the springs are mainly fed from rainwater falling on the adjacent T.M.S. plateau.

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Transactions of the Geological Society of South Africa, 45, 75-78, 1 pl

By concentration from a large weight of rock, small amounts of rutile and zircon with less of cassiterite and scheelite have been found in the Merensky Reef and the associated rocks. The methods of recovery and properties of the minerals are described.

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Transactions of the Geological Society of South Africa, 45, 79-80, 2 pl

Concretionary structures of unusual size and character are described from the Angola border in the north-western corner of Northern Rhodesia, where they occur in a medium-grained sandstone which is possibly of Karroo age. They consist of ferruginous box-like structures developed on the weathered upper surfaces of rectangular joint blocks 10 to 15 inches in length; each consists of a flat-floored depression two to three inches deep surrounded by a steep-sided flat-topped wall, an inch or two in width, which runs around the edges of the block; from the centre of the depression a symmetrical boss rises to the height of the enclosing wall. The structures are regarded as weathered-out concretionary bodies due to the symmetrical concentration of iron in the central and marginal parts of the upper layers of the joint blocks.

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Transactions of the Geological Society of South Africa, 45, 81-108

The geology of an area along the western margin of the Complex in the Marico district is described. A detailed mineralogical and petrological study of the basal rocks was undertaken for the purpose of a correlation of the igneous rocks belonging to this area with those already described in other parts of the Complex. The results show that the rocks belong to the Basal zone. The variations in diabase intrusions, as well as an account of the metamorphosed argillaceous sediments of the Pretoria Series, are given.

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Proceedings of the Geological Society of South Africa, 45, xxiii-xlv

Geology is a science, and science is the search for truth by experiment, observation, and logical deduction. In an address to the British Association for the Advancement of Science in the year 1991, General Smuts said "Our aim is not only more knowledge, and ever new discovery of truth, but also the promotion of social welfare, and the building of the great society as a fit habitation for the spirit of man".
Here in the young country of South Africa with its ever-growing economic needs, I like to think that the economic geologist, in the application of his science, has made a material contribution to the growth and well-being of the people. I like to feel that every ounce of gold, every parcel of diamonds, every ton of coal, iron, limestone, chrome, manganese, or asbestos that is won from the soil of the country, is helping to lay the foundation of a great and united people in the future. In my address tonight I shall endeavour to show how the economic geologist has played his part in the development of the mineral resources of the country. So wide is the field covered by his activities, that my choice of illustration must perforce be selective. In that selection I have been guided by a number of considerations. I have chosen from the spectacular, because I wish to capture your interest; I have chosen from the prosaic, because of the material contributions made by its methodic progress; I have chosen from the historical, because of the background it sometimes lends to current activity; I have chosen from recent achievements, because we have just passed through a period when the economic geologist has been particularly active. Mainly I have relied upon the work of others, but I have also drawn upon my own personal experiences as a readily available source of material, illustrating the work of the economic geologist. I have endeavoured to show not only what results he has gained, and his contributions to the wealth of the nation, but his method of work in the application of his science, his problems and his reasoning.

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Transactions of the Geological Society of South Africa, 46, 1-13

Most of the extractable underground water in igneous formations is stored in the decomposed rock. Basin of decomposition can be located by the electrical resistivity method and borehole sites can be selected accordingly. The electrical resistivity instrument and method are briefly described, and their application is illustrated by a discussion of some actual surveys. In addition, some statistics concerning the boreholes drilled in igneous rocks in South Africa, are given.

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Transactions of the Geological Society of South Africa, 46, 107-118

The magnetometric anomalies obtained on Karroo dolerites and the interpretation of these anomalies are described. The use of the magnetometer for the selection of sites for water boreholes on granites is discussed, with additional reference to the delineation of a Karroo basin underlain by Bushveld granite

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Transactions of the Geological Society of South Africa, 46, 119-126

A suggested new nickel-magnesian-hydrated silicate is described from the same deposit from which trevorite was described as a new mineral in 1921. The properties of trevorite in reflected light are also given for the first time. Some details of the mineralogy of the deposit are also given. The opaque ore is by no means mono-mineralic as was originally thought. Deposits of such material can be easily overlooked, but the properties in reflected light are characteristic enough to identify trevorite

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Transactions of the Geological Society of South Africa, 46, 127-153

This paper provides a record of the sub-surface geology of an area south-west of Odendaalsrust in the N.W. Free State. The value of geophysical investigations prior to drilling in an unchartered area is indicated. Detailed descriptions and the structural pattern of a definite succession of beds between the base of the Ventersdorp lavas, which underlie the Karroo Series, and the "Basal Reef" are given prominence. Four important local markers are recognised. In age these beds are established as being somewhere between the Lower Witwatersrand and early Ventersdorp Systems. A sub-division of these predominantly arenaceous beds, based on lithological character, into Ventersdorp and Elsburg sediments is tentatively suggested

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Transactions of the Geological Society of South Africa, 46, 13-22

Within recent time, evidence of negative eustatic shifts of sea level is forthcoming from a study of the South African coastline. These strandline movements are studied with reference to the Southern Natal coast, the main line of investigation being that of the river profiles and associated river terraces

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Transactions of the Geological Society of South Africa, 46, 23-38

The Bushveld iron ores contain up to 1,5% V2O5. This constituent is fairly evenly distributed in individual bands of ore, but some bands are richer than others. The highest concentration occurs in the lower band of the Principal group of magnetic iron ore bands. The vanadium is not present in a mineral which can be separated from the ore by physical means. If a suitable method of separation could be operated the potential ore reserves would probably exceed 1 000 000 tons V2O5. The same ores also contain from about 8% to 25% TiO2. The titanium is contained in the ilmenite which occurs in the pres either as granules, or else as exsolution lamellae in maghemite (or magnetite). When in granular form the ilmenite can be separated magnetically. The content of granular ilmenite, rather than the total percentage of TiO2, will, therefore, indicate the results to be expected from methods of magnetic separation. There is an antipathetic relation between V2O5 and TiO2 in the iron ores

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Transactions of the Geological Society of South Africa, 46, 39-45

In a succession of altered sediments and lavas lying along the contact between the granite and the basic rocks of the Bushveld Complex, some of the quartzites were mobilised during their metamorphism by the latter and were intruded into the overlying altered sediments on a grand scale, forming rheomorphic injection breccias in which the enclosed fragments show corrosion and rhythmic zoning

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Transactions of the Geological Society of South Africa, 46, 47-53

A fine-grained basaltic rock and the dolerite dyke into which it has been intruded have almost identical chemical and mineralogical compositions. Inclusions of more basic mineral aggregates occur in the younger fine-grained basaltic dolerite. Detailed descriptions of the mineralogy and petrography are followed by a discussion on the origin of the composite intrusion and the xenocrysts

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Transactions of the Geological Society of South Africa, 46, 55-73

The dikes of the two Transkei Gaps have been traced to the neighbourhood of Cathcart, where they both die out. The N dike, when followed towards the west, first shows signs of acidification and ultimately becomes represented almost solely by mobilised sediment. It is suggested that the dolerite-pegmatite which forms the bulk of the rock in the Transkei was itself derived from an ordinary dolerite magma through contamination by the invaded Beaufort sediments

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Transactions of the Geological Society of South Africa, 46, 75-90

This is an account of a tear fault in East Geduld and Grootvlei Mines, which has an observed strike slip of over three thousand feet, and which has produced conspicuous dynamic metamorphism. Its relationship to the tectonics of the area and its origin are discussed, and the existence of a series of such faults in the Far East Rand is suggested. It is compared with the typical tear faults of the Jura Mountains. Its effects upon mining are briefly suggested

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Transactions of the Geological Society of South Africa, 46, 91-106

The domical-columnar structure, which is of common occurrence in the limestones of the Dolomite Series, is described in detail along with other associated structures, and reasons given for believing that it is a purely mechanical effect. The supposition that the structure is of algal origin is critically examined

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Proceedings of the Geological Society of South Africa, 46, xxiii-xxxviii

This subject is one which has increased greatly in importance in recent years. In South Africa we are not merely concerned with just obtaining water on a farm for domestic purposes and animal husbandry, but large supplies of good quality are required for industrial purposes, or for maintaining military camps. Chief among the activities of the various Colonial geological surveys on the African continent is that of locating and maintaining adequate water supplies, a matter which has been greatly stimulated by the Colonial Development Fund. Further, post-war settlement schemes in the Union visualise large brooks of land sub-divided with water supplies on each holding. The load put on to local industries and transport has made it essential that more sources of water be tapped and larger quantities be drawn off from them.

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Transactions of the Geological Society of South Africa, 47, 1-4

The nature and evolution of hillslopes are described. It is shown that most slope dongas are related to the waning slope, and the significance of this is discussed.

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Transactions of the Geological Society of South Africa, 47, 107-122

Syntectic and anatectic phenomena are not confined to small veins of mobilized sediments, but also affect large masses of sedimentary material found at the top of the thicker dolerite sheets. Masses described originally as granophyre and microgranite and associated in this way with Karroo dolerite are generally, of not always, of such a nature. Three cases examined in some detail are those at Gonubie source, Ibeka near Butterworth, and Gqunqe near Mazeppa Bay.

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Transactions of the Geological Society of South Africa, 47, 123-136

The iron ores of the Postmasburg and Thabazimbi regions resemble each other closely; in the former area deposits of manganese occur associated with, and apparently genetically related to the bulk of the iron ores. A study of the textural and mineralogical features of the ores in both localities has led the author to believe that they are replacement deposits formed through the agency of ascending thermal solutions. Previous opinions on the mode of origin of the ores are discussed and the chemistry of the mineralizing processes is considered. A comparison is drawn between the above deposits and an occurrence in the Lake Superior region.

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Transactions of the Geological Society of South Africa, 47, 137-142

Clear evidence of stylolitic solution in quartzites belonging to the Witwatersrand System, including the well-known Green Quartzites, is described.

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Transactions of the Geological Society of South Africa, 47, 143-156

There are six intrusions in the Far East Rand which are the result of subterranean subsidence, of a distinctive type. Four of them are quartz-dolerite of Ventersdorp age, and two are probably of Bushveld age. One of the latter is a noritic dolerite, and has altered the sediments immediately above it, particularly the shales, to a syntectic granophyre. One of the Ventersdorp intrusions has produced locally a similar effect upon the sediments. A brief comparison is made between the noritic dolerite intrusion and the Bushveld lopolith.

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Transactions of the Geological Society of South Africa, 47, 157-182

Mining operations at Zaaiplaats have during the last fifteen years revealed large bodies of low-grade ore entirely different from the well-known cassiterite pipes which are now more or less worked out. A brief description is given of the different types of ore bodies as well as the post-ore deformation, and the problem of ore genesis is discussed. The mineral associations in the pipe and pod ore bodies are of special interest as they include the rare earth species, allanite, parisite, xenotime (?) And possibly also bastnaesite, besides an unusual variety of pumpellyite. A ferro-ferri-silicate, possibly belonging to the garnet group, was found as a vein in the microgranite immediately below the contact pegmatite.

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Transactions of the Geological Society of South Africa, 47, 183-196

Large and easily recognisable gravitational anomalies were found to exist on the sedimentary belts of this structure, and when these anomalies were traced to the covered south-eastern portion, the structure was found to have rather the shape of a pear, with its smaller end pointing to the south-east, instead of being circular. On this new information and the regional distribution and attitudes of the gravitational anomalies and geological structure, a new explanation of the origin of the structure is put forward.

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Transactions of the Geological Society of South Africa, 47, 197-254

This paper deals with the geology of portions of Bechuanaland and Griqualand West, situated on the eastern edge of the Kalahari in the Northern Cape Province. The normal geological succession is described in brief, and the anomalous relationships found along and to the west of the Gamagara rand are treated more fully. The brecciated equivalents of the upper portions of the Dolomite and of the lower and upper portions of the Lower Griquatown stage are described separately; their close association with post-Matsap earth movements is indicated and a post-Matsap age and a tectonic origin assigned to them. The area is divided structurally into three belts: an intensely folded and over-folded western belt; a central belt of low-angle compressional faults, of which six are described, and a gently folded eastern belt, in which marginal reverse and tear-faulting have taken place. The nature and age of the earth movements are discussed briefly, and their relation to the mineral deposits of the area indicated.

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Transactions of the Geological Society of South Africa, 47, 255-282

A description of the Natal Drakensberg is followed by an account of its origin and evolution. General questions of the mode of development of planed land surfaces and scarps are examined, and estimates of rates of erosion compiled.

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Transactions of the Geological Society of South Africa, 47, 283-299

After a concise theoretical consideration and the derivation of the probable errors ob observations by torsion balance and gravimeter, the applicability of these instruments to typical geological problems is discussed.

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Transactions of the Geological Society of South Africa, 47, 47-78

The distribution, modes of occurrence, interrelations, petrographical features and variations of Bushveld granites of three different ages are described. The Bushveld granophyre is contrasted with the Rooiberg pseudo-granophyre. The significance of this new information in relation to the problems of mineralisation and the general theory of the Bushveld Complex is briefly discussed. Six new analyses of Bushveld granites are given.

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Transactions of the Geological Society of South Africa, 47, 5-8

A specimen of fossiliferous silicified sandstone, found amongst Pipe Sandstone rubble overlying the Kalahari chalcedony of Victoria Falls, Rhodesia, has been examined by M. A. Jamotte, who compares it with the grès polymorphe of the Belgian Congo, and records Chara sp., Limnea sp., Cypris sp., and Planorbis sp. The Pipe Sandstone, included within the Kalahari Beds, rests on an erosion surface that is probably of post-Tertiary age, and it is overlain unconformably by gravels referred to the Lower Middle Pleistocene; its age is therefore probably Lower Pleistocene.

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Transactions of the Geological Society of South Africa, 47, 79-92

The basal portion of the beds occurring in the Transvaal Drakensberg, which have previously been described as sediments of the Black Reef series, are shown to include tuffaceous and effusive strata. It is held that volcanic action was contemporaneous with sedimentation and evidence is given to show that the strata described most likely form an integral part of the Black Reef series, and do not belong to any older formation. A hitherto undescribed volcanic vent, situated at the foot of the Great Escarpment, is also reported on and its possible relationship to the extrusive rocks and the Palabora Igneous Complex is discussed.

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Transactions of the Geological Society of South Africa, 47, 9-46

The paper describes the erosion surfaces of Northern Rhodesia, and discusses the age and origin of the main watersheds, valleys, and troughs. The erosion surfaces comprise principally the peneplains referred to the mid-Tertiary. Or Miocene, and the end-Tertiary; some post-Tertiary surfaces; and also remnants of pre-Miocene surfaces - the sub-Plateau, the sub-Karroo, the late Jurassic and the Vipya. The mid-Tertiary peneplain, at an average elevation of about 4,600 feet, extends along the Congo-Zambezi watershed and along wide spurs branching from it to the north and the south. It occupies also a wide zone fringing the Abercorn highlands to the west, south, and south-east. Its elevation falls gently towards the Nyasaland border on the east and the Zambezi uplands on the south.
During the later Tertiary broad, relatively shallow basins, subsequently gently warped, were eroded into the mid-Tertiary peneplain, the basins so formed were confluent through wide shallow gaps eroded across the uplands due to remnants of the older peneplain. The broadly undulating surface so formed, referred to the end-Tertiary cycle, followed the Congo and Zambezi valleys and their main tributaries, including the Kafue, Luangwa, Luano, and Chambezi-Luapula, as well as the Mweru basin and the Tanganyika and Nyasa troughs.
The Northern Rhodesia landscape is, accordingly, in the main, due to the mid-Tertiary and end-Tertiary cycles, modified by slight post-Tertiary warping and local faulting, by remnants of pre-Tertiary cycles, and by post-Tertiary cycles. The Kafue, Lukanga, Bangueulu and Chozi lakes and swamps follow a north-easterly line in prolongation of the Okavango-Ngami-Linyati depression of Bechuanaland. The basins in which they lie are shown on physiographic grounds to be essentially erosion-basins of the end-Tertiary cycle, which subsequently - possibly in the Middle Pleistocene - were subjected to gentle warping.
The depression occupied by Lake Mweru and the Mweru swamp is held to be of similar origin, although in this case the warping was associated with slight faulting. The rift-faulting of Lake Tanganyika bears a similar relation to the end-Tertiary surface. The association of the Congo-Zambezi watershed and the subsidiary divides with Karroo and pre-Karroo structures, and the presence on them of numerous remnants of pre-Tertiary erosion surfaces, show that these features were determined essentially by the gentle folding of the early post-Karroo, modified by adjustment to pre-Karroo structures as denudation proceeded; the main valleys and troughs similarly follow the trend of the early post-Karroo disturbances.

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Transactions of the Geological Society of South Africa, 47, 93-106

Columnar, conical and other structures occurring in the dolomites of the Otavi system are described and their origin, which is considered to be organic, is discussed. Comparisons are drawn between these growths and similar ones occurring elsewhere in Southern Africa and in overseas localities.

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Proceedings of the Geological Society of South Africa, 47, xxiii-xlvii

The choice of a subject for a Presidential Address to this Society is always a matter of some difficulty, and in my own case it has not been easy because some of the subjects that interest me more particularly have been admirably dealt with in recent years. Thus Dr. R. J. Bridges, two years ago, gave you a lucid exposition of " The Economic Geologist and His Work in South Africa". Where my address tonight has a similar trend, I shall endeavour not to overlap on what has been so well said before, but where he touched more particularly on the wider personal aspect of the work of the economic geologist, I wish to confine myself to the narrower issue of the mining side of applied geology, and as such it will be my endeavour to stress the more practical side in non-geological language, for whilst my remarks are in the first place addressed to my fellow geologists, they are also intended for the benefit of the mining engineer, the mine official, the miner and the mining student. My theme will be dealt with under the following five principal headings:-
I. Finding a Mine.
II. Following the Reef in the Mine.
III. Following the Gold Within the Reef.
IV. The Value of the Work, the Status and Future of the Mine Geologist.
V. The Teaching of Mining Geology.
While the two latter chapters may appear to diverge from the main theme, they are nevertheless relevant inasmuch as they form the basis of applied mining geology.

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Transactions of the Geological Society of South Africa, 48, 1-10

A pleochroic variety of cassiterite from two South African localities is described. Some microscopical, spectrochemical, and chemical data are provided, plates exhibiting the spectra of selected particles of pleochroic cassiterite being included. Results obtained by concentration tests are given.

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Transactions of the Geological Society of South Africa, 48, 103-124

The theory is developed that the successive zones of hypersthene or enstatite, amphibole (cummingtonite) and plagioclase felspar around a core of olivine are the directed stress, which can exist only in the solid, crystalline state, in olivine produces hypersthene, and in hypersthene cummingtonite. The function of the plagioclase felspar is to transmit the shearing components of the directed stress. The minerals olivine, pyroxene, amphibole and felspar are a series arranged in order of increasing rigidity - resistance to shearing stress.

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Transactions of the Geological Society of South Africa, 48, 11-14

Diamond Drilling at Randfontein Estates has exposed a zone of reefs not hitherto seen. These resemble the Upper Monarch, Monarch, and White Reefs of West Rand Consolidated so closely, that there is not the slightest doubt of their correlation. A detailed description of the section is given showing the Beatty Reefs at Randfontein to be another zone lying about 170 feet below the White Reef. Great resemblance was also observed between the so-called Livingstone Reefs at West Rand Consolidated and the East Reefs at Randfontein, confirming their original correlation by G. Carleton Jones. This leaves the Randfontein Johnstone Reefs with no recognised equivalent at West Rand Consolidated, but the author has little doubt that they exist there. A description of the Pepper and Salt Reef, as a new marker in the Kimberley Series at Randfontein, is also given.

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Transactions of the Geological Society of South Africa, 48, 125-134

The "Jurassic", "Cretaceous" and "Miocene" surfaces of the Natal Drakensberg are discussed, and reasons are given for regarding the Natal "4,000-foot" surface and the 1,5000-foot Drakensberg scarp behind it as due not to the erosion of the Miocene but to a post-Miocene cycle, probably the Pliocene, down to the level of which the lower part of the Natal 4,000-foot surface has been eroded.

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Transactions of the Geological Society of South Africa, 48, 135-142

Lacking direct proof, evidence is deduced in three localities to prove that the Numees tillite is older than the Nama system. New beds, containing a tillite, are described at the base of the latter between Nabas and the Chamgab River.

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Transactions of the Geological Society of South Africa, 48, 143-160

The paper deals in some detail with the geology of an area north of the Zoutpansberg and Blaauwberg. Attention is focussed particularly on the relationships of rocks encountered there, the deformation they have undergone, and the physical features that have resulted from diastrophism. Evidence is adduced for the existence there of an interesting fault trough of post-Karroo age. Trough-faulting is considered to have resulted from the operation of tensional stresses and to be connected with regional post-Karroo subsidence of an area which was previously subjected to uplift over a long period. The geological history of the area prior to subsidence is briefly outlined. One geological map and two sections accompany the paper.

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Transactions of the Geological Society of South Africa, 48, 15-16

Two methods for the determination of small amounts of chromium in igneous rocks are discussed with respect to the concentration of Cr2O3 (p.p.m.) in the rock and the degree of accuracy required.

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Transactions of the Geological Society of South Africa, 48, 161-206

Conformable seams of Crocidolite and Amosite asbestos occur in the Cape and Transvaal in Banded Ironstones and Jaspers of the Transvaal System, which are merely the oxidised and silicified equivalents of sediments generally rich in iron. At least seven species of amphibole and the soda-pyroxene acmite were developed through the transformation of suitable iron-rich or iron-soda-rich layers. The order was: mass-fibre, cross-fibre and prismatic amphibole. The species Cummingtonite, Grunerite and "Montasite" are described. The asbestos was generated in several phases under crustal deformation of post-Matsap-post-Waterberg-age. Evidence is advanced for regarding the "Malips River Type" of metamorphism (Hall) as post-Bushveld. Fibre-quality was largely developed within the zone of weathering. Nine new analyses are given.

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Transactions of the Geological Society of South Africa, 48, 17-26

The following minerals from South African manganese deposits are described: hausmannite, jacobsite, ferrian braunite, amesite, acmite, andradite garnet and chalcophanite. The properties of several of these (ferrian braunite, amesite, acmite) differ to a greater or less extent from the properties of previously described specimens. More detailed information than has hitherto been available is also given on the ore-microscopical properties of chalcophanite. Chemical analyses of all the minerals described, with the exception of the garnet, are provided.

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Transactions of the Geological Society of South Africa, 48, 207-231

Employing a spectrochemical method, a description of which is given, numerous specimens of minerals (chiefly potassium-rich) of igneous origin have been analysed quantitatively for thallium and rubidium. The results of these analyses show that thallium and rubidium are very closely associated geochemically, and it is possible that this relationship between these two elements is closer than that of any other pair of elements. The limits of variation of the ratio Rb2O/Tl2O (by weight) are from 30-650, with a mean ratio of 110. If the analyses are confined to a single area or source, the value of Rb2O/Tl2O remains almost exactly constant within the limits of experimental error; a constancy in the ratio is approached which is almost equal to that of a ratio of isotopes. Thallium and rubidium are confined essentially to potassium-rich minerals. Of these, lepidolites are richest in both thallium and rubidium, with mean values of 0.015% Tl2O and 1.5% Rb2O.

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Transactions of the Geological Society of South Africa, 48, 27-30

A new occurrence of fossiliferous Upper Cretaceous (Senonian) Beds is described from the South Coast of Natal. In mode of occurrence, lithology and faunal content, these marine beds are identical with those known to occur to the south (Umzamba Beds, Pondoland) and to the north (Umpenyati Beds).

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Transactions of the Geological Society of South Africa, 48, 31-42

East London has received scant attention in geological literature, its chief claim to fame being in connection with the Needs Camp limestone deposits and the silicified plant remains at Fort Grey where barytes has recently been mined. George McKay (1827-1902) was a pioneer in the study of East London's geology and collected a number of fossil reptiles from the Beaufort beds which still need accurate dating. The author has mapped an area within a radius of five miles of East London and the results are given and discussed.

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Transactions of the Geological Society of South Africa, 48, 43-48

Brief descriptions are given of three types of nodular bodies occurring in the Dolomite, two of them supposedly of algal origin, the other concretionary and composed of chert. The sediment associated with the second of the types described is of unusual interest, as it includes the petrified fragmentary remains of organisms.

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Transactions of the Geological Society of South Africa, 48, 49-74

Vanadates of lead, zinc and copper are found in commercial quantities in the calcareous rocks of the Otavi system. A brief outline of the geology of the mineralised area and of the mode of occurrence of the vanadium deposits is given. The deposits are found in collapse breccias, tectonic breccias, solution cavities, "sand-sacks" and are intimately associated with oxidised sulphide ores. The vanadates are considered to be of supergene origin. The lead, zinc and copper were derived from oxidised sulphide deposits, whereas the vanadium is an original constituent of the sediments of the Otavi system. By a process of weathering and solution these elements were removed from their original deposits and eventually united to form insoluble vanadates which were deposited either at the sub-outcrops of sulphide deposits or elsewhere at suitable localities, e.g., breccias, "sand-sacks", etc.

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Transactions of the Geological Society of South Africa, 48, 75-82

During recent years considerable attention has been focussed on the geochemistry of the rarer elements as a result of the introduction of sensitive physical methods of analysis, such as the use of X-ray spectra and optical line spectra. The use of the latter in particular as a quantitative method of analysis has yielded fruitful results and geochemical data, of both academic and practical value, is accumulating rapidly. South Africa is, in this respect, almost entirely virgin territory and in an area of such mineralogical and petrological interest, ample material is provided for a host of investigators. It is hoped that in collaboration with other investigators, a portion of this work can be completed, the results of which will appear from time to time as a series of publications in this Journal. Further, it is hoped that the work embodied in these publications will aid in providing a stimulus for others to embark on research in this fruitful and fascinating field. - Using a spectrographic method fifty-seven specimens of feldspar and fifty-five of mica, were analysed. Almost without exception all the micas contain lithium, which varies very considerably and which may sometimes be present in appreciable quantity. In contrast, the presence of lithium in quantities greater than 0.0005-0.001% Li2O is exceptional in feldspar. For a given area it appears that lithium is enriched in muscovites of later crystallization.

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Transactions of the Geological Society of South Africa, 48, 83-102

On 25th July, 1943, at 5.35 p.m., a stone meteorite, weighing 3,880 gms. (8.62 lbs.) fell in the grounds of Mr. J. W. Groenewald, Plot No. 45, Rynfield Agricultural Small-Holdings, roughly 5 miles north-east of Benoni Central, Transvaal, South Africa. The fall was witnessed by Mr. Groenewald and family. Details of the fall as reported by eyewitnesses are given. The meteorite has a Sp. Gr. of 3.70 and is made up, by weight, of 73.99% silicates (mainly olivine and bronzite), 18.95% nickel-iron, 5.8% troilite, and 1.12% accessories. The silicates are to a large extent brecciated and contain a considerable number of small chondrules of olivine and bronzite, the latter often in radiating aggregates. The meteorite is, therefore, a chondritic stone meteorite (aerolite), corresponding closely with Prior's Kroonstad type.

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Transactions of the Geological Society of South Africa, 48, i-iv, 1 pl

Half a century has passed since the Geological Society of South Africa was formed, the inaugural meeting having been held on 8th April, 1896. The first President was Dr. Hugh Exton, M.D., F.G.S., who delivered his opening address before the Society on that date in the Board Room of the old Camber of Mines building in Market Street, Johannesburg, facing the present War Cenotaph of 1914-1918. The first Hon. President was Mr. Lionel Phillips, Chairman of the Johannesburg Chamber of Mines, and for the first four years all the hon. Presidents were Chairmen for the year of the Chamber of Mines. The Hon. Vice-Presidents were Prof. T. Rupert Jones, F.G.S., F.R.S., and Dr. W. Guybon Atherstone, F.G.S. The first Vice-Presidents were A.R. Sawyer, F.G.S., and John Ballot. The first Committee consisted of 20 members, amongst whom were a few local geologists, and number of well-known South African mining men of the time. The first Secretary and Treasurer was Mr. David Draper, F.G.S. , who has rightly been termed the founder and father of this Society. The young Society was heartily welcomed by the geological societies of other countries, but in South Africa - as Draper remarked to an enquiring pressman - the going had not been very easy, because "geologists are looked upon as faddists, whose theories are of no value, and should be held up to ridicule. Because a few cab drivers and butcher boys from Australia (who in the early days of the Rand Mines gave erroneous opinions as to the permanency and value of these deposits) posed as geologists, the science has been in bad repute".
In spite of this, however, the first list of members, published at the end of Vol. 2 in December, 1896, showed a total of 236, of which 16 were honorary members, which compares very favourably with our present membership of 241 in 1945. When the Society was formed, the total white population of Johannesburg was only about 50,000 Europeans, whereas today it is seven times that figure, namely, 350,000. Our membership has thus not grown pari passu with the population, but it will be freely conceded that the quality of our geological transactions has reached a much higher standard - probably equal to anything in the world. In the early years local geologists were faced with many difficulties, for want of more extensive knowledge relating to South Africa in general, and the Rand in particular. Our geology, as Cunningham Wilson-Moore remarked, was "patchy and imperfect", "loose and promiscuous", and the position of geologists at that time "comparable to a child with a puzzle". There were, as Wilson-Moore rightly said, "a number of geological odds and ends, each a fitment, which had been placed in our hands by the sayings and writings of those who have gone before us in the field. They have given us a jumble from which we can but pick out a few of the pieces which lie contiguously. As an incohesive heap they are well-nigh useless; pieced together they form an accurate pattern of the crust of South African soil". This was the position in 1895, when Johannesburg was in the throes of a great gold boom, and the mining and financial public were thirsting for knowledge relating to the Rand gold-bearing conglomerates.

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Transactions of the Geological Society of South Africa, 48, v-vi



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Transactions of the Geological Society of South Africa, 48, vi



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Proceedings of the Geological Society of South Africa, 48, xxi-xxxvii, 5 pl

Geologically, the Eastern Province offers no features of world-wide interest like the Bushveld Igneous Complex, the Witwatersrand conglomerates or the Kimberley mines; nor is this shortcoming compensated by any deposits of appreciable economic significance. The climate of the Eastern Province is clearly transitional between the summer rainfall type of Natal and the winter rainfall type of the Western Province, and in its broad features the geological structure represents a similar transition between the Fold Belt of the south coast and the more faulted region of southern Natal.
When I first settled in Grahamstown some 18 years ago, the surroundings, delightful enough from a scenic aspect, seemed to offer but trifling scope for geological investigation, although I have since seen many places considerably less inviting. I had been brought up as a mineralogist and here I was stranded some miles from any igneous rocks, and even such as occurred within a reasonable distance consisted only of dolerite. At that time, the Port Elizabeth sheet of the Geological Survey had not been published, and I waited impatiently for Dr. Haughton's map and explanation to appear in print. Even odd references in the literature to this area were rare enough.
As a result, I spent some time in my first few years working through the mineral collection of the Albany Museum, on specimens sent to me from various sources and on material in the McGregor Museum, Kimberley. The pegmatite minerals seemed to me the most interesting and I paid one or two collecting visits to the Kenhardt and Gordonia districts.
After the publication of the Port Elizabeth sheet, I became curious to find out how far the geological structure of the area to the east was related to that on the published sheet, and I was also interested to check up on details of the immediate surroundings of Grahamstown, as I had had very little experience of geological mapping.
I have subsequently completed the mapping of an area lying to the east of the Port Elizabeth sheet as far as East London on a scale suitable for publication in the new series, including the material for Sheet 136, which has been in the hands of the Geological Survey for some time, but has been held up by war-time difficulties.
In addition, there was, and for that matter still is, a gap of some 200 miles between the Grahamstown and Umtata districts where very little detailed work had been done. The Pondoland and Transkei maps by Dr. du Toit were the nearest areas mapped in detail in this direction, while in the Kentani division the Karroo dolerite had been mapped away back in 1902 by Rogers and Schwarz, but they had given very scant attention to the invaded sediments. I have, from time to time, covered the greater part of this gap in a rough sort of way, sufficient perhaps to give a general idea of the geological structure of the area concerned.
In this way, special problems have been encountered and I have published separate accounts of them, such as on the Gap dikes of Kentani, mobilisation of sediments by Karroo dolerite at Gonubie River mouth and other places, certain pebble-bearing formations within the Beaufort series, and some peculiar basin-like hollows in dune-rock. Perhaps it will be simplest to review the salient and more interesting features of the Eastern Province by treating them chronologically.
The rocks older than the Cape System occupy only a very small area and have been partly mapped by former students of mine, F. L. Amm and J. J. Frankel. They include the calcareous sediments from which samples of lead and copper ore were obtained at the beginning of last century in the Maitland River valley near Port Elizabeth, and also the limestone quarried further west by the E.P. Portland Cement Company.
In the Eastern Province, the magnesium content of these old limestones is generally very low and they are high-grade commercial rocks. Great thicknesses of sandstone among these older rocks are sometimes difficult to distinguish from the younger Table Mountain sandstone, nor is there always any angular unconformity between them. Small dolerite intrusions in these rocks are highly altered and regarded as pre-Karroo, but there is no actual proof of their age.
Formations of the Cape System are relatively uninteresting and even the Bokkeveld Series, elsewhere important on account of its fossils, is in the Eastern Province practically barren. Sporadic occurrences of fossils have been recorded and in particular, a student of mine, L. Marais, has collected crinoids and brachiopods, though somewhat distorted, from near Uitenhage; but east of this district almost the only fossils in this series are plant stems and Spirophyton, which occur sporadically near the top of the series. My predecessor at Rhodes University College, the late Professor Schwarz, described somewhat poor material of this sort from the Grahamstown and Port Alfred districts, specimens now housed in the Albany Museum.

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Transactions of the Geological Society of South Africa, 49, 1-33

This paper gives the history, methods and results of the pioneering prospecting operations carried on by Western Holdings, Limited, from February, 1937, to June, 1940, in the Orange Free State, which led to the discovery of a potential gold field. Some of the relevant history relating to prospecting for gold-bearing conglomerates in the Orange Free State is given and the story of how Western Holdings, Limited, found the gold-bearing conglomerates in the St. Helena area, South of Odendaalsrust, by means of geophysics and drilling. A description is given of how geophysical methods were applied to prospecting for gold-bearing conglomerates in the Witwatersrand System in an area which is covered entirely by horizontal Karoo Formation. The detailed results and interpretations are given. This is followed by a description of how and why a series of boreholes was sited in relation to geophysical anomalies. Borehole data are given together with interesting assay values. The geological succession, as disclosed by the interpretation of the borehole data, is given and correlations are suggested and discussed. The strata passed through and the sub-Karoo geological structure in the St. Helena area are described.

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Transactions of the Geological Society of South Africa, 49, 103-132

A general account is given of the succession of the Rooiberg series, the areal distribution of these rocks and of the chief dislocations affecting them. A detailed description is then given of portions of the farms Nieuwpoort 11, Blaauwbank 433 and Vellefontein 1334, especially with regard to the nature and distribution of the faulting and related folding. The close association of the deposits of tin ore with the faults, which are characterised by mineralised breccias, is pointed out and the possible importance of pitching synclinal structures in the immediate vicinity of the faults is indicated. Finally, field evidence is given in support of a tentative hypothesis as to the manner in which the faults originated as a result of the granite intrusion.

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Transactions of the Geological Society of South Africa, 49, 133-154

The paper is divided into three main sections: - (a) the development of general procedures for qualitative mineral and rock analyses, (b) particular observations on the detection of certain elements, and (c) a comparison of the sensitivities obtainable when using anode and cathode layer excitations.
(a) In the first section the importance of selective volatilization is stressed and because of this phenomenon it is shown that particular attention must be paid to anode shape in order to obtain optimum sensitivity; several anode shapes are discussed.
(b) The second section is devoted to the detection of rubidium, thallium, fluorine, tellurium, phosphorus and gold.
The detection of rubidium using Rb 4201.85 is particularly interesting because it is hazarded by interference from Fe 4202.03 and a method is outlined whereby this interference may be satisfactorily countered in most instances. The spectrochemical detection of flourine by CaF 5291 is more complex than the use of line spectra and in the presence of much alkali metal vapour sensitivity is lowered very considerably. A procedure is outlined whereby optimum sensitivity is attained under most conditions, and an alternative test for fluorine using SrF 5772, is described. (c) An interesting conclusion from the third section is that provided sufficient material is available for analysis, anode excitation appears to be equally sensitive and in a few instances superior, to cathode layer excitation for the analysis of trace constituents in minerals and rocks.

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Transactions of the Geological Society of South Africa, 49, 155-208

The orientation of the minerals of the Bushveld gabbro from Bon Accord and of pyroxenite from another part of the Complex is defined in terms of the relative dimensions and of certain optical and crystallographic directions of the constituent grains. The results are expressed statistically, as measured on three mutually perpendicular planes selected relative to the plane of igneous lamination. It was found, i.e., that some of the crystallographic directions of feldspar and orthypyroxenes preferably lie in the plane of igneous lamination, but that these faces have a random orientation in that plane. The clinopyroxenes, on the other hand, hardly show any preferred orientation.

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Transactions of the Geological Society of South Africa, 49, 209-211

Hitherto, the quantitative estimation of graphite in graphitic schists and pegmatites has been carried out by chemical methods. It is suggested that graphite may be estimated with reasonable accuracy by a mechanical method, using suitable heavy liquids.

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Transactions of the Geological Society of South Africa, 49, 213-242

There are two kinds of simple dykes on the Far East Rand, the fresh dolerite of Karroo age, and the older and altered, ilmenite diabases. The Karoo dolerite dykes occur in a reticulate pattern of two sets striking N.30 deg. W., and N.75 deg. W. Sills of similar age do not occur below the "Green Sill", a sill of Karroo olivine dolerite, the position of which appears to be related to depth below surface rather than to the host rock. These groups of intrusions indicate special stress conditions best explained by E.M. Anderson's methods, and endorsing his conclusions. The magma was probably emplaced by flow vertically upwards. The ilmenite diabase dykes are peculiarly irregular intrusions, and their irregularity is probably due to special stress conditions. A summary of the age and alteration of intrusives on the Far East Rand intrusives is given.

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Transactions of the Geological Society of South Africa, 49, 243-262

The general character of the Vaal river basin is described and the nature of the Vaal as a superimposed river, now flowing over the lowest beds of the Karroo System and the newly-exposed pre-Karroo surface, is discussed. It is shown that the present course of the Vaal below Barkly West is partly due to capture by a tributary of the Hartz River and that certain high-level diamond gravels north of Bloemhof can be ascribed to capture of a former tributary of the Vaal by the Hartz River. The nature and origin of the diamond-bearing high-level Older Gravels and of the lower terraces of Younger Gravels (also diamondiferous) are discussed and the general climatic sequence which aided their formation is considered. It is concluded that the terrace formations was to a great extent controlled by the rapid deepening of the Hartz River in soft rocks occupying a pre-Karroo valley. There is also evidence of climatic changes and the Older Gravels were probably deposited under conditions of high but declining rainfall culminating in an arid period and the Younger Gravels belong to a later period of relatively high rainfall. These two "pluvial" periods - termed the "Older Pluvial" and "Younger Pluvial" - were succeeded only by minor climatic fluctuations. The Younger Gravels, which contain abundant stone tools of the Stellenbosch culture, are referred to the Middle Pleistocene on faunal evidence and the Older Gravels are inferred to be mainly Lower Pleistocene.

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Transactions of the Geological Society of South Africa, 49, 263-276

A brief description, together with a generalised geological map, of the stratigraphy of the Richtersveld and the eastern Sperrgebiet is given, strata varying in age from the Kheis to the Tertiary being described. A new assemblage of sediments, the Gariep system, is noted and the tentative correlation of this system with the Damara suggested. Four periods of magmatic activity are mentioned. Finally, the geological history of the area is briefly described.

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Transactions of the Geological Society of South Africa, 49, 277-288

Die geskrif handel oor sekere gesteentes wat in die verlede onder die Ventersdorp-sisteem gegroepeer is in die gebied rondom Schweizer-Reneke, suidwestelike Transvaal. Daar word aangetoon dat daar in werklikheid twee groepe gesteentes is wat deur 'n diskordansie geskei word. Die ouer groep bestaan grotendeels uit kwartsporfiere en tuwwe wat met beide die Zoetlief-serie en die Dominionrif-serie ooreenstem en daar word tot die gevolgtrekking gekom dat dit hier te doen is met gesteentes van dieselfde algemene ouderdom in verskillende gebiede. Dit word aan die hand gedoen dat die naam Dominionrif-serie voorkeur moet kry bo Zoetlief-serie. Die jonger groep gesteentes bestaan uit 'n onderste sedimentêre gedeelte van grintstene, kwartsiete, konglomerate, skalies en tufagtige sedimente gevolg deur 'n vulkaniese gedeelte van andesitiese en trachitiese lawas, breksies en tuwwe. Die lawas is van dieselfde algemene ouderdom as die Pniel-lawas of, soos hierdie lawas in die Transvaal genoem word, die Ventersdorp-lawas. Daar word op gewys dat daar moontlik 'n tydsverloop was tussen die afsetting van die sedimente en die uitvloei van die lawas. Enersyds kan die sedimente met die Pniel-sedimente gekorreleer word en andersyds met die Gold Estate-lae. Hierdie korrelasie bring meer die vraag te berde of the Elsburg-lae nie met die Ventersdorp-sisteem gekorreleer moet word nie en welke een van die baie name, wat nou gebruik word om rotse van skynbaar dieselfde ouderdom aan te dui, voorkeur moet kry. Aangesien ons kennis van hierdie gesteentes nog baie onvolledig is, word daar nie aanbevelings gemaak nie.

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Transactions of the Geological Society of South Africa, 49, 35-102

Field observations in some of the corundum fields of the Northern Transvaal indicate that corundum occurs in a deep zone (katazone) of the basement rocks where it is very difficult to differentiate the process of metamorphism from that of pegmatite formation. A petrographic study indicates that some acid pegmatites when intruding basic schists have been calcified to form basic plagioclase which, with the introduction of more proto-type microcline, reacts to form hydroxyl-bearing mica minerals. It is possible that mineralizers like fluorine and boron which are readily associated with these compounds, played an important role as catalysts in the dissociation of the feldspars and the formation of the micas and corundum. It is shown that the idea of enrichment in alumina of the pegmatitic solution solely as the result of desilication cannot be upheld on theoretical grounds. This is also borne out by field evidence. The origin of the hypersthene bearing rock types in the vicinity of Bandolierkop is discussed and it is shown that they have resulted from the metamorphism of rocks of the primitive system by the intrusion of the Older granite.

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Transactions of the Geological Society of South Africa, 49, 35-49

Disregarding ilmenite, hematite, goethite, spinel and rutile, the magnetite grains in the iron ores of the Bushveld Complex from various localities are composed of up to five different types of material, four of which form a concentric, zonal structure, while the fifth is present as a fine, almost submicroscopic network. Etch tests for these various types are described. It is suggested that these micro-structures may be due to the progressive disintegration of an originally homogeneous mineral of complex chemical composition.

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Proceedings of the Geological Society of South Africa, 49, xxxv-lxxxii, 3 tab., 29 pl

On this memorable occasion in the history of the Geological Society of South Africa it would seem appropriate to choose a subject with an historical background - the first South African rocks to attract the attention of scientists. In the address which I have the privilege and honour of delivering tonight I shall endeavour to review briefly the salient features of the younger pre-Cambrian plutons of the Cape Province.
One hundred and thirty-three years ago Captain Basil Hall discovered the Platteklip Gorge granite-hornstone contact. He communicated his observations to Professor J. Playfair, the staunch supporter of the Huttonian school of thought.
The rocks of the Glen Tilt area in Scotland and in the vicinity of Cape Town, therefore, contributed in no small measure to the termination of the Werner-Hutton controversy and the laying of an important foundation stone in the progress of the sciences of petrology and geology. It is important to remind the advocates of the theory of the large-scale metasomatic origin of granites - a trend of thought not wholly modern - that the study of these classic localities more than a century ago provided some convincing evidence of the magmatic origin of granites, thereby contributing in no small measure to the present status of petrology.
The systematic geological survey of the Western Province commenced in 1897, and brief descriptions of the granites are scattered through the annual reports of the Geological Commission of the Cape of Good Hope, the publications of the Royal Society of South Africa, the Quarterly Journal of Science (London), the Geological Survey of the Union and the Transactions of this Society.
With the exception of the Great Brak River and Cape Town sheets no further geological survey has been attempted in this region since 1907. At the present day very little more is known about the stratigraphical succession of the Malmesbury Series than almost forty years ago. The most recent connected account of the granites intrusive in the Malmesbury Series appears in the second edition (1939) of A. L. du Toit's "Geology of South Africa". Granite plutons of post-Numees and post-Malmesbury age are known to occur in a belt of country approximately ninety miles wide and almost seven hundred miles long, extending from the mouth of the Orange River southwards along the West Coast of the Union, around the Cape, and then eastwards practically to Steytlerville.
For descriptive purposes a convenient basis of subdivision would be an arbitrary line connecting St. Helena Bay on the West Coast with St. Sebastian Bay on the South Coast. The younger pre-Cambrian granitic plutons lying to the north or east of this line may be referred to as the Northern and Eastern Plutons respectively, while those to the south-west of it may be termed the South-Western Plutons.

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Transactions of the Geological Society of South Africa, 50, 1-16, 1 pl

Certain rocks, located south-east of Potgietersrust and previously correlated with the Waterberg system, are shown to belong to the Timeball Hill stage of the Pretoria series. The anomalous position of these beds is proved to be due to a transcurrent fault. A brief description of this fault and of structures in the area in general is given. Evidence is adduced to show that the fault is of Bushveld age and has resulted form torsion induced by the simultaneous operation of tangential and radial forces in an actively forming syncline.

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Transactions of the Geological Society of South Africa, 50, 105-120, 2 pl

Slope elements typical of a sub-humid region are described, and the following factors tending to produce or modify these are discussed: - (a) Horizontal structure with alternate hard and soft strata. (b) A sub-humid climate with a summer rainfall of the convectional type. (c) A base-level that is stable or slowly falling.

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Transactions of the Geological Society of South Africa, 50, 121-160, 8 pl

Stretching across the explored extent of Marievale Mine is a series of granophyres. One apparently continuous body has been traced for twenty thousand feet in an east-west direction. Its width at Main Reef varies from three hundred feet to nothing. A second and similar body of the same rock lies parallel to the first and to the north of it. Transverse sections show that these granophyres do not penetrate more than thirty or forty feet above the Main Reef, and that over the greater part of their width they are underlain by sediments. They replace the strata and do not displace them; they are metamorphic rocks and not intrusions. The upper part of these bodies is granophyre consisting almost entirely of albite-oligoclase feldspar and quartz with the intergrowth of these two minerals, which varies from a small amount to the greater part of the rock. This rock grades downwards into an amphibolite. Underground development has explored these granophyres in greater detail than is generally possible when they are to be observed only on the ground surface, and therefore the evidence for their origin by replacement is good.

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Transactions of the Geological Society of South Africa, 50, 161-170, 2 pl

A short description is given of some altered and partially mobilised sediments at and near their contact with the Bushveld granite. The metasomatism was selective, some layers of quartzite being more highly altered than others, while impervious rocks, like shale and felsite, were not altered at all. Near the granite the material added to the sediments consisted of about equal amounts of potash felspar and quartz, while farther away from the granite it consisted mainly of albite with some quartz. The albitisation probably preceded the granitisation in time as well as in space.

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Transactions of the Geological Society of South Africa, 50, 17-22

The X-Ray powder investigation of a suite of synthetic samples of the Parkerite Series reveals no significant change of pattern throughout the series ranging in composition from pure Bismuth-Parkerite to pure Lead-Parkerite and it is assumed that the crystal structure is constant over a large range of the series. Re-investigation of the chemical composition of natural Canadian "Parkerite" from Sudbury is necessary before its identity with the South African Parkerite from Insizwa can be established.

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Transactions of the Geological Society of South Africa, 50, 171-176, 1 pl

The paper deals with the field relationships, petrography and chemical composition of some acid lavas from the Rehoboth Bastergebiet and suggests their probable age.

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Transactions of the Geological Society of South Africa, 50, 177-178, 2 pl

A geological section through the Witwatersrand drawn in 1885, by Fred Struben, was recently discovered, together with an explanatory letter, in which he also foresees a great future for the Witwatersrand Goldfield.

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Transactions of the Geological Society of South Africa, 50, 23-54, 1 pl

The natural radioactive decay of rubidium into strontium, Rb87-Sr87, has been utilized for assessing the geological ages of certain minerals. Ten specimens of lepidolite, two of muscovite, one of amazonite and four of pollucite were analyzed. For the determination of Sr/Rb ratios, a spectrochemical method was developed, which depended essentially on rendering strontium volatile in the arc; this was done by pre-treating each mineral with hydrofluoric acid. The ages of ten specimens of lepidolite which were determined by Sr/Rb ratios, correspond reasonably well with their expected positions in the geological age span as computed from Pb/U age data. One may therefore infer that a rubidium half-life period of 2.3 x 10(6) years, should not be in very serious error. Observations made on Ca/K ratios in the ten specimens of lepidolite indicated that the value of this ratio is not a simple function of age in lepidolite.

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Transactions of the Geological Society of South Africa, 50, 55-62

Consideration is given to the nature and mode of deposition of the Australopithecine-bearing rocks of the Taungs and Krugersdorp areas and the conclusion is reached that, contrary to certain other published statements, they are contemporaneous. Attention is drawn to recent recommendations that an African terminology should be used in Africa in place of the Eurasian terms Pliocene, Pleistocene and Recent, at least for the time being, and that this terminology should be based on the accepted East African succession. The problem for solution is to locate the South African rocks within that succession.

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Transactions of the Geological Society of South Africa, 50, 63-72, 1 pl

Rotse wat met 'n sedimentêre kontak op die Swaziland-sisteem en 'n rooierige graniet rus, en diskordant deur die Swartrif-serie bedek word, word bespreek. Litologiese en strukturele gegewens word verstrek om aan te toon dat die rotse moontlik tot die Witwatersrand-sisteem behoort.

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Transactions of the Geological Society of South Africa, 50, 73-104, 9 pl

The petrology of a transgressive sill in the Waterberg sediments is briefly described. The sill consists of dolerite, tonalite and granophyre, and is regarded as composite. It is suggested, as a preferred hypothesis, that the composite intrusion was formed by staccato injection of the residual liquid from a basaltic parent magma during its crystallisation somewhere at depth. The trends of the variations in composition of the exposed rocks, and of the deduced crystalline products of the parent magma, are compared.

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Proceedings of the Geological Society of South Africa, 50, xxiii-lii, 2 pl

The face of Southern Africa has been described as "polygenetic and complex thing" meaning thereby that it consists of many facets of varied derivation. It shall be our purpose tonight not to describe those facets but to investigate the principles behind them and the canons by which they should be studied.
Some of the principles may seem over-familiar to you - textbook stuff of the schools and school-men - but I say to you now, that familiar though they may be, one seldom sees them applied consciously and conscientiously in the African veldt.
But always, when the principles behind land features and land processes are sought and examined, new light is shed upon those features and new points for investigation and testing are revealed. Africa is full of queer departure, from normal in its topography and questions such as: "Why this hill? why this aggradation? why did this route require me to cross an extra valley?" often lead to interesting and complex solutions. Frequently it is the country, and not the topographer, that is wrong.
Here, also, I take the liberty of reminding you that our South African landscape is superlatively rich in certain types of land-form. It yielded to the early masters of geomorphology, W. M. Davis and S. Passarge, information and instances of primary value. From South Africa inselbergs were first described; its high interior plateau early excited wonder as an example of planation by the elements; its congas were among the first of such features recorded; and all have remained wonders ever since. Of recent years, under the scrutiny of Dixey and others, it has revealed an astonishing erosional history without known parallel in any other continent. Long hence it may be expected to yield as richly to those who probe its secrets.

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Transactions of the Geological Society of South Africa, 51, 1-36

The Swartbank, Kuboos and Tatasberg plutons are three major intrusions in a tectonic zone which extends from the west coast of Little Namaqualand in an east-northeast direction into South-West Africa. Coarse porphyritic granite is predominant in the Swartbank mass which, for lack of more definite evidence, is regarded as a stock. The Kuboos pluton consists of an earlier composite stock of fine- to medium-grained granite and syenite, almost completely surrounded by a later and much larger body of coarse porphyritic granite. The attitude of the outer contact and the general centroclinal dip of the flow structure of this body of coarse granite indicate that it is an ethmolith which has made way for itself around the central stock by wedging into the adjacent sedimentary formations, lifting the upper blanket and depressing the peripheral beds. The Tatasberg plutons comprise a south-western composite intrusion where a shell of younger, coarse porphyritic granite encloses an older core of medium-grained granite and a north-eastern mass consisting of medium- to fine-grained granite exclusively. Both plutons have steep, outward-dipping walls, and are regarded as stocks. The regional tectonics and their application to the fracture pattern within the Kuboos pluton, are discussed in some detail.

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Transactions of the Geological Society of South Africa, 51, 133-178

The description of the vermiculite deposits is introduced by a brief description of the general geology of the Loolekop area. Loolekop is built of a roughly elliptical mass of dolomitic marble, fairly rich in magnetite and grading into a peripheral zone composed essentially of serpentine, magnetite and apatite, with some vermiculite and carbonates.
The limestones are surrounded by a larger mass of pyroxenite, which is also not of uniform composition, but constituted of two central serpentinised areas, surrounded by normal pyroxenite which has a border zone of feldspathised pyroxenite where in contact with the Palabora granite.
The Palabora granite and associated syenites are intrusive into the pyroxenite mass which they have assimilated in places and feldspathised along the contact. From the available evidence it is concluded that the marbles and pyroxenites represent highly metamorphosed remnants of original limestones and lime-rich sediments, which have become enveloped in a sea of granite.
The syenites associated with the granitic rocks seem to have originated through the desilication of granite magma by the inclosed lime-rich rocks.
Two types of vermiculite found at Loolekop are described, the black, iron-rich type or hydrobiotite, and the golden-brown hydrophlogopite or true vermiculite. The former has a far less pronounced basal cleavage in the unexpanded state than the yellowish and brownish varieties, is distinctly heavier and has a smaller linear expansion, the average being 11 times. It is widely distributed in the pyroxenite as stringers, pockets and larger bodies and is usually associated with apatite. The true vermiculite has the pronounced basal cleavage characteristic of the mica family and a high linear expansion, the average being 26 times. It is found as small flakes in the central marble mass, as disseminations in the serpentine magnetite-apatite rock surrounding the marble and in bodies of serpentinised pyroxenite, which also exhibit mineral zoning, within the large pyroxenite mass itself. Field and laboratory studies of the vermiculites, supplemented by a series of chemical analyses, indicate that they are hydrated micas, derived from both biotite and phlogopite through the removal of iron and alkalies and the addition of water.
The process of vermiculitisation seems to be related to the present-day land surface and due in the main to ordinary ground water. Several observed features seem, however, to prove the operation of hydrothermal solutions on a restricted scale. Such solutions at high temperature might also have been responsible for the formation of olivine, which is found at random in the serpentinised pyroxenite as well as in the marbles. Finally, it is pointed out that the vermiculite deposits at Loolekop rank among the largest in the world.

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Transactions of the Geological Society of South Africa, 51, 179-194

Glass intrusions, glassy selvedges, glassy mesostasis and fused sediments are types of glassy materials associated with certain of the Karroo dolerites. A brief account is given of the last three types, but the first is described in detail and its relationship to dolerite magma discussed. Chemical analyses show that a glass occurring near Verulam, Natal, is fairly close chemically to the average Karroo dolerite, whereas another from Effingham, also in Natal, is more acidic, shows iron enrichment and has possibly incorporated some siliceous rock. The Effingham glass is fresh, but in the Verulam glass chlorophacite is present along cracks, etc., as a result of late hydrothermal action. Glass intrusions in general appear to be rare.

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Transactions of the Geological Society of South Africa, 51, 195-212

'n Voorkoms van chromiet in karbonaat-serpentyngesteentes behorende tot die Swazilandse sisteem word beskrywe. Hoewel die chromiet somtyds aarvormig optree word dit tog beskou dat die mineraal omtrent dieselfde ouderdom is as vermoedelike olivien wat nou deur karbonaat en serpentyn verteenwoordig word. Interessant ook is 'n netvormige verspreiding van die chromiet en afgeronde knolvolmige ertskorrels. Die chromiet self is van 'n baie goeie gehalte en bevat bykans 60 persent Cr2O3. Die erts is egter hoofsaaklik 'n gedissemineerde tipe en alhoewel daar moontlik meer as 50,000 ton erts in die voorkoms is, bevat dit maar omtrent 33 persent van die hoë gehalte chromiet. Dit is dus twyfelagtig of die afsetting lonend afgebou kan word.

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Transactions of the Geological Society of South Africa, 51, 213-248

Part I of this paper deals with the mode of occurrence, the nature and principal characteristics of the Carbon Leader of the Far West Rand, and gives the reasons for its correlation with the North Reef of the Central Rand. Part II describes in detail an experiment carried out at Blyvooruitzicht G.M. Co., Ltd., whereby it was proved that a very large proportion of the gold contained in rich Carbon Leader, can be lost in borehole cores obtained in drilling. It points out the difficulty experienced in an endeavour to improve the core recovery by means of experimental drilling, but concludes with a description of improved core recovery obtained by the use of a special core-barrel and the application of specialised technique in cutting the Carbon Leader once its exact position is known. In the latter part of the paper the author, while stressing the importance of the result of core and gold loss on rich carbon seam horizons, emphasizes that the result obtained in this experiment must not be regarded or applied as a factor to all borehole intersections on carbon seam horizons.

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Transactions of the Geological Society of South Africa, 51, 37-52

The forms and combinations of slope elements responsible for the variety of landforms in the coastal hinterland of Natal are described, and the following factors tending to produce or modify these are discussed: - (a) Rock type and structure varying from weak granites, tillite and shale to resistant quartzitic sandstones. Weak and resistant rocks succeed one another and faulting is common. (b) A humid sub-tropical climate combining both a well distributed rainfall with heavy convectional downpours. A falling base-level.

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Transactions of the Geological Society of South Africa, 51, 53-62

An account is given of two extensive bands of algal domes occurring in closely spaced zones in the lowermost beds of the Dolomite Series in Griqualand West. The interest of the account centres in the description of the trapped fossil remains (noted in a previous paper (9, p. 44) by one of the authors), which are the oldest yet discovered in the rocks of the Union of South Africa; the association of these with pyroclastic material; and the exceptional character of the composite domes in which they are found.

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Transactions of the Geological Society of South Africa, 51, 63-76

Two xenoliths of sedimentary rocks occur in the Bushveld Granite, 35 miles north of the village of Brits. Most of the sediments consist of limestones and banded ironstones belonging to the Dolomite Series. Quartzites and shales belonging to the Black Reef, Pretoria and Rooiberg Series constitute part of the larger of the two xenoliths. All these sediments have been folded into a series of synclines and anticlines. At a later date the structure was further complicated by normal faulting. Several magnetometric traverses made across the area proved to be of great value in confirming and further elucidating this structure.

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Transactions of the Geological Society of South Africa, 51, 77-80, 1 pl.

A soda-amphibole exhibiting extremely strong dispersion of the optic axes and bisectrices occurs in a fine-grained hematite ore near Zesfontein in the Kaokoveld South West Africa. It is present as brown needles, a few tenths of a millimetre in thickness and several millimetres in length, which are distributed at random through the ore. Under the petrographic microscope its colour is light olive yellow. It has the following optical properties:
b = Z. Extinction angle cΛX=9°-21° (sodium light); angle for red light is larger than that for green light by 10°-16°. Refractive indices α=1.659, β=1.665, γ= 1.668 (all ±0.002).
Biaxial negative, 2V = 49°-52° (sodium light); 56°-59° (red light, 6563 A); 0°-20° (green light, 4861 A).
Chemical analysis: SiO2 54.4 %, Al2O3 2.9 %, Fe2O3 14.5 %, FeO 2.3 %, MgO 15.8 %, MnO 1.5 %, CaO 1.5 %, Na2O 6.5 %, H2O 0.8 %, total 100.2. The formula derived from this analysis is Na2 (Mg, Fe")4(Fe"',Al)2Si8O24. A suitable name for the mineral is magnesian riebeckite.

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Transactions of the Geological Society of South Africa, 51, 81-132

This paper deals mainly with the general characteristics and structure of the various ore-bodies in this area, the ore-microscopy of the associated ore minerals, and the valuable elements. These deposits are regarded as belonging to the mesothermal class of hydrothermal deposits. A summary of the genetic features such as the disposition of the reefs, processes of reef formation and the source of the mineralising solutions will be published in a later paper. Furthermore, the chemical composition and petrological features of eight dykes, sills and the granites below the Black Reef Quartzites will be discussed in detail.

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Proceedings of the Geological Society of South Africa, 51, xxv-xxxiii

I am frequently asked what the geological profession has to offer to young men who are trying to decide upon a profession. There seems to be considerable doubt in the minds of a great many people as to what the qualified geologist is supposed to be able to do, and quite a number of geological graduates are not very clear where they are expected to fit in to the general scheme of things.
I suppose most geologists have been through this phase in their early years after leaving University. I am going to try, in this address, to answer some of the questions that arise in this connection in the hope that students, young graduates and others may, perhaps, benefit from my experience. It is a subject of vital interest to Geology as a profession and to the community as a whole. Geologists, in their study of the structure and contents of the Earth's Crust, have carried out an enormous amount of very valuable research work and collected an enormous amount of valuable data. This has helped us to understand better the crust of the Earth on which we live and has contributed very materially to the achievement and maintenance of the standards of life to which modern man has become accustomed. It is our main function as geologists to find for mankind such materials as can be obtained from the Earth's Crust and to be able to supply information concerning the structure and contents of the Earth's Crust.
I doubt whether, collectively, geologists have achieved status and remuneration comparable with their achievements. I think that the reason for this is very often to be found in the mental attitude of the geologists themselves, largely because they tend to limit themselves almost entirely to Geology, as a so-called "pure" science. If the geologist is to play a more important role in the discovery, development and exploitation of ores and other materials required by man, he must apply his knowledge to the solution of practical problems. Greater demands are being made on geology and geologists as time goes on. There is no reason why we should not be equal to these demands if we are given adequate facilities - and funds for carrying out the necessary research, and provided that we maintain a severely practical outlook. All branches of geological research should be supported and encouraged in the hope that new techniques may be developed to deal with the increasingly difficult problems which will have to be solved. The geology of the future will require the best brains the world can produce.

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Transactions of the Geological Society of South Africa, 52, 1-198, 1 pl

Detailed mapping of an area north of Pretoria shows that a sedimentary succession of approximately 20,000 feet (6 096 m) in thickness and comprised of alternations of quartzites, shales and limestones disappears westward into the basic belt of the Bushveld Igneous Complex. Field, petrographical and chemical evidence indicates that the basic belt originated by the transformation of the sedimentary column in place, and that the physical and chemical laws governing this transformation process, all other things being equal, depend on position of the sediments in a three-dimensional continuum before transformation. Evidence is also detailed to show that felsite and granophyre are arrested roof manifestations of this transfiguration.

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Transactions of the Geological Society of South Africa, 52, 199-202

Pumice is known to occur at or above high tide mark on many beaches along the coast of the Cape Province. It is of uniform character and has the chemical composition of a highly leucocratic phonolitic trachyte. Its origin and distribution along both the west and south coasts of the Province present an interesting problem for which no satisfactory solution has so far been found.

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Transactions of the Geological Society of South Africa, 52, 203-204, 2 pl

Unusual mudcrack forming radiating patterns in saline mud are described. The cracks start forming in very wet mud, usually while still covered by a very thin film of water.

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Transactions of the Geological Society of South Africa, 52, 205-229, 2 pl

About 25 miles east of the Pilansberg, and near the confluence of the Pienaar's and Crocodile rivers, a suite of volcanic rocks have broken through a xenolith of rocks belonging to the Transvaal system. The various rock types in the order of their intrusion and extrusion are porphyritic basalt, trachyte, syenite and volcanic breccias with acid lava. The syenites have been largely replaced by calcite along the contact of an inclusion of dolomitic limestone. This occurrence is considered to be related to the Pilansberg.

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Transactions of the Geological Society of South Africa, 52, 231-264, 3 tab.

In the Union of South Africa seventy-four springs are regarded as thermal, i.e., issuing at temperatures exceeding 25°C the year round. Those above 37°C are classed as hot, whilst a special group styled scalding waters has been created for those with temperatures exceeding 50°C. The combined discharge is estimated to be 8,000,000 gallons (36,290 cbm.) a day, one spring alone being responsible for almost a third of this total. Thermal water also flows from several boreholes, in five of which it was struck at depths greater than 2,500 feet (762 m.). Twenty-five analyses representative of all the types of thermal water known in the country are given, and of these seventeen have not been published previously. The waters contain up to 86 mgm. per litre of silica, the possible states of which are discussed. Sulphuretted waters, which are defined as containing more than 10 mgm. of dissolved hydrogen sulphide per litre, are uncommon in South Africa. It is suggested that the terms "moderately sulphuretted" and "slightly sulphuretted" should be used for those containing from 5 to 10 and from 1 to 5 mgm. per litre of the dissolved gas respectively, Fluorine is a prominent minor constituent, up to 13.2 mgm. per litre being present.
Strontium, an element seldom sought in waters, occurs to the extent of 7.2 mgm. per litre in water from a deep borehole near Trompsburg. Residues obtained by evaporation w ere spectrographically examined by Dr. B. Wasserstein of the Geological Survey. Selected minor elements seemed to characterise waters issuing from certain geological formations. Rough quantitative data indicated that the elements Li, Sr and Ba did not form more than 0.1% of the residues, while Pb and Mo both had maximum values around 0.005%.
The gas associated with the waters is of two types, one is mainly air from which most of the oxygen has been abstracted and the other mainly methane, accompanied in some cases by hydrogen. Thirteen new analyses are given Spring deposits are not common and are represented only by ferruginous ochres and sinters formed by springs in the Cape system.
Manganese is an important constituent of these deposits. Four new analyses are given.
In most cases a close relationship in composition exists between the thermal waters and waters struck in shallow boreholes or issuing as cold springs from the same geological formations. When differences other than in degree of concentration were noted, it was found that the thermal waters were characteristic of the deeper underlying rock formations.
All the thermal waters are considered meteoric. Geological sections illustrate the structures upon which the emergence of thermal waters depends. These are artesian basin, artesian slope, barrier, and faults. The source of the heat is probably the normal geothermal gradient in the crust. It is calculated that the total amount of heat being brought to the surface by the South African thermal springs is approximately 5.8 x 10(-10) cal./cm²/sec. or about a two-thousandth of that normally dissipated by conduction through the crust.
Less is known about the thermal springs of the Territory of South West Africa Twenty-four springs are known to be thermal, of which nine are scalding, a much higher proportion than in the Union of South Africa. Thermal water has been struck in many fairly shallow boreholes. A few analyses are given, all old. The potassium content greatly exceeds that of the thermal waters of the Union; this is attributed to the higher potassium content of the granites of South West Africa. The Windhoek springs have deposited extensive layers of calcareous tufa. The South West African thermal springs, too, are believed to represent the return of meteoric water to the surface mainly through fault fissures, and in some cases fractures, associated with volcanicity possibly of Cretaceous age.

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Transactions of the Geological Society of South Africa, 52, 265-300, 3 figs

An interpretation of the geological history of the Upper Witwatersrand sediments from a study of sedimentation cycles, and in particular those connected with the banket reefs of major economic importance is given. A close connection is shown to exist between sedimentary features and payable conglomerate horizons. Suggestions regarding the modification of existing correlation are made and conclusions drawn which point to the formation of economic banket deposits as a direct result of a particular cycle of geological events.

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Transactions of the Geological Society of South Africa, 52, 301-330, 6 pl

An examination of borehole cores in the Klerksdorp and Odendaalsrus areas reveals that the rock types and beds have much in common. A detailed study of literature dealing with both areas, together with more recent available information proves that similarity is sufficiently pronounced to enable a definite statement to be made. The Vaal and Basal Reefs are considered to be one and the same reef. Further when comparing the generalized geological column obtained with that of the Upper division of the Witwatersrand system in type areas it is claimed that the Vaal-Basal Horizon falls either within the Bird Reef group, or alternatively in the Main Reef group of conglomerates. In order to substantiate the latter claim a paper entitled "The Economic Auriferous Bankets of the Upper Witwatersrand Beds and their Relationship to Sedimentary Features", is being presented simultaneously by Dr. J.W.N. Sharpe.

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Transactions of the Geological Society of South Africa, 52, 331-342

Thin dykes from the Trompsburg district, Orange Free State, slightly more basic than the Karroo dolerite into which they are injected, are similar to a younger chromiferous olivine dolerite described previously. Another type of thin later veins similar to average Karroo dolerite is described from the same locality near Trompsburg and from the Queenstown district, Cape Province. These rocks may be a slightly differentiated product of average Karroo magma in which there is some concentration of iron, while the chromiferous olivine dolerite is considered to represent typical Karroo dolerite magma enriched by olivine and picotite of very early formation.

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Transactions of the Geological Society of South Africa, 52, 343-376, 8 pl

The petrology of a pseudostratified suite, approximately two miles thick, is described. The lower, and greater part of the succession is formed by diallage gabbros. In the upper part of the series occur ferrohortonolite-bearing gabbro, fayalite-bearing diorite, fayalite-bearing granodiorite and fayalite-bearing granophyre. Olivine-free granophyre and alkali granophyre occur at the top of the succession. The change between the different rock types in this pseudostratified series is gradational. Above this series, and with a sharp contact against it, fine grained acid rocks are found. Bushveld granophyre and small bodies of melanocratic granodioritic and granitic rocks, occur as transgressive intrusions in the fine grained acid rocks. Several diabasic dykes, aligned along approximately E-W and NE-SW directions, cut through all the Bushveld rocks.

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Transactions of the Geological Society of South Africa, 52, 377-384, 3 pl

The geology of Dassen Island off the South-West Cape is described, the island being found to consist in the main of a fairly fine-grained tourmaline-granite with subsidiary areas of biotite-granite. The relationship of the different granites is discussed and comparisons are drawn with similar rocks on the mainland. Two new chemical analyses are presented and one hundred joints are plotted diagrammatically.

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Transactions of the Geological Society of South Africa, 52, 385-402, 2 pl

A deposit of iron-aluminium phosphate occurs about 70 miles northwest of Potgietersrust. The country rock is grit of the Waterberg system the bedding of which is more or less horizontal. The ore bodies are veinlike - either vertical, inclined or interbedded with the grit. The largest ore body is about 17 feet thick and 400 yards long. Prospecting has shown that the phosphatisation is only a near-surface phenomenon: at various depths, 30 feet at the most, dolerite was encountered in the vertical and inclined veins. The phosphate presumably originated from the offal of birds of prey and others which live in the mountain cliffs overlooking the deposits. The phosphate-bearing solutions replaced the dolerite, already partially decomposed, from the surface downwards and in this way originated the iron-aluminium phosphate. The material very much resembles surface limestone. The phosphate content is generally fairly high - some samples contain up to almost 40% P2O5. An estimate of the ore reserve indicates 24,000 tons containing on an average 24% P2O5.

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Transactions of the Geological Society of South Africa, 52, 403-412, 1 pl

The area described in these notes lies along the north side of the Limpopo river between Beitbridge and the border of Portuguese East Africa at the southernmost point of the colony of Southern Rhodesia. The Basement Complex shows high grade regional metamorphism, comprising garnetiferous paragneisscs, with coarsely crystalline banded ironstone layers and some serpentinites. The Karroo System is represented by shales and sandstones of presumed Ecca age, overlain unconformably by the Cave Sandstone. This in turn is overlain by basaltic and rhyolitic flows, which are intruded by a mass of granophyre considered to have the form of a sill. In a small area between the Nuanetsi- and Limpopo rivers, at and near the Portuguese border, loosely consolidated conglomerates are believed to be of Cretaceous age. An important fault striking ENE, with downthrow to tho south is responsible for the preservation of the Karroo sediments, while another one, striking nearly east and west throws basic and ultrabasic lavas down against the sediments near the Limpopo river. The granophyre and supposed Cretaceous conglomerates are later than the faulting. Certain alkaline (trachytic) dykes are also thought to be of Cretaceous age.

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Transactions of the Geological Society of South Africa, 52, 413-431

Differential thermal analysis curves are given for a number of representative South African fireclays and other ceramic materials. The application of the differential thermal analysis method to the investigation of the constitution and ceramic behaviour of these South African materials is discussed in conjunction with data available from other determinative procedures.

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Transactions of the Geological Society of South Africa, 52, 433-495, 7 pl

An account is given of an area consisting of schists, granulites, and gneisses belonging to the Kaaien series of the Kheis system. The meta-sediments are intruded by gabbro granodiorite, charnockitic adamellite, and pegmatite. Detailed studies indicate that all the granitic rocks of the area are of sedimentary origin, or represent migmatites of sediments and granodiorite magma. Apparently the Kaaien sediments originally approximated more closely to the quartzo-feldspathic rocks of the Kakamas area than to the quartzites and quartz-schists of the type area between Upington and Marydale. During, or shortly after weak initial foldings of the sediments, olivine-gabbro magma intruded the crust. The emplacement of the granodiorite appears to have coincided with the main period of Kheis orogeny. The charnockitic adamellite and the pegmatites succeeded the orogenic period. The pegmatites are referred to younger granitic intrusions occurring outside the Kakamas area. The sequence of events is compared with that of the pre-Cambrian of Finland and Mozambique, and it is inferred that the Kheis system is considerably older than has hitherto been accepted.

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Proceedings of the Geological Society of South Africa, 52, xxix-lxxxix

In recent years the utilization of geological knowledge, in times of peace as well as of war, has been so varied and extensive as to force the conclusion that the practical value and importance of the science of geology are at last becoming to be fully appreciated. This development is not without significance for the future of the geological profession, for, having regard to the known resources of the world and the future needs of mankind, it can only be interpreted as foreshadowing the ultimate status of geology in industry.
With few exceptions perhaps, the time is now past forever when in South Africa, as in other countries, exploitable mineral deposits can be discovered by traversing an area with old- time tools of hammer, lens and prospecting pan, and when anyone can select a. borehole site from surface indications by hit-and-miss methods or give advice on engineering projects after a casual examination of the terrain.
For its ever expanding needs the nation will require ever larger supplies of water and economic rocks and minerals, and it will have to undertake with ever increasing tempo defense schemes and the construction of harbours, dams, bridges, canals, etc. In the proportion that construction enterprises become more complex and the location of new mineral deposits at depth becomes more difficult, there will be an increasing demand for men who command a sound scientific knowledge of the structure of the earth's crust and of rocks, their composition and properties.
We have, therefore, every reason to feel optimistic about the future of our profession, and I would even hazard the prediction that in the very near future geology will be properly integrated with industry and geologists will be called upon more and more to take a share in supplying the essential and vital requirements of the country. May I, however, appeal to members of my profession to be thoroughly equipped and fully prepared for any task we may be called upon to undertake when that happy day da

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Transactions of the Geological Society of South Africa, 53, 1-12, 3 pl

Radioactivity logging of boreholes has been extensively used in the oilfields of the U.S.A. Recently the Geological Survey has undertaken the application of this method to some of our local geological problems. The paper deals briefly with the basic considerations of radioactivity logging, followed by a general account of instrumental and recording details. The results of such a survey, carried out in a borehole which penetrated sediments and conglomerates in part of the upper Witwatersrand system, and the conclusions reached, are given. A detailed survey of the same borehole indicated that greater detail could be observed by a decrease in operational speed. The difference in radioactive normal between Dolomite and Ventersdorp lava, as observed in a further borehole, is discussed. An account is given of the possible uses of radioactivity logging.

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Transactions of the Geological Society of South Africa, 53, 13-34, 2 pl

The relief of the Tygerberg Hills reflects the thermal metamorphism of unusually quartzitic Malmesbury sediments. Details of relief correspond to variations in the degree of alteration, reflecting irregularities in the surface of the underlying granite batholith. The western slopes show a possible marine bench between 250 and 350 feet above sea- level. The dissected eastern slopes, graded to a sea-level 300 to 325 feet above that of today, form part of the uplifted peneplain now undergoing erosion in the Western Coastal Lowlands. Stream profiles provide additional evidence of this former base-level. The present drainage pattern is a radial system showing some measure of structural control. The drainage changes brought about by uplift have caused this phase of adjustment to pre-Cape structures. More recent changes are a prelude to the re-establishment of earlier radial patterns.

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Transactions of the Geological Society of South Africa, 53, 131-157, 1 pl

The Vredefort Ring, consisting of an overturned collar of 40,000 feet of sediments and lava around a core of older granite, is situated at the deepest portion of a geosyncline which differs from most of the described geosynclines of the world in that it never gave rise to a folded mountain chain. The outer rim of the basin discloses a set of converging faults of great displacement which, when projected inwards under the cover of younger beds, circumscribe the granite core. Evidence is presented to show that these faults are of extremely early age, thus of very deep penetration, and that they have had repeated movement throughout the ages. These faults, it is submitted, released a column of old granite which became a safety valve to relieve the tremendous maladjustments caused by the concentrated accumulation of sediments.
A slight trade away from an original hub is postulated giving a wedging action which would convert the vertical upthrust into a radial centrifugal pressure in the crust, evidences of which are abundant (apart from the overturning of the collar). The structure is thought to be the surface expression of a terrestrial process which worked on the principle of the hydraulic jack. This inevitably demands the presence of a liquid, at depths below the zone of possible observation. The liquid would be a basaltic or andesitic magma, of which there is plenty of surface evidence. The other essential requirement is a confined space containing the liquid, without which the principle cannot operate; this is presumed to be the space into which the geosyncline subsided. The importance of this interpretation of the structure is that it illustrates one way in which purely vertical upward forces can operate in the earth's crust.

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Transactions of the Geological Society of South Africa, 53, 159-167, 1 tab.

With the assistance of the Geological Survey of Southern Rhodesia, a series of specimens was collected across the Great Dyke. The vertical variation in the mineral phases and the compositions of these phases were investigated. The results are presented in this note. The uppermost rocks found are fine grained, magnetite-bearing dolerites which presumably represent a chilled roof facies of the intrusion. Speculative suggestions are made as to the structural development of the Great Dyke, taking into consideration Weiss' gravimetric profile and the petrological data.

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Transactions of the Geological Society of South Africa, 53, 169-191, 7 pl

The paper deals with a suite of rocks which have not been recorded previously, and which in respect of mode of occurrence, petrological character, and diversity are somewhat exceptional. They occur as minor intrusions in the gabbros and allied rocks of the Bushveld igneous complex immediately south-east of the store at Magnet Heights, and, arranged roughly in order of age, consist of
(a) an elongate body of lamprophyre and albitite;
(b) a plug of ariégite, peridotite, and related rocks;
(c) a dyke of pyroxenite, and a composite dyke of analcite picrite and prehnite-aegirine rock;
(d) five pyroclast-filled, volcanic pipes (diatremes) oriented along a north-south direction parallel to the dykes of younger eruptives,
(e) a vein of carbonatite intersecting the diatremes symmetrically; and
(f) a bifurcating dyke of dolerite.
A brief description, accompanied by five new analyses, is given of these rock-types and their relation to one another, and it is concluded that they constitute a petrographic unit, and are most probably satellitic to the alkali complex at Spitskop in Sekukuniland.

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Transactions of the Geological Society of South Africa, 53, 193-204, 4 pl

The chances of striking water in boreholes sunk in Karroo sedimentary rocks are a function of the resistivity of the formation, and are very small in the mudstones and shales with resistivities varying between 200 and 3,500 ohm. cms. Good supplies are, however, struck in the indurated contact zones of dykes which cut these sediments. Yields of 1,000 to 4,000 gallons per hour are commonly struck in boreholes sited within two feet of the contact. The author describes a field technique for determining the contacts of dolerite dykes under a cover of soil by plotting peaks of vertical magnetic anomalies observed across the dyke and claims an accuracy of 3 feet. Electrical methods for tracing dolerite dykes are also listed and discussed shortly. The author maintains that the electrical methods are greatly inferior to the magnetic method both for speed and accuracy and should be employed only if the dykes are non-magnetic.

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Transactions of the Geological Society of South Africa, 53, 205-208

The suggestion is made that the rocks of the Loskop system, as defined by F.C. Truter (1949), and those of the Matsap system in the Union are synchronous and equivalent in age to the "Lower Dordabis beds" and the Auborus series of South-West Africa. This essentially continental system was strongly compressed and eroded before the deposition of the Waterberg succession in the Union and the Nama succession in South-West Africa and the west of the Cape Province. The possibility of the Waterberg and the Nama being contemporaneous is suggested, the calcareous rocks of the Nama being a local possibility marine development of a widespread system whose members are predominantly red and arenaceous.

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Transactions of the Geological Society of South Africa, 53, 209-227, 1 pl

The stratigraphical features of the area are first described, particular attention being given to the Livingstone and Bird Reefs. The former are well-developed conglomerates with payable gold values only in the North Randfontein area which is thought to have been the site of a river estuary during their deposition. An outline is given of the general structural features of the area followed by a more detailed description of the faults and igneous intrusives observed in the underground workings. It is suggested that the faults encountered in the mines are related to the Witpoortje Fault and are probably of Ventersdorp age, the faults being the channels up which the Ventersdorp lavas travelled. In conclusion, a summarized broad reconstruction of the geological history of the area is given.

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Transactions of the Geological Society of South Africa, 53, 229-242, 4 pl

A contour map of the base of the Karroo System in the area surrounding Odendaalsrus, based on the data obtained in boreholes drilled in the area, indicates considerable and regular sub-Karroo relief, including a deep valley which it is suggested was cut by a valley glacier. The Karroo succession includes the Dwyka series, consisting principally of tillite, which shows great variation in thickness, being thickest where the sub-Karroo contours indicate valley conditions. The Ecca series includes only the Middle and Upper Ecca beds; the former consisting of both sandstone and shale, with coal seams, the latter only of shales. Lower Beaufort sandstones and shales cover the S.E. portion of the area. South of the area, at Trompsburg, deep boreholes indicate that the Ecca series is completely argillaceous. A contour map of the base of the Upper Ecca beds shows only moderate relief, indicating that the sub-Karroo relief is primarily due to pre-Karroo topography.

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Transactions of the Geological Society of South Africa, 53, 243-252, 5 pl

The stratigraphy of the Kimberley-Elsburg Series is described from observations of boreholes and underground workings of five mines in the Far East Rand. One particular conglomerate, the may Reef, has proved to be of economic importance and criteria are given which help to distinguish it from the numerous other beds of conglomerate in the series. The areas in which payable ore have so far been found seem to follow the trend of certain of the underlying beds.

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Transactions of the Geological Society of South Africa, 53, 253-260, 2 pl

Transverse limestone terraces in the Lower Henkries Valley are mapped and described. The implications of Rogers' suggestion that they are constructional features are reviewed in the light of observed facts, and an alternative view is offered, that they are erosional escarpments. Deductions are made as to the present state of the drainage in this area, and its relevance to the question of past climates.

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Transactions of the Geological Society of South Africa, 53, 291-304

Obituary - List of Papers.

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Transactions of the Geological Society of South Africa, 53, 35-52, 2 pl

During 1943 a tungsten-tin deposit was discovered at Van Rooi's Vley, Gordonia district. It proved to be of importance and is being mined at the present day. A brief description is given of the host rocks, the mineralised fracture zone, the ore bodies and the minerals encountered, together with their sequence of crystallisation and relative amounts. The problem of the genesis is discussed and it is concluded that mineralisation is largely the result of replacement along a shear zone. Of special interest is the intensive replacement of scheelite by wolframite which is the antithesis of the usual relationship.

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Transactions of the Geological Society of South Africa, 53, 53-64

The writer describes a case of the directional deflection of a borehole. He proposes a scheme of recording the survey details and plotting the data on a plan, and he suggests possible application to structural problems in areas as the Free State Goldfields or other ore bodies at depth.

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Transactions of the Geological Society of South Africa, 53, 65-72, 4 pl

This paper deals mainly with the metamorphism of the rocks of the Transvaal system at and near the base of the Bushveld igneous complex north of Potgietersrust. Rocks of sedimentary origin, now highly metamorphosed, are more widespread than was previously recorded. They include felspathised quartzites, cordierite-garnet-sillimanite hornfels and pseudo-granophyre. The hornfels was mapped by previous investigators as norite and the pseudo-granophyre as granite. The dolomite suffered profound alteration and in some places the original rock is hardly recognisable.

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Transactions of the Geological Society of South Africa, 53, 73-80, 1 pl

Boreholes sunk in recent years prove that much of the north-eastern Bechuanaland Protectorate is occupied by rocks belonging to the Karroo System, covered for the most part by Kalahari sands.

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Transactions of the Geological Society of South Africa, 53, 81-130, 11 pl

The complex is entirely surrounded by Bushveld granite and granophyre. The irregular outer zones of the complex consist, from the outside inwards, of alkali granite, quartz syenite, red umptekite and white umptekite, all of which are obviously fenitised Bushveld granite and granophyre. The granitic rocks and umptekites have a concentrically sheeted structure with centripetal dip. Nepheline appears in places in the inner umptekites, so that undoubted pulaskitic fenite also occurs. The umptekites are followed inwards by fayalite diorite and theralite. The former is considered to be a fenite, but the origin of the latter is doubtful. The central mass of the complex consists mainly of red, coarse-grained ijolite, black, fine-grained ijolite, and dark melteigite and jacupirangite. The last two rock-types are regarded as fenitised fayalite diorite and theralite.
The fine-grained ijolites probably represent nephelinised biotite pyroxenite, in part at least. The coarse-grained, red ijolite is intrusive into the other ijolites, and may be a truly magmatic rock.
A poorly exposed, stock-like body of biotite pyroxenite is clearly older than the ijolites, but intrusive into the theralite.
Inside the complex are two big ring-dykes of foyaite intrusive into the ijolites and theralites, and in the Bushveld granite outside the complex there are numerous cone-sheets of foyaite and tinguaite. Inside and outside the complex are numerous radial dykes of foyaite, tinguaite, dolerite and lestiwarite.
A big, eccentrically situated body of limestone in the ijolites is considered to be an undecapitated, composite ring-dyke of carbonatite which is younger than the ring-dykes of foyaite. Small plugs of alkali basalt inside the complex, and a calcareous diatreme in the granite outside the complex mark the volcanic phases of the eruptive activity. The small complex of peridotite, ariégite, albitite and carbonatite at Magnet Heights is considered to be a satellite of the Spitskop complex, and it is tentatively suggested that the latter is genetically associated with primary peridotitic magma.

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Proceedings of the Geological Society of South Africa, 53, xxix-xxxviii

I propose giving a brief history of the correlation of the Witwatersrand System and at the same time to indicate the value of geological work to our gold mining industry. Earlier presidential addresses have dealt with particular features of Witwatersrand geology. In this address I deal with the evolution of our ideas in a broad manner. I shall not trouble you with maps, sections or dark intervals with our somewhat dim epidiascope. Such material can be studied at leisure in our Transactions and the published work of the Geological Survey. I regard our annual meetings as a social event - a meeting of friends from various parts of Southern Africa. I shall be as brief as possible. The story can be conveniently divided into two parts - (1) The exposed Witwatersrand Areas, and (2) The Concealed Areas, although there was considerable overlap in their exploration.

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Transactions of the Geological Society of South Africa, 54, 1-10

A volcanic vent about 340 m in diameter cuts quartzites of the Table Mountain Series (T.M.S.) 3 Km ENE of Lambert's Bay. The contents consist of basaltic agglomerate into which an irregular mass of olivine basalt has been injected. The vent differs from all others in the Western Cape and there is no evidence as to an upper age limit.

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Transactions of the Geological Society of South Africa, 54, 11-26

The greisenized stanniferous pegmatites of the Bikita tin-field are concentrated near the eastern end of the Victoria "schist belt", the country-rocks being mainly volcanic greenstones with irrterbedded metamorphosed sediments. These pegmatites mostly form sheets with low to moderate dips and consist largely of albitite with muscovite, large quartz masses and "pockets" of lepidolite greisen and beryl, associated in one area with a stock-like body of friable muscovite-albite granite. Besides cassiterite, the ore-bodies contain tantalum-bearing minerals which include notantalite, microlite and simpsonite. Lithium minerals comprise abundant lepidolite, slightly less abundant petalite, and scarce spodumene and amblygonite, all but the first being concentrated in the southern part of the field. Accessory minerals include topaz, garnet, and zircon.
Wall-rocks are altered to hydrobiotite and zinnwaldite, with black tourmaline, apatite and rutile. At one place diopsidic pyroxene is developed. Microlite and simpsonite have been under exploitation until recently, when the attention of the workers on the field was diverted to beryl, which, with a little amblygonite, is now the only mineral in production. The total output of tin and tantalum concentrates from the field since 1916 is valued at £77,310.

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Transactions of the Geological Society of South Africa, 54, 27-32

A detailed geological survey of the Natal coalfields shows that the coal seams occur in a series of basins, so-called coal provinces, separated from each other by barren or thin-coal areas. Thus far four coal provinces are identified, known as those of Vryheid, Utrecht, Newcastle and Dundee. Each of these provinces differs from the other in the number of major coal seams present, the thickness of the sedimentary partings between them and in the nature and quality of coal contained in them. Each individual coal seam has its own characteristics which are consistent only within the province in which it occurs. The thin-coal areas separating the coal provinces have several points in common and can easily be envisaged as constituting a system of connected channels draining the coal-forming swamp at the time of the deposition of the coal. Repeated inundation and gradual sinking of the sub-continent gave rise to sedimentary partings and the shifting of the coal-forming swamps from east to west at successively higher horizons.

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Transactions of the Geological Society of South Africa, 54, 33-64

Rhodesian landscape has developed under a number of cycles of pediplanation (scarp retreat and pedimentation) which have crated plains or partial plains arranged step-wise in the landscape. The various land-surfaces are dated, and their distribution is depicted on a map. Deformation undergone by the various surfaces is discussed, as also the influence of "solid geology" upon landscape forms.

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Transactions of the Geological Society of South Africa, 54, 65-68

A short cyclical sequence of varved sediments of the Nama System is described. In this sequence of probably late Algonkian age a cycle of 11.4 units is exhibited. If the varves are interpreted as of yearly origin, the cycle corresponds to the sunspot cycle.

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Transactions of the Geological Society of South Africa, 54, 69-84

The relatively unknown Chimanimani Mountains form the most easterly portion of Southern Rhodesia, on the frontier with Portuguese East Africa. The southern end of the range lies at approximately 20°S., 33°E. It rises to nearly 7,500 feet and is carved from various metamorphic rocks. The rocks strike north and south. The structure consists of a series of isoclinally folded quartzites on the west, which are separated from the Umkondo sediments by a powerful north-south normal fault. Thrusting has carried two blocks of metamorphosed sediments over the isoclinally folded quartzites. The rocks caught between the two major thrust planes have suffered intense shearing and folding, which has resulted in retrograde metamorphism. 'Thrusting is well developed and acted from east to west. The metamorphism due to this movement in distinguishable from an earlier period of regional rnetamorphism on which its effects were superimposed.

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Transactions of the Geological Society of South Africa, 54, 85-88

From 1911 to 1938 earthquake observations were collected by the Meteorological Office at Windhoek. During that time, 435 earthquake observations on 223 different tremors were reported. The tremors were mostly weak, only a few strong ones, ranging from grade 6 to 7 according to Mercalli's scale, were recorded. The geographical distribution shows that the seismicity is chiefly concentrated in the Escarpment Region. The coast and the eastern parts of the country seem to be practically free from earthquakes. The yearly and monthly distribution of the tremors is briefly discussed.

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Transactions of the Geological Society of South Africa, 54, 89-98

A description of the mineralogy of a number of specimens of manganese ore from Otjosondu, South-West Africa, is given. The following minerals were identified in the material studied: Braunite, jacobsite, "vredenburgite", hausmannite, bixbyite, hollandite, hematite, calderite garnet, celsian, hyalophane, barite, diopside-acmite, rhodonite and manganese peroxides. The deposit is probably of sedimentary origin, but its present features are to a large extent the result of metamorphism by intrusive younger granite.

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Transactions of the Geological Society of South Africa, 54, 99-133

The principle of radiometric logging in boreholes of narrow diameter has been applied to problems of correlation and the location of auriferous and uraniferous conglomerates of the Witwatersrand system. The results of this work have shown a very well defined cyclic distribution of the uranium in specific well-defined zones out of which it is seldom found. The remarkable continuity of these radioactive markers has enabled correlation to be made between widely separated areas in the Orange Free State. Due to the fact that the uranium deposition is not greatly affected by facies changes in the sediments, extensions, hitherto unsuspected, have been found to the conglomerate horizons of the Leader-Basal zone. Suggestions are made as to the general conditions prevailing during the deposition of the upper sediments of the System. The possible future uses of this method of prospecting in problems facing the geologist who has to deal with the Witwatersrand System are discussed.

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Proceedings of the Geological Society of South Africa, 54, xxvii-lxvi

Recent developments of methods for determining the age of rocks by radioactivity bring the time near when a world-wide nomenclature of Precambrian eras comparable with the classification of fossiliferous rocks should be considered. Recent work by L. H. Ahrens on lepidolite indicates that the gold-bearing formations of Southern Rhodesia were formed more than two milliard (2,000x10(6)) years ago. Published determinations of the age of rocks in other parts of Africa relate mainly to younger Precambrian formations.
The Rhodesian gold-bearing formations are described and stress is laid on the undifferentiated nature of the Archaean sedimentary rocks and the conclusion is stated that a sedimentary suite of rocks highly differentiated into clays, sandstones and limestones whatever its state of metamorphism may be, is unlikely to be of very great geological age.
Attention is drawn to the remarkably low grade of metamorphism of the Archaean rocks in the central part of the Colony, although the rocks usually dip at angles exceeding 45 degrees. The structure of the gold belts suggests gravitational subsidence of a thin crust in a lighter medium, and appears to be determined not by the intersection of orogenic belts, but by the location of gregarious ovoidal batholiths (gneiss domes), between which the schists have a synclinal structure often cleaved by cupolas or triangular in shape. In dealing with rocks formed when the world was less than half of its present age, a strict adherence to the doctrine of uniformitarianism is considered unjustified.
The Rhodesian Archaean granites are studied on the basis of published and other information, and four main periods of eruption are recognized. The first is an old tonalitic gneiss which is post-Sebakwian but older than the principal gold-bearing formations comprising the Bulawayan and Shamvaian systems, into which the younger tonalitic gneiss is intrusive. The principal lepidolite bearing pegmatites and the main sulphur-gold mineral

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Transactions of the Geological Society of South Africa, 55, 1-11, 3 pl

Tillites with striated boulders and associated varved sediments have recently been discovered in the lowest part of the Karroo rocks in the Eastern Sebungwe district of Southern Rhodesia. These are considered to be of late Dwyka age. The varved sediments show evidence of a cycle of about 12 years duration, which is compared with the well-known sunspot cycle. The correlation of the divisions of the Lower Karroo sediments in Southern Rhodesia is revised in the light of the recognition of the Dwyka conglomerate.

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Transactions of the Geological Society of South Africa, 55, 125-132, 1 pl

Underneath a thick, but variable cover of Kalahari beds, the Karroo rocks of the Bechuanaland Protectorate are believed to form a huge basin, extending from Keetmanshoop to near Francistown. Over much of this area Karroo basalts have apparently been preserved. It was found that impossible to differentiate petrographically between Karroo- and post-Waterberg dolerites. Many so-called post-Waterberg dolerites are probably of Karroo age. A new petrographic type of Karroo dolerite is described.
Karroo dolerites of the eastern part of the Protectorate are generally quartz-rich, while the associated basalts contain small amounts of olivine. Throughout southern Africa dolerites of Karroo age show a rough regional zoning of predominant petrographic types. A rare, iron-rich type of Karroo dolerite in the Karroo basin proper is of common occurrence in the north-eastern part of the Protectorate, where it is found in dikes and lava flows, but apparently not in sheets. Synthetic phenomena associated with dolerite intrusions have been found in only four localities. It is believed that the paucity of such phenomena, as compared with the Karroo basin proper, may be due to a relatively thin cover of sediments throughout the eastern part of the Protectorate.
The dolerite sheet at Khale is described in greater detail, and it is noted that clouded plagioclase occurring in parts of the sheet is probably due to auto-metamorphism. Several minerals found in epidotised joints in the dolerite also occur in pegmatitic segregations of the surrounding Gaberones granite.

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Transactions of the Geological Society of South Africa, 55, 13-18

Two actinolites and a chlorite have been separated from actinolite schists occurring in the Prieska district. The analysis, formulae and optical properties are given. The chlorite is considered to be a ripidolite.

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Transactions of the Geological Society of South Africa, 55, 133-154, 5 pl

The distribution of radioactive material in the West Witwatersrand area is discussed and compared with that of similar sediments in the Klerksdorp and Orange Free State areas. As a result of this comparison the conclusion is reached that the succession is the same in all three areas, and the great majority of the radioactivity cycles, although showing some variation, preserve their position and characteristics remarkably well over the whole area. From the logs illustrated it is considered that the Monarch, Vaal and Basal reefs occurpy the same position within their cycle, while the Monarch Upper Leaders can be correlated with the Vaal Reef Leaders and the Leader reefs of the Orange Free State. Logging has shown that areas in which the Vaal and Basal reefs are auriferous from an economic point of view, give radioactivity curves which differ from those obtained over gold barren areas and suggestions are made as to the cause of this. The apparently abnormal distribution of activity in the Van den Heevers Rust area is discussed and shown to follow the general pattern of the Orange Free State.

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Transactions of the Geological Society of South Africa, 55, 155-174, 3 pl

The granites in this area consist chiefly of two varieties of Bushveld granite: a very coarse-grained type, carrying biotite and hornblende, and a much finer-grained, porphyritic variety with both feldspar and quartz insets in a matrix which contains feldspars, quartz, and biotite. The latter granite occurs as sills in the former. Large areas, particularly to the west, appear to be underlain by granitized sediments. The granites and granitized sediments have been subjected to processes of fenitization (desilication) at a number of places, especially where these rocks are traversed by veins and dykes of carbonatite (beforsite). An isolated occurrence of volcanic breccias on the farm Tweerivier is regarded to be related to the period of carbonatite emplacement. A large xenolith of Transvaal dolomite, entirely surrounded by Bushveld granite, is described. Gabbro (in bosses) and beforsite (in dykes) intrusive respectively into the southern and northern halves of the dolomite xenolith have also been investigated.

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Transactions of the Geological Society of South Africa, 55, 175-198, 2 pl

Dolerite dykes below the Cave Sandstone in the North-eastern Cape Province are not amygdaloidal and seldom contain glass, above this level they are usually glassy and sometimes amygdaloidal. The younger member of a pair of intersecting, olivine-bearing dykes contains, if anything, the more magnesian olivine.
Pigeonite is present in about half the number of dolerites examined; orthopyroxene occurs in only one dyke rock. A genetic relationship between volcanic vents and conical sheets of dolerite is suggested by their complementary distribution. The vents are taken to have been drilled by agents which emanated directly from the conical sheets. The latter, in turn, were fed from sills which caused overlying conical fractures by uneven uplift of their roofs.
The dolerite of the conical sheets is of the Perdekloof type and bears, i.e. olivine (2Vα=73°±3°) and pigeonite. No fresh olivine was found in any of the basalts, excepting in three specimens from Basutoland, previously recorded by Stockley. This olivine (2V about 90°) has the same composition as that occurring in the glassy limburgites and nepheline basalts of the Kruger National Park.
A nephelinite from this area contains, i.a., anorthoclase but is free from both glass and olivine. The northern Lebombo region also contains Karroo rocks of granitic composition: rhyolite, granophyre occurring as plutons and microgranite in dyke form. They are all regarded as of magmatic origin. Petrographically these rocks differ from one another and amongst themselves mainly in differing proportions of the same constituents. Sixteen new chemical analyses are reported.

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Transactions of the Geological Society of South Africa, 55, 19-31

The dolerite intrusions in the coalbearing Ecca series in Natal have affected the economic value of the coal, and are responsible for the complicated geological structure of the Natal coalfields. The so-called faults are now known to be due to uplift of sedimenatary beds above the sheet intrusions. Various types and ages of dolerite are present and their mode of intrusion and origin are discussed. Metamorphism in the sedimentary beds invaded by dolerite is confined to heat effects. The coal beds are devolatilised to a greater or lesser extent and a relationship is found to exist between the thickness and distance away of an intrusion and the volatile content of the coal.

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Transactions of the Geological Society of South Africa, 55, 199-232, 6 pl, 1 tab.

The four common types of amphibole asbestos, anthophyllite, tremolite-actinolite, amosite and crocidolite were examined by X-rays and differential thermal analysis. Proof was found to classify amosite as a member of the cummingtonite-grunerite series. The intimate association of amosite and crocidolite is described where seams of amosite and crocidolite lie next to each other. Crocidolite and amosite are also mixed within a single seam, which has a lighter blue colour than pure crocidolite. The presence of magnetite and quartz as impurities in the fibres was determined and may account for the varying chemical analyses quoted in the literature. It is suggested that a process of thermal metamorphism has formed grunerite and riebeckite (the lamellar amphiboles) and a subsequent process of shearing caused the actual fibre growth from both or one side of a seam inwards.

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Transactions of the Geological Society of South Africa, 55, 233-280, 6 pl

In this study information on the emplacement of the Merensky Reef and associated rocks was sought by means of petrofabric analysis. Special reference is made to the structurally disturbed portions of the reef, which are characterized by peculiar "circular depressions". The diameter of these depressions is up to ten times their depth. Inside the depressions the reef widens out towards the sides so that they resemble an inverted funnel. They are isolated structures having no relationship to each other and have not been formed by faulting or other mechanical deformations after crystallisation. A brief description of the mineralogy and petrography of the various rock types is given. Petrographical data for the undisturbed Merensky Reef is compared with that of the reef in the "circular depressions".
A detailed study of the orientation of the orthopyroxenes and feldspars indicated that: -
(a) these minerals are orientated with their largest faces parallel to the pseudostratification;
(b) the orthopyroxenes in the undisturbed reef show no directional alignment in the plane of the pseudo-stratification, in the disturbed portions they are aligned parallel to the sides of the "depressions".
It is suggested that the Merensky Reef and associated rocks were formed by crystal settling. A theory is put forward that the "circular depressions" could have formed by the swirling motion of currents in the magma chamber.

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Transactions of the Geological Society of South Africa, 55, 281-328, 10 pl

In quarries near Vereeniging, Transvaal, South Africa, in Middle Ecca (Lower Permian) beds, five species of Glossopteris have been found, each with a characteristic fructification attached to the leaf. In each case at least several attached specimens, and a larger number of detached ones, have been found. A sixth species has only been found detached. The fructifications on G. browniana, G. indica, G. tortuosa, G. conspicua and the sixth detached form have much in common and have been placed in one new genus which has been called Scutum as they are shield-like. The fructification on G. retifera differs sufficiently to be classed in another genus Lanceolatus. The species are described and the characteristics of the fertile leaves on which they grew reviewed. The fructifications are all impressions but the evidence points to their being the megasporophylls or seed-bearing organs rather than the pollen-bearing organs. The classification of plants bearing Glossopteris leaves as pteridosperms is now confirmed. A comparison is made with fructifications previously described as associated with, but not connected to, Glossopteris leaves. The contribution of these fossils to the elucidation of evolutionary palaeobotanical problems is considered.

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Transactions of the Geological Society of South Africa, 55, 329-330, 2 pl

The occurrence of a readily accessible and well defined glacial pavement is described. The pavement, formed by Dwyka glaciation, is on striated Table Mountain Sandstone, near Maidstone, Natal. The striations already exposed by quarrying operations, cover an area of approximately 80 square yards, and have a strike of 47° E. of N.

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Transactions of the Geological Society of South Africa, 55, 33-52, 8 pl

The method of correlation in the Witwatersrand system, using radioactivity logging equipment in narrow boreholes, has been applied to problems in the Klerksdorp area. As in the goldfields of the Orange Free State, remarkable continuity of markers characterised by specific degrees of radioactivity was found, and extensive use has been made of these in the developement of a classification covering the Upper Division of the Witwatersrand system and based entirely on the radioactive content of the sediments. The Vaal reef is readily recognised on the radioactivity logs and extensive use was made of this in determining its position when core recoveries were incomplete, or the gold values too low to permit of positive identification. Some aspects of variation in normal of the Ventersdorp lavas and the Dolomite are recorded and suggestions made as to future use of such variations.

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Transactions of the Geological Society of South Africa, 55, 53-71, 4 pl

Auriferous conglomerate, quartzite, shale and rhyolite (the last changed in places to granophyre) are described. All these sedimentary and extrusive rocks are grouped by the author in part with the Dominion Reef system and in part with the Hospital Hill series of the Witwatersrand system. Intrusive hyperite shows marked contact-metamorphic effects with the rocks enumerated. Ten new analyses are included of which eight are of the intrusive suite. Geophysical work carried out, satisfactorily elucidated the geological structure of the area and showed that the rocks occur in the form of a large syncline which pitches towards the south. The formations comprising the syncline form an inlier in the younger Ventersdorp system. The possible extenison of the syncline southwards beneath the cover of younger rocks is discussed and it is pointed out that the Government Reef Series including its gold-bearing bands may be developed under cover at higher horizons in the same way as at Klerksdorp.

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Transactions of the Geological Society of South Africa, 55, 73-88, 4 pl

South-west of Umlaas Road, Natal, certain fault-bounded hills, capped by Table Mountain Sandstone, occur in an area that is predominantly underlain by Dwyka Tillite. Rocks of the Basement Complex appear in the valleys adjacent to these hills. All the faults are post-Karroo in age, being associated with the Natal Monocline. The sandstone-capped hills are not horsts but monadnocks on a pediplain.

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Transactions of the Geological Society of South Africa, 55, 89-123, 2 tab.

The use of an automatic temperature recording instrument is discussed and its accuracy compared against measurements made with mercury thermometers. The thermal behaviour of the Pretoria and the Dolomite series, the Ventersdorp lava and the Witwatersrand beds as intersected in the Stilfontein-Hartebeesfontein area is dealt with and the influence of structure on temperature discussed. On the basis of temperature surveys in ten boreholes, the higher temperatures prevailing at depth in the Orange Free State are related entirely to the presence of overlying sediments.

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Proceedings of the Geological Society of South Africa, 55, xxix-lviii, 1 pl

It is an established fact that industrial development is retarded to a considerable extent if a country lacks adequate supplies of that black rock called coal. It is generally accepted today that no nation can achieve greatness in the industrial world without sufficient reserves of coal. The United States of America, England, Germany and Russia are all examples of nations that have reached industrial heights because of their resources of coal. Last but not least the Union of South Africa may be cited as an example of a young country on the way to industrial expansion mainly due to sufficient supplies of coal and iron ore.
On reviewing the mineral industry of the Union of South Africa we find that we are indeed fortunate in that, apart from gold and diamonds, the value of our total coal production exceeds that of any other mineral substance.
In spite of recent events, and the enormous strides that have been made in research on nuclear energy for the use of mankind, coal is likely to remain an important source of energy. It plays an important role in both national and international affairs.
The distribution of energy-producing resources determines the trend of world trade. It has been recorded that the traffic in fuels, especially petroleum and its products, constitutes 40% of international trade, and it is therefore not necessary to expound further on the importance of such resources, of which coal is a very essential one. It can be put to thousands of different uses, even excluding its immediate conversion into a source of power.
The chemical study of coal and its different products has also advanced enormously within the last few decades, but it may be regarded as trespassing on dangerous ground for a geologist to wander into this field. As will be shown subsequently, the Union possesses extensive reserves of coal; although it is perhaps not everywhere very high-grade, the quality is in general by no means poor. Exploitation for the normal uses to which coal

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Transactions of the Geological Society of South Africa, 56, 1-19, 2 pl

Detailed mapping of the outer marginal belt of the north-eastern sector of the Vredefort dome in the Barrage-Lindequesdrift area shows that the structures displayed by the strata belonging to the Transvaal system may be divided into three structural zones, which diverge towards the south-east. These three zones comprise a northern and a southern zone with imbricate structures and isoclinal folds and an intermediate zone with brachystructures. The salient features are the en echelon disposition of the brachystructures and of some isoclinal folds within the zones with imbricate structures; the transition in a north-western direction of the intermediate zone into the zone with imbricate structures; the bending or folding of thrust-planes; and finally younger fault-systems, such as tear-faults between brachy-anticlines, transverse faults, and thrust-faults branching off the northern zone and extending into the intermediate zone. All evidence collected indicates that the intermediate zone served to take up differential adjustments between the zones with imbricate structures, and that the brachystructures were caused by rotational stresses. Finally it is concluded that the radial pressure exerted in the northern sector of the Vredefort dome was more prowerful than that in the eastern sector. A short description is given of the intrusive rocks of the area, in particular of the alkali rocks.

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Transactions of the Geological Society of South Africa, 56, 121-129

Evidence is cited to the effect that land in the vicinity of Durban is subsiding with respect to sea-level at a rate of one-quarter of an inch to one inch per annum.

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Transactions of the Geological Society of South Africa, 56, 131-148

The temperature of artesian water found in boreholes through Karroo (Ecca) sediments in Southern Rhodesia has provided data on the thermal gradients in these rocks. These figures show that the crust is in thermal equilibrium and that the thermal gradient is steep. In the light of these results and recent stratigraphical studies, the origin of natural thermal and mineral springs in the middle Zambezi region is re-examined. The conclusion is reached that even the hottest springs are of meteoric origin, the temperatures being due to the depth to which the water has penetrated. The rise of the water to the surface is attributed to natural artesian conditions, the water running down dip underground and rising along faults and other fissures.

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Transactions of the Geological Society of South Africa, 56, 149-176, 2 pl

The use of differential thermal analysis in the identification of minerals has become well established during the past twenty years. The method is of exceptional value in clay mineral investigations and in the identification of other fine-grained hydrous materials. The technique of differential thermal analysis is described and details of the two types of apparatus used in this study are given. Differential thermal curves of sixty-one South African minerals are illustrated and a comprehensive list of references on the subject is included.

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Transactions of the Geological Society of South Africa, 56, 177-182

Agate pebbles collected along the south-east coast of the union in the Peddie and East London districts, in the Transkei and also in Natal, are considered to be derived from Drakensberg lavas. The nearest outcrop of the lavas to some of these localities is about 140 miles, but the lavas may have originally occurred much nearer.

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Transactions of the Geological Society of South Africa, 56, 183-186, 1 pl

A description is furnished of a new brachiopod from Manuan Creek, Zululand, T. manuanensis, and comparisons are made with similar species from other regions.

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Transactions of the Geological Society of South Africa, 56, 21-35, 2 pl

Details are given of the installation and operation, on behalf of the Geological Survey, of four modern short-period seismographs at Pretoria, Grahamstown, Pietermaritzburg, and Kimberley. The methods of locating near earthquakes, and the use of cards for collecting observer reports, are described. Previous earthquakes are reviewed and the distribution of some 70 new earthquakes in Southern Africa is given with an estimate of their magnitude. The use of sensitive seismographs has increased the number of local earthquakes observed from about 5 to 50 per annum and some new centres of seismicity have been revealed.

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Transactions of the Geological Society of South Africa, 56, 37-43, 1 pl

Between Mariental and Keetmanshoop the Dwyka succession contains at least two zones of marine sediments that have yielded fossils. These sediments are interspersed between beds of glacial origin, having been deposited by ice that came from the west and northwest. Pre-Dwyka valleys containing remnants of glacial deposits have been observed in several parts of the country. These suggest that many of the present-day valley systems already existed in pre-Dwyka times. Two pre-Dwyka peneplains have been recognised, one into which the valleys are cut, and one on to which they emerge. The lower peneplain is surmounted by monadnocks. The Joubert mountains in the Kaokoveld seem to represent a pre-Dwyka watershed from which the Dwyka glaciers moved eastwards and westwards.

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Transactions of the Geological Society of South Africa, 56, 45-58, 2 pl

An account is given of a small, satellitic and asymmetrical dome north of Vereeniging, which was formed on the north-eastern boundary of the synclinorium around the Vredefort dome. The diameter of this structure, for which the name "Vereeniging dome" is proposed, is approximately seven miles. Its central portion is occupied by the Dolomite series, whereas the marginal zone, with the exception of the south-eastern sector, is composed of the Timeball Hill and lower Daspoort beds. The structures displayed in the maginal zone are the result of the interaction of the updoming forces and the stresses which formed the regional structures, such as minor anticlines and synclines of the synclinorium. The resulting structural features are isoclinal folds and shear-faults in the north-eastern and western sectors and cross-folds in the north-western and northern sectors. Some of these structures are small replicas of those represented in the outer marginal zone of the Vredefort dome. Post-doming faulting and subsidence took place on a small scale. Intrusions of Bushveld age in the north-western and northern sectors of the marginal zone of the Vereeniging dome were emplaced at the end of the updoming period. The intrusive rocks are diabase, gabbro and pyroxenitic norite. The problem of the origin of the dome is not yet solved. The two alternative hypotheses put forward are magmatic updoming and a tectonic origin similar to that of the brachystructures around the Vredefort dome.

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Transactions of the Geological Society of South Africa, 56, 59-91, 5 pl

A Burdigalian (Lower Miocene) marine fauna from Uloa, Zululand, is described. It is of warm-water environment and indicates, in comparison with the modern fauna, a slow rate of organic evolution for the region. It is Indo-Pacific in type, comparing very closely with Tertiary faunas of East Africa and India, but is at variance with Tertiary faunas from the Cape Province.

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Transactions of the Geological Society of South Africa, 56, 93-98, 1 pl

Seams of crocidolite occur in coarse-grained arkoses of the Chuos Tillite horizon. The seams are made up of tufts of fibre which are elongated in all directions parallel to the bedding planes. The rocks in this area were metamorphosed regionally. The arkose was converted to a quartzitic rock with minor amounts of muscovite and biotite. Thin intercalations of argillaceous matter were altered to biotite schists. Subsequent introduction of sodium and boron gave rise to feldspathization and tourmalinization. After all the alumina-rich minerals (presumably muscovite, andalusite, etc.) had been converted to soda feldspar, the biotite, both in the arkoses and in the schists, was almost entirely replaced by crocidolite.

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Transactions of the Geological Society of South Africa, 56, 99-119, 3 pl

The attapulgite-montmorillonite deposit in the Springbok Flats is closely related to the basalt of the Stormberg series from which it weathered progressively via montmorillontie to attapulgite. The clay was probably concentrated in certain areas by local tranportation. Samples obtained from pits and boreholes were subjected to an extensive investigation by means of chemical, differential thermal, and X-ray diffraction analyses. The experimental data which led to the identification of the attapulgite, as well as the clay mineralogy of the deposit, are described in detail. Variations occur in the clay mineral constitution and carbonate contamination throughout the deposit. The importance of this fact in the exploitation of the deposit is stressed. The possible industrial applications of the various types of material are also considered.

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Proceedings of the Geological Society of South Africa, 56, xxxi-xli

The last centennium has seen an enormous increase in the use of chemical analyses by petrologists. But the difficulty, tediousness and high cost of silicate analyses has been a restricting factor, despite the necessity for many such analyses if information of any value is to be obtained concerning the paragenesis of rock suites. A recent co-operative research project has shown that chemical analyses of silicate rocks are not so accurate as commonly imagined by petrologists and this has serious implications. Improved methods of micrometric analysis suggest the possibility of calculating the chemical composition from the mode. Simple tests show that in the case of medium or coarse-grained basaltic rocks, results might be obtainable which for plotting purposes would be almost as useful as those determined chemically.
If such methods can be developed, much time and money will be saved, but a wider knowledge of the chemistry of silicate mineral series is a sine qua non. The potentialities of spectrographic analysis are discussed and emphasis is laid on the importance of spectrochemistry to petrologists and economic geologists in the Union. A plea is also made for closer co-operation between chemists and geologists.

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Transactions of the Geological Society of South Africa, 57, 1-18, 4 pl

Of the non-alkaline intrusions of post-Transvaal age in the southern Transvaal the Losberg Intrusive Complex represents the most complete differentiation sequence. The rocks comprising the complex range from ultrabasic to acid differentiates, such as harzburgite, pyroxenite, norite, granophyric gabbro and granophyre. There are also basic and granophyric hypabyssal rocks. The complex is intrusive into the sedimentary rocks of the Magaliesberg stage along the major axis of the synclinorium around the Vredefort dome. The irregular structural disposition of the Magaliesberg quartzite in the vicinity of Losberg is mainly due to large-scale fragmentation by intrusive action. The shape of the main intrusive body is ethmolithic. Contact-metamorphic rocks, such as hornfels and feldspathised quartzite, grading into granophyre, are locally well developed. Chemical data point to a close relationship with the non-alkaline marginal intrusions of the Vredefort and Vereeniging domes. The differentiation of the intruding magma is considered to be mainly controlled by intermittent supplies in quick succession from deep-seated reservoirs, by gravitational differentiation in depth and to a minor extent in situ, and by hybridization, i.e. replacement and assimilation of sedimentary rocks, in particular near the roofs of the intrusions.

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Transactions of the Geological Society of South Africa, 57, 125-172, 6 pl

The Okonjeje complex is one of a series of related Post-Karroo intrusives in the Damaraland region of South West Africa. Exposed over a roughly circular area of about 20 square kilometres, the igneous rocks of the complex can be clearly differentiated into (a) an earlier tholeiitic series showing continuous mineral and chemical variation from olivine gabbro through ferrogabbros to rocks of acid composition, followed by (b) a series of alkali rocks ranging from olivine gabbro and essexites to pulaskite, foyaites and tinguaites with an associated radial dyke suite of alkali lamprophyres. Both series are considered to have been derived from a common parent basic magma by processes of fractional crystallization involving dominant fractionation of mafic and felsic constituents respectively. Structures are of the ring type, together with evidence for faulting and cauldron subsidence accompanied by magmatic injection.

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Transactions of the Geological Society of South Africa, 57, 173-195, pl 1

It was previously thought that the small outcrop of arkoses and conglomerates exposed in the headwaters of the Nachipere Stream, Southern Nyasaland, represented the unmetamorphosed equivalent of the Basement Complex (Pre-Cambrian) of that part of the Protectorate. Accordingly the name Nachipere series was given to these Basement Complex rocks and a suggestion made that they could be correlated with the Lomagundi system of Southern Rhodesia. Subsequently work has shown, however, that the unmetamorphosed sediments in their type locality contain poorly-preserved fossil plants and are probably of Upper Palaeozoic (Cape system) age. Petrological and structural evidence also lends support to this conclusion. A local post-Nachipere series, pre-Karroo system period of metamorphism has also since been deduced. It is suggested, therefore, that the term Nachipere series should henceforth be used only in its restricted sense, that is for the small outcrop of sediments on the upper Nachipere Stream, their local metamorphosed derivatives, and any outliers that may subsequently be found. Pending the geological mapping and detailed correlation of the Pre-Cambrian rocks of Southern Nyasaland with those of neighbouring territories, it is proposed that they should simply be termed the Basement Complex. Thus the original Nachipere series (F. Dixey) includes both the Nachipere series (s.s.) and the Basement Complex as defined above.

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Transactions of the Geological Society of South Africa, 57, 19-26

Two revisions are proposed in the landscape history for South-East Africa. The first suggests that new landscape cycles pass farther up the rivers than has been generally conceded hitherto; the second postulates an extra cycle, the "post-Gondwana", between the "Gondwana" and "African" landscape cycles. Correlations of erosional landscape cycles with continental and marine depositional cycles are tabulated at the end.

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Transactions of the Geological Society of South Africa, 57, 197-208, 3 pl

The carbonatite at Loolekop is the innermost portion of a near-vertical, plug-like body of sub-volcanic rocks with a zonal structure parallel to the periphery. The outer zone of syenitic rocks is followed inwards by shonkinite, pyroxenite, pyroxene-vermiculite-olivine pegmatoid, magnetic-olivine-apatite rock, and finally carbonatite. The carbonatite contains an interesting suite of minerals: apatite, baddeleyite, calcite, dolomite, chondrodite, olivine, biotite and phlogopite; the sulphides chalcopyrite bornite, chalcocite, pentlandite and valleriite; and the oxides magnetite, ilmenite, spinel and uranoan thorianite. As far as could be ascertained, baddeleyite and uranoan thorianite are reported for the first time from the Union of South Africa. Spectrographic analysis indicates the possibility that carbonatitic carbonates differ in composition from limestones of sedimentary origin. Trace elements previously reported in carbonatites from other localities are also present in the Loolekop carbonatite; it was possible to determine the minerals in which these elements occur. Two chemical analyses of uranoan thorianite indicate variation in composition with depth. The calculated age is between 1,100 and 2,000 million years. It is suggested that the suite of rocks at Phalaborwa formed as a result of the reaction between carbonatitic magma and granite.

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Transactions of the Geological Society of South Africa, 57, 209-227

The method of geological age determination, involving the decay of the uranium isotopes and of thorium to different isotopes of lead, is applied to uraninite and "carbon" concentrates from the Witwatersrand system. The reliability of the mass spectrometric results is proved and details are presented of the method of computing the results. Uraninite concentrates and samples of galena, where the latter were obtainable, cover the area from the Far East Rand through the West Rand to Klerksdorp and into the Orange Free State goldfields. Almost every one of the recognized series of the Witwatersrand system is represented in the suite of samples studied. Despite the unsuitability of these uraninites as age index material it is concluded that all the uraninites of the Witwatersrand system fall within narrow age limits and that they are apparently all derived from the same ancient source which is older than the sedimentary system. The results obtained seem to favour a most probable age of between 1850 and 1950 million years. The facilities available at present do not permit of a more complete study of secondary processes which seem to be involved. Suggestions are made as to future studies to be undertaken.

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Transactions of the Geological Society of South Africa, 57, 228-230, 1 tab.

Since age determinations calculated from mass spectrometrical results are based on chemical analyses, the analytical procedure is briefly described and the accuracy of the results is discussed. The ores analysed may be divided into two groups, the one consisting of relatively pure uraninites with a uranium content ranging from about 45 to 60%, and the other of carbonaceous material containing uraninite as a minor constituent. In the latter group the uranium content varied between about 0.1 and 10%. One sample, an impure Marievale uraninite, fell between these groups with a uranium content of 25.9%, but analytically it could be classified under the first group. The weights of samples used for analysis are shown in Table VII. Two methods were used to effect solution of the ores. Samples belonging to the first group were dissolved in hot concentrated nitric acid, while those from the second group had to be digested with a mixture of nitric, perchloric and sulphuric acids to destroy carbonaceous material. The silicious residue from the nitric acid digestion contained no detectable amounts of thorium and lead, and never more than traces of uranium.

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Transactions of the Geological Society of South Africa, 57, 27-37, 1 pl

The microfossil content of the economically important coal seams, mined near Dannhauser, has been examined, in order to provide a basis for correlating these seams with the coal seams which are found in other parts of South Africa. Twelve new species of spores which have been isolated from these seams have been described. These spores have been assigned to existing genera, but no new specific names have been created. One of these species seems to have a very limited range in time, and should be of value for correlation purposes. This paper should be regarded as preliminary rather than exhaustive in nature.

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Transactions of the Geological Society of South Africa, 57, 39-60, 4 pl

This paper deals mainly with a suite of acidic hybrid rocks occurring in the upper portion of the Transvaal system which forms the floor of the Bushveld Igneous Complex north-east of Pretoria. It is concluded that these hybrid rocks consolidated under complex conditions involving both assimilation and differentiation.

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Transactions of the Geological Society of South Africa, 57, 61-75, 1 pl

The deposits of manganese ore are found some 50 miles SSW of Postmasburg, on the flanks of low, rounded hills of banded, siliceous and ferruginous rocks belonging to the Lower Griquatown stage of the Pretoria series. The ore-deposits themselves are confined to a bed of banded ironstone, 25-30 feet thick, which lies just below the Tillite zone. This bed of banded ironstone, as well as the underlying, more siliceous rocks, has been thrown into a series of synclinal and anticlinal folds of small amplitude, along the flanks of which the ore-deposits are found. The ore-bodies take the form of well-defined bands, up to 3 feet thick, with sharp upper and lower contacts, which are conformable to the bedding of the banded ironstone and which convey the impression that the ore has been deposited contemporaneously with the banded ironstone and is therefore of sedimentary origin. Closer examination reveals that these apparently bedded deposits grade in places into the underlying banded ironstone and laterally either wedge out or fade away into a manganiferous, banded ironstone. Most of the deposits take the form of stout lenses, more or less conformable to the bedding of the banded ironstone, or of irregular masses from which offshoots finger into the country-rock in all directions or follow joint-planes into the overlying and underlying strata. This indicates that the ore has been formed by replacement subsequent to the deposition of the banded ironstone and presumably during the Matsap orogenic epoch, and that it is to a large extent of hydrothermal origin.
The individual deposits, which have been opened on several farms, appear small on the surface and their extent in depth still has to be proved. The ore is of low grade the Mn content being on the average 35% and the Fe content 25-27%. As a small producer of low-grade manganese ore, this area may, however, be of economic importance for several years to come.

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Transactions of the Geological Society of South Africa, 57, 77-82, 2 pl

The occurrence of chromite veinlets cutting across pyroxene bands in the lowermost part of the Critical Zone of the Bushveld Igneous Complex is described. Details are given of microscopic features of the chromitites and pyroxenites and it is concluded that the major part of the chromite crystallized from a chrome-rich residual liquid.

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Transactions of the Geological Society of South Africa, 57, 83-124, 11 pl

The Messum complex belongs to the line of the big late-Karroo volcanoes and plutons which stretches from Cape Cross at the coast to Okorusu north of Otjiwarongo. Messum shows a greater variety of igneous rocks and a more complex structure than the other plutons. The following sequence of events can be recognised:
(1) Extrusion of basaltic Stormberg lavas,
(2) Building up of a huge volcanic cone containing acid tuffs, basaltic and rhyolitic lavas, and coarse agglomerates,
(3) Intrusion of a massive gabbro lopolith and differentiation of anorthosites from the thickest gabbro sheets,
(4) Cauldron subsidence of the whole volcano, intrusion of aplogranite on the ring-faults and granitisation of tuffs and lavas,
(5) Cooling and subsequent intrusion of radial dolerite dykes,
(6) Cauldron subsidence of the core, intrusion of microsyenite followed by uprising of a tinguaitic ring-dyke,
(7) Intrusion of a foyaite into the vent accompanied by nephelinisation and syenitisation of the agglomerates,
(8) Cooling and subsequent intrusion of nepheline basalt, nephelinite and nepheline-basanite dykes.
The other big plutons show the same connection of intrusion and cauldron subsidence. Cone sheets are not developed, and this is explained by the assumption that the whole region was probably in a state of undirected tension. Such a state can be deduced from the distribution of the Karroo beds and of the dolerite dykes. Probably the grantie magma was not differentiated from the basalt magma. The granites of the Jurassic plutons may be composed of sial molten through a rise of the geoisotherms in connection with the wide spread Stormberg volcanism.

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Proceedings of the Geological Society of South Africa, 57, xxxi-xliv

The end of the present year will mark the passage of sixty years since the founding of the Geological Society of South Africa, and it may be appropriate at this stage to review the work of the Society and some of the results it has achieved during this period. The events which led up to the formation of our Society and the early history associated with it, were admirably dealt with by Prof. R. B. Young in his Presidential Address of 1928. We had further interesting accounts of some of the activities of a few of the more prominent pioneer members of the Society in the reminiscences contributed to our Jubilee Volume in 1945 by Dr. du Toit, Prof. Young and Mr. Harold Harger.
In all these accounts of the early days of the Society, the major credit for the founding of the Society is given to David Draper. It was mainly through his enthusiasm and the interest taken in his pioneer work on the geology of the Southern Transvaal that our Society first came into being. In the Preface to Volume I of the Transactions, it states: " In the latter part of 1894 the Witwatersrand Chamber of Mines engaged the services of Mr. David Draper, F.G.S., to collect specimens of the rocks in this part of the country, and to make a sectional drawing of the position of the various strata. When this was completed and exhibited in the Chamber of Mines, a great deal of interest in geological matters was aroused amongst the population of the mining town of Johannesburg, and the promoters of the present Society considered it a favourable time to appeal to the public for their support".

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Transactions of the Geological Society of South Africa, 58, 1-12

Obituary - Biographical memoir and bibliography.

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Transactions of the Geological Society of South Africa, 58, 101-254, 23 pl

Detailed mineragraphic work shows that, like the gold, uraniferous constituents are widely distributed throughout the various conglomerate horizons and pyritic quartzites of these geological formations. Uraninite is the principal uraniferous constituent of the various ore-bearing conglomerates and quartzites locally known as "reefs". Microscopic and other evidence, discussed in detail, show that the uraninite is present as detrital grains. X-ray studies show that the uraninite is crystalline and that grains of the same mineral are distributed throughout the various conglomerates. Detrital uraninite is a prerequisite for the formation of secondary uraninite and thucholite. The secondary uraninite has been produced from detrital uraninite by metamorphic and/or chemical action. It is prominent in the Bird Reefs.
Thucholite, commonly described as "carbon" on the Witwatersrand, is widely distributed throughout the various reefs, and consists of a heterogeneous mixture of hydrocarbon, detrital uraninite, secondary uraninite and other non-radioactive constituents. It originated by the replacement of detrital uraninite by hydrocarbon. Many phenomena discussed indicate that the hydrocarbon (solid) was formed by the irradiation of hydrocarbons (gaseous and/or liquid) by detrital uraninite. X-ray, chemical and optical data show that the remnants of uraninite are identical to the hydrocarbon-free uraninite.
The gold is mainly authigenic in its present form and only occasional detrital grains have been found. Evidence of the changes that the detrital gold in the Witwatersrand conglomerates and other reefs has undergone is discussed in detail; evidence for this reworking is provided by the pyritic quartzites and Ventersdorp Contact and Black Reefs in which the gold, because of its derivation from the eroded Witwatersrand beds, was obviously originally detrital. The existence of a general sympathetic relationship between the gold- and uranium-contents of the various Witwatersrand conglomerates is discussed. This relationship indicates that the gold and uraninite were deposited simultaneously and that whatever origin applies to the one must necessarily also apply to the other.
The uraninite is detrital and the gold, notwithstanding its present form, must thus also be of detrital origin. This evidence, as well as other features discussed in detail, support the modified placer theory for the origin of the gold and uraniferous constituents.

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Transactions of the Geological Society of South Africa, 58, 13-30, 4 pl

A sequence of land surfaces is proposed for Namaqualand and its bearing on the ages of surface deposits in the southwestern Kalahari is examined. In Little Namaqualand a Namaqua Highland surface at 3,900 feet is distinguished from the Bushmanland surface at 3,200 feet, the Kangnas dinosaur-bearing valley fill being placed in an intermediate river cycle. The Highland surface is related eastwards to be "Kaap" peneplain of Du Toit. Subsequently rejuvenation is expressed in four subcycles in the Orange River valley at 2,600, 2,200, 1,500 feet and below.
A corresponding sequence exists in Great Namaqualand, namely, the Khomas Highland surface at above 6,000 feet, an Intermediate surface and below it the Kalahari Limestone and Great Namaqualand Plains, these latter being regarded as interior (Kalahari) and exterior (Atlantic) phases of a single (African) cycle. The pre-Kalahari surface, although probably composite, is equivalent to the Khomas and Namaqua Highland surfaces of Cretaceous age; all follow the sub-Karroo floor closely.
The Kalahari Limestone and underlying fluviatile beds are dated as early Tertiary and equated with the Middle Kalahari of the Congo, while the overlying red Plateau Sands precede the Kalahari valley incision of end-Tertiary or later date and are termed Upper Kalahari. Although the region shows similarity to other parts of Southern Africa, the oldest cyclic land surface appears to be Upper Cretaceous or later at the coast, which does not favour King's concept of a "Gondwana" land surface.

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Transactions of the Geological Society of South Africa, 58, 255-264, 1 pl

This paper gives some details of raised shorelines between Saldanha Bay and Plettenberg Bay in the Western Cape Province. It is complementary to other work that has been done in this field, and to some extent differs in that it is confined to the details of the actual shorelines formed by high-level seas, as distinct from a general consideration of areas of land which have been subjected to marine action in the past. It will be seen that, with one or two exceptions, the presumed shorelines are at altitudes of approximately 25, 60, 95, 200 and 300 feet above the present sea level, which are so similar to those in other parts of the world as to suggest the same cause and the same periods of formation.

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Transactions of the Geological Society of South Africa, 58, 265-280

Following a review of erosion processes it is concluded that in the reduction of a land surface to a lower base level, after initial incision by major streams as a result of uplift, the new surface is roughed out by some form of slope or scarp retreat, varying with climatic conditions, and that the later stages of reduction are normally affected, on formations of low resistance, such as weak sediments or deeply-weathered rocks, on formations of low resistance, such as weak sediments or deeply-weathered rocks, by the lowering of divides by the gradual flattening of slopes. During scarp retreat from the coast and the major streams the interfluvial levels of the old surface remain largely unaffected by erosion, apart from steady reduction in extent, but as the remnants largely unaffected by erosion, apart from steady reduction in extent, but as the remnants disappear slope flattening on the weaker rocks becomes increasingly important as a result of weathering and mass wastage.
Various methods of naming an erosion surface are reviewed, and it is concluded that, owing to the speed with which the effects of uplift normally appear far inland along stream courses, in relation to the total length of time required for the erosion of the new cycle, the naming of such a surface by the date of uplift at the coast, as determined by the related sedimentary succession, is the most satisfactory. Various methods of mapping erosion surfaces are also considered.

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Transactions of the Geological Society of South Africa, 58, 281-356, 9 tab., 2 pl

Heavy concentrates from sandstone of several occurrences of the Karroo system in the Transvaal and Northern Orange Free State were studied in order to determine to what extent a heavy mineral investigation can aid in the correlation of the different sandstone members of this formation. In order to decide on the technique best suited for the study, various methods in use in the investigation of accessory minerals in sediments are reviewed critically. Alternative modes of presenting the data are also considered.
The most satisfactory technique to treat Karroo sandstone is to separate the heavy minerals from the -200 mesh size-fraction, and to express the relative quantities of the different mineral species and types in terms of 1,000 zircon grains. The various species of heavy minerals present in the concentrates are described. Some of these, like zircon, tourmaline and rutile, are subdivided into several types according to certain diagnostic features such as zoning, colour, pleochroism and shape. The concentrates show surprisingly little qualitative variation, vertically as well as laterally, in spite of the large variety of heavy minerals present.
Nevertheless, each of the four occurrences investigated is characterized by certain peculiarities in the concentrates, such as rutile grains with pointed outgrowths in the concentrates from the Springbok Flats; the abundance of well-shaped crystals of authigenic rutile in concentrates from the Witbank coalfield, the grains of pleochroic apatite in concentrates from the Kestell area; and the superabundance of square crystals of anatase in many concentrates from the Waterberg area. The relative quantities of the heavy minerals fluctuate considerably according to the stratigraphical position of the relevant sample. Although the consistency in the proportion of certain types of rutile or tourmaline of some horizons has a limited lateral persistence, this feature may nevertheless be of use in the solution of problems of local correlation. On the other hand the relative quantities of certain types of zircons are remarkably persistent laterally and serve to identify the different members of the System in all the widely separated localities. For example, the proportion of zoned to unzoned zircon grains proved a very useful criterion for differentiation and correlation. Both major as well as minor constituents of Karroo sandstone indicate a predominantly granitic or gneissic distributive province situated relatively close to the sites of deposition.
The Archaean Granite and Gneiss. which at present covers wide tracts in the northern and eastern Transvaal, and in Southern Rhodesia, is suggested as a likely source for most of the northern occurrences of the Karroo system. The stratigraphical position of certain occurrences of sandstone, presumably of the Karroo system, in the Transvaal was determined by means of a heavy mineral investigation. Inter alia: sandstone from near Vaalwater, the correlation of which was somewhat doubtful in the past, has now conclusively been proved to belong to the Waterberg system; a small occurrence of sandstone in granite country on the farm Weihoek 761, near the Leeuwpoort Tin Mine, shown on the Geological Survey Sheet No. 10 as "Rooiberg" series but recently recognized by Mr. G. P. Fourie as Cave Sandstone, isolated by faulting, contains the heavy minerals so typical of the last-mentioned formation; the identification by Mr. J. J. Spies of a fragment of Cave Sandstone in a breccia pipe topographically at present on the same elevation as the Dwyka series in the Middelburg district (Transvaal) could be confirmed by heavy mineral analysis 5 the correlation of the grit underlying volcanic breccia at the Pretoria Salt-pan with the Ecca series by Wagner was confirmed, and Du Toit's contention that this sediment represents an ancient granitic soil derived from the underlying granite is therefore disputed. Although no impressive results have accrued from the investigation, the author is satisfied that the foundation has been laid for the correlation of Karroo sediments by petrographical means, and that heavy mineral analysis can supplement palaeontological evidence in the solution of problems of Karroo stratigraphy in southern Africa.

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Transactions of the Geological Society of South Africa, 58, 31-43, 1 pl

The lowermost part of the Lusaka series of the Kafue Gorge is characterised by glacial and basic volcanic rocks; these rocks suggest a correlation with the Deweras series to the south-east, and possibly with the Bas Congo Tillite of the Belgian Congo. Parts of the Lower Lusaka series have previously been assigned to the "Basement", possibly because they had been felspathised by the local granite. This granite is part of the widespread "Hook Granite": it has granitised or removed much of the Lower Lusaka series during its emplacement. The value of the "Rufunsa Volcanics" as an indicator-horizon is reviewed in the light of the presence of basic lavas in the Lower Lusaka series.

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Transactions of the Geological Society of South Africa, 58, 367-387, 4 pl

A theory of glacial origin for the major reef horizons on the Witwatersrand is propounded and some of the properties of the major reef horizons are discussed in the light of this theory.

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Transactions of the Geological Society of South Africa, 58, 45-70, 3 pl

Detailed mapping and structural analysis of pegmatite bodies in the United States and Brazil during and since World War II have indicated that mineral distribution in pegmatites is closely related to the internal structure of these bodies. The concepts developed have served as a basis for exploration of pegmatites and for estimation of tonnage and grade of pegmatite mineral deposits. A brief examination of some 60 pematites in the Karibib-Omaruru and Warmbad areas of South West Africa indicates that many of these pegmatites have internal structures comparable to those described from the Unites States. It therefore appears that structural analysis could be successfully applied to problems of prospecting, exploration, and mining of pegmatite mineral deposits of the two areas.

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Transactions of the Geological Society of South Africa, 58, 71-99, 6 pl

The Madumabisa Shales, with a maximum known thickness of about 1,600 feet, are the highest division of the Lower Karroo succession in the Middle Zambezi region which covers the area from the Wankie Coalfield to the Kariba Gorge. Over much of the region they are covered by Upper Karroo sediments. In the eastern part of the region the succession is now well known from old and new boreholes, and a number of new fossil localities have been discovered. Lithological and palaeontological subdivisions are described, and the successions in other parts of the basin are described and compared. Facies changes in the lower subdivisions are traced from area to area. Variations in the total thickness of the shales in the eastern part of the basin are due to an unconformity at the base of the succeeding Upper Karroo, and it is suggested that variations in other parts of the basin are due to the same cause, rather than to differences of original thickness. Two new species of conchostraca are described, and several fossils not previously recorded are discussed. The ecological significance of Leaiadidae in Gondwanaland is considered.

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Proceedings of the Geological Society of South Africa, 58, xv-xxxii

In this country, so bountifully endowed with mineral wealth, we are, I think, as mineral minded a people as any in the world. It is common knowledge that doctors, lawyers, businessmen, storekeepers, adventurers and even just the man-in-the-street have all tried their luck at some time or another at the romantic game of prospecting. Virtually every farmer knows of some vast or valuable mineral occurrence on his land although in reality the evidence for this is in most cases nothing but a pipe dream or as in one authentic case, just a piece of Banket reef from the Rand built into a kraal wall on a Free State farm. The almost universal human interest in mineral finding is due to the spirit of adventure and more particularly to the get-rich-quick gamble, but, as I shall show, the old days of prospecting are giving way to organised scientific mineral exploration. It is no longer a small man's game but one for large companies and governments; it calls for large expenditures and highly trained men. Today those fortune seekers who enter the field of prospecting without expert knowledge, have the dice heavily loaded against them and the outcome of their labour is almost certainly destined to failure and financial loss. As little has been written on the subject of modern mineral exploration it is hoped that this brief appreciation of the subject may be of some general interest.

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Transactions of the Geological Society of South Africa, 59, 1-22, 5 pl

New evidence is presented in favour of the alluvial origin of the gold in the auriferous reefs of the Witwatersrand system. The Basal Reef of the Orange Free State sometimes consists of two distinct reefs, of different though nearly contemporaneous age, the younger being disconformable upon the older. The distribution of the gold in each is such that it is concluded that the gold was present at the time the reefs were formed and that the younger reef, at the time of its formation, incorporated gold initially deposited within the older reef. It is also shown that the economically important reefs generally rest upon disconformities, are of wide lateral extent though, relatively, extremely thin and are conglomerates of a particular kind, distinguishable by eye from the barren conglomerates of the system. It is accepted that the system is of continental origin and, from the evidence cited, it is concluded that it is most logical to assume that the auriferous reefs are formed of detrital material left upon a subaerial surface - which is thought to be a pediment - after a long period of subaerial weathering and concentration. Several applications of the theory are considered.

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Transactions of the Geological Society of South Africa, 59, 123-133, 4 pl, 2 tab.

This report gives details of the distribution of earthquakes which occurred in Southern Africa and the surrounding Indian and Atlantic oceans during the period January 1953 to December 1955, with an estimate of their magnitudes. The seismograms used for the location of South African earthquakes were obtained from four short-period vertical seismographs at Pretoria, Kimberley, Grahamstown and Pietermaritzburg, operated on behalf of the Geological Survey.

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Transactions of the Geological Society of South Africa, 59, 135-148, 2 pl

This paper briefly describes two sandstone dykes occurring in a jointed dolerite sill 1.4 miles southeast of Devon, Nigel District, Transvaal. It is shown that the dykes described in this paper bear little relationship to the so-called syntectic veins, rheomorphic veins, and mobilised sediments previously set forth by other South African authors.

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Transactions of the Geological Society of South Africa, 59, 149-194, 7 pl

The African Shield can be broken down into a homogeneous mosaic of rigid tesserae separated by appropriate hinge zones which coincide to a large degree with the major rivers of the present drainage pattern. Southern Rhodesia represents the type unit. This particular mosaic is thought to have originated in the late Pre-Cambrian. A more recent mosaic of much coarser pattern has units the size of the Kalahari and Congo structural basins. An Archaean mosaic of a very fine pattern can be discerned within the Southern Rhodesian "crustal fragment". The train of thought leading up to this conclusion involved the use of several concepts which possibly deserve recognition if they have proved useful tools in a structural analysis:
1. Arcuate Structures: These are not confined to island arcs and mountain arcs. They are ubiquitous.
2. Global Geology: Measurements of earth features reduced to angles of arc show a great preponderance of aliquot angles, relating earth features to the fundamental fracturing of the crust of the globe.
3. Structural Great Circles are found by projecting linear geological features on their respective great circles. A structural great circle is the limiting ease of a structural small circle, and its functions are much the same. It is related to fundamental pre-Cambrian structures.
4. Vertices: These are common meeting points of groups of great circles, and they are intimately related to the shapes of continents. They have a geological meaning but most are depressions and are obscured. The Bushveld Igneous Complex is the vertex whose geology is best known.
5. Geological Geometry: The vertices are not haphazardly distributed. Measurements between them show 45°, 72° and 90° to be favoured. Angles between converging circles of a group show preference for smaller aliquots. The obtuse supplement of these angles is frequently observed in any geological map.
The ubiquity of structural angles confirms the ubiquity of vertical tectonics. An ellipse provides a convenient way of recording a polygon, but usually an ellipse comes close to being the actual shape of a tessera. 6. Measurements: The above geometrical relationship is reflected in earth movements. Shields show a preference for 36°, 22½°, 18° etc., continents for 72°, 45° and 36° seismically-bounded Units for 120°, 90°, 60°; orogenically-bounded units (Tertiary) 180° and 150°. Older orogenies show progressively smaller units.

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Transactions of the Geological Society of South Africa, 59, 199-209, 5 pl

Rift valleys of Pleistocene age are shown to exist in Brazil along major crustal arches affecting early and late Tertiary cyclic erosion surfaces. They show great similarity to the African rift valley system.

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Transactions of the Geological Society of South Africa, 59, 211-236, 7 pl

Two species of fossil fructifications have been found near Vereeniging, Transvaal, South Africa, which belong to the genus Ottokaria of which the only previously known specimen, from the Karharbari beds of India, was figured in 1902 by Zeiller who, from this limited evidence, misinterpreted the organ as a leaf. The genus is, therefore, redescribed. Of the two new species, Ottokaria buriadica is attached to Gangamopteris buriadica (recorded for the first time from South Africa), the other, Ottokaria transvaalensis is closely associated with Gangamopteris obovata - (G. cyclopteroides). These are described. The genus Ottokaria has much in common with the form genera Scutum Plumstead and Lanceolatus Plumstead fructifications from the same site, described in 1952. This botanical relationship constitutes the first reliable link between the leaf genera Glossopteris and Gangamopteris, the most common members of the Glossopteris flora. It is proposed that the three genera should now be placed in a distinct class, the Glossopteridae.

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Transactions of the Geological Society of South Africa, 59, 23-57, 4 pl, 2 tab.

The Messum Ring-Complex of South-West Africa, 105 miles N.N.W. of Walvis Bay, measures 14 miles by 12 miles. It shows a wide variety of rock types. This paper provides a petrological supplement to Martin's previous work on the structure and general geology. Thirty-three new rock analyses are included together with spectrographic data for the trace elements of twenty-eight of these analysed rocks. The sequence of events can be divided into three main phases (a) volcanic (b) intrusive (c) alkaline. In the volcanic and intrusive phases which are characterized by a repetition of the basic-acid rock association this Complex shows affinity with some of the British Tertiary ring-complexes. Limestone syntexis is thought to be the cause of the changes in chemistry from calc-alkaline to alkaline.
Virtually no carbonatite occurs associated with the felspathoidal rocks of the alkaline phase. The extensive metasomatism accompanying the intrusion of a foyaite magma was facilitated by the permeable nature of the acid tuffs and agglomerates, while the latter are admirably suited to show relict structure. Basalts and dolerites here acted as 'resisters' and their continuity of outcrop within the area of fenitization proves that the surrounding rocks were the products of metasomatism and not of igneous intrusion.

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Transactions of the Geological Society of South Africa, 59, 237-258, 1 pl

A petrological account is given of an area in which a large deformed block of crystalline dolomitic marbles with associated minor quartzites and amphibolites is surrounded and invaded by granites and gneisses which are in part of charnockitic type. In the marbles with siliceous impurities metamorphic decarbonation has attained the forsterite and diopside stages while wollastonite-bearing assemblages are developed near some tongues of intrusive granite. Aluminous impurites have entered into phlogopite and locally spinel. Chondrodite marbles occur marginally in a few localities. All the rock types are considered to have been developed by the varying response of pre-existing sediments and minor intrusives to plutonic activity, the response involving metamorphism, metasomatism or anatexis according to the bulk composition of the original rock.

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Transactions of the Geological Society of South Africa, 59, 259-276

The "equilibrium" beta-gamma method for the analysis of ore samples has been investigated and some refinements were found necessary due to the gamma activity of the uranium group. For rather high grade urano-thorianite (non-leached) and Rand ore (leached) samples the use of 18 gm samples is suggested. Samples weighing 70 gm are used for low grade material, involving a slight alteration to the beta-counting unit. A minimum activity of 0.005% U3O8 or its equivalent in non-leached uranium-thorium and leached uranium-thorium ore samples is also discussed. A detailed experimental procedure for the analysis of ore samples on the beta-gamma unit is given in one of the two Addenda.

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Transactions of the Geological Society of South Africa, 59, 59-76, 2 pl

Olivine of the "shell" dunite of the Onverwacht pipe is chrysolite, averaging about Fa25; that of the "core" dunite varies from hyalosiderite (Fa44) to hortonolite (Fa55). Chromite occurring in chromite-rich lumps and in crystals disseminated in the chrysolite dunite is magnetic, with a Cr:Fe ratio of 1.11, whereas the chromite associated with coarse platinum in slabs in the hortonolite dunite is strongly magnetic and has a Cr:Fe ratio of 0.54. It is concluded that the platinum-rich chromite is not of xenolithic origin, but that the two varieties of chromite are normal crystallization products of the two respective dunites, which in turn, owe the difference in their composition to crystal fractionation. In this respect the chromite-dunite association exhibits the same relationship as the comparable layered rocks, i.e. the sympathetic variation in composition of chromite with its associated silicates. A chromitite occurring in a nickel-bearing pipe on Vlakfontein 902 is probably of xenolithic origin.

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Transactions of the Geological Society of South Africa, 59, 77-93, 3 pl

This investigation represents an extension of a portion of the comprehensive account by Nell and Brink of the dolerites of the Western Province. The Peninsula dolerites show a wider range in mineral composition than had been suspected and new types carrying orthopyroxene and pigeonite are recorded. Later basaltic veining is a common and variable phenomenon. Speical attention is given to the chilled contacts and it is found that the early part of the cooling history of the magma can be traced by study of the phenocrysts in the basaltic margins. New analyses and micrometric data are presented and the relationship of the Peninsula dyke swarm to the main Karroo activity is discussed.

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Transactions of the Geological Society of South Africa, 59, 95-121

The distribution of minerals in ore bodies tends to follow the log-normal probability curve. The parameters of this curve can be readily evaluated graphically. Study of the distribution parameter leads to useful information regarding the character and genesis of a mineral deposit and relationships between the various minerals. Sympathetic ratios between the constituent minerals appear unusual in Hydrothermal mineral deposits. Placer deposits and ores formed by gravity separation of magmatic minerals show sympathetic ratios between the constituent minerals. In the gold bearing conglomerates of the Witwatersrand System sympathetic ratios are found between gold, silver, uranium and osmiridium. The last mineral is unquestionably of placer origin and the sympathetic ratios between it and the other minerals indicate that the pattern of value distribution is the same as that of a placer deposit.

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Proceedings of the Geological Society of South Africa, 59, xiii-xlvi, 12 figs

Many of the requests for advice received from farmers by the Director of the Geological Survey pertain to the perennial safe pumping rate of boreholes. These requests are all very similar: "I have just had a borehole drilled and pump-tested at 4,000 gallons per hour. Please advise me at what rate can I pump the borehole without depleting the supply". The farmer thus expects to be advised as to the safe yield of a borehole when he supplies only its tested yield to the Survey. It is commonly assumed that the safe yield of boreholes, which are to be used for proposed water-supply schemes for municipalities or other local authorities, can be established similarly before such schemes are embarked upon. The procedure to be followed by a local authority in obtaining the sanction of the Administrator to carry out a water-supply scheme is set out in Administrators' Notices.
Under the Appendix dealing with the plans and documents which must be submitted to the Irrigation Department by the Provincial Secretary when forwarding a proposed scheme for scrutiny, the following paragraphs deal with boreholes and pumping rates.

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Transactions of the Geological Society of South Africa, 60, 1-13

Obituary: S. James Shand

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Transactions of the Geological Society of South Africa, 60, 127-175

Lineament patterns can be constructed for every terrain from alignments to straight to be fortuitous. A lineament pattern is entirely characteristic of its terrain. Lineament grids, with evenly spaced sets of parallel lineaments, are helpful in predicting unsuspected lines or zones of weakness, and in relating the lineament pattern to the global picture, which should form the basis of structural analysis. Global lineaments, encircling the globe as great circles, intermittently coincide with a hinge zone axis which is the average of a bundle of sub-parallel lineaments characterising that hinge zone. A global lineament, although an undoubted reality on the global scale, becomes lost intermittently on a detailed map in a confusion of lineaments. Locally it must weave its tortuous way, possibly as a network. Tortuous persistence is a necessary characteristic of a global lineament to allow it to be recognisable as a great circle feature. This emphasizes the importance of working from the general to the particular.
The establishment of the usefulness of an axis as a tectonic lineament leads to a consideration of the disposition of continental and oceanic axis. A series of hitherto unsuspected primordial symmetries is revealed, quite incompatible with the concept of laterally shifting continents. A procedure is described for finding lineament grids related to the geometry of continents. The sharing of a lineament grid by more than one continent is further evidence of the relative permanence of continents. Many terrestrial features, such as rivers, deltas, lakes, and basins, when examined in the light of lineaments, reveal a structural control. Oceanic features share common patterns with continental features, and the conclusion is that the crust under the oceans has failed in the same manner as the crust in continental areas. The forces which produced the Pacific must have left their mark on the entire crust. The world pattern seems to bear this out.
The problems raised are mostly old ones presented in a new light. This paper constitutes merely an "approach", with the emphasis on patterns, whether they be adequately understood or not. It presents an assembly of structural data in a manner which may have a fresh message for the physicist, and it provides a manner of relating tectonic details to the global picture. The globe must be the foundation of structural geology if that science is to progress. A course is indicated which structural geology should take, if it is to avoid being swamped in its own debris.

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Transactions of the Geological Society of South Africa, 60, 15-20

"South African Jade" from the Transvaal is identified as a member of the hydrogrossular series of minerals. The garnetoid is intimately associated with anorthosite bands (often with chromitite, layers) of the norite zone of the Bushveld Complex and with textural relationships that make clear its derivation as a pseudomorphous replacement of plagioclase of the anorthosite.

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Transactions of the Geological Society of South Africa, 60, 177-197

Co-ordination of effort within the Geological Society of South Africa appears to be practicle. The annual congress offers an opportunity for putting a combined effort into effect. A list of subjects for successive congresses is suggested, in which the emphasis is placed upon features or aspects of geology which Southern Africa can regard as its specialities. In these specialised fields South Africa's contribution could be, through concerted effort, much greater than it has been. In certain fields South Africa could set the pace. The Geological Society of South Africa thus has an opportunity of becoming a truly vital force in the advancement of geology.

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Transactions of the Geological Society of South Africa, 60, 21-60

The Marrattiaceous fern Asterotheca fuchsil (Zeiller) Kurtz is described, and it is concluded that the fertile specimens attributed to Dicroidium lancifolium and D. feistmanteli by Walkom (and others) are specimens of A. fuchsii. The genus Dicroidium Gothan is redefined, largely on cuticle characters, and its age and distribution are discussed. Four species of Dicrodium are described, D. odontopteroides (Morris) Gothan - the Type - D. feistmanteli (Johnston) Gothan, D. superbum (Shirley) com. noy., and D. coriacium (Johnston com. nov. Certain leaves originally placed in D. odontopteroides or D. feistmanteli by Feistmantel, Antevs and others are separated into a new genus, Hoegia, of which two species are described, H. pappillata sp. nov., and H. antevsiana sp. nov. Some general discussion of the cuticles of Dicroidium is offered.

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Transactions of the Geological Society of South Africa, 60, 61-80

The Miocene Uloa sandstone crops out near the small village of Uloa, Zululand, Natal Province, Union of South Africa. Fifty-three species of Foraminifera from these beds are recorded and illustrated. Eight new species are systematically described. The fauna may be classified as a warm water type, littoral-neritic, and having forms characteristic of both open seas and lagoons. The Foraminifera show a striking resemblance to East Indian, Mediterranean and Caribbean Middle Tertiary faunas.

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Transactions of the Geological Society of South Africa, 60, 81-84

The deposits of iron and manganese ore are found to the east of Broken Hill and are closely associated with lenticular bodies of dolomite and dolomite limestone, which form part of the tightly folded schists of the Lower Division of the Basement Complex. The manganese ores are thought to have been formed through the oxidation of primary manganese-bearing minerals which are found as veins cutting across the calcareous rock.

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Transactions of the Geological Society of South Africa, 60, 85-126

Five granites are described, in addition to a complex suite of gneisses which are believed to be derived from the Swaziland System by processes of granitization during the major period of orogeny following the deposition of the Swaziland System and the intrusion of the Jamestown Complex. With the exception of one of the granites (namely G.3) the remaining granites are believed to have evolved along the lines of Read's Granite Series. The Swaziland granites show a textural change with age from the oldest gneissic granites to the sharply cross-cutting plutons of the youngest granite. Comparable textural changes are traced in granites from extra-Swaziland areas. Twenty-five chemical analyses of Swaziland granites are given.
It is suggested that the tin mineralization in the G.4 granite is associated with a slightly more sodic phase of the granite. The correlation of the granites is discussed. It is pointed out that the Swaziland G.4 granites are associated with the main period of mineralization, giving rise to a comparable suite of minerals such as occur associated with the Rhodesian Group B granites. This Group of granites belongs to the Shamvaian cycle; The G.4 granite intrudes the Mozaan Series (which is equated in the Union of South Africa with the Witwatersrand System) and thus a correlation of the G.4 granite with the Rhodesian Group B confounds accepted chronological schemes.
Absolute age determinations of Swaziland rooks and minerals are seriously lacking and, hence, cannot be used to solve the problem.

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Proceedings of the Geological Society of South Africa, 60, xiii-l

The aim of this address is to review and summarise our knowledge of the structure of South Africa up to the present, particularly in view of its importance in the development of our mineral resources. In the second chapter the dualistic nature of the mountain-building process, i.e. the alternation of epochs of crustal tension with epochs of compression and the periodicity of orogenic movements are indicated, and two fundamentally important concepts in structural geology, namely the geosyncline and theorogenic cycle are defined. It is further shown that an orogenic cycle is characterised by four successive phases in its development, i.e. a geosynclinal phase during which deposition proceeds apace with the growth of the geosyncline, a compressional phase during which folding, compressional faulting, and the main uplift takes place, a tensional phase characterised by gravity-faulting, and a magmatic phase during which bodies of intrusive rock invade the root-zones of mountain-masses.
In the succeeding chapters the different orogenies are described in detail. During the Archaeozoic and Proterozoic Eras two geosynclinal regions existed, one in the Transvaal and the other in the Northwestern Cape, each characterised by its own distinct suite of sediments. During the Archaeozoic Era there were two epochs of crustal disturbance, of which the first was mild, whereas the second, designated the Moodies-Gariep orogeny,is characterised by overfolding compressional faulting, and the extensive invasion of the unstable crust by granitic magma. During the Proterozoic Era there were six epochs of crustal disturbance.
The first or Kapok orogeny led to extensive granitisation of the older formations in the Northwestern Cape. The fourth or Bushveld orogeny is characterised by extensive magmatic activity, i.e. the emplacement of the Bushveld Complex in the Transvaal. During the sixth or Matoop orogeny compressive stresses were directed radially inwards towards the Vredefort Dome, which is th

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Transactions of the Geological Society of South Africa, 61, 1-4

Biographical memoir.

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Transactions of the Geological Society of South Africa, 61, Annexure, 50 pp., 61 pl

The geological explanation of the mineralisation of the conglomerates of the Witwatersrand is most controversial. DAVIDSON has recently introduced strong arguments for the "hydrothermalists" and against the "placerists", especially on the basis of the joint occurrence of gold and uranium. The weight of his argument lies in the consideration that the "Uranpecherz" could not, on account of its chemical instability, have been concentrated in placer formations, and thus must have been introduced later, together with gold. He supposes this to be true for pyrite too, for he thinks the common assumption that it has formed from black sand is unsupported because the TiO2 content is too low.
Careful microscopic investigation of a wide range of material in very well prepared polished sections has shown quite clearly that most of DAVIDSON 's arguments are unsound, although the results achieved by the author of this paper undoubtedly tend to make the interpretation more complicated instead of simpler. "Uranpecherz" did in fact come into the conglomerates as small pebbles and, in keeping with its high specific gravity, was concentrated near the footwall. In part, it still exhibited at the time of sedimentation an octahedral cleavage and was, thus, presumably geologically still quite young. Its pebbles were later extensively (or entirely) destroyed; but their position and their shape are still easily recognisable from relict-structures ("ghosts"). The main portion of the uranium is now contained in the "carbonaceous matter", i.e. polymerised hydrocarbons, partly as metal-organic compounds, and also partly in Uranpecherz dispersed in a peculiar way as angular grains. This "carbonaceous matter" is traced back by DAVIDSON to migrating methane from the Karroo coal seams.
This view is not only improbable but demonstrably wrong. At least a considerable portion of the "carbonaceous matter" must be extremely old. Pyrite is of polygenetic origin. An important role is played by true pyrite pebbles that came into the conglomerates unweathered, presumably from lode-type occurrences. Other modifications of pyrite have developed as concretions in sizes up to that of a hazelnut, during or shortly before the formation of the conglomerate. The most widely distributed modifications, but by no means the most numerous, generally speaking, are crystals which have developed in situ, partly around small pebbles. Rutile in structures of former titaniferous magnetite and ilmenite and also pseudomorphs of many other iron-rich individual minerals and rocks are very common. Gold was undoubtedly (at least for the most part) recrystallised, but migrated only a very short distance. The redeposition is younger than the main mass, at least of the carbonaceous matter. In their present condition gold and "Uranpecherz" have nothing whatsoever to do with each other, which nevertheless does not necessarily mean that they were not deposited together originally as heavy minerals, for it is even possible that they were derived from the same veins. Pyrrhotite has formed in highly variable amounts, apparently through dissociation of pyrite during heating up to a high temperature over a long period.

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Transactions of the Geological Society of South Africa, 61, 103-136, 1 pl

The investigation was undertaken to ascertain if the Foraminifera provide any evidence whether the calcareous sandstones above and below the intraformational conglomerate just above sea-level at the Bluff, Durban are appreciably different in age and whether the sandstone of the Berea ridge is appreciably older than that of the Bluff. Eight species were found - all well-known. The presence of Amphistegina radiata indicates comparatively warm-water conditions. On the data provided by the Foraminifera, the sandstones are all of the same order of age, viz, Pleistocene. For comparative purposes specimens of calcareous coastal rocks from East London, Port Alfred, Bushmans River Mouth and Saldanha Bay were also examined. The forms recognized are also all of Pleistocene to Recent Age.

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Transactions of the Geological Society of South Africa, 61, 111-124, 1 pl

Field-work undertaken whilst the author was on the staff of the Sudan Geological Survey between 1948 and 1955 covered wide areas of the Sudan. A series of ring structures were found which, in view of similar discoveries elsewhere in Africa, are of great interest (Delaney, 1955). The purpose of this paper is to describe a volcanic series, closely associated with the sodic intrusions which constitute the ring structures. The volcanics, which include rhyolite and trachyte and associated pyroclastics, occur in the northern Central Sudan. The name Sabaloka Series adopted for the rocks derives from the type locality, some 80 Km north of Khartoum on the River Nile, where detailed mapping was undertaken. The volcanics lie unconformably on the older, much folded crystalline series, are themselves only locally metamorphosed and intruded by riebeckite of aegirine soda granite and syenite. Closely allied petrographically with the lava is felsite and, at the Sabaloka, a granite-porphyry ring-dyke. Basal conglomerate of the Nubian Series contains pebbles of rhyolite and shows that the extrusion took place before Mesozoic times.
Rocks of the Sabaloka Series are described in the following localities: J. es Sufr (15°50'N. 32°40'E), J. Qeili (15°31'N. 33°47'E), J. Mundara (15°01'N. 34°27'E), J. Katul (14°16'N. 29°23'E), J. Haraza (15°05'N. 30°25'E), Gilif Hills (17°47'N. 32°34'E).
Further geological investigations will surely result in other occurrences of similar rocks being found elsewhere in the Sudan. Thick Quaternary deposits frequently mask the relationship between the Sabaloka Series and other crystalline rocks. The geology of the crystalline dome of the Sabaloka Gorge where the Precambrian rocks are well exposed, is briefly oulined.

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Transactions of the Geological Society of South Africa, 61, 125-136, 1 pl

Numerous basic intrusions, the majority of which show pronounced igneous banding, occur in the Hargeisa and Borama Districts of Somaliland Protectorate. Five of these were chosen for more detailed mapping to investigate the possibility of economic chromium, nickel and platinum concentrations. In general the intrusions are composed of gabbro, olivine gabbro, troctolite, anorthosite, peridotite, pyroxenite and iron ore. Large amounts of a late, very coarse pegmatite gabbro cut all the intrusions. A rare orbicular gabbro and some multiple reaction coronas are described from the Dudub mass. Spinel-corundum rocks are noted from Rakdasafaka. In the Hamar intrusion a moderate iron ore deposit, formed early in the history of the intrusion is described. Associated with the iron ore are occasional bands of pleonaste-hercynite rock and banded pleonaste-hypersthene rock; both of which are regarded as new rock-types. They are thought to be the results of intense, local differentiation of the magma. Much reaction and assimilation of calcium- magnesium- and aluminium-rich sedimentary material is thought to have occurred in the Gul Sakar intrusion.

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Transactions of the Geological Society of South Africa, 61, 137-181, 2 pl

Reliable data relating to the absolute age of the Transvaal System are crucial to the delineation of a quantitative time scale for South African stratigraphy. Since 1954 the authors have approached this problem through four independent investigations: (i) Rubidium-strontium age determinations on micas from four Bushveld igneous rocks. (ii) Uranium-lead and thorium-lead age determinations on six monazites from Houtenbek 392, Moos River District. (iii) Uranium-lead age determinations on three zircon concentrates from a granite near Ottensville, Central Bushveld. (iv) A study of the lead isotopic compositions of galenas emplaced within sediments of the Transvaal System. The data obtained in these investigations are examined critically, and compared with measurements made by other workers on similar minerals. It is concluded that the new age determinations are consistent, with few exceptions, and that an age of 1950±150 million years can be assigned to the intrusion of the Bushveld Igneous Complex. The deposition of the Transvaal System has therefore taken place at a time greater than 1950±150 million years ago, and it appears that existing chronologies of South African strata need revision.

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Transactions of the Geological Society of South Africa, 61, 167-181, 2 pl

Economic development of coal at Wankie is virtually confined to one seam of wide extent and often of considerable thickness. This is known as the Wankie Main Seam. The lack of cyclic coal measures in the European sense is one of several differences between the deposits at Wankie and those of the European Carboniferous System which have long been quoted as evidence of a detrital origin for Wankie coal. Recent work, however, suggests that these differences are due to contrasting ecological conditions governing growth in situ in both cases, not to different modes of formation. The acceptance of an in situ origin for the Wankie Main Seam is of great economic importance since it narrows the search for further coalfields of Wankie quality in the middle Zambezi valley to the area around the edge of the Karroo basin as it ran during the early Ecca period.

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Transactions of the Geological Society of South Africa, 61, 183-196, 1 pl

The contention that uraninite is too soft and brittle to report as a clastic constituent of sediments was put to test in the laboratory by comparing its resistance to mechanical wear with that of a few other minerals known to occur as elastic grains. It was found that the uraninite is slightly more resistant to diminution than monazite; it is abraded faster than pyrite, but resists wear much more successfully than either fluorite or barite.

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Transactions of the Geological Society of South Africa, 61, 19-50, 6 pl

Shales and sandstones from the Lower and Upper Divisions of the Witwatersrand System have been examined in hand specimen and under the microscope. Microscopic features, mineral compositions and textures are described and particular attention is paid to features of quartz grains in rocks belonging to the Upper Division of the System. Available chemical data are reviewed and three new chemical analyses are represented. Identification of fine-grained phyllosilicates in the sandstones was assisted by X-ray powder analysis. Pyrophyllite, hitherto unrecognised in quartizites from the Upper Division of the System was found to be a common constituent of the Main Bird Series and lower levels of the Kimberley-Elsburg Series. Its distribution and origin are discussed and it is concluded that propylitisation occurred during a period of hydrothermal activity which preceded the consolidation of the sandstones.
`The compositions of chlorites from the Upper and Lower Divisions of the System have been determined by X-ray analysis. Classification of rocks from both divisions of the system is discussed. In the Lower Division it is suggested that the name quartzite only be applied to formations in the Hospital Hill Series, while the term subgraywacke be used to describe sandstones from the Government Reef and Jeppestown Series. Sandstones from the Upper Division of the system are interpreted as hydrothermally altered feldspathic quartzites.

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Transactions of the Geological Society of South Africa, 61, 197-207

The age of the Robinson Dyke, measured on samples taken at depth in the Robinson Deep Mine, has been determined from the 87R+87Sr decay. The concentrations of 87Rb and radiogenic 87Sr were determined using a mass spectrometer and isotope dilution methods. Based on a half-life for the decay of 87Rb of 5.0 x 10(10) years the age of the dyke is 1,290±180 million years. The error quoted represents the 99% confidence limits of the determinations made. Since the dyke shows post-magmatic hydrothermal alteration, the detailed mineralogy is described in so far as it has bearing on the age determination. The conclusion is reached that this alteration must have been confined to a short period of time immediately after crystallisation. The relationship of this dyke to the dyke system and the Pilanesberg intrusive itself is discussed. It is concluded that the age determined for the Robinson Dyke may be extended to the rest of the Dyke system and, therefore, to the Pilanesberg intrusive itself. This age determinations means that the Waterberg System is older than 1,300 million years and, if its correlation, with the Matsap is valid, rules out the possibility of the correlation of the latter with the Table Mountain Sandstone.

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Transactions of the Geological Society of South Africa, 61, 209-224, 3 pl

A series of specimens of dolerite obtained from the Karroo dolerite sill at Coedmore quarries near Durban have been picked out to illustrate progressive acidification of the dolerite by incorporated Table Mountain sandstone. This is not a process of mechanical entanglement of sediment in dolerite magma but a metasomatic process where the contact between sediment and dolerite remains sharp. There appears to be some suggestions on of a limit to the amount of acidification that occurs, corresponding to a silica percentage of about 63. The series shows the introduction of micropegmatite and separate quartz grains, the reduction in anorthite content of plagioclase and the introduction of hydrous minerals such as chlorite, hornblende, zoisite and prehnite. Chemical analyses show that the character of the acidification is in fact similar to what would be obtained by simple mixture with sediment.

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Transactions of the Geological Society of South Africa, 61, 225-262, 4 pl

In order to ascertain the nature and origin of a so-called "granophyre" of doubtful age, the relation between this rock and the Transvaal System was determined. It has been concluded that this "granophyre" is actually a gneiss which originated from felsite of the Onverwacht (?) Series as a result of metamorphism (and perhaps a little metasomatism) during intrusion of the Bush veld Complex. Chemically as well as mineralogically the gneiss differs entirely from Bushveld granophyre, Bushveld granite and Archaean granite, and contains Rapakivi feldspar. The general appearance of the zircons in the felsite, however, suggests that they are sedimentary. This could be explained by the theory that the felsite assimilated sediments during its extrusion or that it represents a leptite. The Transvaal System was metamorphosed intensively by the Bushveld Complex and was folded into a dome as well as an anticline. Petrofabric analyses suggest that these two folds differ in age, but both resulted from the intrusion of the Bushveld Complex. Further, the Elandslaagte dome is considered to be younger than the Swartkop-Marble Hall anticline.
Pre-Transvaal rocks occur in the core of the Elandslaagte dome. Unfortunately it is not possible at present to correlate these rocks with any known geological formation in South Africa, but they are regarded tentatively as Archaean. The metamorphism of the Transvaal System is dominantly thermal, and is of a higher grade than that caused by the bushveld granite in other parts of the Transvaal. However, the possibility exists that the metamorphism could be due to the gabbroic rocks which would occur underneath the granite in the pseudostratified succession of the Complex. The intensity of the metamorphism increases in a southerly direction, and an attempt was made to delineate metamorphic zones. Owing to the fact that outcrops are rather poor, however, the attempt was not very successful. Four new chemical analyses of felsite, gneiss, metamorphosed diabase and cordierite-garnet hornfels, are given, and their petrogenic significance is discussed.

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Transactions of the Geological Society of South Africa, 61, 263-282, 3 pl

The small ultrabasic body making up Chimwadzulu Hill, in southern Nyasaland, is composed largely of epidotized, occasionally garnetiferous, amphibolite - both massive and lineated, some of which is corundum-bearing. The amphibolite is associated with serpentinized peridotite and with rocks containing varying proportions of actinolite, tremolite, and nephrite. Within the ultrabasic mass, small "pods" of chlorite-talc rock are common and the whole is cut by thin veins of drusy white quartz. The petrography of the various rock types is described and a chemical analysis of hornblende from a typical amphibolite is given. Qualitiative spectrographic analyses of most of the different rocks and minerals are included. Finally the possible petrogenesis of the ultrabasic mass and its affinities with similar rocks elsewhere is discussed. It is concluded that the body was originally a sill - or dyke - like mass of peridotite, intruded into geosynclinal sediments during the early stages of a major orogeny and elongated parallel to the regional fold axes. Early differentiation may have resulted in both peridotitic and pyroxenitic parts. The present pod-shaped character of the mass is thought to be due to breaking up of the initial sill or dyke into a series of semi-parallel boudins, of which this is the largest, under increasing stress. Serpentinization followed intrusion and could equally well have been caused by either autometasomatism or derivation of the necessary water from the enclosing sediments. It almost certainly took place after the mass had attained its final position. Retrograde metamorphism, accompanied by metasomatism, was responsible for the change from peridotite/pyroxenite, first to amphiboltie, and finally to tremolite and actinolite. The chlorite-talc rocks were formed by late- or post-kinematic hydrothermal activity, the final stage being general quartz-veining of the whole mass.

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Transactions of the Geological Society of South Africa, 61, 283-358, 10 pl

Evidence is submitted that the Great Dyke of Southern Rhodesia, which is intrusive into Archaean granite for more than 97 per cent of its length of 332 miles, is composed of four separate igneous complexes. All the complexes composing the Dyke exhibit a marked layering and rhythmically repeated zoning of the component rock-types. The dip of the layering is inward, being steeper at the margins than towards the centre. The succession in the individual zones is normally dunite below, through harzburgite to pyroxenite. Gabbroic rocks overlie the uppermost pyroxenite in the four complexes. Optical determinations of the minerals of the layered rock-types forming the Hartley and Wedza complexes indicate that all the lower olivine-rich layers consist of forsterite Fo94 and decrease to Fo84 in the upper-most harzburgite. Serpentinization in the Dyke is a surface phenomenon and is confined to the olivine-bearing rock-types. The phenomena is not strictly a function of depth and disappears below a depth of 940 feet in the Wedza Area. No olivine is present in the monomineralic portion of the pyroxenite bands or in the gabbroic rocks. Clinopyroxene (augite) is not present in the lower ultramafic zone, but becomes increasingly more important from the picrite zone (Wo29En71Fs18) below the uppermost pyroxenite to the gabbroic rocks (Wo29En32Fs39). No orthopyroxene has been found below a depth of 3,000 feet in the Wedza Bore-hole. The orthopyroxene varies from enstatite Mg94 in the ultramafic zone to hypersthene Mg58 in the upper portion of the mafic rocks. Chromite seams occur at the base of a zone, i.e., below harzburgite (where this rock-type is succeeded downwards by pyroxenite) or in duntie. Chemical analyses of gangue-free samples of the 10 chromite seams in the Hartley Complex exhibit some relationship with the layered rocks. High Cr/Fe ratios (which increase from 1.90 in Seam No. 1 to 3.62 in Seam No. 7) are also indicative of high chromic oxide values (which increase from 51.02 to 59.06 per cent Cr2O3 downwards). The formation of asbestos, which is related to the degree of serpentinization, is mainly confined to areas in the immediate vicinity of major faults in the Dyke. The metamorphic effects produced on the rocks marginal to, as well as those enclosed in the Great Dyke are mainly thermal. Blastoporphyritic and micrographic textures are developed. The metamorphic aureole is small, being only a few feet wide. Inclusions of original greenstone in the Dyke now exhibit sieve texture and poikiloblastic development of both clino- and orthopyroxene. The rock-types of the Dyke exhibit characteristic margins upwards in the succession and indicate that separate magma inflows differentiated in place and that the order of crystallization resulted in different layers. The trend of the differentiation in the silicate rocks calculated from the chemical analyses and expressed as Niggli values exhibit a decrease in magnesium upwards in the succession from mg = 0.85 in the ultramafic rocks to mg = 0.48 in the mafic rocks. The fm values decrease similarly from 97 to 47.
The trend of the differentiation, the emplacement of the Dyke magmas as separate inflows and the resulting structures indicate that three stages were involved:
(a) A period of fissure formation and the injection of the magmas as separate inflows. Vertical fissures aligned along a more or less straight line acted as feeders to a sheet-like pluton extending over a considerably larger area than that occupied by the Dyke at present. The approximate positions of the feeders are now demarcated by outcrops of gabbroic rocks.
(b) Subsidence of the floor, the formation of a graben and concomitant basin formation in cross- and longitudinal sections.
(c) Erosion down to the present level.
The results obtained from the Wedza Borehole and from gravimetric traverses at the south end of the Dyke lend further support to the theory advanced that the Great Dyke is not a dyke, but the remains of four lopoliths preserved in a graben. The composition and thickness of the various layers of the Great Dyke are compared with those of other igneous complexes. The Great Dyke was probably derived from the same source as the Bushveld Igneous Complex.

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Transactions of the Geological Society of South Africa, 61, 359-365, 3 pl

The paragenesis of the ore minerals of the Phalaborwa Complex is described. The properties of two unknown minerals, an oxide and a sulphide-probably nickel-bearing are recorded. The following new features relating to radio-active minerals are noted:
1. Magnetite in contact with "uranoan thorianite" exhibits a marginal colour change and innumerable small pores.
2. Carbonate gangue adjacent to radioactive minerals is discoloured and broken by fine radial fractures - a result of radioactive blasting.
3. Inclusions of "uranoan thorianite" in baddeleyite have given rise to radioactive haloes and attendant isotrophism in the latter mineral.
4. Large "Uranoan thorianite" crystals show distinct zonal growth dependent on the UO2:ThO2 ratio.
The effects of radioactive, cataclastic textures and microvein fillings and replacements indicate a well-defined paragenetic succession commencing with magnetite containing exsolution products, baddeleyite and "uranoan thorianite". This early stage of mineralization is regarded as pegmatitic-pneumatolytic. A hydrothermal stage, characterized by sulphides, followed under conditions of falling temperatures. Some "descendant" supergene sulphides have been subsequently deposited.

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Transactions of the Geological Society of South Africa, 61, 367-375, 5 pl

In the Wheal Julia Mine small cavities occur in a horizontally fractured zone of post-sulphide age. Along the fractures the diorite is altered to clayey seams and the cavities are lined with botryoidal and stalactitic chalcopyrite. The stalactitic bodies show cores of the chalcopyrite with shrinkage cracks arid occasionally bornite. In the Nabeep West Mine the diorite along a vug zone is well altered to a chloritic mass and partly replaced by anhydride. Cavities are lined with quartzose encrustations or partly filled with selenite, and mixed with the secondary material are small bodies of botryoidal or hair-like stalactitic sulphides intergrown with fine crystalline chalcocite. Stalactites and botryoidal knobs are concentrically zoned: commencing with a core of white chalcocite a layer of blue chalcocite, followed by a bornite layer, and an outside thick cover of chalcopyrite. In longitudinal section some stalactites display a beautiful cone-in-cone pattern. The unusual shape of the copper sulphides is ascribed to deposition in a colloidal state.

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Transactions of the Geological Society of South Africa, 61, 377-386

An X-ray diffraction method suitable for cameras of small radius (diameter 57.3 mm.) and using the (0, 10, 0) or (226) reflection is described. Six analyzed olivine samples were investigated in order to compare the results obtained by this method with the results given by other physical methods.

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Transactions of the Geological Society of South Africa, 61, 387-400, 1 pl

During an investigation of the chromite, platinum and magnetite deposits north of the Pilanesberg in the Western Transvaal in 1956 and 1957 it was found that each of the constituent rock-types of the mafic portion of the Bushveld Igneous Complex, namely pyroxenite with chromitite seams, anorthosite, norite, porphyritic pyroxenite, pegmatitic pyroxenite, gabbro, ferrogabbro, dunite and magnetite, represents a separate intrusion. It was further disclosed that the so-called "breaks", which were known to occur in the platiniferous and chromiferous rocks and which were thought to be due to faulting, are actually the results of the complete transgression of the uppermost ferrogabbro across the whole succession right down to the sedimentary base at two localities. The platiniferous Merensky Reef was found to be a sill-like pegmatitic pyroxenite intrusive into a sheet of porphyritic pyroxenite which in turn is intrusive into a chromitite seam, xenolithic in anorthosite. Below this horizon two further lithologically similar suites of rocks with sill-like disposition was found to occur, so that compared with other known areas the repeated injection of pegmatitic pyroxenite has tripled the strike-length of platiniferous rocks. On the other hand, the before-mentioned transgression of the ferrogabbro across the succession has caused the chromiferous and platiniferous rocks to be absent over no less than 17 miles, although: it had the effect of more than doubling the strike-length of the magnetite bands.

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Transactions of the Geological Society of South Africa, 61, 5-17

Detailed mapping in the Kandabwe area, coupled with data obtained from concurrent drilling operations, has led to a fairly complete knowledge of the lower part of the Karroo System in the locality. Glacial deposits encountered in the course of the work constitute the second discovery of the kind to be made in Northern Rhodesia of recent years, and help to refute the suggestion that the Dwyka Series is not represented in the Territory. The basal Karroo sandstone-conglomerate of the Gwembe District is equated with the Lower Wankie Sandstone of Southern Rhodesia, in view of several important characters common to both formations. There is good evidence that the single coal measure formation in the Gwembe District is the correlative of both the K2 and lower K5 coal measures of Southern Rhodesia, and that the Upper Wankie Sandstone is not present on the northern side of the river. Successiosn revealed by drilling in the Umi-Kaonga area some years ago may well represent an intermediate stage relating the coal measures as they are known in Southern Rhodesia to the Kandabwe sequence. Although the best known Lower Karroo localities in Southern and Northern Rhodesia are at Wankie and Kandabwe respectively, at neither place is the coal measure succession typical of the mid-Zambezi valley as a whole. The section exposed in the Sjegega stream is considered typical of the Gwembe Coal Formation, and is briefly described. Suggestions are made as to the environmental factors which led to the formation of thin coal seams of poor quality over the greater part of the mid-Zambezi valley, and of thick seams only locally at or near the base of the coal measure sequence.

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Transactions of the Geological Society of South Africa, 61, 51-79, 7 pl

This paper includes the descriptions of a number of new forms of fructifications belonging to the southern hemisphere class of fossil plants previously named the Glossopteridae by the author. The leaves of these plants belong to the leaf form genera of Glossopteris, Gangamopteris, Palaeovittaria and possibly Taeniopteris. The fructifications, whilst showing a strong relationship between these plants, provide further evidence that the 'old leaf' classification is unreliable. It is suggested that even these early Permian members of the class, all from a single locality, fall into at least six distinctive subdivisions. These are not of equal numerical importance and are possibly not of equal status, for from the present evidence, it is not yet possible fully to evaluate each group. The subdivisions, however, provide a basis for future investigations and a means for comparison with the classification proposed recently by members of the Indian school of Palaeobotany, based on cuticular studies of certain Glossopteridae. The fructifications serve to emphasise further, not only the highly developed nature of these plants, but an extraordinary diversification within this single class, unparalleled in Palaeozoic plant history, for which possible causes are reviewed.

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Transactions of the Geological Society of South Africa, 61, 81-96, 8 pl

An attempt has been made to sum up all available evidence about the habit of growth of the Glossopteridae with a view to making, ultimately, a more realistic reconstruction of the plants than that in current use. Evidence is drawn from the common autumnal deposits of massed Glossopteris, from the association of large fossilised tree trunks with leaf deposits in quarries and from South African coal. In particular the literature dealing with attached groups of leaves and with Vertebraria is reconsidered in the light of new specimens from Wankie, Southern Rhodesia, in which large clusters, or short shoots, of leaves are seen growing, at well-spaced intervals on thick, rather fibrous stems, and with similar but detached clusters from Vereeniging. Evidence is produced to show that this peculiar habit of growth was probably characteristic of the class as a whole. Reasons for the very rare preservation of attached leaves are discussed. All this evidence, both factual and circumstantial, leads to the conclusion that the Glossopteridae were mainly deciduous, woody plants of arborescent habit and that the leaves, flowers and fruits grew as short shoots, at fairly wide intervals from the woody stem, and also terminally, and that they represent a new experiment in plant evolution in Palaeozoic times.

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Transactions of the Geological Society of South Africa, 61, 97-101

Specimens of sphalerite from the West rand area have been analyzed for iron by both chemical and X-ray methods and the temperatures of their formation determined from data provided by Kullerud and Coleman. Temperatures average about 450°C and are higher than would be expected from depth of burial alone. The area from which the specimens were taken has been intruded by dykes of several ages and it is suggested that the sphalerites crystallised during a period of hydrothermal activity associated with the earliest (Ventersdorp) phase of post-Witwatersrand volcanism.

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Proceedings of the Geological Society of South Africa, 61, xiii-xxxii, 1 pl

A recent book Aspects of Form (L. L. White (Editor) 1951), written by selected experts in various branches of science, art, and psychology, takes as its theme "the realisation of the unity of spatial form in the complex processes of physics, biology, psychology and art". A remote and possibly unattainable goal is the healing of the seemingly permanent breach between the Democritus approach which reduces things to atoms and the Plato-Aristotle approach which deals in form, unity and symmetry. The two approaches may be complementary but in eighty generations no one has suggested how to combine them into a simple and comprehensive way of thinking. The Platonic bias of the book is revealed in its title, as is mine in the title of my address. Sir Herbert Read, in his introduction to the book, lists from all four elements comprised in the theme, a number of inherent patterns which can only be characterised as aesthetic. "All this development" he says, "has brought works of art and natural phenomena on to an identical plane of enquiry. Aesthetics is no longer an isolated science of beauty; science can no longer neglect aesthetic factors". It is proposed to examine that statement with relation to geology in general, and to structural geology in particular. One of my more versatile friends in this age of specialisation is a navigator, a geologist, an artist, and an instructor commander teaching diverse subjects. Amongst his many hobbies is the weaving of carpets of novel design, and one of the designs he selected was the geological map of Nova Scotia. The result was colourful and pleasing, and at first glance it might be classed as rather modern art. The pattern is literally as old as the hills, and it is God's artistry. The Almighty designed an aesthetic pattern, that is, one that has a subtle appeal to the senses. We simply copy His design in miniature, which is what geological mapping is. Then how can science and aesthetics be kept apart ? Yet it is fashionable in science today to shun aesthetics like the plague. This substantial connection between the two was through no contrivance of the scientist, who may not know (or who may prefer not to know) that his work has involved aesthetics in any way. Bernard Shaw has told us "You must not fall into the error that your feeling for beauty is universal. It is a precious gift".

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Transactions of the Geological Society of South Africa, 62, 1-31, 2 pl

The Kapalagulu Complex is situated some 70 miles south of Kigoma, on the eastern shore of Lake Tanganyika. The Complex is sill-like to lopolithic, is intrusive into the Basement System (Archaean), and is overlain unconformably by sediments of the Bukoban System. Locally, both the Complex and the country-rocks are tilted to a subvertical position, and consequently are exposed in stratigraphical cross-section along the land surface. Three principal zones, following conformably on one another, are recognized in the Complex:
(1) A Basal Zone of bronzite picrite;
(2) An Intermediate Zone of banded olivine hyperite; and
(3) A Main Zone, in which the most common rock-type is hyperite.
There is a narrow interstratified anorthosite band in the Main Zone. Mineral variation in vertical traverses indicate that the Complex was formed by gravitational differentiation in the typical manner. Within the Basal Zone is a horizon along which there is a relatively high concentration of sulphides. The sulphide of quantitative significance in this ore-zone is pyrrhotite, which presumably concentrated by sinking on becoming immiscible in the magma. As an alternative to existing hypotheses on the origin of rhythmic layering (which are outlined in the paper), it is suggested that this phenomenon may arise from periodic undercooling or metastability of a magma, and consequent rhythmic generations of crystals.

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Transactions of the Geological Society of South Africa, 62, 113-138, 1 pl, 1 tab.

The cyclic erosion surfaces of south-eastern Australia include a smooth early Tertiary planation that may be recognized far and wide upon the higher parts of the terrain. Below this level appear two late Tertiary sub-cycles of broad valley-planation, and finally deep canyons of Quaternary age. The attitudes of the several surfaces were examined in order to elucidate Tertiary and Quaternary crustal deformations in the region. Correlation of the landscape cycles and interpolated vertical tectonic movements in south eastern Australia, South Africa and Brazil is suggested in Table I.

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Transactions of the Geological Society of South Africa, 62, 139-150, 1 pl

Two rock sequences are identified, the Jembia River Granulites and the Mafingi Mountains sediments. Stratigraphic and structural features of each are described, correlations suggested and the views of previous workers reviewed. An area north-east of the Mafingi Mountains is shown to be different from either, particularly in regard to its structure which is post-Muva in age.

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Transactions of the Geological Society of South Africa, 62, 151-165

Various hypotheses of the origin of Rift Valleys and associated eruptives have taken insufficient notice of the changes of volume and energy involved. In the interplay of gravitational and thermal forces, the latter may entirely dominate the former, and over-ride all questions of isostatic equilibrium. Rift-valleys seem to be closely related to the Moho-layer which, it is suggested, is the seat of the main transformations of energy and the source of enclaves of hot, gas-charged magma. The African and other rifts may have started with an original bulge upward due to magma-pressure along a given line; then, either by release of lavas at surface or by laterl migration at deep level, support was removed and the arches collapsed, leaving the flanking ramps intact but for the remanent faults.
This is virtually a rejection of compressional and tensional theories and a reversion to J.W. Gregory's original explanation. The genesis of geosynclines with their associated vulcanicity, and of basins and swells, is also attributed to transformations of energy and volume at or near Moho level, and to migrations of magma, not necessarily in an upward direction. Attention is drawn to the scale of various crustal phenomena in contrast to the great size and stored energy of the earth, to questions of rigidity, and the limits between which natural principles such as isostasy may be deemed to be effective. The paper concludes by considering various structural forms and their development in a thin skin under the control of thermal and gravitational agencies.

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Transactions of the Geological Society of South Africa, 62, 167-177, 2 pl

The geologist and amateur photographer, when availing himself of recent improvements in miniature camera design and photographic films, is now able to produce aerial photographs of a higher quality than was possible with amateur equipment hitherto. These photographs, though not of the highly precise standard of those taken with expensive aerial cameras, are accurate enough for most purposes of geological mapping. The main advantage of the method is its adaptability to individual requirements. Photography for detailed mapping of small areas can be planned with due consideration of the geology. In addition to black and white, colour and infra-red photographs can be taken with the same equipment at relatively low cost.

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Transactions of the Geological Society of South Africa, 62, 179-201, 1 pl

Geological and geophysical evidence support the view that the mafic exposures of the Bushveld Igneous Complex are not structurally part of a lopolith but consist of two deep curved troughs of mafic rocks having a superficial synclinal structure. These mafic rocks are obscured by being partly covered by younger rocks along the inner margins of the postulated troughs. The central area of the Bushveld appears to have been updomed and there is evidence which indicates the probability that the mafic rocks were never emplaced over this updomed structure. A third exposure of mafic rocks, possibly of similar structure projects northwards outside the basin of the Transvaal System in which the first two lie. A fourth flat sheet extends west wards of the Pilanesberg to link the western limb with a basin structure north of Zeerust. Interpretation of gravity anomalies suggests that the troughs of mafic rocks may have dyke-like central feeders, capped with a superficial synclinal sheet, thus apparently having a structure very similar to that postulated for the Great Dyke of Southern Rhodesia. The Bushveld Igneous Complex taken as a whole appears to be a unit in a chain of bodies similar in character extending from the Zambesi River to the Orange River along a nearly straight line. The gravity anomalies pose a serious difficulty to Van Biljon's transformation hypothesis.

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Transactions of the Geological Society of South Africa, 62, 203-217

Geophysical investigation by airborne electromagnetic methods is now widely used in the search for sulphide ore bodies. Six electromagnetic systems which differ mainly in coil configuration provide advantages and shortcomings not necessarily common to all systems. The choice of a particular E.M. system for an airborne survey is determined by the expected shape, attitude and electrical properties of the type of body sought, the geological environment, the topography and the electrical properties of the overburden. The success of an E.M. survey depends on the selection of the most suitable system, the skill and experience of the interpreter and careful planning of subsequent ground follow up.

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Transactions of the Geological Society of South Africa, 62, 219-238, 1 pl

Drilling results obtained in the Union Mine of Rustenburg Platinum Mines Limited revealed an unexpectedly complicated succession between the Merensky Reef and the underlying Upper Chrome Group. A detailed study leads to the theory that the forces causing the emplacing of the igneous suite of which the Merensky Reef forms the basal part, have, prior to the emplacement of the latter, resulted in gentle folding of the formations which generally underlie the Reef. During the initial stage of emplacement of this igneous suite, the more pronounced elevated portions of the plane of emplacement are considered to have acted as elongated "islands" in the magma, and only became engulfed or "submerged" at a later stage of the emplacement. As a result, part of the area of Turfbult 989 and Zwartklip 988 shows incomplete development of the Merensky Reef and even absence of the latter in certain instances. It is concluded that similar conditions may well exist in other parts of the Bushveld Igneous Complex. Evidence has been obtained indicating the occurrence of Post-Bushveld cross-faulting, and the existence of a faulted zone passing through Turfbult 989, as well as of a major fault in the extreme eastern part of Zwartklip 988, seems to be without doubt.

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Transactions of the Geological Society of South Africa, 62, 239-255, 2 pl

In the vicinity of Steelpoort, Eastern Transvaal, basal rocks of the Bushveld Complex, consisting of norite, pyroxenite and gabbro seem to transgress across rocks of the Upper Magaliesberg Stage of the Pretoria Series, in what has been known as the "Steelpoort Bulge". It is shown that the "bulge" is the result of folding which has thrown the rocks of sedimentary origin, mainly quartzite, hornfels and dolomitic marble, into a mild syncline and an anticline which pitch towards the north. Rocks of the Critical Zone, spotted anorthosite, bronzitite, chromitite and the Merensky Reef, are shown to transgress across the older rocks and have also, to a lesser extent, been affected by the folding.

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Transactions of the Geological Society of South Africa, 62, 257-324, 2 pl

New data on the pre-Cape stratigraphy and structure of the post-Ntingwe thrust- belt are described. The salient points concerning the revised succession, considered in ascending order are as follows:
(a) the Nkandhla Series, previously regarded as part of the Basement Complex is now classified as the lowermost member of the Tnsuzi Series;
(b) the extensive mass of granite in the northern part of the area is shown to be intrusive into the Insuzi Series and is therefore not part of the Basement Complex as reported in earlier publications;
(c) the Mfongosi limestones formerly regarded as Basement are placed in the Ntingwe Series which rests unconformably on the Insuzi and older series and is now correlated with the Transvaal System.
Three periods of pre-Cape metamorphism are described. In order of development they are:
(a) regional metamorphism and migmatization of the Basement which is shown to be of pre-Insuzi age,
(b) contact metamorphism related to the intrusion of the post-Insuzi granite and
(c) extensive dynamic metamorphism attributable to the post-Ntingwe thrust movements.
Several thrust-faults not previously recognized are described. A tectonic interpretation is advanced which indicates that the post-Ntingwe thrust movements were controlled by pre-existing structures in the foundation. It is suggested that failure occurred by clean-out thrusting within a deep syncline of Basement schists, which was compressed by tangential forces acting from the south, between two rigid, previously consolidated crystalline masses. These masses consisted of a foreland of folded Insuzi strata and the post-Insuzi granite on the north and migmatized Basement rocks on the south. Thrust-Wedges moving upward and towards the north elevated and folded the cover of Ntingwe sediments slices of which appear within the frontal thrust-sheets. Undisturbed patches of Ntingwe strata occur along the southern margin of the foreland.

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Transactions of the Geological Society of South Africa, 62, 325-372

No existing definition of "orogeny" can apply to the Archaean without causing a dilemma. The choice between (a) accepting huge African orogenies reconstructed on the basis of widely scattered and quite puny Archaean synclines, and (b) abandoning uniformitarianism as applied to the Precambrian, led to a search for demonstrable geological constants applicable to all geological time. Size is not one, certain ratios are, which leads to a suitable definition. An orogeny is a linear mobile belt between two inert blocks or cratons of an appropriate relative size. An Archaean arcuate mobile belt helps to frame a small hub in the same manner as the Cordillera flanks a continent. The ratio of the magnitude of a mobile belt to the diameter of its craton is roughly constant whatever the age, hence the size of those units should show a progression with time. This is amply demonstrated by graphs. The orogenic evolution is reflected in reverse by the number of orogenic belts per era, varying from two in the Tertiary through thirty in the Palaeozoic, hundreds in the Proterozoic to thousands in the Archaean. The graphs indicate the existence of a zero point indicating a pre-Archaean era of no sedimentation. The Archaean fold belts, small and relatively simple, are discrete orogenies separating "gregarious batholiths", which must then constitute the primordial crust disguised by granitisation. The age relationship of the granite contacts, as in the case of mantled gneiss domes, is thought to be obscured by reactivation of the granite, and the alleged younger age of this granite is challenged. The First Unconformity is believed to be as widespread as the Archaean.

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Transactions of the Geological Society of South Africa, 62, 33-58, 4 pl

On geophysical evidence, seven boreholes were drilled in the country around Trompsburg. An igneous mass, intrusive into massive marble (probably of Transvaal age) and overlain unconformably by Karroo sediments, was revealed at a depth of more than 3,500 feet below surface. The pluton has a more or less circular sub-outcrop, the radius being approximately 15 miles. A zone of hybridised rocks, sometimes containing titanaugite, is developed at the contact between the marble and the igneous rocks. The igneous rocks consist of gabbro, anorthosite, melanocratic gabbro, olivine gabbro, troctolite, titaniferous magnetite bands (confined to the troctolite) and granite. The gabbroic rocks are probably emplaced as a composite sheet-like body 6,000-10,000 feet thick. Approximately 200 feet of red granite body of unknown form was intersected by the borehole nearest to the probable centre of the intrusion. The composition of the major rock-forming minerals in the various gabbroic rocks remains practically constant, the main control of differentiation being the fractionation of clinopyroxene crystals. The titaniferous magnetite contains significant quantities of ulvöspinel. Chemical analyses of the different rock-types are provided. The high Fe2O3 content of the gabbroic rocks and the abnormal association of massive iron ore and troctolite, are ascribed to a high partial pressure of oxygen during crystallization.

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Transactions of the Geological Society of South Africa, 62, 373-397, 3 pl

Mrima Hill represents the carbonatite facies of a post-Karroo alkaline province on the Kenya coast. Four different types of carbonatite which occur at Mrima are described and some partial analyses of these rocks are given. The geology and mineralogy of a large body of limontitic and kaolinitic rocks is described. These geology and mineralogy of a large body of limontitic and kaolinitic rocks is described. These rocks are believed to be weathered derivatives of carbonatites, non-calcareous igneous rocks and fenitised sediments. One chemical analysis and some physical data are quoted for gorceixite, a phosphate mineral prominent in the weathered rocks. The results of some observations are given concerning the mode of occurrence of pyrochlore in the carbonatite. The distribution of niobium in the weathered rocks and soils is discussed. The niobium-rich weathered rocks are considered to present a special example of the formation of a mineral occurrence by residual concentration through chemical weathering.

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Transactions of the Geological Society of South Africa, 62, 59-73, 2 pl

An area of 20 square miles was mapped in the vicinity of the Driekop dunite pipe in the Lydenburg district. The composition of the pipe was determined and the relationships of the various rock-types which belong to the Early Plutonic Phase of the bushveld Igneous Complex, were studied with a view to establishing the origin of that part of the Complex. The chronological order of emplacement of the rock-types in this area could, in most cases, be determined. The pyroxenite and chromite bands were emplaced during the Pyroxenitic Subphases. The Critical Subphase consists of noritic rocks which show a large variation in mineralogical composition, and a pegmatitic felspathic pyroxenite. The Peridotitic Subphase followed and is represented in the area by the dunite pipe and a serpentinite occurrence. During the emplacement of the gabbroic rocks of the Main Subphase, some mixing with the noritic rocks of the Critical Subphase took place, and a hybrid rock was formed which is described as a hyperite. The composition of olivine at various places in the dunite pipe was determined by means of X-ray diffraction photographs. No signs of zoning in the pipe were found. Differentiation in depth, rather then differentiation in situ, is held responsible for the great petrographic variation of the rocks in the area.

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Transactions of the Geological Society of South Africa, 62, 75-80, 2 pl

In 1955 an iron meteorite was unearthed by Mr. J.W.E. Keeble on portion N.W. 48, Bellsbank Estate, about 27 miles N.N.W. of Barkly West. The meteorite consists of kamacite (Fe-Ni alloy) with schreibersite (Fe, Ni)3P, as irregular veins up to 1 cm wide. The surface is pitted and the products of weathering are magnetite and goethite. Silicates are minor constituents. A chemical analysis and etch-tests, which reveal Neumann lines, confirm its identity as a nickel-poor iron meteorite of subgroup hexahydrate. The laboratory examination includes etch- tests, physical properties, X-ray diffraction data and analyses of the kamacite and schreibersite.

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Transactions of the Geological Society of South Africa, 62, 81-111, 2 pl

The dolerite forming the Khale sheet, Bechuanaland, is in many respects similar to the Downes Mountain type of Karroo dolerite, and contains numerous lenses of coarse-grained dolerite pegmatite. The plagioclase feldspar is described with special reference to the variations in grain size, the features of zoned crystals and the possible causes of a distinctive brown clouding seen in thin section. Both pigeonite and augite occur in medium-grained rock and the dolerite pegmatite, and as phenocrysts in the fine-grained marginal dolerite. The zoning of pyroxenes is described. Micrometric data indicate that the mineral composition of the various specimens is largely governed by the state of oxidation of the iron, and show that the marginal rock is enriched in the darker and heavier minerals. Three new chemical analyses show that the dolerite pegmatite is enriched in iron and alkalies relative to the parent dolerite, and the relation of ferric iron to ferrous iron in this instance is unusual in Karroo dolerites.

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Proceedings of the Geological Society of South Africa, 62, xxi-ixxx, 10 tab., 3 pl, 1 fig

The Bushveld complex is considered to be a funnel-intrusion complex emplaced in a stable continental shield. It seems more reasonable to explain the diversity of the rock-types by differentiation in the venue of emplacement and assimilation to some extent than to relegate their origin to abyssal processes which are difficult to appraise. The mafic sills in the Transvaal System show variation in composition and facies to a considerable measure depending on their proximity to the Complex. The metamorphism in the encircling sediments is essentially thermal in character and not of an extremely high grade. Advanced metamorphic effects are related to the distribution of the ultramafic rocks of the main body of the Complex. In thermal metamorphism, as revealed in the Bushveld aureole, the composition of the original material generally determines the nature of the metamorphic product, but in conditions of low-grade metamorphism directed pressure is readily effective so that typical thermal metamorphic minerals are not always consistently developed.

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Transactions of the Geological Society of South Africa, 63, 1-10, 10 pl

A gravity anomaly of unique magnitude, at Trompsburg, O.F.S., South Africa, discovered by B.D. Maree, was investigated with gravimetric and magnetometric surveys. The survey shows that a circular gravity anomaly with a maximum amplitude of 99.5 milligals coincides with a modest magnetic high. In addition two zones with conspicuous magnetic anomalies showing amplitudes of 300-400γ were found in the north-west sector of the surveyed area. Diamond drilling indicated a lopolith comprised of basic rocks of pre-Karrroo age. The study of borehole cores revealed a similarity between the rocks from the Trompsburg pluton and those of the Bushveld Igneous Complex. The former are mainly gabbros and anorthosites, characterized by an abundance of titaniferous magnetite and frequent specks of sulphides, mainly pyrrhotite, chalcopyrite and pyrite. Red granite, undistinguishable from that of the Bushveld Complex, was found near the centre of the gravity anomaly. Pseudo stratification having an average dip of about 30°, was disclosed by drilling. The base of the lopolith, at least in the north-west sector, was found to rest on crystalline limestone of pre-Karroo age. Of the two magnetic anomalies in the N.W. secotor, the inner one was due to titaniferous magnetite. The more interesting, outer anomaly, which lies near the contact of the igneous body with the surrounding strata, was not investigated by diamond drilling, and as it has not been investigated, the opinion is expressed that the potential value of the Trompsburg Igneous Complex cannot as yet be assessed. It is hoped that some day this omission will be made good and the exploration of the Trompsburg Igneous Complex completed.

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Transactions of the Geological Society of South Africa, 63, 11-50, 3 pl

The lithology and structure of rocks of Bukoban type in a large area of Western Tanganyika are described. A new rock stratigraphic unit classification is proposed. The influence of Rift faulting on structure and sedimentation is shown. The problem of correlation of the rocks with those in other areas is discussed.

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Transactions of the Geological Society of South Africa, 63, 119-135, 2 pl

Reconnaissance mapping shows the Chaone hill syenite body to be a ring structure similar to other complexes of the Chilwa Series of southern Nyasaland. The main rock type is pulaskitic syenite with lesser amounts of perthosite and foyaite. Small outcrops of downfaulted hornfelses representing early volcanics are preserved in the west. The youngest rocks are alkalic dykes and these follow east-west and north-south trends. Ring-dykes are not as well developed as on Chikala hill to the east, although more detailed mapping on Chaone might emphasise the concentric structure. Later faulting is complex and is partially related to Rift Valley-type movement. It is thought that Chaone hill and Chikala hill may represent trends in composition which might also be recognised in the Mongolwe and Chindusi hills, which complete an east-west alignment of four syenitic ring complexes, north of Zomba Mountain.

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Transactions of the Geological Society of South Africa, 63, 137-152, 4 pl

Some occurrences of pale material as inclusions and veins in Karroo dolerite sheets of the eastern Cape Province are described under the headings of mobilized sediments, xenoliths of sedimentary origin, dolerite pegmatite, coarse granophyre and albitic rocks. Ten new chemical analyses are given. Only those in the last category are of doubtful origin and may, in fact, include some examples of magmatic origin and others of sedimentary origin. No criteria could be found to distinguish with certainty between the two types of origin and, until individual occurrences can be traced directly into types of established origin, the question of the origin of the albitic rocks must be left open.

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Transactions of the Geological Society of South Africa, 63, 153-159

A sufficiently close relationship exists between the weight percent ages of ilmenite, rutile and zircon in the sand dune deposit, to enable the zircon and rutile contents of a sample of the sand to be predicted with sufficient confidence from the experimentally determined ilmenite content of the same sample. A study of these minerals in the sand showed that the relative abundance of the various heavy minerals in the source-material must have remained practically the same whatever the grain size. Under such conditions the ratio between the different heavy minerals deposited together is not affected by changes of grain size or degree of sorting.

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Transactions of the Geological Society of South Africa, 63, 161-174, 2 pl

Recent mapping near Molepolole in the south-eastern Bechuanaland Protectorate has revealed a sedimentary succession which can be correlated with Loskop rocks. The fact that these sediments overlie strata previously included in the Waterberg System necessitates a review of the distribution of Waterberg and Loskop beds in southern Bechuanaland.

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Transactions of the Geological Society of South Africa, 63, 175-187, 1 pl

Mapping of the cyclic erosion surfaces in Swaziland has focused attention upon the completeness of planation in the Quaternary Lowveld. The adjacent Lebombo Escarpment fails to display several characteristics normally consequent upon long-distance erosional retreat. It is suggested that (a) The geomorphic history of the Swaziland Lowveld differs vitally from that of Quaternary areas elsewhere in South Africa; (b) The Lebombo Escarpment is not of erosional origin; (c) The Swaziland Lowveld possesses the characteristics of a Rift Valley.

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Transactions of the Geological Society of South Africa, 63, 189-230, 1, fig, 1 pl

A contribution is made to the stratigraphy of the Klerksdorp area from a study of borehole cores and underground development. The Kimberley-Elsburg beds are treated as one series down to the base of the Kimberley Reef. The Kimberley Shale is placed in the Main-Bird Series which terminates at the Ada May Reef. The Government Reefs, at the top of the succession of beds which has hitherto been regarded as comprising the Government Reef Series, are placed in the Jeppestown Series, and new stages, the Boulder and Bonanza, have been added to the Government Series. A suite of sedimentary rocks that starts with a basal conglomerate deposited on shales is taken as representing a cycle of sedimentation. Since the basal conglomerates form only a small percentage of the total sediments in a succession, the word "reef" has been dropped from the stage nomenclature such as Elsburg Stage to conform with the titling of the system and series such as Witwatersrand System, Kimberley-Elsburg, Main-Bird and the Jeppestown Series. The word reef is only introduced to distinguish the reef zones in the stages.

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Transactions of the Geological Society of South Africa, 63, 231-263, 4 pl

A Lower Cretaceous sequence of conglomerates and finer-grained lacustrine sediments containing a fossil flora is exposed immediately to the east of the bracket bridge on the left (north) bank of the Umfolosi River. Identification of the fossils other than wood has established that this formation is the equivalent of the Wood Beds (Wealden age) of the Uitenhage Series of the Eastern Cape Province and Pondoland. Coarse conglomerate overlaps on to steep pre- Cretaceous slopes of easterly dipping Stormberg basalts on the west; to the east, the sediments are less coarse. A fossiliferous Upper Cretaceous marine sequence, probably Santonian to Campanian in age, overlies the Wealden rocks with disconformity and indicates a break in the Cretaceous succession in Middle Cretaceous time. The planed surface on the older formations carries a thin cover of Pleistocene sand with a akin basal conglomerate. Umkwelane Hill, on the right (south) bank of the river, has Stormberg basalts exposed at the base on the north-east and along the northern flank to the west.
A relatively thin succession of fossiliferous Upper Cretaceous marine sediments lies with overlap on the basalts along the eastern flank of the hill. A foraminiferal formation, of Lower Miocene age, rests on the planed surface of the Upper Cretaceous. A cover of Pleistocene sand is spread from the uppermost part of the eastern slope over the Tertiary sediments to the basalts on the west. The Cretaceous succession from Umkwelane Hill eastwards to the exposures along the eastern shore of Lake Eteza is probably lower Coniacian to Santonian or Campanian in age, and includes the continuation along strike of the sediments that lie along the left bank of the Umfolosi River. The major fault, now named the Eteza Fault, between the Basement rocks and the Stormberg basalts, which trends north-east, from near Empangeni into the present area, is post-basalt and probably pre-Cretaceous in age. The Tertiary beds at seven and fifteen miles inland from the present coast lie on a gentle seaward sloping surface. This indicates slight seaward tilting only along the coastal plain since post-Cretaceous times.

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Transactions of the Geological Society of South Africa, 63, 265-282

The Rooiberg tinfields are situated in a folded roof-pendant of pre-Cambrian quartzites resting on granite of the Bushveld Igneous Complex with which the tin mineralisation is genetically connected. Folding and faulting of the sediments occurred together with the intrusion of the granite during the post-Transvaal orogenic phase. Mineralisation took place probably during late stages of tectonic stress in part continuing beyond cessation of the latter. The structure of the area is dominated by two synclines which enclose a broad anticline. Each syncline is accompanied by a major thrust zone. These thrusts as well as foot-wall branches are mineralised in places. In the centre of the area an extensive stockwork is mineralised. Two mineral assemblages of different age occur.

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Transactions of the Geological Society of South Africa, 63, 51-64, 4 pl

Mapping in the Empangeni area of Zululand, between the Natal and Lebombo monoclines, has disclosed the existence of an extensive fault system. Further study revealed that the granitic range of the Ngoye is a tilted block or horst, bounded on the north and north-west by the Umhlatuzi fault and on the south and south-east by the Umlalazi River, the rocks exhibit a landward dip in contrast to that prevailing elsewhere along the coast. A third fault, the Eteza fualt, enables the system to be dated as it passes beneath undisturbed Cretaceous at Umkwelane hill. The age of the faulting is late Jurassic and is possibly associated with the disruption of Gondwanaland.

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Transactions of the Geological Society of South Africa, 63, 65-70

New chemical data are provided on the alkali granites and the associated nepheline syenite dykes of the alkali province of the Vredefort Mountain Land. The genetic problem of the porphyritic members of the feldspathoidal dyke suite carrying phenocrystic microcline is discussed in the light of experimental synthesis.

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Transactions of the Geological Society of South Africa, 63, 71-74, 1 pl

This paper describes the construction and operation of a light, portable drilling and the orienting instrument used to produce oriented cores to a depth of 3 feet.

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Transactions of the Geological Society of South Africa, 63, 75-85, 1 pl

A shear-zone in the gabbro of the Bushveld Igneous Complex could be traced from the Pilanesberg in a south-easterly direction for 14 miles and it continues still further. Magnetite-bearing mottled anorthosite is intrusive into the gabbro along this zone and fissures, filled out with prehnite and quartz, and veins of graphic granite occur along it. Field and microscopic data strongly suggest the anorthosite to have formed by the partial refusion of the lower anorthosite in place and re-injected as a crystal mush into the overlying gabbro along the shear-zone. The prehnite and graphic granite were probably formed under hydrothermal conditions. The decomposition of the plagioclase could have provided albite and anorthosite. The albite together with orthoclase and quartz formed graphic granite; the anorthosite reacted in the presence of water with calcium silicate, provided by the decomposition of clinopyroxene, and formed prehnite.

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Transactions of the Geological Society of South Africa, 63, 87-97, 3 pl

During 1957/58, while panning for gold in the Indus river in the Hazara district and in the Gilgit agency, uraninite and other minerals were found in the concentrates. In one section uraninite was found to occur continuously in the river sand for over a hundred miles, but in another it was possible to obtain samples only from three places. Some hundred samples and panned concentrates were obtained from different localities. Tests on the transportation speed of the uraninite were carried out by means of a scintillation counter. The samples were also tested in laboratories in the United States, England and Germany where, as far as known, similar results were obtained.

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Transactions of the Geological Society of South Africa, 63, 99-117, 1 pl

Chikala Hill, situated 20 miles north-east of Zomba in southern Nyasaland, is the eastern member of a range of four hills comprising a group of syenite and nepheline-syenite intrusions belonging to the so-called Chilwa Series. Chikala Hill itself, is a syenite ring-complex emplaced in gneisses of the Basement Complex, and is composed of an intricate series of ring-dykes whose composition varies from syenite to nepheline-syenite. Three main rock types are distinguished and these are, in probable order of intrusion. 1. Perthosite, 2. Pulaskite, 3. Microfoyaite. This sequence suggests a progressive reduction of silica in successive intrusions with, in some cases, multiple ring-fracturing resulting in arcuate screens of earlier dykes being enclosed in later ones. A group of black hornfelses, representing former basic volcanics, forms a subsided block within the syenites and similar rocks are also present as xenoliths in the syenite ring-dykes. An analysis suggests that these are alkaline basalts, and a close genetical connection with the Chilwa Series is thought possible.

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Transactions of the Geological Society of South Africa, 63, xix-xlii

The basis for my address is the travels, trials and tribulations of a small band of geologists, engineers and physicists quite a few of which have and do hold office in this Society and who, together with an equally vital assortment of drivers, storemen and labourers took part in a "water safari" probably the longest ever undertaken, and which, beginning in Pretoria in 1940 took them over the next five years all through Africa, the Middle East and into Europe itself. The story of this remarkable journey has never been fully told although a considerable number of technical papers dealing with specific problems of surveys undertaken by members of the safari have been published. I propose, therefore, making an attempt to place on record a description of the wanderings of this detachment, the members of which despite their small numbers, covered an enormous area and rarely saw their companions except when some major move was contemplated.
The story of the 42nd Geological Unit of the South African Engineering Corps - to give it its full title, really began in 1934 when Dr. Haughton, then Director of the Geological Survey, instituted a geophysical branch in the Union Geological Survey. Dr. G. L. Paver and I were the first recruits followed by Dr. J. F. Enslin and Mr. B. D. Maree.
Experimental work with various geophysical methods was started and the application of electrical resistivity and magnetometric methods to underground water problems under Dr. H. F. Frommurze, made such progress that when War broke out in 1939 a nucleus of geologists trained in geophysical work was available. Members of the Geological Survey were officially listed as "key men" but in 1940 when the South African Engineering Corps was being formed and equipped plans were set afoot by Dr. Haughton to incorporate in the Corps a Geological Unit whose function it would be to advise on water and mineral problems and undertake selection of drilling sites.
The formation of this unit was a novel idea in the history of warfare and it proved to be the only one of its kind in existence in all the Allied forces although individual geologists were employed in some commands. The demand for its services left no doubt as to the useful role it played During 1940 plans were finalised and Dr. Frommurze, Dr. Paver and I were released for military service and sent to Premier Mine for rapid conversion in a matter of weeks to officers and gentlemen. Conversion to the former was never really completed and throughout its life the unit was never considered one of the show pieces of the Engineering Corps from a purely military point of view - we considered ourselves primarily scientists. On completion of the course which was supposed to equip us to deal with anything from gas warfare to gunnery the Unit which had now been joined by Mr. Digby Roberts sailed in a state of partial preparedness for East Africa. The hectic days prior to departure gave way to a reasonably pleasant cruise interrupted only by boat drill and various minor duties which gave ample time to speculate as to what lay ahead.
On arrival at Mombasa the Unit was moved up to Nairobi and, after the usual military manoeuvres, it was decided that we should be H.Q. Troops stationed in Nairobi. This action very definitely had its advantages as it meant that during spells between field trips we could enjoy the fleshpots of Nairobi with its large variety of Country Clubs scattered round the town. A more practical advantage however was that the risk of being attached or adopted by area commanders to form part of their own little empires was ruled out. A few days after our arrival it was decided that acquaintance should be made with the local Rift Valley geology and a trip was laid on for this purpose on a Sunday. On our return to base we had our first introduction to the military machine which had decreed that a field party must move forthwith to select borehole sites. The fact that our equipment had not yet arrived made no difference - the game was on. From this time onwards the Unit was split into small detachments comprised usually of one officer plus a technical N.C.O., drivers and labourers, with these detachments operating from H.Q. as and when required. Prior to the war years Kenya had its European population who were derived largely from Britain, concentrated in the pastoral highland country. The more arid areas or "bundu" surrounding the highlands were in consequence rarely visited by people other than Government officials, many of whom as District Officers and Commissioners, spent their tours in conditions of extreme isolation. Excursions into the Northern Frontier Districts had to be in the nature of well organised safaris with several vehicles and ample supplies of water and fuel. In some areas a distinct hazard existed in the form of tribesmen who were usually against everyone else and often indulged in some particularly unpleasant forms of mutilation of their enemies. As a result of the restricted movement within these areas no recent geological map of the territory was available, particularly in the more remote areas. The Unit was therefore forced to make use of whatever information was available, often in the form of notes and sketches of early explorers. It was soon realised that a unique opportunity existed for members of the Unit who were penetrating into the most remote areas, to prepare a more up-to-date geological map for their own and others use.
The Unit had now been joined by Lt. A.L. Eales from the Union and Lt. Huddleston from the Gold Coast who, on finding fellow geologists, transferred to us. The latter was the first of a succession of geologists who joined the Unit either for training or to be with a geological unit and on his shoulders, ably assisted by Lt. Digby Roberts, fell the task of compiling existing and new data supplied by the Unit, into a geological map of the territory. From this map it will be seen that Kenya is underlain basically by three major formations. The low-lying coastal belt particularly in the northern coastal areas is occupied by Pleistocene to Recent Northern Frontier District or N.F.D. sediments-shales, sandstones end clays in varying stages of consolidation. These are derived largely from granitic detritus and were in consequence often confused with the older formations underlying them. Passing inland the Pre-Cambrian or Basement Complex occupies a broad belt varying from 100-200 miles in width which sweeps northwards round the Mt. Kenya area until it disappears under the recent lavas at the south end of Lake Rudolph. The Pre-Cambrian rocks are in turn overlain by the Cretaceous to Recent Volcanics which occupy most of the western area of Kenya along the Rift Valley faulting, with the exception of the area between Mt. Elgon and the southern tip of Lake Rudolph. In addition to the above the north-eastern corner of the territory between Wajir and El Wak is occupied by Cretaceous sandstones and Jurassic limestones which were explored in post-war years for possible oil-bearing structures. Finally in the extreme S. W. corner of Kenya a small complex area is found with Kisii sediments of possible Palaeozoic age overlying Pre-Kavirondian volcanics and Basement Complex rocks. It is in this area that virtually all mining operations are centred. Each of the above formations have their own particular underground water characteristics and I propose dealing only briefly here with the main forms of occurrence in each.

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Transactions of the Geological Society of South Africa, 64, 1-22, 1 fig

Cymatogeny, "the undulating orogeny", is defined as a mode of crustal deformation between epeirogeny and orogeny in which the earth's surface is thrown into great waves or undulations commonly hundreds of miles across and thousands of feet high. These undulations are determined by mapping of Cainozoic denudational surfaces that are dated by reference to unconformities or hiatuses in sequences of Cainozoic rocks deposited in relatively depressed areas. Examples are given. Landforms developed during, or following upon, cymatogeny are examined, with examples. Cymatogeny is deemed to develop by vertical laminar movements within the earth's crust, that at suitable depths and temperatures are thought to create tectonic gneisses. Insofar as rejuvenation is common upon earlier cymatogens following denudation and a restoration of isostatic equilibrium, denudation and isostasy may be deemed as contributing to the formation of tectonic gneisses at depth within the crust; but the main cymatogenic impulse is believed to come from the subcrust.

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Transactions of the Geological Society of South Africa, 64, 101-145, 6 pl

The Dorowa and Shawa carbonatite complexes with their related suite of nephelinitic and ijolitic minor intrusions intersect the granite gneiss of the Basement complex and associated dolerite sheets of eastern Southern Rhodesia. The Shawa complex consists of a plug of serpentinized dunite surrounded by a zone of fenitized country rock. An arcuate body of ijolite has been intruded between the dunite and the fenite, and a ring dyke of dolomitic carbonatite is situated within the dunite plug. The smaller Dorowa complex is occupied largely by fenite and mobilized fenite, together with minor amounts of carbonatite, magnetite-apatite-serpentine rock and mica-apatite rock. These complexes are regarded as representing the root zone of a large nephelinitic volcano analogous to the Napak volcano in Uganda. Evidence is put forward to show that the parent magma of Dorowa and Shawa had the composition of a volatile-rich ijolite or olivine ijolite.

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Transactions of the Geological Society of South Africa, 64, 147-161, 1 pl

Shatter cones are unique structural forms found in rocks that are presumed to have been subjected to very intense shock. They are very abundant in almost all rocks of the Vredefort area. The radial orientation of cones found in Witwatersrand quartzites points to a shock locus situated more or less in the centre of the ring. Furthermore, the "explosion" appears to have occurred before the sediments were uptilted and overturned and may well have been intimately associated with the deformation.

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Transactions of the Geological Society of South Africa, 64, 163-191, 4 pl

The stratigraphical data of a successful exploration campaign are recorded so that at some future time when the Western Deep Levels Gold Mine is sufficiently developed, an assessment of the accuracy of borehole deductions may be made. A second objective comprises an attempt to define some concepts pertaining to structural and sedimentational features characteristic of the rim of a tectonic basin of deposition, and to show that the observed features of the mine lease area fit harmoniously into the larger picture. The broad regularity of this portion of the "West Wits line" is interrupted drastically by the Bank fault, which appears to have been active throughout geological history, having played a role in controlling the shape of the Upper Witwatersrand basin, hence of the sedimentation, and having displaced rocks of four systems by varying amounts. Contours, sub-outcrops and isopachs all point to the Bank re-entrant as a fundamental structure in the geological history of the Witwatersrand basin. Sedimentological, structural and erosional features are closely interlinked by their common response to the effects of the entrant.

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Transactions of the Geological Society of South Africa, 64, 193-219, 3 pl

The "J-lines" ore-body is one of a number of pyrometasomatic copper-lead-zinc occurrences in intensely folded micaceous and quartzose schist of the Piriwiri Beds, Precambrian in age, in the north-western part of Southern Rhodesia. The ore is mainly sulphidic and has replaced a sporadically developed dolomitic bed and its metamorphic equivalents. This bed is intensely folded like the surrounding schist and follows the outline of an oval-shaped, concordant granodiorite stock in the core of a large anticline. The important sulphides present are pyrrhotite, sphalerite, chalcopyrite, and galena in the order of relative abundance. In addition, arsenopyrite, cubanite, valleriite, magnetite, pyrite, and marcasite are found. The paragenetic sequence of these minerals has been established as follows: arsenopyrite first and then pyrrhotite which is replaced by sphalerite, chalcopyrite, galena, and pyrite in the order listed. Cubanite, valleriite, magnetite, and some of the pyrite result from transformations, and marcasite and some of the pyrite are due to secondary alteration. Microscopical investigation of the ore-textures suggests that the sulphides were emplaced at the final stage of the regional metamorphism accompanying the folding and the orogeny of the Piriwiri Beds. This view is confirmed by the following: Field relations indicate a connection between the ore-deposits and the granodiorite in as much as the gossan outcrops follow a definite zone around the oval-shaped stock. Furthermore, the granodiorite is synkinematic. Ore-deposition started above 500°C and ended at about 250°C as concluded from the mineral association, the ore-textures, and the iron content of pyrrhotite and sphalerite. This temperature range agrees with the possible temperatures prevailing in the granodiorite during emplacement and the possible temperatures prevailing in the surrounding schist during the regional metamorphism. The granodiorite is considered to represent Basement granite and gneiss mobilized and forced into the sediments during the orogeny. Following the ideas of some Scandinavian authors it is suggested that the ore-forming emanations were formed during the granulation and mobilization of the Basement. They were driven out of the palingenetic centres to be redeposited and concentrated in a favourable calcareous member of the metamorphosed sediments.

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Transactions of the Geological Society of South Africa, 64, 221-246, 3 pl

The Shoshong-Makhware intrusives comprise two distinct geographic sub-provinces, comparable with the Bushveld "diabases", and ranging from undersaturated dolerites on the one hand, to acid granophyres and granites on the other. The widespread compositional differences in the first sub-province resulted primarily from a complex history involving successive magmatic influxes tapped from a differentiating subterranean magma body. It is shown that in the formation of large acid bodies in two of these sills, assimilation- differentiation was an important supplementary process. Finally, rhythmic- layering, which is confined to the Shoshong sill, shows features compatible with convection, primary magmatic flow, rhythmic differential setting and filter press action.

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Transactions of the Geological Society of South Africa, 64, 23-54, 3 pl

A size analysis was carried out on the uraninite, zircon and chromite fractions of several samples of Witwatersrand banket in order to investigate the possibility of hydraulic equilibrium existing between the uraninite and the detrital minerals. Study of the size data shows that (1) the median grain-sizes of the uraninite, zircon and chromite fractions fluctuate sympathetically from sample to sample, and from reef to reef, (2) the ratio between the median grain- sizes of these three fractions corresponds approximately with the ratio calculated from the theoretical considerations (the small deviations from this value could be due to the effects of hindered settling and deposition from muddy waters), and (3) the cumulative curves illustrating the various uraninite distributions show the same shape and gradient as the size distribution curves of the accompanying zircon and chromite fractions. The only explanation for the well-matched size distributions is that the uraninite grains were deposited together with the zircon and chromite fractions from a suspension in water. Comparison of the zircon and chromite fractions of the banket with those occurring in the hanging wall and other unmineralized arenaceous or rudaceous strata in the Witwatersrand succession shows that hydraulic conditions, favourable for the deposition of uraninite grains, were not confined to the periods of banket deposition. Uraninite is, therefore, probably genetically linked with the special conditions pertaining during the formation of the bankets.
It is suggested that (1) uraninite was precipitated as minute compact nodules in the muddy floors of marshes or shallow lakes covering the penelained surfaces or flood-plains during long intraformational breaks, and (2) the muddy deposits, containing the uraninite nodules, were reworked during the period of renewed wave-action initiating a new cycle of sedimentation, which caused the heavy grains to become concentrated and sorted, redistributed, mixed with other sedimentary material and eventually deposited together with the detrital components of the banket. Features such as the hydraulic equilibrium between uraninite and accompanying detrital minerals, the patchy distribution of uraninite in the banket, the tendency of the grains to form clusters, the occurrence of roundish aggregates composed of uraninite particles, and the presence of an occasional composite grain all find a ready and natural explanation in the type of origin suggested here.

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Transactions of the Geological Society of South Africa, 64, 247-256, 3 pl

Extensive mapping of the faults in the coastal areas of Natal has revealed the presence of a number of large arcuate structures. The significance of these and such related features as the topographic distribution of certain rock types are examined in the light of the prevailing theories of structural origin of the Natal coast. The conclusion is reached that the structure of coastal Natal is, in the main, one of step-faulted tilted blocks analogous to that of Zoutpansberg. The arcuate structures and step faulting have been induced by a tension acting approximately at right angles to the present coastline. The significance of off-shore bathymetric data is also discussed in the light of these facts, and it is further concluded that portions of the continental margin are most probably due to faulting.

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Transactions of the Geological Society of South Africa, 64, 257-278

Many lineaments described and drawn in the literature have a larger element of conjecture than would appear at first sight. In numerous instances, these should rather be termed vincula - alignments which refer to an incidental continuity or extraneous analogy. These latter lack the substance and documentation of lineaments, being thus alighments of a lower order. Examples are given from three different regions of the world where a more careful scrutiny would disclose that several of all of the lineaments postulated should be demoted to vincula. It is proposed that lineaments be more prudently distinguished and treated, that the parameters be specified and that they be not unduly extended where supporting evidence is lacking.

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Transactions of the Geological Society of South Africa, 64, 55-71, 4 pl

Evidence of slumping in the Table Mountain Series was observed at some 60 localities, mainly in cuttings along four roads crossing that part of the coastal region which extends 90 miles northwards of Durban. The evidence consists predominantly of intraformational contortions, which range up to 10 feet in height and generally involve two or more lithological units. An unusual feature of the slumping appears to have been the high mobility of the sandy units compared to that of the thin clay beds. Contorted sandstones underlain or separated, wholly or in part, by thin undisturbed lutites, were observed at several localities. Examples of slipped blocks and placoidal cleavage were also encountered. The slump sheets range from 1 to 50 feet in thickness, but the lateral extent of these masses could not be determined. The sediments provided ample evidence of fluviatile deposition. Slumping may have been caused in certain cases by movement into contemporaneous washouts, and in other cases by local overloading on depositional slopes. However tentative conclusions concerning the stratigraphical distribution of the slumped beds and the inferred directions of sliding, suggest that the inherent instability of the beds may have been related to contemporaneous tilting.

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Transactions of the Geological Society of South Africa, 64, 73-84, 1 pl

The attribution by Stanton and Schermerhorn to submarine mud-flows of certain deposits in the West Congo geosyncline previously classed as tillites has led to a further consideration of published information relating to possible glaciation in Central and West Africa at the end of Precambrian times. This information is presented in summary form. It is concluded that there exists sufficient evidence to justify the hypothesis of a widespread glaciation having semi-continental dimensions and existing for a long period with fluctuating degrees of intensity. Exact correlation between the glacial and periglacial deposits of the separate regions is conjectural at present, as are the exact positions of the deposits in the geological time-scale.

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Transactions of the Geological Society of South Africa, 64, 85-98, 1 pl , 1 tab.

An attempt is made to find an explanation for the origin of chloritoid in the Witwatersrand system. It is found that chloritoid occurs mainly in shales with a high alumina content. These shales could be the residual weathering product of arkosic sediments. The composition of these arkosic sediments is compared with Karroo tillite and found to be similar. The occurrence of high alumina clay overlying Dwyka tillite and the chloritoid shales overlying Footwall Beds which look like tillites are compared. A glacial environment for the formation of chloritoid shales is suggested.

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Transactions of the Geological Society of South Africa, 64, ix-lviii, 5 pl

Contents: Forensic Mineralogy: General aspects, diamonds, gold, "salting". Historical "salting" cases: The Drakenstein mining episode (1740), The Arizona diamond hoax (1872), .The Roodedam fizzle (1898), The Madagascar fiasco (1905), The Doornhoek debacle (1934), The Bantjes Consolidated Mine swindle (1925-1926), The Zandpan mystery (1956). The Erfdeel inquiry: historical review, laboratory examination, general aspects, results of investigation: (a) examination of borehole samples, (b) samples containing extraneous gold, (c) uranium values, (d) examination of clothing (waistcoat). Discussion of observations: Nuggets of gold, shavings, coated gold, 4. behaviour of gold during grinding and gravity separation, distribution of particles of gold in a conglomerate reef, gold-uranium ratios, evidence obtained from clothing (waistcoat). Summary and conclusions.

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Transactions of the Geological Society of South Africa, 64, lxvii-xcviii, 2 diagrams

Two diagrams are presented, covering the known extent of the Witwatersrand Basin: No. 1 portrays the surface geology of this area; No. 2 attempts, by the removal of younger, obscuring formations, to reveal the complete distribution of the Witwatersrand System. Linked with these diagrams, an historical review is presented, illuminating the events which led up to the discovery of the gold-bearing reefs of the Witwatersrand, the discovery itself and the progress of exploration and development of the Witwatersrand proper, of remote outcrop areas, and, eventually of the hidden extensions of the System.

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Transactions of the Geological Society of South Africa, 64, p99, 1 pl

Recently, during a geological tour to the Transvaal for senior and post-graduate students, it was noted that the stoep of the Standard Bank building at Hoedspruit in the Lowveld, is paved with the typical sole-structures usually associated with the deposition of turbidite successions. Enquiry indicated that these flagstones occur in great abundance in the area surrounding Ohrigstad. On the return journey from Phalaborwa an excellent exposure of these structures was found at Branddraai (30°35' E, 24°38' S), about six miles north-east of Ohrigstad. The sediments in which these structures occur are stratigraphically quite near the base of the Pretoria Series, and might possibly be correlated with the Rooihoogte facies. The sediments which are exposed in the road-cutting and along the slopes of the low hill west of the road are mostly red, micaceous, silty flagstones and shaly mudstones which make up a typical turbidite succession. A great variety of sole-structures and other markings occur on the undersides of the siltstone beds, too many types to describe in any detail at this stage. Generally these sole-markings have a characteristic lobate appearance with an asymmetrical longitudinal section (Plate X). The tongues of these lobate structures sometimes exhibit a slight spiral twist and occasionally even overlie one another. Other markings are sets of parallel linear striae which are casts of original grooves; sometimes two sets of these delicate striae cross one another at a small angle. Not uncommonly striae are developed on the lobate casts, in which case the two directions of lineation are always essentially parallel. In no instance was it observed that these cast-structures extended for more than a few millimetres either below or above the general level of the bedding-plane surface. Various arborescent and other irregular load-cast impressions also occur, and one single impression appeared to be filled-in mud-cracks. No current-ripples were noted, though the siltstones are in places gently cross-bedded. Measurements on the lobate sole-markings tentatively indicate that at this locality in the Transvaal depositional basin, some of the turbidity currents which deposited these sediments moved in a direction about 30 degrees east of south.
Turbidite sole-markings and associated casts are also known from the Nama System near Vanrhynsdorp, from the base of the Table Mountain Sandstone at Stellenbosch, from the top of the Witteberg Series near Kommadagga, from the Ecca Series near Klipplaat, from the Middle Beaufort Stage near Graaff-Reinet and from the Burghersdorp Beds near Sterkstroom. It is obvious that these apparently overlooked and undervalued primary structures are quite abundant in the South African stratigraphical column and it must be stressed that they merit intensive investigation.

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Transactions of the Geological Society of South Africa, 65(2), 1-12, 1 map

All the gypsum deposits in South Africa are of Quaternary age and are predominantly a gypsum-clay or gypsite type. The more important gypsum occurrences are in the N.W. Cape Province. Smaller, but still economically exploitable, deposits occur in the central Transvaal, and in the eastern Cape Province. Gypsum reserves are adequate to meet local requirements for many years to come.

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Transactions of the Geological Society of South Africa, 65(1), 1-17, 1 fig

Stable sulphur isotopes may aid in distinguishing sulphides of a magmatic hydrothermal origin from sulphides containing biogenic sulphur. For those sulphide ore deposits that are intimately associated with the intrusive body from which it is inferred their ore solutions were derived, the variation in δ34S values is generally less than ±5‰. Biogenic sulphides, on the other hand, exhibit a broad spread in δ34S values that is rarely less than a few permil. The reason for this is that the sulphur produced, as hydrogen sulphide by anaerobic bacteria, is isotopically fractionated by variable amounts resulting in a relatively broad spread in δ34S values. A sulphur isotopic study of more than 200 sulphide minerals collected from several Copperbelt deposits reveals variations in δS34 values between a few permil to more than twenty permil for given deposits. Sulphides from Mufulira, Roan Antelope, Kansanshi, and Chibuluma exhibit δ34S values that are characteristic of sulphide deposits, the sulphur of which is biogenic in origin. In fact, for Mufulira, the δ34S values suggest a correlation with the copper ore tenor and carbon content. In contrast, Chongwe North and Chongwe East, two prospects located in or close to basement rocks, for which a non-biogenic origin is indicated, exhibit δS34 values that are typical of magmatic hydrothermal deposits.

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Transactions of the Geological Society of South Africa, 65(2), 101-117, 4 tab.

The heavy residues as well as the light constituents and grain size of 105 samples of Cape and Karoo System sandstones, conglomerates and tillites were studied. It was found that the Cape System residues are quite different from those of the Karoo System but the two groups are remarkably uniform in composition. The concentrates of the former System consist of a small number of stable species whilst the Karoo System residues are composed of a greater number of mineral species and characteristically but not invariably contain garnet.

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Transactions of the Geological Society of South Africa, 65(1), 105-111

A composite dyke traversing the Venterspost Gold Mine was studied petrographically and samples of the mafic margins collected for radioactive dating of the intrusion. Petrographical and geophysical data indicate that the Gemspost Dyke is genetically related to other so-called Pilanesberg fissure intrusions which radiate southwards from the Pilanesberg massif. The dyke consists of dolerite along the margins and syenite in the core. The petrography of both zones and the degree of alteration in the dolerite are discussed. Biotite was separated from the dolerite and the proportions of radiogenic Sr and Rb in this mineral were determined by stable isotope dilution techniques. Three measured specimens yield a mean age of 1330±80 million years for the biotite. The error represents an estimate based on the coefficient of variation of the measured values. This dating agrees well with an age previously determined for the Robinson Dyke (another well-known Pilanesberg intrusion), indicating 1310±60 m.y. as the most probable age for this dyke-system. The error quoted is the 99% confidence limit of the determinations on both dykes.

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Transactions of the Geological Society of South Africa, 65(1), 113-124, 1 fig

Recently developed ion exchange enrichment-spectrochemical methods have been used to estimate several trace elements in South African rocks. In part I, the Sc, Y, La, Nd, Ce, Sn, Mo and Ga contents and the K/Rb and K/Cs ratios in 13 granites, and related rocks are presented and discussed. Part II is confined to a study of the Y, La, Ce and Nd contents of 8 basic rocks.

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Transactions of the Geological Society of South Africa, 65(2), 119-137

The weathering of two dolerite dykes ten miles southeast of Middelburg, C.P., was studied using cores obtained by diamond drilling. Microscopic studies of the weathered rock revealed that in all the samples the mafic minerals had undergone appreciable alteration, whereas the labradorite had decomposed very little. The latter, however, showed cracks due to the development of secondary minerals of greater volume. X-ray and differential thermal analyses were carried out on the clay fractions and it was found that the minerals mainly represented the products of weathering: chlorite, vermiculite, montmorillonite, talc, hydrous mica, and in one sample indications of kaolinite, were found. With the exception of hydrous mica, which resulted from the weathering of labradorite and was present only above the water table, all the minerals were produced by the decomposition of the mafic minerals, clinopyroxene and olivine. Vermiculite was found only in a few samples from a borehole away from a water-course. The first mineral to develop was chlorite, and in some samples it could be determined that on further weathering montmorillonite was formed. In the X-ray patterns of all the samples a diffraction peak was observed at 9.5 Å which may have been caused by talc formed, possibly, as a result of the decomposition of mafic minerals.

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Transactions of the Geological Society of South Africa, 65(1), 125-176, 1 map

A general account is given of the geology of that portion of the Bechuanaland Protectorate which lies to the south of latitude 20°30' south and west of longitude 25° east. The solid geology is described on the basis of the rock exposures which have been located in this predominantly sand-covered region and from a study of sludge samples from percussion drilled boreholes. Sporadic outcrops of rocks of the Basement Complex occur. In the south and south-east the lavas of the Dominion Reef System have a relatively wide distribution. The Transvaal System also underlies large areas in the south and south-east where it forms the continuation of the northern Cape, Transvaal System basin. In the north-west of the region an extensive area is underlain by the Ghanzi Beds. The regional correlation and age of this predominantly sedimentary formation are still in doubt, but possible correlations are discussed. Quartz feldspar porphyries of the Kwebe Porphyry Series are apparently intrusive into the Ghanzi Beds and the association of the Ghanzi Beds with these intrusives suggests a correlation of both formations with the Sinclair System of South-West Africa. The extension of the Matsa Beds from the northern Cape has been traced for a considerable distance into the Kalahari and these rocks are now known to have a much wider distribution in the south-central Kalahari, north of the Molopo, than had been thought previously. A major, centrally disposed depositional basin, filled with sediments and lavas of the Karroo System, forms the main structural feature of the region. The sediments and lavas in this basin constitute the link between rocks of the Karroo System present in the Transvaal and Southern Rhodesia and those present in South-West Africa and the northern Cape. A description is given of the distribution and lithology of the various members of the System present in the Kalahari-Karroo basin.
A correlation between the Middle Ecca Stage of the Waterberg coalfield area and the sandstones present in the Auobartesian horizon in South-West Africa is suggested on the basis of evidence from the central Kalahari area. Kalahari Beds of Tertiary to Pleistocene age mantle the greater part of the region and the various lithological types are described briefly. It is suggested that the term "Bottle Beds" which is frequently used in reference to these deposits, should either be redefined or, preferably, that the use of this term should be discontinued. In this semi-arid region the possibility of developing groundwater supplies is of very great importance. The water-bearing properties of the various geological formations present are described briefly and some details are given of the chemistry of the three main types of groundwater present in the Kalahari region. The conclusion is reached that the depth of unconsolidated Kalahari Beds has an important bearing on recharge possibilities under present day climatic conditions and consequently on the possibility of developing potable groundwater supplies in all formations present in the Kalahari.

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Transactions of the Geological Society of South Africa, 65(2), 13-40, 2 figs

Study of borehole sections of the Transvaal System around the Western Areas gold mine gives a clear picture of the stratigraphy of the lower part of the System. Surface mapping discloses severe strike faulting in the Pretoria Beds, persistently down faulting the strata to the north thus causing repetitions of the beds. Younger dip faults displace the strike faults. Boreholes indicate that there is no comparable faulting in the underlying Black Reef Series or the pre-Transvaal formations. It is therefore apparent that "slump faulting" of exceptional magnitude is responsible for the structure. Pretoria Beds have subsided as much as 2,600 feet into the Dolomite. It is believed that this evidence suggests, as a definite possibility, that the duplication of the Pretoria beds in the Thabazimbi and Postmasburg areas may prove to be the result of slump faults rather than overthrusts. Borehole cores of the diabase sheets show features more characteristic of lavas than of intrusive sills. Their invariable association with the Pretoria sediments, in which they occupy apparently constant stratigraphic horizons over long distances, also suggests extrusion. The sheets are therefore interpreted as contemporary lavas.

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Transactions of the Geological Society of South Africa, 65(2), 139-152, 2 pl

Igneous breccias, consisting of angular or rounded xenoliths of basalt, gabbro, and dolerite contained in a medium-grained matrix, are frequently intimately associated with granitic ring complexes in the southeastern part of Southern Rhodesia. In the Dembe-Divula Complex the breccias are marginal to the granitic ring-dykes and roof-sheets which are thought to have been passively emplaced into late-Karoo basalts and rhyolites. During intrusion the country rocks suffered net-veining, brecciation, contact metamorphism, and some metasomatism. The nomenclature of igneous breccias is reviewed briefly.

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Transactions of the Geological Society of South Africa, 65(2), 153-180

The distribution of pegmatites relative to the Mtoko batholith is described. The form and orientation of the pegmatites seem to have been controlled by the regional structure. A description of the internal structure of some pegmatites together with a brief summary of their mineralogy is given. A discussion on some aspects of the crystallization of pegmatites in general is also included.

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Transactions of the Geological Society of South Africa, 65(1), 177-195, 1 pl

Two deformational facies of a Lower Katanga conglomerate in the Southern Province of Northern Rhodesia are described. The first is situated in an environment of slightly overturned isoclinal folds where pebbles are elongated parallel to the principal fold axes (the tectonic b direction). Their lengths coincide with the trend of the dominant lineation. The second, seen along the line of the Mulundika Hills about six miles to the south-south-west, occurs in a shear zone where pebbles are stretched in the direction of movement, the tectonic a axis. This is also the direction of the main lineation locally. These opposing trends were at first thought to be evidence of two separate orogenies, but subsequent work showed that this is not the case. They are related, though independent, expressions of a single period of tectonism, the contrasting structural features of the conglomerate being the product of differing stress environments.

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Transactions of the Geological Society of South Africa, 65(1), 19-42, 1 fig, 2 pl

The Knysna-Wilderness lakes occupy east-west valleys parallel to the coast and approximately at right-angles to the main rivers entering the coastal belt, the valleys being defined by parallel ridges of Pleistocene dune rock. The rivers tend to be deflected along the valleys, while the estuary of Swartvlei is cut through at least two of the ridges. The present nature of the lakes, except Groenvlei, depends on the access of fresh water from outside their own catchment areas, channelled along the lateral valleys by the pointing effect of estuarine bars. Marine transgression has affected the lakes within the past 7,000 years and probably earlier. The history of these lakes and the adjacent shorelines is tentatively sketched in terms of fluctuating relations of land and sea levels since the Upper Pleistocene. Present evidence does not completely preclude any of several modes of origin in the Pleistocene, e.g. as coastal lagoons behind offshore bars, flooded inter-dune depressions or for mercourses of rivers diverted by dune formation to seaward. During periods of low sea level the lakes were probably dry, the Recent lakes, appearing to have formed by reflooding of the existing, and probably deepened, depressions on their former sites. High sea level terraces and benches at 7 to 8 m., 4 to 5 m. and 1 to 2 m. above present mean sea level are recorded and related to the lake and dune formations.

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Transactions of the Geological Society of South Africa, 65(1), 197-202, 1 pl

Metamict uranothorite was identified as the constituent containing important quantities of acid soluble thorium in the Dominion Reef. Chemical analysis of this mineral indicates a content of 34.9% ThO2, 9.5% U3O8 and 13.9% Pb. Unheated material does not furnish an X-ray pattern, but the pattern of included galena is obtained. After heating to redness a thorianite pattern is produced which persists even after prolonged heating when a weak pattern of a thorite phase is also developed. Anhedral uranothorite, containing innumerable small inclusions of galena, replaces grains of uraninite to varying extents. It is considered that the uranothorite originated through the replacement in situ of relatively thorium-rich grains of uraninite by siliceous solutions.

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Transactions of the Geological Society of South Africa, 65(1), 203-205, 1 pl

A fracture pattern produced in a clay model by tensional stress shows remarkable similarity to the fault pattern of Coastal Natal. This suggests that the Natal Coast may have been formed by tensional deformation.

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Transactions of the Geological Society of South Africa, 65(1), 207-230, 2 pl

Pseudotachylite penetrates all rocks of pre-Karroo age in the Vredefort dome and the Potchefstroom synclinorium, with the exception of the basic granophyre and the Pilanesberg dykes. Veins and sheets of pseudotachylite can be distinguished. They are irregular in form and contain numerous inclusions of the adjacent rocks. The pseudotachylite is patchy in its distribution. Recrystallized pseudotachylite is the rule rather than the, exception. An intrusive and non- intrusive type of pseudotachylite are present in some veins. "Shatter cones" are closely associated with and appear to be related to the pseudotachylite in origin. The different theories on the origin of the pseudotachylite are reviewed, and it is concluded that the pseudotachylite represents tuffisite, which originated through gas action related to a central pluton and its satellitic intrusions. The basic granophyre evidently represents the ultimate stage in the development of the pseudotachylite through mixing of pseudotachylitic material and magma.

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Transactions of the Geological Society of South Africa, 65(1), 231-247

This paper reports on results of fracture measurements at nine stations in the granitic core of the Vredefort dome. The fracture pattern can be accounted for by the symmetry of the dome, radial compression from the central hidden gabbro pluton, the Bushveld trend, movements of the granitic core relative to the rim, and gravitational sliding of the franitic rocks over the rim. Geological age relationships are re-examined and it is concluded that the following stages in the formation of the structure can be recognized: pre-Bushveld doming, main upthrust during Bushveld times resulting from the emplacement of the central hidden gabbro pluton, subsequent gravitational spreading of the uplifted core under its own weight, later apparently minor events such as the emplacement of the alkali granite plutons, the formation of the pseudotachylites, and the injection of the enstatite granophyre dikes.
It is suggested that the pseudotachylites may be fine-grained tuffisites, rather than the equivalents of ultramylonites. The Vredefort dome is compared with other domes in the region, including the Bushveld dome. In the Bushveld dome, large gabbro ethmoliths were emplaced concentrically around the base of the dome, but in the Vredefort dome the plain volume of basaltic magma was emplaced as the hidden pluton within the dome, resulting in further uplift and gross exaggeration of the earlier dome structure. The gabbroic rim intrusions are regarded as satellitic injections from one or more cone sheets emanating from the central pluton. The rim intrusions probably contributed to over turning in the Vredefort rim, which was further enhanced by subsequent gravitational spreading of the core. Comparisons are made with the Lodgepole pluton and the Beartooth Block of Montana and Wyoming. Further problems for research are briefly summarized.

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Transactions of the Geological Society of South Africa, 65(1), 249-251

Age relationships - Because of the abundance of doleritic intrusions in the collar of the Vredefort dome "in contrast with their relative paucity in the outer parts of the Vredefort rim" and "the fact that the intrusions are faulted off in one locality, while in another locality they cut across faults in the rim", Poldervaart concluded that they were "emplaced during or shortly after the major uplift of the dome" (p. 8-9). In the light of new observations made in the course of fieldwork and petrographic studies, however, this conclusion, as well as some of those previously published on the age relations of igneous rocks in the Vredefort dome, are no longer acceptable. The doleritic intrusions in the Vredefort dome belong to at least four different ages.

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Transactions of the Geological Society of South Africa, 65(1), 253-262

The structure southwest of Pilanesberg is dominated by the big Rustenburg fault which could be traced in a northwesterly direction. The faulting, which took place after the emplacement of the gabbro of the Bushveld Igneous Complex, caused the displacement of the chromitite seams; on the other hand, the fault-zone provided lines of weakness along which dunite, magnetite, diallagite-pegmatite, bronzitite-pegmatite and bodies containing sulphides were intruded. Dunite, diallagite-pegmatite, magnetite and sulphide bodies are genetically related, but the sulphides must have been more particularly connected with the pegmatites. Prospecting along the fault-zone may reveal the presence of more sulphide bodies.

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Transactions of the Geological Society of South Africa, 65(1), 263-279, 1 pl

Three hundred and twenty-four measurements of cross-bedding orientation, made underground at ten mines and on surface outcrops at seven localities, indicate a consistent south-southeasterly direction of transport for the Main-Bird Series quartzites in the East Rand area. This trend continues as far south and southeast of Heidelberg as the Series can be traced, and no evidence of a limit to the Main-Bird depositional basin in this direction has been encountered. The orientation of 39 ripple-marks measured under ground, is anomalous, in that the ripple axes appear to be oriented parallel to the deduced direction of sediment transport, which is from northwest to southeast.

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Transactions of the Geological Society of South Africa, 65(1), 281-292, 2 pl

Chemical, modal and optical data are given for the alkali granite of Spitzkop, South-West Africa, and comparisons made with the other post-Karroo complexes of Cape Cross, Erongo and Messum and with the older autochthonous Salem granite of the same area. Particular attention is paid to zircon as a petrographical aid and a statistical analysis has been made of zircon samples from the Spitzkop and Salem granites. T.F.W. Barth's method of determining the temperature of formation of a rock from the distribution of soda between the two feldspar phases yields the following results: Spitzkop granite, 620°C; Salem granite, 540°C, and Cape granite, 690°C. (average of two determinations). It is pointed out that in the case of porphyritic magmatic granites the phenocrysts may have formed at a late pegmatitic stage and that the temperature recorded is therefore likely to be lower than for equivalent equigranular magmatic rocks.

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Transactions of the Geological Society of South Africa, 65(1), 293-294

A study of the field relationships of the Shawa carbonatite Complex by one of the authors has shown that this Complex was probably emplaced in post-Karroo time. Rubidium-strontium isotopic measurements on very coarse biotite from the Shawa ijolite yield an age of 209 million years, with a standard error of ˜16 million years. The deductions from the geological evidence are consistent with the age measurement data.

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Transactions of the Geological Society of South Africa, 65(2), 41-46, 1 pl

The island Osmussaar in the Finnish Gulf off the Estonian coast has apparently been displaced during the Glaciation Period by pivoting counter-clockwise through 17½° in a horizontal plane. This is indicated by the observed rotation of the rhegmetic network of joints and by the discrepancy of the present position of the island relative to the surrounding sea bottom. Subsequent to the shifting the ordinary joint pattern had been formed again, thus demonstrating the perpetuity of the formation of rhegmatic joints in the earth's crust which obviously follows predetermined directions.

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Transactions of the Geological Society of South Africa, 65(1), 43-74, 2 pl

This paper is mainly concerned with the depositional history and provenance of Karroo rocks in the south-west Gwembe District, Northern Rhodesia. A brief description of each formation from the point of view of areal distribution, lithology, petrography and facies variation is followed by an analysis of this information and a reconstruction, so far as it allows, of the physical and structural environment in which deposition took place. In this way the development of the Karroo basin of sedimentation is traced from its initiation in Dwyka times to its later stages at the end of the Stormberg. It is concluded that most of the sediment was derived locally from the Basement Complex, and that the Karroo rocks of the mid-Zambezi region record an episode of tectonically controlled basin filling.

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Transactions of the Geological Society of South Africa, 65(2), 47-55

Different opinions have been expressed as to the relative ages of the Stormberg lavas and the sheets and sills of Karroo dolerite. Palaeomagnetic measurements on the dolerites (Graham and Hales, 1957) and on the lavas (van Zijl, Graham and Hales, submitted for publication) suggest that the dolerites were intruded from the beginning of the effusive phase. The order of emplacement of certain dolerite intrusions is discussed and it is remarked that a series of measurements on the Lobombo sequence might throw further light on the order of events in the period of Karroo vulcanicity.

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Transactions of the Geological Society of South Africa, 65(2), 57-62, 1 pl

Chlorite pseudomorphs after detrital grains of some original silicate mineral are common in certain banket reefs. The original cleavage which is still recognizable in some of the pseudomorphs, indicates that the mineral was an amphibole. The association of roundish grains of uraninite with the less resistant amphibole demands an explanation.

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Transactions of the Geological Society of South Africa, 65(2), 63-78, 3 pl

The calcareous and argillaceous rocks of the Otavi Series show a gradual variation in sedimentary facies parallel to the rims of depositional basins, but much more abrupt change at right angles to this direction, accompanied by progressively more intense metamorphism across the transitional zone between "Otavi" and "Damara" facies. The essentially dynamic metamorphism just exceeds the greenschist facies, and was brought about by regional stress which operated from south to north, causing overfolding of the formations in the southern half of the area.

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Transactions of the Geological Society of South Africa, 65(1), 75-91, 2 maps

Re-examination of the Karroo succession of that part of the upper Luangwa valley originally described by Dixey in 1937 has resulted in two important conclusions. His six fossil reptile horizons can now be regrouped into four; the lowest represents the Endothiodon zone and the middle two the lower Cistecephalus zone, but the upper one contains only unidentifiable rolled bones and coprolites. The three lower horizons occur in the top half of a mudstone formation. It is demonstrated that Dixey's Grey Shales (K3) are equivalent to his Green Mudstones (K5) which have been repeated by major faults. The fossil reptiles prove these formations to be homotaxial with the Madumabisa Mudstone of the mid-Zambezi valley. The overlying Purple Grits (K4), and not the Red Pebbly Grits (K7), are thus the local equivalent of the Escarpment Grit. Dixey's supposedly Cretaceous Dinosaur Beds prove to be part of the Karroo succession and of Stormberg age.

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Transactions of the Geological Society of South Africa, 65(2), 79-83, 1 pl

Aurostibite, AuSb2, has been found as minute grains intimately associated with gold in the Lone Hand and Jessie mines in the Gwanda district. In its manner of occurrence, physical properties and etch reactions it closely resembles the type material discovered in the Giant Yellowknife and Chesterville mines, Canada, except that it tarnishes more rapidly. Identification has been confirmed by X-ray and microprobe analyses, the latter technique having also indicated the presence of an unknown nickel-antimony mineral in the Lone Hand ore.

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Transactions of the Geological Society of South Africa, 65(2), 85-99

The location and characteristics of Sandstones of Cretaceous and Pleistocene age are described. Particular attention is paid to the variation of unconsolidated grits, sands, clays and silts of Quaternary age in the Durban area. A Black Stratum overlying the Cretaceous System is sporadic but widespread.

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Transactions of the Geological Society of South Africa, 65(1), 93-104

The paper deals with fossil dicotyledonous woods from the upper Cretaceous Umzamba-Beds of East-Pondoland, C.P. Altogether 72 samples were investigated. They belong to two families, the Monimiaceae and Euphorbiaceae, which are considered to be old phylogenetically, the bulk of the fossils agrees with the Monimiaceae. One sample represents a new species of the fossil genus Hedycaryoxylon Suess (sub-family Monimioideae). For the others which are closely related to the sub-family Atherospermoideae a new genus Protoatherospermoxylon is introduced. It includes 5 species and has no living analogue. According to their structure the South African Monimiaceous woods occupy a relatively primitive stage. The importance of the results with reference to the evolution and the area of origin of the family is discussed. Three isolated samples correspond best to the Euphorbiaceae. Two are described as new species of the fossil genera Paraphyllanthoxylon Bailey and Bridelioxylon Ramanujam respectively: the third represents a new fossil genus Securinegoxylon. Owing to structural convergence the determination of fossil woods comparable with Euphorbiaceae is subject to some uncertainty.

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Proceedings of the Geological Society of South Africa, 65, xxxi-xxxvii

Man requires two basic commodities for his existence - the air he breathes and the food he eats. However, if he is to develop beyond a primitive state, he must have access to a wide variety of minerals or the products derived from them. The passing of time has seen Man develop successively through the Stone, Bronze, Iron and Steel Ages, and he now stands on the threshold of what has been termed the Nuclear Age. The very fact that we have considered it appropriate to name these different Ages after various materials derived from the earth's crust, is in itself an indication of how Man's material advance has been dependent upon the greater use he could make, in various stages of his development, of the mineral matter at his disposal. With the passing of time, two distinct trends have become apparent in Man's utilization of materials from the earth's crust. Firstly, the number of metals and minerals which have found some application in industry has increased. For example, 2,000 years ago only the metals lead, tin, copper, iron, silver, gold and mercury were known - albeit in somewhat impure form - and were used as such or as natural alloys in household articles, weapons and coins. Precious stones were used for personal adornment and natural construction materials found a comparatively limited application.
By comparison, the picture had already changed considerably at the turn of the nineteenth century. The application of James Watt's steam engine - invented in 1768 - and the discovery by Abraham Darby some 50 years earlier of the technique of producing large quantities of high-grade iron cheaply by using coke for smelting purposes, set the stage for the development of the industrial era. New circumstances were created which needed new materials and so large numbers of metals and base minerals came into use.
However, it is particularly during the past 50 years that there has been the biggest increase in the variety of metals and industrial minerals used in industry. Metals that were really little more than chemical curiosities at the turn of the century are today considered indispensable to Man's needs, for example, uranium, zirconium, beryllium, niobium, tantalum, vanadium, tungsten and germanium, to mention but a few.
Various industrial minerals have come into prominence and the derivatives of the fossil fuels have a spectacular field of application. There can be no more striking measure of Man's ingenuity than the extensive use he makes of the wide variety of materials which are available to him in the crust of the earth.
The second trend that should be stressed is the ever-increasing rate of consumption of these materials. Consider for example the following data selected at random from the literature:
Firstly: more metal was produced during the past ten years than during the whole period of Man's existence up to the end of the eighteenth century.
Secondly: from the year 1800 up to the present time the production and consumption of metals has increased more than 230 times, as compared with only a four-fold increase in the world's population.
Thirdly: the total annual production in long tons of the metals aluminium, copper, lead, tin and zinc at 50-year intervals is approximately as follows: In 1800 - 50,000 tons, 1850 - 270,000 tons, 1900 - 2,000,000 tons, 1950 - 8,500,000 tons, 1955 - 11,250,000 tons, 1960 - 14,000,000 tons.
Fourthly: in 1800 the world's output of pig iron amounted to only about half a million tons, or about a fifth of the Republic's present output. In 1960 approximately 250,000,000 tons of pig iron and ferro-alloys were produced, that is to say, twice as much as in 1950 and 500 times as much as in 1800.
It is interesting to note that the steel production of the United States of America in 20 years' time is expected to be the same as the world production of today.
The same trends are apparent in the utilization of fuels, non-metallic minerals, other base metals and natural construction materials. The past four decades have seen the greatest increase in consumption of materials derived from the earth's crust, the per capita consumption being the highest in those countries which are the most advanced industrially and which as a result enjoy the highest standard of living, such as the United States of America, the United Kingdom, West Germany and Sweden. The per capita consumption in the so-called under-developed countries is, comparatively speaking, very low.
There are two important features of mineral deposits that require comment: firstly, they are wasting assets and once exploited cannot be replaced, and secondly, they have an entirely haphazard global distribution. As a result of the latter feature, no single country has within its borders all the mineral raw materials required to support a modern diversified industry. Some countries are more fortunate than others and have, or have had, the basic raw materials iron ore and coal, which together with other favourable factors have led to the establishment of the steel plants upon which modern industries are dependent. Others, again, lack these essential commodities and are destined to remain essentially agrarian in character. Between these two extremes, all variations occur. The erratic distribution of mineral deposits in a world which is becoming more and more industrialized has resulted in a large and diversified mineral trade between nations and this in turn has produced a host of problems, often with serious international implications. The fact that mineral deposits which are being exploited are wasting assets is of considerable significance. The more a country becomes industrialized, the greater are the demands on its mineral resources and the sooner these become depleted. An excellent example is afforded by the United States of America which, in a period of 20 years, has changed from a position of virtual self-sufficiency in copper, lead, zinc, iron and petroleum products to present-day dependence on foreign sources for much of this material. Even Western Europe which 100 years ago was virtually independent of imports of non-ferrous metals, must today obtain much of its requirements from overseas.

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Transactions of the Geological Society of South Africa, 66, 1-8

A fossil conifer, found in association with Glossopteris spp. and other elements of the Glossopteris flora, is described from the Lower Permian beds of Vereeniging, Transvaal. The nature of these beds and the sites where the fossils were collected are briefly described. The description of the species is based on external morphological features only. A comparison is made on these features with other fossil conifers previously described, and reasons are given for assigning the new South African conifer to the genus Walkomiella Florin from the Southern Hemisphere. Attention is drawn to the close resemblance between the South African plant and the type-species, walkomiella australis (Feistm). Florin, from Australia. The possibility of identity of the two species is discussed and arguments are advanced in favour of the institution of a new species, Walkomiella transvaalensis, for the South African plant.

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Transactions of the Geological Society of South Africa, 66, 109-113

A combined solvent extraction-spectrochemical analysis procedure has been used to estimate trace-amounts of niobium in ten South African granitic and related rocks. Reference-granite G-1 served as a standard.

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Transactions of the Geological Society of South Africa, 66, 11-47

Structures in the anorthosite (associated with chromitite), in the South African jade (hydrogrossular), and in the chromitite and magnetite, all occurring in the Basic Belt of the Bushveld Complex, are compared. This comparison comprises the following considerations: spacing, parallelism, contacts and form of ore bands, together with structures relating to faulting, folding, inclusions and transgressive relationships. It is difficult to understand how any theory based on intermittent crystallization or crystal settling, whether promoted mechanically or chemically, is competent to explain the various structural features in the anorthosite and "jade". These structures are finally compared with those in the limestone and associated "chert" which occur in that part of the Pretoria Series transgressed by the Basic Belt. The large number of points of correspondence in this comparison suggests that metasomatic processes acted selectively on former existing carbonate strata.

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Transactions of the Geological Society of South Africa, 66, 115-121

Algal structures have been discovered in a local facies of impure dolomitic limestones of the Ventersdorp System intersected in a borehole WNW of Wesselsbron in the Orange Free State. They are separated from the well-documented occurrences of similar structures in the younger Dolomite Series of the Transvaal System by two unconformities, two periods of sedimentation, and one or two phases of volcanicity. The stromatolites indicate that the Ventersdorp dolomitic limestones and associated marls are of primary origin. They were probably deposited in shallow lakes in an area of low relief after eruptions of acid and basic volcanic rocks. The discovery provides a link between the accepted prevalence of biogenic processes 2,000 million years ago during the time of deposition of the Transvaal System and the problematic origin of oolitic structures in the Swaziland System formed more than 3,000 million years ago.

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Transactions of the Geological Society of South Africa, 66, 129-156

Six individual thermal springs issue over a distance of 800 yards from a major fault. Temperatures vary from 38.2 to 41.1°C, and yields from 4,100 to 18,700 gallons per day. The total yield of all springs is 65,000 gallons per day. The content of dissolved salines ranges between 280 and 359 ppm. By far the most abundant cation is sodium, the preponderating anions being bicarbonate, carbonate, and silicate. The waters are thus siliceous alkaline, one spring being in addition sulphuretted. Radioactivity is insignificant. The gases are almost pure nitrogen.
Below the horizontal Table Mountain Sandstone and the lower most Karoo sediments there is a great variety of East-West trending and steeply dipping ancient crystalline rocks. They include: banded amphibolites, amphibolite-gneiss, and granulites, containing lenticular bodies of serpentine, talc, and crystalline limestone; massive felspathic amphibolite; hornblende-epidote quartz-diorite and granodiorite, as well as biotite-hornblende-epidote granite-gneiss; banded hybrid gneisses: leucocratic gneisses and granites; red aplitic granite, and innumerable aplites and pegmatites.
All stages of migmatisation are represented, but many of the more acid rock types are intrusive. The major Lilani fault is of the tensional trap-door type with narrow subsidiary graben. The measurable vertical displacement of the Table Mountain Series is 900-1,000 feet. Evidence is adduced to show that the faulting follows an ancient east-west "line of weakness" characterised in the basement by intense shear in a mainly compressive stress-field, involving extensive flow, even injection, of crystalline limestones caught up in the zone of movement. Most limestones contain an abundance of wall-rock fragments. The zone of disturbance appears to have been initiated during the post-Insuzi orogeny (Precambrian) and movements along it were continued at intervals into post-Karoo times, the final tensional faulting being associated with the downwarp of the coastal belt in pre-Mid-Cretaceous times (Lebombo-Natal monocline), now interpreted to include extensive tilt-block step-faulting towards a major offshore dislocation.

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Transactions of the Geological Society of South Africa, 66, 157-189

Three thermal springs are located along the northwestern flanks of the Khomas Highlands, over a distance of 20 miles, within the broad valley of the Swakop River. At Gross Barmen hot water issues naturally from some 12 individual closely spaced orifices, as well as from 2 boreholes. Temperatures vary from 41.6 to 69°C. The yield of the natural springs is 2,060 gallons or 9.4 c.b.m. per hour. The temperature of the hot spring at Klein Barmen, 7 miles away, is 62°C, the yield being 960 gallons or 4.34 c.b.m. per hour. The water of the Okandu spring, 13 miles distant, is only tepid (38°C); owing to absence of well defined orifices its yield could not be measured. Five new chemical analyses are presented. Total dissolved solids range between 944 and 1094 p.p.m. Sodium by far predominates among the cations, the dominant anions being sulphate, chloride and bicarbonate. These waters therefore belong to the mixed alkaline-sulphate-muriate class. Silica is relatively high and at Gross Barmen small amounts of siliceous sinter occur. Gas bubbles are composed mainly of nitrogen. Radioactivity is insignificant. The origin of major, minor, and trace elements is discussed in relation to rocks traversed. Comparison is made with ordinary ground-water of semi-arid and arid regions and the conclusion reached that the springs are of meteoric origin. Details are given of the contamination by the saline springs of the "fresh" subsurface water of the Swakop runoff course. The springs at Klein Barmen and Okandu rise within aplitic granite and no structural control outside jointing is apparent. Dolerite dykes are too distant to be held responsible. The Gross Barmen springs issue from highly jointed, banded biotite-and quartz-biotite schists and structural control is evident in a pronounced shear-zone, parallel to strike, involving marked drag-folds, bedding-slip and fracture-cleavage. Along the latter are aligned innumerable large porphyroblasts of andalusite.

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Transactions of the Geological Society of South Africa, 66, 191-195

The attention is drawn to rhythmically bedded formations in the geological profile of South Africa, which might represent turbidite formations. The oldest, in the upper part of the Fig-tree Series, consists of an alternation of shale and well graded graywacke, in which current-ripples, flute-casts and groove-casts were observed. The second is in the Timeball Hill Stage of the Pretoria Series and consists of an alternation of shale and graded, sandy beds. Again current-ripples, load-casts, slumping movements and groove-casts are present. The third is in the basal portion of the Lower Ecca Stage, as exposed near Laingsburg, Cape, and consists of a flysch-like succession of graded, muddy sandstone alternating with thin beds of shale. Current-ripples, load-casts, shale-pebble inclusions and slum-sheets were observed in them. Although the observed features are strongly suggestive of turbidite formation, more confirmatory evidence is required.

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Transactions of the Geological Society of South Africa, 66, 199-251

The general stratigraphy and lithology of the Damara System is described and variations in facies outlined. The new correlation of these sediments (eugeosynclinal) with those of the Otavi System (miogeosynclinal) in the north is briefly referred to, as well as suggestions that the sediments of the Nama System in the south may represent a shallow-water foreland facies. The old subdivision of the Damara System is brought into line with the new stratigraphic nomenclature. In the detailed description of rock types and stratigraphic succession of the area it is conclusively shown that no break in sedimentation (unconformity) is present between the basal rudaceous and psammitic deposits and overlying predominantly calcareous and pelitic sediments, as has been claimed for the marginal areas of the Damara geosyncline. It is emphasised that local conditions cannot be generalised over so vast a sedimentational basin. It is shown that the main geosyncline was initially divided into two portions by a median anticlinal ridge, termed the Abbabis swell. Two strongly contrasted tectonic styles are developed.
The suprastructure of the Khomas Highlands is marked by regular isoclinal folding and mesograde metamorphism (garnetiferous biotite schists and metagreywackes). Gneisses, granites, and related rocks are absent. The infrastructure is characterised by highly complex folding in which domes and basins, brachyanticlines and -synclines dominate; the sediments are mostly much more highly metamorphic (up to granulite facies) and intimately mingled with gneisses and granites. A considerable portion of these was formed in situ by processes of ultrametamorphism: reddish, sillimanite-bearing leucogneisses and granites from felspathic arenaceous deposits below the resistant Marble Horizon, and porphyritic biotite granites (Salem type) from the pelitic and semipelitic sediments above the latter.
Outwards from the region of ultrametamorphism sillimanite is succeeded in schistose rocks by andalusite and this in turn by staurolite. Concentric mineral banding in spindle-shaped of amphibole-pyroxene-garnet granulite indicates metamorphism to have proceeded pari passu with deformation by the dominant NW-SE directed stress. A large sheet of allochthonous granite (Donkerhoek) was intruded in late-tectonic times between infra- and supra-structure, thereby enabling differential movements between the two styles of folding to be accommodated. Where this granite locally projects into the basal portion of the supra-structure, a zone of pronounced lateral shear has been developed, marked by strongly developed minor folding and fracture-cleavage. Very striking is the stress-orientation of myriads of andalusite porphyroblasts in this zone: predominantly along fracture-cleavage, but subordinately also along bedding-slip planes. A detailed analysis of this local late tectonic phase is given and illustrated with numerous diagrams and photos. Two types of pegmatites ate present: isolated deep-level bodies originating from below the Marble Horizon and often containing columbite-tantalite, beryl, and lithium minerals; and a profusion of pegmatites, mostly barren except for muscovite, schorl, and almandite, associated with the Donkerhoek granite intruded at a higher level.

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Transactions of the Geological Society of South Africa, 66, 259-278

Layered rocks from basic zones in the Bushveld Complex were studied in an attempt to understand the mechanism of their formation. The rhythmic layering is generally persistent and concordant. All types of gradations are present on the contacts, those due to density-layering being the most frequent. Layers of anorthosite are more disturbed than those formed of other rock types. Frequently lenses of anorthosite are present, having planar bases with top surfaces convex upwards. Various types of current action in a magma chamber are thought to be responsible for most of the small-scale structures. Out-wash-channels and intraformational breccias are cited as evidence of scouring and turbulence. Circular depressions and stacking of lenses of anorthosite one upon the other are thought to be due to eddying currents. It is concluded that these features and the cryptic layering can best be accounted for by crystal accumulation on the floor of a magma chamber. Estimation of the depth of the unconsolidated crystal mush have been made from penecontemporaneous faults, 1 to 3 m deep, and from circular depressions, 26 m deep, an apparent paradox. It is suggested that differentiation took place within a closed chamber and that there were minor additions of magma of essentially basaltic composition from time to time. Considering the shape of the intrusion(s) and the features described, the authors postulate a mechanism of combined under-cooling and convective overturn for the layered igneous rocks in the basic zones of the Bushveld Complex.

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Transactions of the Geological Society of South Africa, 66, 283-333, map+2

The Sangu carbonatite group, situated near Karema village on the eastern shore of Lake Tanganyika, consists of three elongate intrusions aligned on a northwesterly trend over 16 miles of strike. The largest occurrence, the Ikamba body, is 11.4 miles long and has a maximum surface width of one mile. These carbonate rocks, hitherto regarded as a band of Basement metasediment, are structurally discordant to the Basement and intrude the post-Basement Bukoban (?) sediments. Individual carbonatite bodies consist of dolomite and white and red calcitic carbonatite. Minor or accessory minerals in carbonatite include apatite, magnetite, ilmenite, phlogpite-chlorite, soda amphibole, zircon, baddeleyite, pyrochlore and rutile. All calcitic carbonatite displays exsolution of dolomite from magnesian calcite. Albitite and aegirine-albite rock, closely associated with the carbonatite bodies, are interpreted as fenitized leucocratic and melanocratic country-rock respectively. The Sangu carbonatites are strongly enriched in strontium, niobium and lanthanides in relation to the carbonate metasediments. The patterns of strontium and niobium distribution in carbonatite, particularly the Sangu carbonatite, are analyzed. All evidence points to a magmatic origin for most dolomitic and white carbonatite, but there is evidence of associated, widespread, though quantitatively minor, metasomatic emplacement of carbonate. The Sangu carbonatite bodies occur on the Ikola-Malambo Fault, which is the unrevived, northwestern continuation of the Tertiary Rukwa Rift Fault. Carbonate rocks, on or near the same fault, at Malambo and Mongwe, are related in origin to carbonatite emplacement at Sangu. The Sangu Carbonatite Group represents an exposure of carbonatite at a deep level rarely found or recognized elsewhere. The absence of alkalic igneous rocks at Sangu supports Holmes (1950) view that carbonatite magma generates alkali-rich silicate magmas through reaction with crustal rocks. Map in colour.

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Transactions of the Geological Society of South Africa, 66, 341-344

A brief description is given of the post-Karoo sedimentary rocks of southeast Southern Rhodesia. These are a series of often calcareous conglomerates and sandstones termed the Malvernia Beds. The distribution of pebbles of pre-Karoo and Karoo rocks in the conglomerates indicates derivation from the north and west.

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Transactions of the Geological Society of South Africa, 66, 345-349

In the vicinity of Swakopmund and Walvis Bay extensive areas of the Namib desert, totalling at least 1,000 square kilometres, are covered by gypsum deposits and gypsum-cemented gravel and sand. The gypsum is an alteration product of Tertiary and Pleistocene calcretes that ranged in composition from pure calcium carbonate rocks to lime-cemented sands and gravels. The alteration proceeded from the surface downwards to depths averaging from one to three feet, with the purity of the gypsum so formed being dependent on the carbonate content of the original calcrete. The enormous quantity of sulphur required for this transformation seems to have been generated as hydrogen sulphide under anaerobic conditions on the Atlantic sea bottom in a deposit of sulphide-bearing, diatomaceous ooze. This azoic zone measures about 15,000 square kilometres and is situated immediately offshore to the west of the gypsum deposits. The hydrogen sulphide was blown inland and precipitated with mist and dew to react with the calcrete. Several million tons of gypsum having a purity in excess of 90% have been proved within a radius of about 30 miles of the towns of Swakopmund and Walvis Bay. The lower grade gypsum deposits of the hinterland of these two towns are of the order of several hundred million tons. These deposits are the largest known in South-West Africa.

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Transactions of the Geological Society of South Africa, 66, 353-398

This paper describes the techniques and results of a structural analysis of a complexly folded region situated in the ancient Archean rocks of the Barberton Mountain Land. The orientations of various small-scale structures are recorded; they are found to be arranged in an orderly fashion and are geometrically related to the major structures. Three successive periods of deformation are recognised. Each successive deformation led to the imprinting of both large-scale and small-scale new structures on the pre-existing structures and also to the deformation of the old structures. The first deformation gave rise to many folds whose steeply-inclined axial planes were probably initially oriented in a northeast-southwest direction. The second deformation resulted in the widespread development of slaty cleavage and schistosity which cuts obliquely across the first folds. Large, very steeply plunging folds were formed locally during this deformation, a feature which is believed to have resulted from the special orientation of the bedding surfaces before the second deformation. The Nelspruit Granite was probably emplaced at this period.
The third structures deformed the previously formed slaty cleavage, and large folds of this generation are recognised in the north of the area investigated. It is thought that the important arcuate form of both the first folds and of the super-imposed slaty cleavage was developed at this time. The geometry of the arcuate structure is analyzed; the folds related to it have orientations which depend on the inclination of the surface before the structure developed. Sets of conjugate shear-folds were superimposed on the slaty cleavage, and these might have been synchronous with the development of the arcuate structure. The orientations of the principal axes of stress which formed them are calculated.
Gold mineralisation is believed to have been structurally controlled by second-phase structures, and it predates the development of the third set of structures. Structures resembling algal forms from the Fig Tree Series are described and illustrated. The relationships of the Swaziland and Moodies sediments to the surrounding granitic rocks are discussed. The granitic and gneissic rocks are believed to represent, in part, a basement complex on which the sediments were deposited. This basement has been metamorphosed and intruded by other granites which postdate the formation of the sediments.

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Transactions of the Geological Society of South Africa, 66, 49-74

The Crocodile River Fragment consists of beds belonging to the Dolomite and Pretoria Series, entirely surrounded by granite, in the western part of the central Bushveld basin. The sediments display the following tectonic features: a thrust, refolding, small normal faults and a regional horst. Rocks formerly correlated with the Black Reef Series are considered to be interbedded with the Dolomite Series. The abnormal apparent thickness of the Dolomite Series is mainly attributed to local folding whereas the thinning and eventual tapering of the same Series are ascribed to the presence of a thrust-plane. The main structural elements of the "Fragment" are a series of domes and basins arranged in such a way that they could have originated by refolding of earlier folds striking in a north-easterly direction. An asymmetric anticline in the southwestern corner was downfaulted from a higher level and represents the second direction of folding. The mass is bordered on three sides by smaller, overfolded synclines which give the impression that the margins of the "Fragment" have been curled up. Two great normal faults on either side of a horst transect the "Fragment" from southeast to northwest. The western fault is interrupted by the Kruidfontein volcano and is therefore probably of pre-Pilanesberg age. There are indications of later, subhorizontal movement along both of them. A double east-west fault is furthermore postulated to explain the occurrence of dolomite along Ramakokspruit. On Duiwelskop a closed syncline of banded ironstone is surrounded by outcrops of chert breccia. This is interpreted as a klippe. Immediately to the south of Duiwelskop is a normal fault with an arcuate trend and downthrow to the south; it is perhaps related to the Kruidfontein volcano. Four hypotheses on the relationship between the Crocodile River Fragment and the Bushveld Igneous Complex are mentioned; preference is given to the hypothesis of cone-fracturing whereby the "Fragment" is supposed to form the core of a great feeding channel.

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Transactions of the Geological Society of South Africa, 66, 75-89

North of Choma, Northern Rhodesia, folding of the Katanga sedimentary cover has resulted in intense refoliation of the adjacent Basement Complex. A transition along the Ngonga River, from original porphyroblastic granite-gneiss, through crushed and sheared granite-gneiss and blastomylonite, to feldspathic "quartzite" is confirmed by examination of thin sections. Original quartz, mica, oligoclase, and microcline of the granite-gneiss have been crushed and partly recrystallised, but microcline porphyroblasts, in particular, have survived as porphyroclasts even into the blastomylonites, which mimic feldspathic quartzite. Quartz veins have been crushed, sliced, boudinaged, and elongated parallel to the lineation to form pseudopebbles; this has led to previous misidentification as sheared conglomerate. Huge areas of basement, 3 to 6 or more miles wide, adjacent to the major belts of Katanga metasediments, have lost their original northeast foliation and acquired a new foliation striking north of west, parallel to the folded Katanga sediments, with development of steeply plunging axes and parallel, steep lineations, whereas early folds in the Katanga sediments have moderate plunges. The evidence from this area, and from other areas in the Central and Southern Provinces of Northern Rhodesia, indicates that rocks ranging from augen gneiss to feldspathic quartzite and schist, with the same trend as the Katanga System, have been produced by deformation of the Basement Complex during the Lufilian orogeny and not by granitisation of Katanga metasediments.

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Transactions of the Geological Society of South Africa, 66, 93-101

All spatial data are plotted on equal-area nets, the resultant point-diagrams contoured, and the following conclusions drawn:
1. There is a definite preferred orientation of the macrofabric.
2. All spatial data is related to one stress system.
3. An orientation of the strain-ellipsoid indicates that the deforming agent operated in an east-west direction.
4. There was rotational stress causing a new set of strike-slip faults, some of which were later infilled with dyke material (ilmenite diabase), and a set of tension-gashes, some of which were later infilled with quartz and others becoming the waterbearing fissures of the area.
5. The importance of strike-slip fault movements is emphasised and it is suggested that they are more frequent in occurrence than recognised. Criteria for their detection should be developed in the preparation of isopach maps of the various horizons.
An understanding of the fracture-pattern should lead to an understanding of the forces responsible for the formation of the basin and its preservation and could ultimately lead to further discoveries or extensions. Solution of such problems as the source of underground water in the mines may well lie in detailed joint surveys being undertaken by the mining companies. Gaps in the record are discussed and the need for further work emphasised.

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Proceedings of the Geological Society of South Africa, 66, xix-lxxii

The pipe deposits of South Africa are classified according to environment as plutonic, volcanic, hydrothermal and supergene; further subdivision is based on their development under either tectonic control or gravity control. This review touches on selected problems of genesis in the light of recent research.
The copper-bearing noritoid bodies of Namaqualand owe their inception to extreme metamorphic differentiation and diffusion of basic elements toward early local flexures, some of which have been distorted into elongate diapirs. The cassiterite pipes at Zaaiplaats, Mutue Fides and Stavoren formed under pegmatitic-deuteric conditions; some may represent granitized hydrothermal lodes. The cylindrical shape of the Loolekop carbonatite is an expression of plutonic intrusion, but the copper ore in the central shatter-pipe may be of later, hydrothermal origin. Textural banding in the limonite-hematite plug at Kalkfeld suggests fluidization-flow of late iron ore-"magma". The platinum-, magnetite- and sulphide-bearing dunite pipes of the Bushveld Complex jointly import pegmatitic-deuteric conditions of deposition.
The most eminent orebodies of the volcanic environment are the diamondiferous kimberlite necks and dykes intruded as ultrabasic "magma" generated in the mantle. Concentration of gemstones in the upper part of most pipes may be attributed to effective sorting by streaming gas. The tubular orebodies at Broken Hill, N.R., denote control by intersecting fissures. Mineralized breccia pipes in the Messina, Harper and Campbell mines are of complex origin, probably involving explosion and hydrothermal stoping under tectonic control. The influence of pre-pipe structure is less evident in the case of the fluorspar-lead-zinc collapse-breccia bodies of Marico. The development of the Tsumeb breccia pipe is ascribed to explosive release of volatiles under guidance of stratigraphy and structure, accompanied by water-hammer and solution-stoping to cause internal collapse. The inclined tin ore-pipes at Arandis developed along plunging drag-folds in the Damara marble. Though initiated by bedding-faults, the Abenab breccia pipe probably owes its final form to solution-collapse induced by circulating ground water that derived its vanadium from a former blanket of Karoo basalt and its lead and zinc from the adjoining Abenab West sulphide ore.

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Transactions of the Geological Society of South Africa, 67, 1-87

Eight occurrences of inclusions in the Hendriksplaats norite i.e. near the outer margin of the Bushveld Igneous Complex, and two in the upper portions of the mafic division of this intrusion have been investigated. These two groups of inclusions are separated from each other in the layered sequence of the Complex by pyroxenite, peridotite, chromitite and gabbroic rocks, the latter with magnetite bands, amounting in all to a thickness of more than 20,000 feet.
Undoubtedly, original, sedimentary carbonate rocks in the Hendriksplaats norite now consist of akermanite, monticellite, olivine, fassaite, wollastonite, a bluish calcite, spinel, rately garnet, vesuvianite and apatite, and intergrowths of monticellite and wollastonite and of monticellite and clinopyroxene. The former intergrowth originated from the disintegration of akermanite and the latter by the reaction of olivine and akermanite, in both examples the result of retrograde metamorphism.
A carbonate inclusion on Avontuur 814 KS in the upper mafic division of the Complex contains besides ophicalcite, also abundant vesuvianite (a reddish and a greenish-yellow variety), garnet, magnetite and wollastonite - an assemblage of minerals rather different from that of the analogous original carbonate rocks in the Hendriksplaats norite. The difference is ascribed to the general poverty in volatile constituents of the assemblage in the Hendriksplaats norite and to the original chemical composition of the rocks, those on Avontuur being more aluminous.
An occurrence of olivinefels at Magnet Heights i.e. in the Upper Zone of the Complex, was previously regarded by other workers as a plug of intrusive rocks. It displays exquisite zoning of its minerals relative to the contact with the surrounding gabbro as follows:
(1) Gabbro forming the country-rock,
(2) a pyroxene-garnet zone,
(3) a garnet-pyroxene zone,
(4) a vesuvianite zone,
(5) a spinel-pyroxene zone,
(6) a spinel zone,
(7) the core of olivinefels.
In this respect it very much resembles analogous indisputable inclusions of pyroxenefels in the Hendriksplaats norite on Groothoek 256 KT, and altered carbonate rocks on Avontuur 814 KS. Reasons are submitted for regarding all the occurrences of pyroxene- and olivinefels as altered carbonate rocks. One occurrence of pyroxenefels in Hendriksplaats norite is very difficult to prove an original carbonate rock because it contains in places chromite grains interstitial to the clinopyroxene and also veinlets of chromitite with which uvarovite is often associated. As far as the addition of constituents to the inclusions during metamorphism is concerned, aluminium and iron could have been introduced from outside sources to the outermost zones, but the amount of silicon is variable in examples of clear zoning. The unsaturated minerals like akermanite, olivine and monticellite are, however, not to be found in adjoining gabbroic rocks, their place is taken by pyroxene, especially orthopyroxene. Where calcium and magnesium figured in a xenolith, they behaved antipathetically - the calcium migrated outwards and the magnesium silicate remained in the nucleus. The association of akermanite and olivine in several of the xenoliths indicates that a temperature of the order of 900 xC or more has been attained.
The question whether decarbonation took place at shallow depth in conditions in the Hendriksplaats norite with affinities to the sanidinite facies, or at great depth at relatively higher temperatures, remains undecided. Nineteen new chemical analyses and a host of optical and X-ray data are provided to bear out the identification and relationships of a number of rare and other minerals, amongst which are, besides those already mentioned, diaspore, perovskite, a Sr-bearing clinozoisite, xanthophyllite, uvarovite and even kalsilite. A K-feldspar which displays remarkable dispersion of the optic axes and a variation in axial angle ranging from 0-80 degrees in the same grain has also been encountered. The rate mineral kalsilite is considered to be present in more than one locality in the xenoliths which contain akermanite and monticellite on Hendriksplaats. The mineral is evidently metamorphic in origin, its formation having been determinated metamorphic in origin, its formation having been determinated by a favourable physical and chemical environment.

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Transactions of the Geological Society of South Africa, 67, 111-118

The rocks outcropping in the Lupata Area of the Lower Zambezi in Mozambique comprise a sandstone-basalt sequence of Stormberg age, followed upward by, unconformable sandstones and rhyolites. These in turn are followed by unconformable sandstones and alkaline lavas. Above the latter there is the "Sena" sandstone sequence not generally considered as part of the "Lupata series" of literature. Minimum age determination by potassium, argon method obtained at the Gulf Oil Corporation Laboratories (USA) gave a jurassic age for the rhyolites and a Lower to Middle Cretaceous age for the alkaline lavas, thus defining their stratigraphic succession and supporting the available geological evidence. The post-Karoo deposition here is therefore subdivided into a lower (jurassic) cycle, sandstone-rhyolite, and an upper (Lower to Middle Cretaceous) cycle, sandstone-alkaline lavas. It is proposed to consider the uppermost, post-alakaline lavas "Senna" sandstones as part of this upper cycle, extending and re-defining the term "Lupata".

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Transactions of the Geological Society of South Africa, 67, 119-128

An interpretation is made of the structure and mode of emplacement of the intrusive rocks of the late-Karoo Masukwe Complex, one of several ring-complexes of the Nuanetsi Igneous Province. The earliest intrusions were of gabbroic composition and were emplaced as a sill and as ring-dykes. Later intrusions of micro-granite and granophyre took the form of cone-sheets, a ring-dyke, and a variety of polygonal dyke and sill-intrusions.

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Transactions of the Geological Society of South Africa, 67, 129-131

Application of experimental data on phase relationships in the Fe-As-S system has yielded an estimate of 1700-2000 bars for confining pressures prevailing during the deposition of arsenopyrite in the Sanyati deposit.

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Transactions of the Geological Society of South Africa, 67, 133-137

Northerly directed overlap of the various stages of the Table Mountain Series causes stratigraphically higher horizons to come into contact with pre-Cape System rocks. Valleys of pre-Table Mountain Series age are filled in with coarse detritus. Three probable tillites occur in the Series.

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Transactions of the Geological Society of South Africa, 67, 139-147

The roundish shape of so many of the platinoid grains found in the Witwatersrand banket has long been cited as evidence of their water-worn nature and therefore, detrital origin. However, a study of the relationship between the shapes of the grains and the internal structures has shown that the ovaloid and spheroidal particles are actually well-preserved nodular grains and not crystals or crystal fragments reshaped by aqueous attrition. It was also established that most of the grains consist of at least two different phases (hexagonal and cubic) and not one only, as has been assumed hitherto.

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Transactions of the Geological Society of South Africa, 67, 149-161

Nsutite, the naturally occurring equivalent of synthetic "gamma-MnO2", is regarded as an essential constituent of battery-grade manganese ore. Two sources in the Western Transvaal are being exploited, both of which occur in shales, in the one locality above the Dolomite Series and in the other in the Lipper part of the Dolomite Series (Transvaal System). The paper deals mainly with the investigation of pure specimens of stalactitic nsutite from the Orient mine. The greyish-black, porous, nsutite has a true specific gravity of 4.52; chemical analysis showed it to consist essentially of MnO2 (92.98%), H2O (2,28%) and MnO (145%), its simplified formula being MnO2-x(OH)x, where x represents the amount of trivalent or bivalent manganese. The X-ray diffraction pattern of nsutite is characteristic, the most intense peak occurring at approximately 4K; in addition, differential thermal analysis and optical data are included. Consideration of the properties of nsutite indicates the reactivity of the mineral to be due to its porosity, chemical composition and crystal structure. The assessment of potential ores is discussed and it is concluded that, for an initial appraisal, X-ray diffraction represents the most practical method.

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Transactions of the Geological Society of South Africa, 67, 163-171

Examination of a number of wave-cut bedrock shelves along a forty-two mile strip of the Sperrgebiet diamond-mining area has indicated that gullies are generally independent of bedrock structural planes though it is thought that these planes may have influenced gully trend, especially on gently inclined shelves. The dominant gully trend is probably normal to former coast-lines which are locally slightly oblique to the present coastline. In view of the rough parallelism of coastline indicated between present day and ancient beaches, it is probable that the main offshore gully trend is approximately normal to the present coastline. A gullying cycle is described and it is thought that its rate of evolution is controlled by shelf slope. Although gully depth may be partially due to uplift, the deepening of closed gullies which are potential diamond traps is thought to be largely a function of shelf slope. Some data is given to show the apparently narrow limits within which gully dimensions and frequency lie.

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Transactions of the Geological Society of South Africa, 67, 173-201

Chemical and microscopic investigation show a range in the more important rock types from leucocratic tonalites with more than 60% SiO2, through diorites, metadiorites and gabbros to amphibolites and altered peridotitic rocks with only 40% SiO2, in this small stock. Minor bands of highly silicic quartz albitite with SiO, exceeding 75% also occur. All rocks show high Na2O:K2O ratios which may reach 50:1 in silicic types. All plutonic rocks are highly altered, with widespread albitization of plagioclase; little original pyroxene is to be found. Greenstone xenoliths and roof-pendants show thermal metamorphic effects such as recrystallization and reconstitution with the development of granular pyroxene. On the basis of eight complete and seven partial chemical analyses it is concluded that all rocks are consanguineous and that the heterogeneity of the assemblage is better accounted for by pre-supposing emplacement in several magmatic heaves, than differentiation in place. The nature of the sulphides pyrite, pyrrhotite, pentlandite and chalcopyrite in the mafic rocks is described and evidence is led that sulphide mineralization was late magmatic, accompanying extensive deuteric alteration. Pyrrhotite contains exsolved pentlandite as well as light-coloured, less anisotropic pyrrhotite lamellae, while pentlandite contains minute inclusions of pyrrhotite which could be due to either exsolution or replacement.

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Transactions of the Geological Society of South Africa, 67, 203-209

Overturned cross-bedding occurs associated with recumbent folds and other features of slumping in several quarries near the top of the Witteberg quartzite at Grahamstown.

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Transactions of the Geological Society of South Africa, 67, 211-217

The zircon grains in the Dominion Reef are extensively altered. The altered portions are usually replaced by secondary minerals. In some specimens the original shapes of the grains can still be discerned. As a result of recrystallization some of the remnants have assumed euhedral and subhedral shapes. It is likely that metamicitization was the initial form of alteration of the zircon grains, and that the remnants represent less metamictized portions of the original crystals. In one sample an analysis of both the present and the original sizes of the zircon grains shows that the median grain-size has been reduced by 76%, and the first and third quartiles by 77- and 75% respectively. In another sample this very substantial diminution is confirmed by comparing the weight percent of zircon (0.15%) present as microscopically visible grains to the original amount of zircon (0.54%), calculated from the chemically determined zirconia content of the sample. The chromite grains are also extensively altered and replaced.

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Transactions of the Geological Society of South Africa, 67, 219-226

Unique pegmatite dykes are described in which quartz has been replaced by, aegirine-augite during fenitisation, and the graphic texture retained. Occurring, as they do, out of petrological context within an alkaline complex, while very similar acid pegmatites are known to be present in the country-rock not too far afield, the dykes as well as the basic rocks intruded by them are considered to be xenolithic. A critical examination is made of arguments previously advanced in favour of the alternative view that the basic rocks are the result of fenitisation in situ.

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Transactions of the Geological Society of South Africa, 67, 227-261

The petrography, structure and geochemistry of the rocks of the southeastern Richtersveld is described and their petrogenesis is discussed. It is inferred that prior to being metamorphosed the Kheis supracrustal rocks consisted mainly of impure siltstones, impure sandstones and lavas (mainly acid). They have attained the almandine amphibolite grade of metamorphism and their schistosity is believed to have resulted from the stress generated and the shearing produced by increases in volume consequent upon the genesis of the adamellitic gneiss. The metamorphism of the Kheis supracrustal rocks, the formation of the hybrid rocks, and the evolution of the adamellitic gneiss are all seen to be part of a single general granitization process.
More than twenty hornblendite and serpentinite bodies of post-Kheis age were found. They had been emplaced as gabbroic and peridotitic magmas respectively. Outcrops of plutonic rocks of the Richtersveld Suite form a belt which trends north-northwest and extends for 120 miles from Soeties (to the south of the area studied) to Aurus Waterhole (in the eastern Sperrgebiet, S.W. Africa). These plutonic rocks were emplaced into the epizone as ring-dykes and stocks. Petrographic and chemical data necessitated a revision of De Villiers and Sohnge's correlation of the rock units of the Rooiberg 2 outcrop with those of the Xaminxaip batholith. The parental magma of the Richtersveld Suite is believed to have developed from the selective fusion of the adamellitic gneiss.
The syenites resulted from two processes:
(1) the assimilation of Fe-, Mn-, Ti- and Mg-enriched roof- and wall-rocks, and
(2) the escape of silica-rich volatiles.
Geochemical, mineralogical and structural evidence all indicate that the porphyritic micro-granite was emplaced late as a residual magma. Subsequent potash metasomatism accounts for the abnormally high K/Na ratio of the porphyritic microgranite and the presence of muscovite-rich veins. The quartz bostonite dykes were found to be more salic than previously recorded. Geochemically they are closely akin to the Richtersveld Suite syenites. The quartz bostonite and hornblende diorite dyke rocks are both considered to be products of desilicated and contaminated parental magma of the Richtersveld Suite. It is suggested that the rocks of the Stinkfontein Formation and the Richtersveld Suite all belong to the same tectogenetic cycle.

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Transactions of the Geological Society of South Africa, 67, 263-282

Confusion in stratigraphic terminology arises from the fact that the words system, series, stage, group, formation etc., are used in several different senses in different parts of the world. The various classifications responsible for this state of affairs are described, compared and discussed. It is contended that, in view of widely divergent opinions even on fundamental matters such as the proper scope of stratigraphy, the time for international conformity has not yet come, however desirable this may seem. The conclusion is reached that the latest attempt in this direction, namely the scheme recommended by the International Subcommittee on Stratigraphic Terminology in 1960, suffers from certain defects, notably the following:
(a) a too all-inclusive definition of stratigraphy leading to categories of units which are not properly stratigraphic and also to the broadening of the scope of terms with a previously well-established meaning such as correlation,
(b) the intermingling of time-significant and facies boundaries in the concept of a lithostratigraphic unit;
(c) the "ideal" instead of practical definition of chronostratigraphic units.
Accepting that a particular time-span, say a Period, is world-wide in its application, the author asks whether a rock system deposited during that Period can also be regarded as world-wide. He points out that a material stratigraphic unit, as opposed to a geological time unit, is geographically limited and concludes that only two sets of terms are needed in order to fulfil the primary aims of stratigraphy when dealing with phanerozoic rocks; one for the time divisions belonging to a world-wide geochronological scale (Era, Period, Epoch, Age) and one for the stratigraphic column of each geographic area (System, Series, Stage, Zone). True stratigraphic units are considered to be inevitably related to time while stratigraphic units and facies units must be clearly distinguished. The only essential difference between the stratigraphic units of fossiliferous and non-fossiliferous rocks is that the former are more readily tied to the geochronological scale. It is recommended that correlations beyond individual areas of deposition (e.g. world-wide correlations) should be stated in terms of geochronologic units and not in terms of stratigraphic units. The author concludes that considerable justification exists for the use of the terms system, series, stage and zone in the "Provincial" sense in which they have been applied in Southern Africa to strata of both cryptozoic and phanerozoic age. No valid reason could be found for the rejection of the existing system of subdivision. In the interests of clarity, the principles of nomenclature and the definitions of terms as used in this country should be published in the form of a Stratigraphic Code. Elimination of the term "formation" seems to be desirable, with either "Beds" or "System" as possible substitutes.

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Transactions of the Geological Society of South Africa, 67, 89-93

A composite radio-activity log, amended from the one drawn up by Dr. D.J. Simpson in 1952 by including the anomalies due to the Intermediate Reefs is presented. Statements made by Dr. Simpson on the correlation of reefs south of the Sand River are revised in the light of the new composite log. The relative concentrations of uranium and gold in a conglomerate are demonstrated to be an additional correlation criterion.

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Transactions of the Geological Society of South Africa, 67, 95-109

I. Grooved and scraped bedding planes in Fish River sandstones are depicted and described. They are interpreted as drag-marks made by thin icefloes which were moved by wind in very shallow water. This new feature seems to occur on one horizon only. The use of this horizon as a stratigraphic marker for future work is suggested. It is pointed out that an otherwise seemingly warm water deposit may have experienced intermittent frost conditions.
II. A lately-discovered well-preserved boulder-pavement in Dwyka glacials near Gibeon is described. Its fabric is studied and compared with that of normal tillite in the vicinity. The agreement is good. It is concluded that discontinuous shear (dislocation) in a glacier tectonite has little or not enough strength to reorientate a fabric. Fabric measurements indicate that near the base a much greater thickness of Dwyka glacials is a ground-moraine than was hitherto thought. Use is made of fabric and morphological studies as well as pebble counts to prove that gravel beds in the glacial sequence originated from sub- or englacial-meltwater. A reproducible and relatively quick method for studying the morphology of pebbles quantitatively, is outlined. The value of this method for stratigraphic analysis is stressed.
III. A glaciated surface below Dwyka tillite near Schlip allows the direction and the sense of movement to be determined by means of several kinds of primary marks. This and other evidence for the direction of ice movement indicates that the ice cap, which originated in the central South-West African highlands, had, at latitude 24°S, not yet become a single tectonite following the regional southward gradient. This is in evidence for the first time south of latitude 25°S.

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Proceedings of the Geological Society of South Africa, 67, xvi-xx

Today I intend to consider the problem of correlation from the general point of view: the particular problem, that is whether X is to be correlated with Y, does not belong here, but rather the question of what factors should be considered when such a particular problem is approached. I intend going further than that and narrowing the question down considerably; the general problem will be that of standards for consideration when treating with the correlation of Precambrian rocks. Correlation of rocks is essentially correlation of time. All geological processes require a period of time to reach fruition, whether the process be one of sedimentation, or of orogenesis, or of magmatism. Correlation is essentially a problem of equating the products resulting from any geological process in an area during any particular period of time with the products resulting elsewhere, possibly from entirely different processes, but during the same period of time. A tillite in one area may be the time-equivalent, and therefore the correlate, of a quartzite elsewhere; and a conglomerate in the east may be the time-equivalent of a tectonic pulse and resultant erosion in the west. The above concept holds true for the Precambrian and for the Palaeozoic and later. Implicit in it, too, is the fact that the adjectives Precambrian, Palaeozoic, etc., may govern various and very differing verities; processes as well as products, for both are basically linked by time which is the common denominator always present. During the Precambrian time-interval, Precambrian strata are formed as a result of Precambrian erosion and are folded during a Precambrian orogeny. The adjective always refers to time: probably to an ever-increasing time-interval as we go farther and farther back in time, but still to time and to the products of whatever processes were operative during that time.

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Transactions of the Geological Society of South Africa, 68, 1-12

Regional zoning of the various ore-mineral occurrences in the Lomagundi-Urungwe Districts is described. Zones, ranging from pegmatitic to mesothermal are developed with mineral associations containing beryllium, columbium-tantalum, tungsten, arsenic, iron, zinc, lead, copper, gold, silver and molybdenum. A distinct relationship between zones of regional metamorphism and metallogenetic zones exists, which is manifested by a preference of certain ore-minerals or associations for distinctive metamorphic environments. The copper deposits in the Lomagundi District are subdivided into disseminated deposits in arkose and dolomite, supergene concentrations and vein- and fracture-deposits. The first-named show interesting relationships in their microcline content and in the Fe:Mg ratio of chlorites to the degree of copper mineralization, thus giving support to the idea of an epigenetic origin of mineralization.

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Transactions of the Geological Society of South Africa, 68, 121-142

Studies of the stratigraphy and of the conglomerates of the Main Reef Zone of the Upper Division of the Witwatersrand System suggest that four cycles, each with a basal gold-bearing conglomerate follow one another in this zone. At the base of each cycle there is evidence, to a greater or lesser extent, for a disconformity between the basal conglomerate and its footwall measures. Four types of disconformity have been observed and studied. Stratigraphical evidence supports the suggestion that the base of the Main Reef group, not the top of the Upper shale of the Jeppestown Series, should be taken as the base of the upper Division of the System. The main Reef cycle was followed by the Carbon Leader cycle, the Main Reef Leader cycle and the South Reef cycle. The disconformities, upon which the first two cycles were laid down, were not, in the area studied, very strongly developed. The Main Reef Leader cycle, in contrast, was preceded by very considerable erosion and peneplanation, including the cutting and refilling of deep stream channels. A suite of inter-cyclical sediments was deposited during the latter stages of this break in the sedimentation. The South Reef cycle was preceded by transgressional erosion, especially in the East Rand areas, during which up to 950 feet of strata were bevelled off. Study and recognition of the disconformities leads to modification in the correlation of the reefs of the Randfontein area and provides further evidence supporting the correlation of the Carbon Leader of the Far West Rand with the West Reef of Randfontein Estates, which overlies the Rock Tunnel Reef, the equivalent of the Main Reef of the Central Rand.

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Transactions of the Geological Society of South Africa, 68, 13-30

The Precambrian Umkondo System consisting of marginal shelf environment sediments and dolerites overlies Archaean shield granites and Mozambique Belt gneisses along the Southern Rhodesian and Mozambique border. The Umkondo System includes the Frontier System and the Gairezi Series, which were previously regarded as quite separate units. In the west, flat-lying limestones, sandstones, and shales are undeformed, while in the east they are folded and metamorphosed along a zone called the Manica Belt. Lithological, structural, and metamorphic changes have taken place across the Belt. The last tectonism is Cambro-Ordovician in age, but the time of deposition of the Umkondo sediments remains problematical.

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Transactions of the Geological Society of South Africa, 68, 143-175

This paper provides a record of the structure of the northern-most area of the O.F.S. Gold-field as determined by underground observations and borehole information. Structural-contour maps and geological sections indicate the general structure and the age relationships of the major faults. The structure of the Elsburg reefs, encountered locally near the western boundary of the mining property, is described in detail. An attempt has been made to reconstruct the complicated tectonic history of the area. There is evidence that both vertical and horizontal tectonics played an important role. Isopach maps of the area where the Elsburg reefs are mined reveal the direct relationship between sedimentation and contemporaneous folding and local overthrusting. The maximum intensity of folding was during the deposition of the Upper Elsburg Stage and was caused by a compressive stress which acted in a direction perpendicular to the elongation of the Witwatersrand basin. The various post-Witwatersrand faults and their age relationships are described. Three major tectonic periods are recognised: (a) post-Lower, pre-Middle Ventersdorp, (b) post-Middle, pre-Upper Ventersdorp and (c) deformations of post-Ventersdorp age. The stress-field orientations of the forces which caused the different faults have been determined by means of stereographic projections. Equal-area diagrams of measured joints indicate a relationship between the joint patterns in the vicinity of major faults and the deformative stresses that caused the faults.

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Transactions of the Geological Society of South Africa, 68, 177-201

The Jurassic igneous province of northern Damaraland comprises a series of ring-complexes with which Paresis is correlated. Central igneous activity at Paresis consisted of an earlier, predominantly volcanic phase followed by the intrusion of felsic ring-dykes and stocks. The intrusive rocks were emplaced into the subsided volcanic superstructure. Volcanic products were exclusively rhyolitic and three cycles are distinguished, characterised, respectively, by feldspar rhyolite, quartz-feldspar porphyry and comendite. Each of these commenced with the building of a high strato-volcano and ended with the intrusion of dykes of a similar composition. Cycles I and III were terminated by cauldron-subsidences and a final collapse occurred along a ring-fault encompassing both of the earlier cauldrons. The regular, centripetal dips of the rhyolite are attributed to the control of subsidence by conical fractures. Distribution and textures of the rhyolites are consistent with their emplacement as incandescent ash flows which were subsequently compacted, welded and recrystallized. Basalt flows - intercalated with rhyolites of Cycles III - and associated gabbroic dykes, are correlated with the regional Stormberg volcanism and are not directly linked to central igneous activity. Dykes of syenite, bostonite, and microgranite are shown to have been intruded, in that order, under high magmatic pressure along conical fractures. The arcuate form of the syenite dyke of the Central Massif is ascribed to asymmetric collapse of the comendite caldera-block, The different focal depths of the syenite and bostonite conical dykes - about 17 Km and 6 Km, respectively - are taken as evidence of a compositional stratification in the magma reservoir. Last in the intrusive sequence was a composite stock of felspathoidal rocks - located on the final ring-fault.

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Transactions of the Geological Society of South Africa, 68, 203-209

A description is given of the field-relationships of the Liwale, Lumusule and Muhuwesi Sand Series in the eastern part of the Southern Province of Tanganyika. Laboratory observations of the quantitative mineral composition of the Muhuwesi Sand Series, the underlying Masasi Series gneiss, and the Tunduru Beds are discussed. It is concluded that both the Liwale-Lumusule and Muhuwesi Sand Series are transported, and on the evidence of similar mineral composition it is concluded that the Muhuwesi Sands are mainly derived from the Tunduru Beds.

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Transactions of the Geological Society of South Africa, 68, 211-224

Geological survey of 1,000 square miles of terrain, mainly on the Tsumis Formation southwest of Rehoboth has established that the Tsumis Formation varies in thickness from 10,000 to 19,000 feet. It may be divided into four stages comprising a Lower Quartzite and Conglomerate Stage, a Calcareous Shale Stage, a Calcareous Quartzite Stage and an Upper Quartzite and Conglomerate Stage. The Calcareous Shale Stage has been further subdivided into 10 zones. The fullest succession encountered is on the farm Klein Aub. The Tsumis Formation is composed essentially of conglomerates, some of which resemble tillites, quartzites and shales, with all the lower sediments being calcareous. Locally narrow limestone bands are developed. No intrusives into the Tsumis Formation were found. The lower contact between the Tsumis and the older rocks is essentially an unconformity. Locally the contact is complex and has been rendered so either by tectonic movements or by plastic flow of the rocks along the contact. The upper contact with the Nama System is unconformable towards the west and possibly also so in the east. The age of the Tsumis Formation is still in doubt. Lithologically it is similar to the rocks of the Deweras Series of the Lomagundi System as developed in Southern Rhodesia. There does not seem to be a South African equivalent of the Tsumis Formation.

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Transactions of the Geological Society of South Africa, 68, 225-235

Structures in thucholite, very similar to algal and fungal structures in certain sapropelic coals, are described. In view of this structural similarity the chemical analyses, calculated on a dry, ash-free basis, of sapropelic coal and of thucholite are compared, and although the thucholite contains less hydrogen than a typical boghead coal, the hypothesis is put forward that thucholite actually represents a high-rank boghead coal, the composition of which has been changed by dehydrogenation as a result of alpha particle bombardment from the uraninite. It thucholite should be a high-rank sapropelic coal, the possibility of an organogenetic origin of the uraninite must be seriously considered.

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Transactions of the Geological Society of South Africa, 68, 31-52

The Losberg intrusion is a flat-lying, layered body, intrusive into shales and quartzites of the Transvaal System and is situated near the axis of the Potchefstroom synclinorium. This is one of many basic intrusions of post-Transvaal and pre-Karoo age. The intrusion, approximately 400 feet thick, consists of three units. From the base upwards these are: orthopyroxene-olivine cumulate (harzburgite), plagioclase-orthopyroxene-clinopyroxene cumulate (norite), and plagioclase-clinopyroxene cumulate (gabbro). This phase layering is accompanied by cryptic variation which, proceeding upwards, shows the following trends: olivine FO86-FO82 orthopyroxene En91-86-En73-69 clinopyroxene Ca44mg45Fell-Ca4lMg26Fe33 plagioclase An78-52-An66-32 Rhythmic layering occurs in the orthopyroxene-olivine cumulate, crystal fractionation, modified by two subsequent major additions of magma, resulted in moderate enrichment of the successive cumulates in iron, alkalies and silicon. The additional influxes of magma were less basic than the original liquid indicating that, before emplacement, differentiation also took place in depth.

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Transactions of the Geological Society of South Africa, 68, 53-60

Twenty-five bodies of ultramafic rock, younger than the Kheis System, were emplaced along two lines of fracture which trend east-west. These hornblendites and serpentinites were emplaced as gabbroic and peridotitic magmas respectively. They were later transformed to their present mineral composition by fluids produced during the evolution of the adamellitic gneiss.

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Transactions of the Geological Society of South Africa, 68, 61-88

Two hundred and thirty two samples of auriferous conglomerate and pyritic quartzite, together with associated foot- and hanging-wall quartzites of the Dominion Reef, reefs of the Witwatersrand System, Ventersdorp Contact Reef and Black Reef, were investigated. The mineral constituents of the samples were studied in heavy concentrates as well as in thin and polished sections of the original rock. A sympathetic relationship exists between the content of gold, uraninite, pyrite and the undoubtedly detrital heavy minerals in each reef. This relationship indicates a sedimentary origin for gold, uraninite and pyrite. Non-sedimentary pyrite, which bears no relationship to the distribution of the detrital heavy minerals, was also found. An analysis of a banded pyritic quartzite showed that the gold as well as the heavy minerals are concentrated in the pyrite-rich layers. No detectable migration of gold from these mineralized layers has taken place. The heavy mineral and pyrite content of gold-bearing reefs was found to be about five times that of the adjacent foot- and hanging-wall quartzites. Several heavy minerals were found in the bankets, especially in the Dominion Reef, but only three: chromite, zircon and leucoxene, occur in sufficiently large amounts to be of quantitative significance. The ratios between chromite-zircon-leucoxene in the heavy concentrates of the various reef groups are often found to be characteristic of the group which it represents; for example, the leucoxene content in the heavy concentrates of the Main Reef Group (bottom of the Upper Witwatersrand) lies between the limits 65-98% whereas it decreases progressively to 0-2% in the Elsburg Reefs (top of Upper Witwatersrand). The heavy mineral suites of the Upper and Lower Bands of the Dominion Reef differ markedly from each other and from the Witwatersrand heavy minerals. The garnet content in the heavy concentrate of the Lower Band is 60% and 1% in the Upper Band, whereas this mineral is almost complete

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Transactions of the Geological Society of South Africa, 68, 89-120

Field work and mapping have shown the north Gap Dyke to be a vertical intrusion 91+ miles long, extending from a point about 4+ miles south of Cathcart to the Transkei coast where it enters the sea about 100 yards north of the Ngadla River mouth. It is composed of several rock types including dolerite pegmatite, granophyric dolerite, subophitic dolerite and, at the western end, it contains a core of mobilized sediment. The essential minerals of the dolerite types include zoned plagioclase and augite. Less important are hornblende and micropegmatite. Accessories include quartz, apatite, ilmenite, biotite, magnetite, actinolite, rehnite, calcite and epidote. Iddingsite (?), saussurite and chlorite occur as alteration products. The mode of origin of the Gap Dyke magma remains an open question: it may have arisen as a result of normal crystal fractionation, as the result of hybridization or as the result of hybridization followed by differentiation.

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Transactions of the Geological Society of South Africa, 68, xviii-lxi

Presidential Addresses to our Society have covered a very wide range of topics. On reading or re-reading those delivered over the past 50 years, it was apparent that nearly all fall into two main categories: those that are essentially new contributions to scientific knowledge, and those that are reviews of current thought or of progress in a specific field. The 30th, 40th, 50th and 60th anniversaries of the Society were appropriately commemorated by the then presidents. Professional matters, however, have received relatively little attention. The exception is Mr. A. Frost's Address in 1948: "Some Thoughts on the Functions of Geology and Geologists". Professor T. W. Gevers devoted the latter portion of his Address in 1937, "The Progress of Mining Geology", to the education of geologists,, especially in the field of mining-geology, and Dr. W. P. de Kock included sections on the status and future of the mining-geologist and the teaching of mining-geology in his Address: "Geology applied to Mining in South Africa with special reference to the Witwatersrand" (1944). The "training" of exploration geologists was also touched on by Dr. J. W. N. Sharpe in his Address: "Mineral Exploration and its Techniques" (1955). Education in the scientific disciplines is now undergoing major, even revolutionary, changes. This, the 70th year of our Society, therefore seems to me to be an opportune time for considering some aspects of geology, both as a discipline and as a profession, in South Africa. I have used the word "status" to cover them - I must admit though that I am not very happy with it, especially after reading Vance Packard's provocative book, "The Status Seekers"! I propose dealing with such matters as geological education, the attracting of suitable recruits to the profession, and the so-called "public image" of geology in our country. For many years insufficient students have graduated in geology at our universities to fill vacancies and newly created posts. Furthermore, the position has been worsened by many qualified geologists having abandoned their profession whilst others have left the country. The Geological Survey has not been fully staffed since 1940, and this despite intensive overseas recruitment. This shortage of geologists, which bodes ill for the future, should be compared with the great enthusiasm amongst matriculants to enter, for example, the medical profession - at the commencement of the 1968 academic year no less than 2,700 competed for the 1,087 first-year places in our medical schools. These are matters of vital concern to our Society and I agree whole-heartedly with Professor Hollingworth who stated in his Anniversary Address to the Geological Society of London that "in the absence of any organization ... catering especially for the geologist in a professional capacity, the liability or responsibility of scientific societies for the wider aspects of the science should surely be considered as an important part of their function". (1962, p. 464).

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Transactions of the Geological Society of South Africa, 69, 1-38

The geology of twenty-three beryl pegmatites is described. The pegmatites occur mainly in amphibolites of Bulawayan age and display diverse geometry, degree of zoning and composition. Some contain major amounts of lithium minerals and among these are also found pegmatites carrying economic quantities of tantalum minerals. Beryl occurs both in a very fine-grained form and as coarse crystals, the latter particularly in zoned pegmatites containing lithium minerals. The pegmatites can be divided into two types, since there is a general tendency for all well-zoned pegmatites to be lenticular in shape and partly coarse-grained, whereas the unzoned and weakly-zoned pegmatites are usually sheet-like in form and dominantly fine-grained. It is considered that pegmatites displaying fold-shapes and corrugated surfaces were formed in their present shape and owe little to flexuring.

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Transactions of the Geological Society of South Africa, 69, 119-126

The lead-silver deposit in question occurs near Argent station about fifty miles east of Johannesburg. Some aspects of the deposit were described in detail in 1924 by Wagner in a paper published in Economic Geology. Willemse subsequently elaborated on the geology and mineralogy of the vein. A brief resume is given in the present paper of the mineralogy of the gossan and of the sulphide vein, from personal observations and from the publications respectively of Wagner (1924) and Willemse (1944). The general geology of the area is only very briefly referred to. The main theme of the paper is a description, an analysis and a synthesis of the vein and the fracture pattern in the No. 1 Shaft workings on the so-called Main Vein of the area. It is demonstrated that almost perfect cymoid structures are formed in the vein and the fracture pattern, and that a post-mineralization strike-fault, lying mostly along the south-western, unmineralized limb of a multiple cymoid structure, cuts in and out of the north-eastern, highly mineralized limb, causing "cut-outs" or "losses of ground" at intervals along the plane of the latter. Drag-ore is conspicuously developed in parts of the mine.

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Transactions of the Geological Society of South Africa, 69, 127-137

During 1958 a diatreme was discovered on Boschlaat 396 about 16 miles south of Bloemfontein. The conduit measures 270 ft. x 100 ft. and is filled with coarse agglomerate composed of fragments of shale, sandy shale, shaly sandstone and arkose. The diatreme lies well to the west of the acknowledged Stormberg volcanoes with which it is presumably to be correlated. Whereas these have seldom been found piercing strata below the Stormberg Series, the surface of the Boschplaat diatreme lies in the Lower Beaufort Stage. The filling and in places also the surrounding rocks carry a high proportion of tourmaline, for example 33.6% in a sample of shale 430 ft. from the south-eastern periphery of the agglomerate. The tourmaline contains some 10% of boron trioxide; the mineral is not detrital but occurs as "suns", like those found in luxullianite (tourmalinized granite). It is surmised that the vent was blown by boron-bearing gases or that such gases or solutions streamed through an existing passage and diffused into the surrounding strata. Because tourmaline does not appear to occur in basic rocks and because boron-bearing vapours are scarce in volcanic emanations, the source of the boron cannot as yet be explained with certainty. The occurrence of scolecite in cavities in the shale surrounding the plug is affirmative of (Stormberg) volcanicity.

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Transactions of the Geological Society of South Africa, 69, 139-154

A detailed description of the petrographic mineralogy of the charnockitic adamellite porphyry, including the cataclastically deformed variety, is given and 20 new modes of these rocks are presented. The varied mineralogy of the rocks lends itself to an assortment of thermometric estimations and the conclusion of relatively high initial temperatures of the magma. This, coupled with high confining pressures and slow cooling, promoted crystallization of pyroxenes, even in a felsic magma. Apart from the implication of high temperature plutonic conditions, the conclusion is put forward as a suggestion worthy of further exploration that the term "charnockitic" refers to rocks which acquired their peculiar appearance (dark colour, greasy lustre) through accidental circumstances, rather than through events of profound geologic significance.

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Transactions of the Geological Society of South Africa, 69, 155-159

A description is given of certain radioactive phenomena observed during an ore-microscopic study of gold-bearing conglomerates from the Orange Free State gold-field. Several types of radioactive blasting haloes in pyrite are described and illustrated, the blasting agents being zircon, uraninite, brannerite, and thucholite respectively. Furthermore, some observations regarding radiogenic corrosion processes caused by brannerite and carbonaceous matter are communicated.

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Transactions of the Geological Society of South Africa, 69, 161-199

Analytical results of major and trace-elements are presented for 45 samples of Cape Granite, two samples of the intrusive gabbro-diorites near Malmesbury, as well as 97 analyses of coexisting minerals from these rocks. X-ray data on K-feldspars are included. Consideration of the geochemical data confirms the view that the Cape Granite plutons formed from a typical high-level, fractionated magma with further strongly increasing degree of differentiation outwards towards the finer-grained margins of the granite bodies. Variable loss of some trace-elements occurred from some of the most strongly differentiated granites. Trace-element data on coexisting K-feldspars and biotites suggest that these minerals crystallized at least in approximate chemical equilibrium. This makes it unlikely that K-feldspar phenocrysts in the Cape Peninsula Granite formed by a general late-stage potash enrichment. On present data, it appears possible, but unproven, that the Cape Granite was formed by mobilization of Malmesbury sediments at depth with subsequent differentiation and intrusion.

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Transactions of the Geological Society of South Africa, 69, 201-210

Foraminiferal analyses proves the occurrence of extensive Pliocene deposits along 600 miles of the Natal-Mocambique coast from Durban to Morrumbene. Such an age is consistent with that of King and King (1959) who used the lithologic and structuro-geomorphic relationships of the deposits. The age of lower Miocene given by Frankel for part of these deposits is rejected, as also his claim that "(5) The depositional surface below the Miocene rises from Uloa to Umkwelane Hill at approximately 9 feet per mile, an amount not sufficient to allow unbroken physical continuity with the early Tertiary land surface of the hinterland". The earth's crust was not broken physically at the Umfolozi in post early Tertiary time.

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Transactions of the Geological Society of South Africa, 69, 211-230

The Mpande Dome, situated at the eastern end of the Kafue Flats, forms a protuberance at the northern end of a large inlier of Basement Complex rocks in the southern part of Zambia. The dome consists of a roughly circular core of gneiss and granite which is mantled successively by quartzite, schist, and limestone of the Katanga System. Stratigraphically below the quartzites but away from the dome is a thick group of acid and basic volcanics with subordinate sediments. Three phases of deformation are recognised. The first resulted in the formation, in the Katanga rocks, of recumbent folds trending north-west and overturned towards the south-west, with axial-plane schistosities which are usually parallel to lithological boundaries. During the second phase granites were intruded into the Basement rocks concomitant with uprise of the core of the dome in a nearly solid state. They are now partly intrusive into the enveloping Katangan sediments. Refolding both parallel and oblique to the margin of core gneiss occurred at this time, resulting in widespread distortion of the normal regional north-west strike. The third and last phase is represented by the crinkling of earlier schistosities along newly formed strain-slip cleavages. The intensity of crinkling increases with rising metamorphic grade towards the core of the dome.

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Transactions of the Geological Society of South Africa, 69, 231-248

The Lomagundi System in north Lomagundi District includes arkosic, dolomitic and argillaceous members and is intruded by dolerite sills. It rests upon a basement of previously folded rocks, mainly gneisses. The Lomagundi System is itself strongly folded on north-northwest trending axes, with north-east trending cross folds parallel to the main structural trend in the basement. In previously mapped areas further to the south, the system is virtually unmetamorphosed, but north of Mangula it enters a field of regional metamorphism ranging, in north Lomagundi, from low greenschist to low amphibolite facies. The metamorphic grade increases westwards towards Miami, and northwards, towards the Zambesi Escarpment. At the maximum grades reached in north Lomagundi, arenaceous rocks are converted to granulite and psammite schist, dolomitic limestones to amphibole-bearing schist and marble, shales to kyanite- and hornblende-bearing phyllite and schist and dolerites to andesine-bearing amphibolite. The gneisses of the Zambesi Escarpment are older than the Lomagundi System.

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Transactions of the Geological Society of South Africa, 69, 39-69

Karoo sedimentation in Northern Rhodesia provides an example of tectonically controlled basin filling of downwarps on a continental surface. Although their positions corresponding approximately to the present rift-valleys, suggest that the downwarps were controlled by much older structures in the Precambrian rocks, there is no genetic relationship; the rift-valleys have merely taken advantage of some of the older directions of weakness.
Following the retreat of the Dwyka ice, shallow linear downwarps began to form; the Barotseland basin is exceptional in that it is not noticeably elongated. The pre-Karroo surface, except in the Gwembe District of the mid-Zambezi valley and the western end of the Luano Valley, was hilly, and the more outstanding features were probably not completely buried until late in Ecca times.
The shallow troughs were soon filled with debris, partly glacial in origin, stripped from the pre-Karroo surface as a result of rejuvenation of the flanking areas consequent upon the initial downwarping. Carbonaceous sediments began to accumulate in widespread swamps but, with the exception of the Kandabwe area, the tectonic environemnt was too unstable to allow thick coal-seams to form; thin seams with a high ash content grading laterally and vertically into carbonaceous mudstones are characteristic of the Ecca successions.
Late in Ecca times the swamps were flooded by shallow fresh-water lakes which filled the depressions and gradually expanded to encroach on adjacent areas that were being progressively peneplaned. The lacustrine sediments generally consist of calcareous mudstones with rare thin limestone, alternating with sandstones and arkosic grits. This alternation is a result of periodic rejuvenation of the source-areas following spasmodic subsidence of the basin or possibly the earliest movements on the boundary-faults.
Towards the close of Lower Beaufort times the lakes were finally filled by sediments which were by now predominantly argillaceous, suggesting that peneplanation of the flanking areas was complete. Swamp conditions prevailed and some of the marshes were inhabited by a varied reptilian fauna. After a break in sedimentation of unknown duration, the first major movements on the boundary-faults caused rejuvenation of the positive source-areas and the troughs were inundated with coarse, often conglomeratic, detritus. Faulting resulted from continued downwarping and eventual failure of the crust along the hinge-zones. Because the troughs were asymmetrical, faulting was probably confined to the steeper limbs of the warps. The Upper Karroo sediments are therefore thickest near the faulted margins, where they may even have been banked against the actual fault-scarps, and become thinner across the troughs. The basal conglomeratic grits are usually succeeded by alternating grit and siltstone horizons, each grit-siltstone unit representing a minor cycle of sedimentation initiated by periodic movements on the faults. Deposition of another major arenaceous horizon in the Zambezi and Luangwa Valleys followed a second phase of major faulting.
Towards the close of Karroo times, when the basins were again filled, further warping resulted in the rejuvenation of the positive areas flanking the troughs, and any remaining sediments deposited on them during the expansion of the basins in Lower Beaufort and again in late Stormberg times were stripped off and redeposited in the basins as alluvial and wind-blown sands. Similar sands are interbedded with the first lava flows, but the intervals between subsequent flows were so short that no sediments or even fossil soils separate them. Major faulting in post-Karroo times resulted in the present aspect of the rift structures, which still retain their original asymmetry. Subsequent "scooping out" of the comparatively soft sediments gave rise to the characteristic rift-valley topography, but his has been modified by recent movements on the boundary-faults and rejuvenation of the fault-line scarps.
These late movements may be allied to the development of the East African rift system. This study of the environments of deposition of the Karroo sediments can be applied to the search for coral in Northern Rhodesia, particularly in areas underlain by Karroo strata but blanketed by alluvium.

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Transactions of the Geological Society of South Africa, 69, 71-85

Dembe-Divula is one of a group of Mesozoic ring-complexes aligned along the centre of the Precambrian Limpopo orogenic Belt. The complex comprises a suite of gabbros, granites and granophyres intruded into basalts and rhyolites of the Stormberg Series. The gabbro bodies are sill-like and three petrological types occur. Ten distinct phases are recognised in the granitic rocks, which take the form of ring-dykes, roof-sheets, plugs and narrow dykes. The mode of emplacement of the various rocks is outlined and attention is drawn to the westward migration of centres of intrusion.

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Transactions of the Geological Society of South Africa, 69, 87-98

The 25,000 feet of sediments and subordinate volcanics that constitute the Stinkfontein Formation of Namaqualand crop out in a north-trending, elongate belt, 95 miles long, that stretches from Kodas in the north to Kleinsee in the south. The sediments are mainly sandstones with conglomerate units at the base and near the middle of the succession. Forty-two percent of these sandstones were found to be orthoquartzites, 23% felspathic sandstones, 19% arkoses and 16% micaceous sand stones. Throughout the Stinkfontein Formation lavas, tuffs and agglomerates of variable thickness and extent occur interbedded with the sediments. Pyroclastics make up at least 50% of the Stinkfontein volcanic pile and they are generally rhyolitic or quartz latitic in character. Biotite and hornblende rhyolites, quartz latites, latites, trachytes and andesites are typical of the lavas. The sediments are believed to have accumulated under oxidising conditions along the flanks of a fault-scarp on the eastern side of a half-graben. Stinkfontein sedimentation, and the evolution of the Richtersveld Suite of plutonic rocks are believed to be two phases of the same tectogenetic cycle.

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Transactions of the Geological Society of South Africa, 69, 99-117

A general description of the geological units of the Precambrian basement of southernmost Natal is accompanied by an account of four occurrences of orthopyroxene-bearing granitic rocks (charnockite). Seventeen new chemical analyses are presented together with volumetric mineral analyses of the major rock types. Rocks showing charnockitic affinities are of igneous, metamorphic and metasomatic origin, the last mentioned taking the form of reaction-rims about xenoliths of more basic rock in relatively younger granite. Evidence is presented which indicates that the orthocharnockites of the Port Edward region form part of a differentiation sequence involving a pyroxene dioritic-granodioritic magma possibly influenced by the assimilation of pyroxene-garnet granulite. Less information is available concerning the rocks of the Bomela area which appear to form a displaced portion of a similar body occurring on the western side of the Renken fault in the Marble Delta area. Crystallization of granitic magma under reducing conditions is considered to be of importance in the development of orthocharnockites. Considerable difference in age exists among the bodies of charnockitic rocks. The Leisure Bay sequence represents part of the oldest preserved sedimentary sequence while the Bomela body is the youngest of the Precambrian formations in southernmost Natal.

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Transactions of the Geological Society of South Africa, 70, 1-14

Recumbent pod-folds in the Mine area plunge at low angles to the north-west, subparallel to the axis of the main Mufulira syncline. They may be an embryonic form of the vast nappe structures to the north in the Katanga province. Similar folds are present in other mines and properties on the Copperbelt including the complex sheet type observed 11 miles south-east at Mutundu-Mutupa. Directive stress causing these folds was towards the north-east and although gravity was important, involvement of the rigid granite in the anticlinal cores proves that horizontal pressure was the main component. Thus, in the Mufulira area evidence of north-eastward displacement shows gradation to the structures of the Katanga province. The stratiform ore-bodies are not genetically related to these folds. The more persistent folds transgress the fringes of the ore-body and pass into barren strata. By contrast, the mineralization is closely related to the irregular sub-Katanga land surface. Over or close to pronounced highs in the Basement, there occur, within the limits of the ore-bodies lenses of low-grade chalcopyrite-pyrite disseminated in "clean" quartzite.

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Transactions of the Geological Society of South Africa, 70, 117-134

The Bremen granite-syenite complex of southern South-West Africa is 115 square miles in area and consists of an inter-penetrating group of stocks, ring-dykes and plugs which are cut by many dykes. The complex lies at the north-eastern end of the Swartbank-Rooibank-Kuboos-Tatasberg line of intrusives. However, the Bremen complex is believed to differ from these other plutons in that it contains rocks belonging to both the Late-Precambrian Richtersveld Suite igneous episode, and the later Kuboos igneous cycle.
The rocks of the Kuboos, or second igneous cycle at Bremen, are intrusive into, and engulf, lower Nama System sediments. These second cycle plutonic rocks are considered to be of Cambrian age which is the same age as the Cape Granites to the south. The emplacement sequence at Bremen is believed to be as follows: first cycle - syenite, microsyenite, alaskitic granite, microgranite, quartz syenite, bostonite, granite porphyry and spessartite; and the second cycle ferro-syenite, bostonite, syenite, microgranite, bostonite, quartz syenite, bostonite and trachyte.
All the granite magma is believed to have been generated by the selective fusion of crystal materials. This magma rested on a hot mafic layer which consisted of a mixture of the residual materials left after the generation of the granitic magma, and the more mobile basaltic material that was primarily responsible for the introduction of the heat required for crustal melting. During periods of tectonic disturbance there was often a falling off in hydrostatic pressure in the magma chamber. This not only weakened the roof rocks but also resulted in the introduction of volatiles and fugitive constituents. The inrush of these latter materials, some of which are believed to have been alkali carbonates, produced a vigorous stirring action, and there was a commingling of large volumes of granitic magma with lesser volumes of mafic and carbonate materials.
The net result of this mixing of magmas was the generation of a syenitic magma significantly more mafic than the original granitic magma. All the Bremen rocks were emplaced into the epizone but the older rocks appear to have been emplaced at a deeper level than the younger. The earliest rock type is the Wetterkopf beacon syenite which occurs as a coarse-grained pluton while the finale intrusive material is trachytic and it appears to represent the congealed material filling a volcanic conduit.

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Transactions of the Geological Society of South Africa, 70, 135-165

This investigation is concerned with the post-Cretaceous geology around Durban and with samples of rock obtained from the Aliwal Shoal, an offshore reef situated between two and three miles from the mainland, 40 miles south of Durban. The samples from the Aliwal Shoal indicate that this offshore feature is a submerged remnant of a coastal dune deposit of probable Pliocene age, and may be correlated with the Bluff Beds at Durban which occur at elevations between 420 feet and -300 feet and have recently also been dated as Pliocene by three independent workers.
A study of critical exposures of the Bluff Beds in the Durban area shows that the Berea (or Coastal) Red Sand, previously regarded as a separate and younger formation, is the weathered counterpart of the Bluff Beds. By recognition of these relationships, allied with the nature of the seaward descent of the floor of the Pliocene strata, it is shown that the depositional sequence comprises thin basal beach-deposits overlain by coastal dune-deposits. This sequence is indicative of marine regression in response to major lowering of sea-level from 300 feet to about -300 feet during Pliocene times.
The Bluff Beds forming the Bluff Ridge are a remnant of a once more extensive coastal dune deposit which accumulated during the period of greatly lowered sea-level.
The Aliwal Shoal is likewise a remnant of coastal dune-rock, now submerged. This interpretation challenges the view that the Bluff Beds and Berea Red Sand in the Durban area represent separate periods of transgressive deposition to repeated seaward tilting about an inland axis and that these events were followed by recent synclinal or faulting movements. Conglomeratic, shelly strata along the seaward side of the Bluff Ridge, previously regarded as intraformational or intercalated horizons in the Bluff Beds are now shown to be younger, probably Pleistocene raised beach deposits, related to a withdrawal of sea-level following coastal submergence to between 20 and 30 feet above present sea-level. The distribution of the Berea Red Sand along the Natal coast records an extensive development of Pliocene strata, now in the weathered state, and there fore the overall interpretation of the Late Tertiary and Quaternary geology of the Durban area can be applied to the entire coastal zone of Natal. Furthermore, the sequence of events now recorded in detail from the Durban region is closely comparable with the Late Tertiary and Quaternary coastal history of the Cape region. Thus the evidence from Natal is consistent with the concept of synchronous development of the Late Tertiary and Quaternary littoral formations along the eastern and southern coasts of South Africa in response to major sea-level movements, as first suggested by Du Toit in 1922.

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Transactions of the Geological Society of South Africa, 70, 15-28

Lithostratigraphic zones in the Table Mountain Series are recognised over wide areas of the northern coastal regions of Natal. Lying on a planed surface cut across highly folded, crystalline Basement formations are about 200 feet of cross-bedded, maroon, felspathic sandstones and grits with numerous intercalated lenses of maroon shale comprising the Basal Zone. Overlying these rocks is a prominent stratigraphic marker, about 60 feet thick, consisting of fine-grained orthoquartzites with a few intercalated shales. This Orthoquartzite Marker is characterised by its remarkable textural and mineralogical maturity. Usually resting conformably on the Orthoquartzite Marker are purple grits and coarse-grained sandstones of the Arkosic Zone, thinning westwards from 150 feet to about 80 feet. Around Durban a quartzite is developed within this Zone which is very similar in appearance to the Orthoquartzite Marker. A coarse pebbly grit, grading into a pebbly conglomerate in the west near Glenside, is intermittently developed and marks the beginning of the Micaceous Zone. This Zone is characterised by the presence of muscovite in sandstones and by the frequent intraformational slump-structures, and is estimated as being 1000-1500 feet thick in the extreme east. Capping the Series around Stanger and Doornkop in the east is an upper quartzite about 20 feet thick upon which the overlying Dwyka Tillite has cut striated pavements.
The mineralogical and textural individuality of the Orthoquartzite Marker has been demonstrated by petrographic and grain-size analyses, but no clear distinction between the remaining zones can be made on these bases. Palaeocurrent evidence shows the provenance area for the Table Mountain Series to lie to the north and the Series was deposited under piedmont conditions. The Orthoquartzite Marker probably reflects a widespread shallow marine incursion with reworking of dune sands by wave action in a wide inter tidal zone. The appearance of muscovite as an important constituent of sandstones in the Micaceous Zone is possibly due to a change in provenance and depositional environment. Lithological changes in the Table Mountain Series are expressed in the topography by changes in slope, the Orthoquartzite Marker in particular exerting strong structural control on the landscape.

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Transactions of the Geological Society of South Africa, 70, 167-175

A brief review of the exploratory work accomplished so far in Southern Africa is presented. The areas discussed are subdivided into three parts, each presenting its particular problems. The coastal fringe of Mesozoic and Tertiary embayments, from Gabon, around Southern Africa to Kenya, is by far the most productive and also the most intensely explored area. The Interior Basins of Southern Africa, from the Congo through Angola and South-West Africa and Bechuanaland into the Karoo Basin proper are considered to be largely of unfavourable facies, and are only now beginning to be explored with modern techniques and large means. The same applies to the Cape Folded Belt, where exploration work has started on each flank. This shifting of the attention from areas that more obviously appear to meet the tenets of petroleum geology, to areas that are believed to be less fortunate in that respect is due to several factors. Firstly, the detailed knowledge of these latter areas is still rather scanty, and, secondly, the geological data that have been accumulating in the petroleum literature in the past twenty years, as pointed out by Hedberg, appear to indicate that the rigid "geological fence" within the limits of which petroleum is believed to have originated and accumulated, is somewhat enlarged. In view of these conclusions, it is not surprising that petroleum is presently being sought also in some of those areas that appear to lie at the very edge of the "limiting geological fence".

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Transactions of the Geological Society of South Africa, 70, 177-187

The deformed and metamorphosed Gairezi Series and the flatlying Umkondo System, assigned to entirely different ages by previous workers, are here shown to be stratigraphically equivalent. It is proposed that the orthoquartzite-pelite assemblages of the Gairezi Series be referred to as the "Gairezi Facies" and that the sandstone-limestone lithology of the undeformed Umkondo System be known as the "Inyanga Facies" of the Umkondo System.

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Transactions of the Geological Society of South Africa, 70, 29-33

Folds are present in shales of the Beaufort Series, exposed in the sidewalls of a quarry, located some three miles east of Bloemfontein. The folds have the shape of elongate domes and are confined to the beds immediately under a cover of 20 feet of soil. These structures are nontectonic in origin and are the result of an increase in volume due to hydration of shales on weathering.

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Transactions of the Geological Society of South Africa, 70, 35-37

A combined solvent extraction - spectrochemical procedure has been used to estimate trace-amounts of thallium in nine South African basic rocks. Reference-rocks, diabase W-1 and granite G-1, served as standards.

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Transactions of the Geological Society of South Africa, 70, 39-63

An account is given of the stratigraphy, structure and petrography of the pre-Karoo formations underlying an area some 90 square miles in extent within the White Umfolozi inlier in northern Natal. Two pre-Karoo unconformities were identified. They are a nonconformity with a crystalline, mainly granitoid basement and an angular unconformity separating two major stratigraphical units, the lower of which contains a high proportion of volcanic rocks. About 8000 feet of pre-Karoo strata are exposed. Previously, about 600 feet of sediments had been reported from this inlier and an intrusive relationship between the granitic and sedimentary rocks had been suggested (Molengraaff, 1902; Humphrey, 1911). The lower and upper stratigraphical units now recognized are correlated, on the basis of similarities in lithology, major stratigraphical relationship and structure, with the early Precambrian Insuzi and Mozaan Formations respectively.
Previously, strata appearing within the White Umfolozi inlier had been correlated with the Insuzi Formation. Being up to 6000 feet in thickness, the Insuzi Formation consists essentially of two thick lithological zones, namely, a group of quartzitic sandstones (2500 feet) and a group of altered lavas, probably propylitized andesites (2300 feet). Subordinate lithological zones consist of shales, lavas and a thin basal quartzite. A notable feature is the occurrence of four lenticles of aphanitic and siliceous, nodular dolomites within the thickest group of sandstones. Dolomites have not been previously recorded from other occurrences of the extensive Insuzi Formation. Also, some pillow structures were noted in the Insuzi lavas. Strata of the Insuzi Formation dip at 15 to 35 degrees northeastwards.
The Mozaan Formation ranges up to 2200 feet in thickness and comprises mainly a lower group of arenaceous and an upper group of argillaceous strata, which dip at 5 to 15 degrees to the east-north-east. The basal beds overstep various members of the underlying Insuzi Formation and the basal Mozaan succession provides evidence of a north-westward overlap. On a regional scale, possible tectonic implications of the stratigraphy of the White Umfolozi inlier are mentioned.

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Transactions of the Geological Society of South Africa, 70, 65-66

Graphite was found to be a rare constituent of the banket in the Orange Free State. It is suggested that it formed as a result of graphitization of "carbon" by regional metamorphism.

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Transactions of the Geological Society of South Africa, 70, 67-80

Between August 1961 and June 1963, the Border Exploration and Development Company Limited carried out a comprehensive prospecting programme in an attempt to find nickel and copper orebodies associated with the differentiated intrusives occurring in East Griqualand and Pondoland. The area was thoroughly investigated. The programme included reconnaissance, detailed geological mapping, an airborne magnetometer survey, ground magnetic, electromagnetic and geochemical surveys. The electromagnetic, geochemical, and detailed geological surveys revealed the most interesting information. Follow-up pitting, trenching, and diamond drilling failed to reveal sulphides in economic quantities. Information gained from the investigation indicates that an economic sulphide deposit associated with the intrusives does not exist. The differentiated intrusive masses are in the form of undulating sheets rather than basin-shaped bodies. The existence of the sulphides in the Waterfall Gorge of Insizwa is thought to have resulted from slight down-warping of the intrusive mass late during the cooling stage.

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Transactions of the Geological Society of South Africa, 70, 81-116

The terms Archaean, Archaeozoic and Proterozoic are both meaningless and misleading in South Africa, and should be discarded. Amongst other general Precambrian terminology Du Toit's term "Primitive Systems" is now etymologically unsound; while the terms Early and Late Precambrian lack definition. The validity of Logan and Hunt's early two-fold subdivision of the Canadian Shield remains: a crystalline lower part, an essentially sedimentary group above, the two being separated by a profound unconformity.
It is suggested that these be referred to as Basement Complex, and Supracrustal or some similar term; these terms to be applied irrespective of age. No international time boundaries have as yet been established in the Precambrian. The erection of worldwide systems is not anticipated in the near future. The recognition of orogenic sequences, where they are developed, or of even broader sequences of events, currently holds greater promise as a means of subdividing the Precambrian.
The growth of internationally recommended stratigraphic nomenclature, culminating in publications of the International Subcommittee for Stratigraphic Terminology at the International Geological Congresses in Copenhagen and New Delhi, is outlined. A fundamental tenet of this involves recognition of a distinction between lithostratigraphic units (Group, Formation, Member, etc.) and chronostratigraphic (System, Series, etc.) units. Disagreement with these recommendations, from South Africa and also from Russia, centres on non-recognition of this distinction. Stratigraphic nomenclature as used in South Africa is critically examined. Basically it is that proposed to the Second International Geological Congress at Bologna in 1881. In South Africa stratigraphic terms lack precise definition and there are cases of inaccurate usage. Additions exist to the supposedly simple dual classification adopted. There are examples where little attention has been paid to stratigraphic principles. Against this background South African stratigraphic nomenclature is re-expressed in accordance with the recent proposals of the International Subcommission on Stratigraphic Terminology. Stratigraphic subdivisions in this country are based largely on lithological characters, in combination with unconformities, and are treated accordingly. To date the ISST recognises only those Phanerozoic units corresponding with the time periods as systems and thus at the outset the only systems that would be acceptable in South Africa are the Cretaceous, Tertiary and Quaternary units which are often not regarded as systems in this country.
The establishment of provisional independent standard sections in the Phanerozoic in regions distinct from Europe is not formally disallowed: on these grounds the Cape and the Karoo, the deposition of which can be defined within reasonable time limits, merit retention as local systems. In the Precambrian no clear mandate exists either for the use or the rejection of local systems. The time-scale remains qualitative: nowhere in the Precambrian, it is believed, is the clarity of the succession Witwatersrand-Ventersdorp-Transvaal exceeded, nor are there significant time breaks between these units, and they too are retained as local systems. The retention of systems is, however, out of place where a clear succession has not been established in supracrustal rocks, or where sediments are dated with reference to the age of granitic rocks.

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Proceedings of the Geological Society of South Africa, 70, lxxi-lxxv

Biographical memoir. List of publications by B. Lightfoot.

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Transactions of the Geological Society of South Africa, 71(1), 1-65, 11 pl.

In section A a short description is given of the minerals encountered in 129 polished sections of conglomerate from the Dominion Reefs Mine. These include:
(a) The radio-active minerals: Thorian uraninite, thorite, monazite, betafite, euxenite, leucoxene and zircon;
(b) The oxide minerals: Cassiterite, chromite, columbite and ilmenite.
(c) The sulphides: Pyrite, marcasite, galena, chalcopyrite, covellite, sphalerite, cobaltite, linnaeite and arsenopyrite;
(d) Gold and some silicate minerals.
In section B a study is made of the literature on various methods used for roundness, form and size studies, and a method is proposed which is suitable for a quantitative study of these properties in polished sections. The results obtained when this method was applied to samples from the Dominion Reefs Mine indicate that the roundness of uraninite is in accordance with that of monazite and zircon. Uraninite in this conglomerate can therefore best be regarded as a detrital mineral concentrated together with other heavy minerals by sedimentary processes. However, some detrital minerals, such as cassiterite and garnet, have such small mean roundness values that they could not have shared the sedimentary history of the other detrital minerals. They were probably introduced into the sediments during another cycle of sedimentation. The same conclusions are borne out by the size distribution data. It is considered that a period of hydrothermal activity and an increase of temperature caused sulphidization and metamorphism of some minerals, the limited redistribution of gold, and corrosion and alteration of many detrital mineral grains.

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Transactions of the Geological Society of South Africa, 71(1), 101-118, 2 pl., map

The lithology and stratigraphy of the Red Beds Stage of the Stormberg Series, Karoo System, as exposed near Elliot, C.P., are described in detail. As gritty beds are found in the Red Beds Stage and red mudstone in the underlying Molteno Stage, it is concluded that it is impracticable to use colour and texture in distinguishing between these two stages. The contact with the overlying Cave Sandstone is also not sharp. The process of sedimentation was therefore continuous, resulting in a gradual passage from the one stage into the other. Palaeocurrent directions in the sandstones of the Red Beds indicate that the sedimentary material was derived from two different, though very similar source-areas, one situated to the north and the other to the south. It is clear also that the Molteno and Red Beds Stages cannot be separated on palaeo-current evidence. The sedimentary structures present within the Red Beds suggest that deposition took place in shallow-water conditions typical of alluvial flats in a continental environment. The red pigment is hematite and was derived either from red soils or from pre-existing red beds. The climate was probably warm and humid, with seasonal rainfall, although the upper part of the Red Beds represents a deposit of an arid basin.

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Transactions of the Geological Society of South Africa, 71 Annex., 103-111

The general aspects of the relationship between geology and underground water storage are discussed. Conditions and the probability of locating subsurface reservoirs in the various groups and formations of the Basement Complex of Rhodesia are described. A conclusion is drawn that greenstones and phyllites of the Bulawayan Group and the paragneisses of the Karoi-Miami Area are the most favourable formations for underground water storage whereas the granites and metasediments are the least favourable. Furthermore as the country becomes urbanized and industrialized it is virtually certain that, in spite of conservation, ground-water potential is bound to deteriorate.

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Transactions of the Geological Society of South Africa, 71 Annex, 113-122

The re-mapping of the Que Que Gold Belt, first mapped from 1926 to 1931 has been undertaken and a revision of the original stratigraphic column is postulated. The oldest system, the Sebakwian, is now thought to be represented only by small ultramafic and sedimentary inclusions in the Rhodesdale Gneiss; the majority is thought to be a narrow ultramafic intrusion of post-Bulawayan age, emplaced along the edge of the Gold Belt. An abundance of fresh pyroxene in the lavas of part of what is thought to be the Bulawayan Group suggested a post-Bulawayan age, but evidence seems to indicate that the lavas, named the Maliami River Formation, are less metamorphosed Bulawayan, related to the more normal greenstones. Together with the exposures near Gatooma, they are thought to be the only unaltered lavas of the Bulawayan Group so far recognized in Rhodesia. The conglomerate, assumed by Macgregor to be the base of the Bulawayan Group, is thought to be merely a minor unconformity in the Lower Bulawayan lavas.

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Transactions of the Geological Society of South Africa, 71(1), 119-120

Ball-and-pillow structures and convolute laminations are described from the basal beds of the Table Mountain Series of the type area.

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Transactions of the Geological Society of South Africa, 71(1), 121-126

Fine-grained calcareous hornfelses, derived by low-grade thermal metamorphism of calcilutites, were found to be abnormally high in alkalis, particularly potash which is carried in microcline. The rocks also contain quartz, calcite and various calcium alumino silicates. The feldspar is regarded as being of authigenic origin as no metasomatic source presents itself. The Inyanga calcilutites are believed by the author to be the oldest high-potash, feldspathic sedimentary rocks yet discovered.

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Transactions of the Geological Society of South Africa, 71 Annex, 125-133

The schist belt rocks of the Rhodesian Basement Complex, in the West Nicholson- Beit Bridge District, and their contiguous metamorphosed granulite equivalents are described. It appears that there is no structural or metamorphic discontinuity between the adjacent facies in the area examined. A pre-Great Dyke age for the granulite metamorphism is postulated.

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Proceedings of the Geological Society of South Africa, 71, xiii-xx

A brief summary of the history of uranium, its discovery, development and uses. The three major uranium producers in the Western World are Canada, the United States of America and South Africa. Figures showing production from various formations are given in tabular form.

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Proceedings of the Geological Society of South Africa, 71, xliv-xlv

The writer makes the suggestion that the comparatively simple operation of the determination of the cube-edge of uraninites or thorianites by X-ray powder technique can often be used for evaluating the relative ages of these minerals. The basis for this method rests on the assumption - on the certainty, in the mind of the writer - that the radiogenic lead resulting from the decay of uranium and thorium, is accommodated in the parent element's crystal lattice position. As the lead ion (Pb(+4) = 0.84 Å) is very much smaller than U(+4) (1.05 Å) and Th(+4) (1.10 Å), a shrinkage in the unit cell's size results with the passage of time. This shrinkage is measurable, and believed to be of the order 0.00X Å per 100 million years - with X probably a small integer. The shrinkage is also variable depending directly on the proportion of the two parent elements present.

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Transactions of the Geological Society of South Africa, 71(2), 132-134

Subsurface erosion occurs in all provinces of South Africa. In parts of Natal subsurface erosion appears to be responsible for producing landscape features of unusual form without the necessity of land movement. On steep hillslopes, valleys already in existence are extended and also some entirely new, somewhat funnel-shaped, valleys are formed. The extension and formation of these valleys is evidently as a result of the collapse of subsurface erosion-produced tunnels, the appearance of sinkholes and dongas, and sloping off of the donga banks. In bottom lands (vleis) occupied by river flood-plains, cone-shaped mounds of soil are produced by subsurface erosion. Coalescence and superposition of many cone mounds aggrades the flood-plains in certain parts and it seems that river courses are forced, at present, to run in positions away from the aggraded parts. The mechanism of subsurface erosion depends mainly on the conditions of climate, soil, bedrock, and possibly vegetation cover.

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Transactions of the Geological Society of South Africa, 71(2), 135-145

Outliers of Tertiary sediments resting on Upper Cretaceous strata have been preserved along the Umfolosi River banks at Umkwelane Hill and The jungle, Peaston, Uloa, Lot U 178, Warner's Drain and farther eastward to within a couple of miles of the present coastline. At Uloa there is evidence for an Eocene formation that was destroyed before or by a Miocene transgression, and from this locality to the east a thin Middle or Upper Miocene coarse coquina ("Pecten Bed") rests unconformably on the marine-trimmed Senonian. A succession of thinly bedded calcarenites and limestones overlies the "Pecten Bed" conformably, as at Sapolwana and Wamer's Drain, or locally unconformably (disconformably), as at Uloa. A line of scattered boulders occurs between the "Pecten Bed" and the overlying strata at Uloa. Calcarenites, limestones, some dune rock, with basal conglomerate, make up the most westerly outlier at The jungle and Umkwelane Hill. Detailed study of Foraminifera (especially the few planktonic forms) and the metazoan fossils has shown that the containing sediments are all within a restricted age range, from Middle Miocene for a "gravel" layer below the "Pecten Bed", to late Miocene and perhaps including earliest Pliocene, for the calcarenites. The palaeontological datings now available accord more satisfactorily with correlation of the strata based on lithology and dip measurements. The geological history since late Cretaceous times that may be read from these flatlying sediments is one of minor eustatic changes, with limited epeirogenic movement and no marked upwarping in this part of coastal Zululand.

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Transactions of the Geological Society of South Africa, 71 Annex., 135-146

The Indarama Mine provides an interesting structural control of mineralization in the Basement Schists. The orebodies occupy a complex fracture-system, resulting from two episodes of folding which deform Bulawayan greenstones. The effects of this deformation are apparent locally and regionally. Serpentinized ultrabasic rocks, formerly correlated with the Sebakwian System have here been found intruded into the Bulawayan System. The mineralization is of two main generations; earlier gold-arsenic and later gold-antimony. Associated with the latter are the rare minerals berthierite, here the chief gold carrier, and aurostibnite. A final phase of the mineralization is represented by stibnite, here not normally gold-bearing.

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Transactions of the Geological Society of South Africa, 71(2), 147-152

Clinoptilolite occurs in extremely fine-grained, soft, old pan sediments exposed in the banks of the Nata River and associated with layers and nodules of hard, white, crustiform silcrete. The environment which is highly saline and alkaline, is such as may be expected for the formation of clinoptilolite, though volcanic ash, from which clinoptilolite is normally considered to be derived, is apparently not present. X-ray diffraction patterns of different fractions indicate that the grain size is between one and five microns.

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Transactions of the Geological Society of South Africa, 71 Annex., 147-158

The observed relationship between economic concentrations of gold in a hydrothermal quartz vein occupying a fissure in Archaean pillow-lava and physical variations in the host-rock resulting from intrusion, fracturing and folding is described.

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Transactions of the Geological Society of South Africa, 71(2), 153-172

The Rooiberg felsite has a considerable development (probably a maximum) in this area. It attains a thickness of 10,180 ft and is subdivided into three zones:
(i) a Lower Felsite Zone which consists of micrographic felsite and leptite,
(ii) a Middle Felsite Zone, consisting mainly of black, amygdaloidal and pseudospherulitic felsite,
(iii) an Upper Felsite Zone which is composed of red, glassy and porphyritic felsite.
The roof-rocks of the layered sequence have a minimum thickness of 14,680 ft and consist of felsite and granophyre. Three different types of granophyre seem to be present in the Bushveld Complex. One type, the so-called "Rooiberg granophyre", is found as large sheet-like bodies at the base of the Rooiberg felsite in the area investigated, and is considered to have originated by melting of the felsite during emplacement of the gabbroic rocks. Another type is related to the Bushveld granite and a third type, termed "Stavoren granophyre", is not present in the area investigated, but has been described by other workers as having originated by metasomatism of quartzofeldspathic sediments.
Four new chemical analyses of felsite and related rocks are given. These, together with chemical data on Rooiberg felsite and Bushveld granite published previously are plotted on variation-diagrams. According to these diagrams the Rooiberg granophyre and the leptite are related to the Rooiberg felsite. The composition of the granophyre related to the Bushveld granite, varies considerably and could not be separated from the Rooiberg granophyre on the grounds of chemical composition. The Upper Zone of the layered sequence is developed only in the eastern part of the area and thins out gradually towards the west. This is explained as the result of a discordant relationship of the gabbroic rocks towards the roof. Outcrops are generally poor and rock types present are diorite and granodiorite. The granodiorite is not considered to be a product of magmatic differentiation, but rather to have formed by assimilation of felsitic rocks.

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Transactions of the Geological Society of South Africa, 71 Annex., 159-174

The Barton Farm Magnesite Mine is one of two in Rhodesia producing magnesite for refractory purposes. The deposit which lies about 6 miles S.S.E. of Gatooma in dolomitic argillites and arkoses of the Barton Farm Formation of the Shamvaian Group is described. Insufficient evidence is available to determine the origin of the deposit. It appears to be either a primary sediment, or a replacement body.

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Transactions of the Geological Society of South Africa, 71(3), 174-200

A petrofabric analysis was made of the Magaliesberg quartzite. One sample of Daspoort quartzite was included for comparison. The results show no preferred orientation of the quartz grains although it seems that the c-axis does occur in the zone between 30° and 60° from the petrofabric c-axis and in the horizontal direction of 120 degrees which coincides well with the source-direction of the sediments as deduced from the strike of the ripple-marks in the quartzite. The rounding of quartz is discussed and it would appear that the cleavage tendency of quartz parallel to the rombohedron and the hardness of the face (1010) are the determining factors of the ellipsoidal shape of the quartz grains. Because no agreement exists as far as the hardness of quartz is concerned with respect to different directions on different crystal faces, scratch hardness tests were executed with the Leitz "Miniload" hardness tester and the "Talysurf". Conflicting results were obtained and this method is not recommended for the determination of the hardness of minerals. By means of the grinding method it was found that the face (1010) has the greatest hardness in the direction of the crystallographic c-axis. A grinding hardness unit is proposed to denote the hardness of minerals in different directions on different crystal faces. The conclusion was reached that there exists no preferred orientation in the quartz grains of the Magaliesberg quartzite. The reason is evidently that the cleavage tendency quartz and the hardness of the face (1010) tend to counteract each other mutually with the result that the ellipsoidal shape of the grains possesses a rather arbitrary crystallographic orientation.

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Transactions of the Geological Society of South Africa, 71 Annex., 175-188

The Mashaba Igneous Complex is a layered predominantly ultramafic intrusion of ancient Precambrian age. It consists of a sheeted portion and a dyke portion presumed to be the feeder of the main part of the intrusion. The ring form of the dyke appears to be unique in ultramafic rocks. The Complex is briefly described together with its subsequent deformation. This is held to be due to the emplacement of the Younger Granite of the area and has resulted in the formation of important deposits of chrysotile asbestos.

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Transactions of the Geological Society of South Africa, 71 Annex., 189-194

The lithology and stratigraphy of the various Precambrian rock units in the area around Shabani are described together with their mutual structural relationships. A table is presented showing the lithological units in the Shabani area.

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Transactions of the Geological Society of South Africa, 71 Annex., 195-204

Chrysotile asbestos is a widespread mineral found in the majority of the Rhodesian ultrabasic bodies. Economic deposits are found in those areas where all the controlling factors of suitable host-rock, the presence of solutions and structural control have been satisfied. The tendency has been to assume a universal growth mechanism but field evidence indicates that fibre occurs as stress-controlled dilation-seams, as a recrystallization product of serpentine minerals and as a result of serpentinization of olivine. The Shabani orebodies are located in a partially serpentinized dunite with localized structural control a noticeable feature. The Sheffield Claims deposit is a classic example of the recrystallization of picrolite to chrysotile fibre. The Gaths deposit differs from Shabani in that the structural control is more regional. King Mine is an example of fibre formation in a serpentinite with a typical structural pattern.

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Transactions of the Geological Society of South Africa, 71(3), 203-208

Previous workers have indicated that the chromitite seams constituting the Main Chromite Subzone extend in a southerly direction to the farm De Kafferskraal 53 J T where the Subzone is then terminated against quartzite of the Pretoria Series. Mapping the seams of the Subzone on the farm Mareesburg 8 JT, north of De Kafferskraal, disclosed that the seams are terminated on Mareesburg either by faulting or down-warping of the rocks on the margin of the Complex. Neither the seams belonging to the Main Chromite Subzone nor the associated pyroxenite crop out on the south-eastern portion of the farm. Anorthositic rocks were traced eastwards to the contact with the Pretoria quartzite. Only the chromite seams that normally occur several hundred feet above the Subzone, within the anorthosite, crop out in this area.

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Transactions of the Geological Society of South Africa, 71 Annex., 205-213

The science of stratigraphy originated in Europe and North America and was concerned with the chronological classification of strata with reference to their fossil content. Stratigraphy has been forced to broaden its basis partly owing to the demands put upon it by other branches of geology, notably the petroleum geologists, and partly by the need to interpret successions in Precambrian rocks which are devoid of diagnostic fossils. Stratigraphic interpretation in Precambrian rocks is further complicated by the vast amount of diastrophism that most of them have undergone. Thus no relative age relationships can be established by the conventional means of superposition and fossil content. The determination of radioactive ages and palaeomagnetic pole positions are two means by which it is possible to establish age relationships in Precambrian rocks. The proper interpretation of these is, however, dependent upon a thorough knowledge of the rocks concerned and involves an understanding of their origin, composition, metamorphism, deformation history and other factors. Thus if stratigraphy is to be apliable to the Precambrian it must further broaden its scope to include all these factors. The objective of stratigraphy should remain the same throughout the geological column; it is the methods of achieving this objective that must change, adapting themselves to varying circumstances.
Three types of stratigraphic terminology are gaining acceptance today; lithostratigraphic involving mappable rock units, chronostratigraphic involving rocks deposited within a specific interval of geological time, and biostratigraphic involving rock units characterized by their fossil assemblages.
It has been found that the mapping and understanding of the Deweras and the Lomagundi rocks in the NW of Rhodesia has been facilitated by the use of the lithostratigraphic terminology in place of the rather hybrid, but basically chronostratigraphic, terminology used hitherto. This is because recognisable rock units have been used as a basis of subdivision, without yet worrying whether or not they have been arranged in strictly chronological succession. It is suggested that the lithostratigraphic terminology should be adopted for naming rock units throughout the Precambrian of Rhodesia.

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Transactions of the Geological Society of South Africa, 71(3), 209-233

The structural features of the composite, planed surface at the base of marine Cainozoic strata, mainly belonging to the Alexandria Formation, and the morphological features of their terraced upper surface are described. These and certain stratigraphic features of the same strata are interpreted with the help of longitudinal profiles of former valley-floor plains of the Sundays valley that were developed in the course of intermittent withdrawal of the sea. It is concluded that probably three major transgressions and regressions occurred during the Cainozoic in this region, one early in Tertiary time, one later in the Tertiary, some time in the Mio-Pliocene, and another that was initiated probably late in the Pliocene and followed by a Plio-Pleistocene regression. Intermittent changes in sea-level and diastrophism in the later history of the region are treated in some detail. Downstream convergences of former valley-floor plains, confined to that part of the region within about 20 miles of the present shore indicate that three episodes of seaward tilting and warping occurred during the late-Cainozoic. The tilting caused a total, maximum steepening of gradients of the order of 33 feet per mile and at least the last of the episodes of tilting was probably accompanied by regional upward movement of about 100 feet. As tilting and warping were restricted to only three of the many occasions when rejuvenation occurred the majority of rejuvenations may have been eustatic in origin. The total amount of eustatic drop in sea-level may have exceeded 350 feet and of this at least 275 feet took place in the Quaternary period. Significant standstills of sea-level occurred at 20, 60, between 80 and 100, 170 and 190 feet above present sea-level and, in the interval between the penultimate and final episodes of tilting, at less precisely determinable altitudes which, after correction for tilting and uplift, are estimated to have been at 210, 275, 300 or lower and 350 feet above present sea-level. From the occurrence of water-worn artifacts in contemporaneous river-gravels it is inferred that at least those beach deposits currently assigned to the Alexandria Formation that were laid down when and since the sea stood 275 feet above its present level are Quaternary in age. It is suggested that a large body of late- Cainozoic silts lying upon the Alexandria Formation in the seaward parts of the Sundays valley is partly marine and deltaic in deposition.

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Transactions of the Geological Society of South Africa, 71(1), 21-32

Geochemical maps are presented to illustrate the regional distribution of certain major elements and their ratios in areas of granite, greenstone and serpentine and related rocks. The analytical data was compiled from the records of the Rhodesia Geological Survey, and was used in preference to any other data available due to the high standard of analytical reliability. Eighty-eight samples of granite are represented, fifty-seven samples of greenstone and thirty-seven samples of serpentine and related rocks. Analytical data for the arenaceous and argillaceous rocks of the Basement Complex were not compiled, due to the paucity of the data. In relation to the geological complexity and size of the Basement Complex the analytical data provides a scanty and incomplete cover and for this reason the interpretation of the patterns is limited to those which are believed to be significant on a regional scale. The geochemical patterns for the granite reflect the presence of two belts which are potassium-rich and these border the northern and southern margins of the craton. This distribution is interpreted as evidence of geochemical fractionation in the granite magma resulting in the concentration of potassium in the upper levels of the craton which, owing to erosion, is now exposed mainly at the shoulders. The geochemical patterns for the greenstone and serpentine and related rocks reveal regional, and some local difference in the concentrations of certain of the major elements and their ratios. The geochemical abundances of the chemical elements in granite and basalt of the earth's crust are compared with the averages of the Rhodesian rocks. The Rhodesian rocks are remarkably similar to the crustal average, except that the granite is relatively poor in potassium and to a small extent in iron and magnesium, whereas calcium is slightly higher than the average. In relation to mineral deposits the geochemical pattern for potassium in granite appears to be significant. The important mineralized pegmatites at Miami and Bikiti are associated with potassium-rich granites on the northern and southern margins of the craton respectively, and there is evidence of a similar association at Kamativi. Other pegmatite belts are well known but the granite in their vicinities is not sampled. The geochemical patterns for the greenstone and serpentine and related rocks are of little significance in relation to mineral deposits due mainly to the lack of data. It is believed, however, that certain types of ore deposits which occur in these rocks are related to recognizable features of primary geochemical dispersion and that these features could be revealed by studies in the regional geochemistry of the minor elements. It is concluded that the study reveals geochemical features on a regional scale which are of fundamental significance to the geology of the Rhodesian Basement Complex, and also are of economic interest. The patterns illustrate a large area for which there is no analytical data, and the results of the study generally indicate the wide field of research which exists in the regional geochemistry of the Basement Complex.

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Transactions of the Geological Society of South Africa, 71 Annex., 215-224

Considerable discussion is taking place at present regarding stratigraphic nomenclature generally, and numerous reports and papers have been published. A fair measure of agreement on principles has been achieved between most countries. Disagreement centres mainly on the scope of stratigraphy and the number of sets of stratigraphic units necessary. A simplified definition of stratigraphy is suggested, and the case for two sets of units, chronostratigraphic and lithostratigraphic, is reviewed. It is concluded that only the largest-scale chronostratigraphic units can be recognized in the Precambrian, and that therefore we should use only the lithostratigraphic terms with the possible use, in addition, of the "System".

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Transactions of the Geological Society of South Africa, 71 Annex., 225-254

The Barberton Mountain Land forms one of the best developed and best preserved remnants of Archaean strata in South Africa. The volcanics and sediments are similar to those associated with geosynclines and island arcs. The Onverwacht Series of the Swaziland System, consists mainly of basaltic and ultrabasic rocks together with siliceous sediments and constitutes the initial magmatic or ophiolite assemblage of the Swaziland geosyncline. The Fig Tree Series, composed primarily of greywackes, shales, banded cherts and banded ironstones, displays characteristics of a flysch assemblage of rocks while finally, the overlying Moodies Series, made up of conglomerates, quartzites, shales and jaspilites, displays the characteristics of a molasse assemblage of a geosyncline. The entire area is surrounded and swamped by granites and gneisses, thereby making it impossible to identify the miogeosynclinal and the cratonic areas associated with the Barberton Mountain Land remnant. Furthermore, the granites are not typical of normal geosynclinal areas and constitute an anomalous event, probably much later than the orogenic episode. Evidence is presented that the Onverwacht and Fig Tree Series of rocks were deposited in a deep trough (pillow lavas, turbidites). A brief account of the structural history of the area is given, and some notes on the mineralization are included. A model is suggested for the major evolutionary events in the development of the Barberton Mountain Land. The first event was the geosynclinal cycle, while the granites make up the second event. It is suggested that the Barberton Mountain Land represents a fold belt in which the geosynclinal and granite cycles are well-displayed, and, as a result, may assist in a better understanding of the evolution and development of other, less well-developed schist belt remnants in Archaean granite terrains of continental shield areas.

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Transactions of the Geological Society of South Africa, 71(3), 235-256

A stratigraphic study of the Kimberley Shales in the Upper Division of the Witwatersrand System has shown a remarkable lateral persistence of marker beds. Lithological changes can be correlated with chemical composition. Eight new chemical analyses of the Kimberley Shales are given. A number of sedimentary structures can be seen in the shales, notably widespread penecontemporaneous deformation. In some localities slumped structures are spectacular. Current structures in the form of grooves, striations and spatulate impressions, occur on the top contact of the shales, and are preserved as casts on the underside of the overlying bed. The current structures are aligned east-northeast to west-southwest, and their shape indicates that initially the current flowed from east-northeast to west-southwest but that the direction was reversed at a later stage. Current ripple marks and oscillation ripple marks are both orientated at right angles to the current direction. Stoping and assimilation of sediment by a diabase sill which intrudes the shales, is described. Certain aspects of the development of the Evander basin are discussed.

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Transactions of the Geological Society of South Africa, 71 Annex., 255-270

The Swaziland System is typical of the ancient greenstone belts of the world. Basal parts of these belts (Onverwacht type) are strikingly like emergent island arcs, and must have evolved upon a thin, unstable crust. In contrast, the succeeding parts of most greenstone belts (Fig Tree and Moodies types) have been derived from, and deposited upon, a progressively more stable, thickening, granitic crust. Moreover, at present, the greenstone-granite terrains of the Barberton type form the thickest, coolest, and most stable shield areas of the world. The enveloping granites exceed the greenstones in volume by an order of magnitude. Some are over 3,000 million years old, and most surficial granite exceeds 2,500 million years in age. Granite must have been added to the green stone-granite terrains during both orogenic and anorogenic periods. Much of it has apparently been passively accreted from below. The basalts and peridotites of the Onverwacht type are depleted in the radiogenic nucleides K, U, and Th. Lavas of this composition have been erupted from the mantle in island-arc environments for over 3,000 million years. They may represent the only primary mafic magma-types. Their constancy in composition throughout decipherable geologic time suggests that their source in the upper mantle also has been of uniform composition. This indicates that the first-order differentiation of the upper mantle and protocore preceded the emplacement of the Onverwacht lavas. The small amounts of K, U, and Th in them indicate that similar, localized source-regions of the mantle cannot have been the source of the associated granites. The origin of the widespread granite appears to be the result of large-scale melting in the mantle prior to, and during, Onverwacht times.

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Transactions of the Geological Society of South Africa, 71(3), 257-271

An account is given of the geological environs of the western boundary of the Early Precambrian Pongola System, within that part of the type-area which extends across the Natal-Transvaal border, for a strike-distance of about 25 miles, to the north-east of Paulpietersburg. Critical exposures along this boundary have indicated that the lower division (Insuzi Formation) of the Pongola System rests with graded unconformity on a granitoid foundation. No evidence was found to support the suggestion by previous workers that the Pongola System has been intruded by granite in this region. Field, microscopic, and X-ray data on the graded unconformity are presented. These data show that granitic rocks pass gradationally upwards into a zone of structureless, gritty, argillaceous rock consisting essentially of quartz, sericite and vermiculite, and ranging from a few to 25 feet in thickness. This zone is regarded as a palaeoregolith. It is overlain by stratified Insuzi sediments, generally feldspathic but showing considerable lateral variation, including lenticular developments of arkosic breccia, probably channel deposits. The outcrop of the unconformity is discontinuous and of limited extent as a result of preferential intrusion at this level of basic and granophyric rocks. Recognition of these relationships within the type-area, provides an explanation for certain regional relationships known to exist in an extensive area to the north, and also strengthens previous correlations with the Pongola System, in both the northern area and in an isolated area of pre-Karroo strata some 50 miles to the south. These regional considerations indicate the existence of an extensive Early Precambrian, Pre-Pongola, granitic basement.

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Transactions of the Geological Society of South Africa, 71(3), 273-290

Sixty samples of visible gold from the Barberton district were analyzed for their silver, copper and iron concentrations using atomic absorption and fire-assay techniques. In addition, the qualitative trace-element compositions were determined spectrographically. On the basis of theoretical metallurgical evidence and known associated minerals, it is suggested that silver, the platinum metals, tin, mercury, molybdenum, cobalt, bismuth, manganese and vanadium are present as alloy constituents in solid solution with the gold. Antimony, copper, iron, lead, nickel, titanium and zinc may be present either as constituents in solid solution or non-metallic inclusions. Aluminium, magnesium, calcium and silicon are most likely due to inclusions of gangue minerals.
The mode of occurrence of beryllium, which was detected in two samples, is not known. Twenty of the samples had been collected from different levels along the Zwartkoppie shoot, Sheba Mine, over a distance of 1,270 feet. The results showed that the composition varied systematically with depth though there was a sharp break in the curves relating concentration and depth in the vicinity of the 20 level. Above this level the copper and iron contents decreased with increasing depth while the fineness increased. Below this level the fineness continued to increase and the iron content to decrease with increasing depth though the copper increased. This anomalous rise in copper content in the lower levels can be correlated with an increase in chalcopyrite in the samples. The discontinuities in the depth-concentration curves coincide with a change in the structural disposition of the shoot and may indicate a break in the original ore-shoot.
The remaining forty samples were collected from localities throughout the Barberton Mountain Land to indicate any areal changes in composition. A regional plot of the fineness values revealed the outline of a possible pattern with values decreasing in all directions from high points around the Agnes, Sheba and Consort Mines, suggesting that perhaps the source of the auriferous fluids lies beneath these areas. There are no apparent systematic changes in the copper and iron contents of these samples and, similarly, the trace-elements show no overall variation. However, elements from the same or from adjacent groups in the Periodic Table do tend to occur together. The results suggest that temperature and pressure conditions (both regional and local) and the chemical environment into which the ore fluids intrude affect the composition of gold. Major constituents such as silver and, perhaps, copper and iron, depend on the former conditions and the minor constituents on the latter. The compositions of three gold samples from Rhodesia and three from the Witwatersrand are given in an appendix.

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Transactions of the Geological Society of South Africa, 71(3), 291-311

The kimberlite in sills in Southern and East Africa usually resembles that found in pipes and dykes, but two sills of magmatic, non-brecciated kimberlite are described. It is concluded that the kimberlite sills were intruded more or less contemporaneously with neighbouring pipes and dykes, and that the factors which control the intrusion of other types of sills apply also in the case of kimberlite sills. Differences in magma viscosity are considered to be the cause of variations in the extent and shape of sills intruded under uniform geological conditions. Some sills are diamondiferous, but none have been found that are of economic importance.

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Transactions of the Geological Society of South Africa, 71 Annex, p. 33

In a paper published in "Some Ore Deposits in Southern Africa" (1964), the writer gave examples of the relationship between the gold deposits and their local structure in Rhodesia. This indicated that they were found under idealized physicochemical conditions following faulting, folding and shearing. The ore bodies were gold-bearing quartz veins in fissures, gold-bearing quartz and sulphide mineral replacements of wall rock in shear zones and silicification accompanied by gold-bearing sulphide mineral impregnations of banded ironstones. The attitude and position of both the bodies and shoots within the bodies were primarily controlled by the structures produced during regional deformation as a result of compressive forces acting on a northerly-trending axis. Further consideration emphasizes that the influence of structure on the localization of economic gold mineralization is the most important factor controlling individual, Rhodesian-type gold deposits. An analysis of a large number of fracture planes was made by plotting the poles on an equal area stereographic projection. This indicated broad, highly generalized stress directions which resulted from the action of a compressive force acting in a northerly-trending axis. The gold mineralization ranges in age from Pre-Bulawayan to Post-Shamvaian and was distributed in patterns corresponding to antecedent, contemporary and recurrent structures. This view contrasts with the longheld belief which associates the ore bodies with the contraction of the intrusive granitic masses.

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Transactions of the Geological Society of South Africa, 71 Annex., 35-45

Attempts have been made to distinguish the underlying regional element in the distribution pattern of exploited gold deposits in the rocks of the Rhodesian basement. Up to eight-order polynomial trend surfaces have been employed to study the areal variations in five production variables. Two principal trends appear to influence the patterns of gold mineralization, one between north- north-west and northwest, and the other between east-northeast and northeast. The regional distribution of gold deposits in Rhodesia can, therefore, be studied by reference to the geometry of interference patterns produced by the super-imposition of two surfaces. Two broad areas are characterized by the optimum regional developments of trends of tonnage of mineralized rock, ounces of gold emplaced, and grade of ore. The distribution pattern of gold mineralization in Rhodesia appears to be the mirror-image of that in the Kaapvaal crustal fragment to the south.

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Transactions of the Geological Society of South Africa, 71 Annex., 47-51

The so-called Basement Complex rocks of Rhodesia can be shown to comprise a number of discernible units and to have been involved in at least four distinct orogenic episodes. The major structural units are shown on a map. It is proposed that the use of the term "Basement Complex" be discontinued and in future the specific units be referred to by name.

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Transactions of the Geological Society of South Africa, 71 Annex., 53-78

The area described is situated near the centre of the Rhodesian craton and was relatively stable during the younger episode of folding and granite intrusion that affected the Basement Complex. It lies between the Chilimanzi and Insiza domes and it was possible to recognize older, pre-dome structures here. Detailed mapping has shown narrow fold belts, each of a different age and trend. The Selukwe Schist Belt was found to be the inverted limb of a nappe structure, thrust over a micro-cratonic basement of gneiss that was later reactivated. There is evidence that the fold belts may have been the sites of small eugeosynclines, so that a lithological correlation between them is not reliable. Differences of tectonic style between the fold belts show that there was an apparently progressive thickening of the competent superstructure. The large gregarious batholiths were mantled gneissic domes that represent a second phase in the development of the shield.

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Transactions of the Geological Society of South Africa, 71(1), 67-100, 1 pl.

Spectrographic techniques are described for the determination of the following elements present in the uraniferous conglomerate from the Dominion Reefs Mine: Ti, Zr, Cr, Fe, Pb, As, Sn, Cu, Ag, Zn, Nd, Pr, Ce, La, Y, Nb, Mo, Co and Ni. From the quantitative data obtained correlation coefficients were calculated for 101 pairs of elements, and high degrees of correlation were found between elements present in detrital minerals and uranium. A relatively low degree of correlation exists between gold and uranium. It is considered that sedimentary concentration of heavy minerals and the subsequent limited redistribution of gold provides the most satisfactory explanation for the geochemical pattern of element distribution that was found.

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Transactions of the Geological Society of South Africa, 71 Annex., 79-88

This paper deals with the end-products of metamorphism of Bulawayan greenstones, a metanorite and certain Shamvaian calc-silicate rocks along the Zambezi Metamorphic Zone north of Sipolilo. An outline of the geology is given so that the setting can be visualized. Their very complex tectonic history is only dealt with in the broadest terms, the imprint of two major events, widely separated in time is clearly discernible. The Great Dyke which intervenes in time, helps in the dating of one of the events.

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Transactions of the Geological Society of South Africa, 71 Annex., 89-90

The rocks belonging to the Basement Schists in the vicinity of Gatooma consist of representatives of the Sebakwian, Bulawayan and Shamvaian Groups. The Sebakwian is only poorly represented by ultramafic rocks and some sediments. The Bulawayan Group has been divided into two formations. The lower, or Mafic Formation, consists mainly of mafic lavas (greenstones), but includes some metamorphosed, mafic, contemporaneous, intrusives while the upper, or Felsic Formation, consists of mafic lavas and sundry quartz-mica schists which include rhyolitic rocks, sediments derived from these by contemporaneous erosion, and rocks of an indeterminate origin. The Shamvaian Group consists of an upper Pebbly Quartzite Formation and a lower Barton Farm Formation. The former consists of quartzites and poorly developed conglomerates, and the latter of coarse- to fine-grained clastic sediments, dolomitic rocks and an associated magnesite deposit. The clastic sediments were derived from fresh volcanic material. The name Umniati Group has been provisionally given to the suite of volcanic rocks which lies beneath the Proterozoic to the west of Gatooma and which hitherto has been regarded as part of the Bulawayan Group. The suite consists of acid to intermediate lavas, agglomerates and tuffs, together with some minor coarse-grained rocks that are probably contemporaneous intrusives. They are remarkably fresh, both mineralogically and texturally; unaltered pyroxene occurs in some types. This is in marked distinction to the Bulawayan Group volcanics which are almost completely altered to a fine-grained aggregate of chlorite, epidote, leucoxene, minor plagioclase and quartz. The evidence available suggests that the Group is younger than the Shamvaian but older than the Deweras Group, which, with the Lomagundi Group, forms the Proterozoic rocks to the N.W. of Gatooma. The N.W. portion of the Rhodesdale Gneiss outcrops in the area. The Gneiss as a whole is an elongated body 75 miles from north to south and about 40 miles from east to west, consisting of intrusive granitic as well as gneissic phases.
Where the Shamvaian Group outcrops adjacent to the Gneiss the contact is faulted and the age-relationship evidence is not conclusive. Large fragments of the Bulawayan-type rocks outcrop around the margin of the Gneiss and could be remnants of a Bulawayan cover over a pre-existing gneiss dome which has subsequently been invaded by the rejuvenated portions of the Gneiss. Portions of two other granite intrusions occur in the area, the Biri and Whitewaters "granites", the latter being associated with the scheelite mineralization that occurs in the country west of Gatooma. The gold mineralization is confined almost entirely to the Bulawayan Group. The Shamvaian, Deweras and Lomagundi Groups are devoid of gold mines in this area and, as far as is known, also of gold mineralization. Gold mineralization does occur, however, in Shamvaian Group rocks to the east of the area and there are a few scattered gold mines in the Umniati Group. The mines within the Bulawayan Group fall into quite distinct groups which appear to be related to the various structural events. It is suggested that there were two major periods of gold mineralization, an older one consisting of gold, pyrite, arsenopyrite and pyrrhotite, and a younger one of gold, pyrite and galena. The first period resulted in a large number of arsenical shear-zone deposits whose emplacement is controlled by the structures resulting from the first recognized period of folding. The shears generally cut very slightly across the lithological boundaries in the Bulawayan Group with ore-shoots sometimes controlled by drag-folds on the limbs of the major folds. This period of mineralization is found at the Chakari, Last Chance, and Eiffel Flats groups of mines.
The second period of mineralization has resulted in quartz-filled dilation-veins which are non-arsenical. They have been controlled by a fracture pattern that has resulted from the intersection of a later period of folding, whose axis trends about S60E and plunges W.N.W., with the earliest recognized period of folding whose axis trends N.E. and plunges S.W. This period of mineralization is responsible for the deposits of the Golden Valley area and may have been superimposed on the first mineralization at the south end of the Chakari area, the north end of the Last Chance group, and at the Cam and Motormine. There is a distinct belt of mines around the margin of the Rhodesdale Gneiss which forms part of a band extending from the Great Dyke in the east to Que Que and beyond in the S.W. Within the area the mines lie almost entirely within the Gneiss, but farther to the N.E., Bulawayan Group rocks outcrop between the Gneiss and the Shamvaian rocks and contain numerous gold mines, whilst the Gneiss contains relatively few. The overall geological relations of the Gneiss suggests that whilst it was originally older than the Bulawayan, the margin was rejuvenated in post-Bulawayan times. The relation of this mineralization to either of the two mentioned above is uncertain but it might be of the same age as the second period of mineralization.

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Transactions of the Geological Society of South Africa, 71 Annex., 9-19

Data concerning gold production, between 1898 and 1932, from 120 of the more important mines in Rhodesia have been subjected to analyses of the general statistics of population frequency distributions. General predictors of the relative economic potential of any host-rock, associated sulphide, or linear structure have been shown by the analyses to be the number of mines containing the geological feature and the third and fourth moments of the frequency distribution of the average size of mines. Greenstones, and then schists, emerge from the analyses as the most important host-rocks for gold mineralization. Optimum conditions also appear to prevail where chalcopyrite, and then stibnite, are present in the ore, in addition to pyrite. There seems to be a preferential concentration of gold mineralization in orebodies which dip into the quadrant between north and east. The distribution patterns suggest that the gold was introduced into the Rhodesian Basement in the greenstones, and that the mineralization is not a direct hydrothermal product of the generation and emplacement of the granites.

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Transactions of the Geological Society of South Africa, 71 Annex., 91-103

The Mont d'Or sediments are structurally homogeneous arkose and greywacke in which six distinct sets of fissures were recognized. The oldest are group six, marked by saddle veins. Those of sets one to four were contemporaneous and are related to the last episode of E.N.E. folding. Set five is related to the younger Surprise Fault zone. There were three main stages of mineralization in the sets one to four fissures, each separated from the other by minor deformation stages. Early white quartz was followed by grey quartz, carbonate and pyrite, which were followed by two divergent types of mineralization, pyrrhotite/chalcopyrite, and galena/sphalerite in stage three. The mineralization is related to a molybdenite/pyrite/chalcopyrite source in soda- rich aplogranite plutons. The mineralization of set five veins is different, with cobalt and nickel arsenides present.

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Proceedings of the Geological Society of South Africa, 71, xcvii-cxi

One of the prime objectives of the Geological Society of South Africa is the advancement of knowledge in the Earth Sciences, and many past Presidential Addresses have reflected the main preoccupation of most South African geologists with problems of ore distribution and genesis and many other geological phenomena for which the sub-continent has become justly famous. I propose on this occasion to depart from tradition by reviewing briefly the recent and rapid advance of knowledge in the field of submarine geology which has contributed so greatly to the development of ideas concerning the evolution of the crustal rocks and structures as recorded in ancient terrains and reflected in the present surface features and behaviour of the Earth. Nearly three-quarters of the Earth's surface is covered by sea. Earth Science is therefore obviously incomplete and inconclusive without knowledge of submarine geology which can be quite simply defined as the study of the solid earth beneath the sea. The past two decades in particular have witnessed a spectacular increase in our knowledge and understanding of the geological structure and history of the sea floor. Much of the new data and concepts appear to have escaped the notice and attention of most professional geologists in spite of the fact that they have contributed so greatly to the development of an entirely new and promising approach to the problems of global tectonics.
If the present does indeed provide the key to the past we should all keep a critically watchful eye upon the current "revolution in earth science" (Wilson, 1968) in the expectation that we may profitably revise our ideas concerning the history of the continents. I have therefore, no doubt rashly, set myself the task on this occasion of attempting to distill from the voluminous literature a summary of the salient data and evolving concepts, with particular mention of problems of ocean floor geology in the South Atlantic and Indian Oceans adjacent to southern Africa. This necessarily brief review will have achieved its objective if it succeeds in stimulating a new approach to old problems and a desire in some to delve more deeply into the fascinating details published in the literature. Appended at the end is a separate bibliography listing some of the more important literature reviews and global or regional syntheses. In order to avoid the publication of a hopelessly outdated review I shall endeavour to revise and amend the manuscript and references to incorporate the more recent advances at the time of going to press.

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Transactions of the Geological Society of South Africa, 72, 1-7

In the Republic of Botswana and neighbouring territories, the uniformity of the succession of the Karroo System and the lateral persistence of its units usually permit acceptable inter-regional correlations on the lithostratigraphic basis. This is especially true of eastern Botswana, the Transvaal and Rhodesia. It appears anomalous that the strata currently accepted as belonging to the Middle Ecca Stage in eastern Botswana, when traced westwards across the Kalahari should apparently link up with the upper part of the Dwyka Series in South-West Africa. Results of a borehole in south-western Botswana suggest moreover that correlatives of the Dwyka Series of South-West Africa may underlie the ostensibly Middle Ecca Stage beds of the western Kalahari within Botswana. Similarly, results of boreholes in South-West Africa near the border with Botswana can be interpreted on the basis of the recognition of a Middle Ecca Stage equivalent within the upper part of the succession. It is suggested therefore that the Dwyka Series of South-West Africa may pass beneath the Middle Ecca Stage on the western side of the border between Botswana and South-West Africa.

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Transactions of the Geological Society of South Africa, 72, 115-121

Superficial Tertiary sediments in the vicinity of Lüderitz, South West Africa, reveal a possible relationship between envi ronment and carbonate precipitation in fluvial, estuarine and marshy conditions. Whereas calcite is the sole carbonate in the fluvial sediment, dolomite is present in local evaporitic sediments and predominates in lenses of terrestrial argillite surrounded by calcite-cemented eolian arenites.

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Transactions of the Geological Society of South Africa, 72, 123-125

Limestones of the Alexandria Formation at Birbury, hitherto assigned to the Upper Eocene, are shown to contain a mixture of two distinct microfaunas. These have been clearly dated as of Lower Eocene and Miocene age.

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Transactions of the Geological Society of South Africa, 72, 127-150

The pre-Cape sediments in the area between Vanrhynsdorp and Nuwerus consist of a sequence of limestones, phyllites, quartzites and shales. These rocks overlie the paragneisses of the southern Namaqualand Gneiss Complex unconformably with a sedimentary contact and belong to the Kuibis Series of the Nama System. The previously called "Malmesbury" Formation has been incorporated in the Kuibis Series in this area as it is identical with the latter with respect to lithology and tectonic pattern. The Nama beds show low-grade metamorphism and have been affected by two pulses of deformation which are tentatively correlated with the Damara orogeny. The Kuibis Series around Vanrhynsdorp may be a correlate of at least parts of the Malmesbury Formation of the Cape Peninsula and neighbouring areas.

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Transactions of the Geological Society of South Africa, 72, 151-158

The lower portion of the Southern Ecca Facies is considered to represent, in part, a typical flysch succession. Evidence of this is presented, and the significance of such geosynclinal sedimentation in the Cape-Karroo trough is discussed.

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Transactions of the Geological Society of South Africa, 72, 23-27

Based on a petrographical study of a hydrogrossularite-bearing serpentinite from the Tugela Randt Intrusion, in which calcic feldspar is replaced by the mineral assemblage hydro-grossularite, diopside, calcite, and aluminous serpentine, a revision of the existing theories on calcium silicate formation in ultramafic rocks is suggested. It is considered that the concentration of calcium in bodies of cafemic rocks in serpentinites is the direct result of serpentinization and of the inability of the serpentine to accommodate calcium in its lattice. Calcium from an external source, that is, from a source other than the cafemic rock, which is altered to rodingite, is hardly necessary.

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Transactions of the Geological Society of South Africa, 72, 29-30

Reconnaissance mapping of the Cape System in the Willowmore and Steytlerville Districts proves the existence of an abnormal contact between the Bokkeveld and the Table Mountain Series. About 12+ miles south of Steytlerville the Baviaanskloof Range exhibits clear evidence of an eroded nappe. In its entirety the overthrust tongue of Table Mountain Series attains a length of 37 miles and has a north ward displacement of some 3+ miles.

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Transactions of the Geological Society of South Africa, 72, 31-35

A brief account is given of a section intersected in a borehole drilled within , mile of the Swaziland border south of Goedgegun. A succession of tillites, mudstones, varved shales and rhythmically banded shales totalling 1,051 feet in thickness occupies a glacial valley. The most distinctive pebbles and cobbles in the tillite are those of Rooiberg felsite indicating a source towards the north-west. From the evidence of sporadic occurrences of the Dwyka Series an attempt is made to reconstruct the course of this glacial valley which was carved mainly in various granites, gneisses and rocks of the Mozaan Series.

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Transactions of the Geological Society of South Africa, 72, 38-45

Leach solutions of sulphide concentrates of the Dominion Reef lava from three separate localities yielded colinear Pb207/Pb206 ratios. The specimens which were enriched in radiogenic lead appear to indicate proportionate additions of radiogenic Pb206 and Pb207 isotopes to a primary lead that existed at the time of crystallization of the magma. The Pb207/Pb206 ratios conform with an age of 2,800 q 60 million years for the lava.

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Transactions of the Geological Society of South Africa, 72, 47-48

Griesbach in 1870 reported a finely striated Patella and some small bivalves from the Lower Devonian Table Mountain Series of Natal. It is argued from the evidence available that these fossils are actually Cretaceous in age.

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Transactions of the Geological Society of South Africa, 72, 49-60

The percentage flattening of pebbles of deformed conglomerates from the Moodies Group of the Eureka Syncline was calculated and compared with values obtained for the combined shortening and flattening of isoclinal folds found in Fig-tree strata of the Lily Mine, a gold-mine situated six miles east of the pebble occurrences. For both the fold and pebble deformation examples, only the amount of flattening suffered by the rocks could be calculated directly. Empirical values reflecting the shortening of the formations during the initial stages of deformation were added to the calculated values in order to obtain a measure of the total deformation that affected the area. The mine folds were found to be shortened and flattened by approximately 63% while the mean pebble deformation amounted to approximately 61%; a striking parallelism. Both the conglomerate and fold localities occur in the greenschist zone of a contact-metamorphic aureole produced by the emplacement of the intrusive phase of the Nelspruit Granite along the contact of the Archean successions in the northern part of the Barberton Mountain Land. The example suggests also that in this particular case the cleavage or "similar" folding was the direct consequence of flattening processes with shearing only of secondary importance in the production of the fold deformation.

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Transactions of the Geological Society of South Africa, 72, 61-78

In a selection of boreholes from the mafic rocks of the western part of the Bushveld Complex compositions were determined of major, and a few trace element components of orthopyroxenes and plagioclases. By distinguishing the cumulus and intercumulus minerals it was found that the components in the former generally display cryptic layering which contrasts with the rather irregular compositional pattern shown by the intercumulus minerals. In a continuous 5,000 foot borehole it was found that the cumulus orthopyroxenes range from En8l to En69 and the plagioclases from An80 to An70. As indicated by the cumulus minerals the cryptic layering is only occasionally interrupted by what may constitute chemical discontinuities, the latter being of small magnitude.
Eight orthopyroxenes were analysed for Cr, Co, Cu, In, Ni, K, Ti, V and Zr and seven plagioclases for Cr, Cu, Mn, Ni and K. In the cumulus orthopyroxenes Cr, Ni, Ti and V show a general decrease in concentration with the later differentiates, whereas K and Zr concentrations show the reverse trend. Co, Cu and In show only small indistinct variations. In the cumulus plagioclase series K decreases with differentiation whereas, by contrast, Cr and Mn show an increase with differentiation. Cu and Ni display very little variation. In both the orthopyroxene and the plagioclase series the limited number of chemical analyses of the intercumulus mineral phases show an apparently irregular trend.
Petrofabric analyses of selected specimens indicate that the cumulus plagioclases and orthopyroxenes possess a lamination with the the development of lineation maxima within the plane of lamination. From the relatively small cryptic variation displayed within an uninterrupted sequence of 3,500 feet it was concluded that, at least during some periods, differentiation took place from a magna chamber of considerable thickness without further magma additions having taken place. From the petrofabric analyses it was further concluded that in all probability gentle currents were present in the magma chamber at the time of deposition to produce the alignment of the elongate mineral grains.

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Transactions of the Geological Society of South Africa, 72, 79-113

Published and unpublished radiometric age determinations available up to early 1968 for material from Rhodesia have been collected together, listed in tables, and recalculated to conform with mod ern decay constants. A total of 61 Rb-Sr isotopic, 9 Rb- Sr spec trographic, 61 K-Ar, 11 U-Th-Pb and 61 common lead analyses are quoted. There is a concentration of dates in the 2,500 my. to 3,000 my. interval in materials including basic igneous rocks of the Great Dyke (2,500 my.) and pegmatites. The chronological results tentatively indicate periods of granite emplacement at circa 3,300 my., 3,000 my., 2,800 my., 1,800 my. and 200 my. Metamorphic events around the margins of Rhodesia evidently occurred at: about 2,000 my. in the Limpopo belt in the south; 1,000-1,800 my. along the western margin, and 400-650 my. in the Zambezi and Mozambique belts along the northern and eastern districts. Karroo igneous activity occurred 160-200 my. ago. Few stratigraphic divisions in the geological column for Rhodesia can be dated directly from the available information, but broad limits can be provided for some of the sedimentary units:-
Bulawayan System 3,000-3,300 my.; Shamvaian System >2,650 my.; Lomagundi System 1,950-2,650 my.; Umkondo System 1,785-2,050 my.; Sijarira Series <1,250 my.; and Karroo System 400-206 m.y.

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Transactions of the Geological Society of South Africa, 72, 9-21

The quartz porphyry of the Upper Zone or acid volcanics of the Onverwacht Series of the Swaziland System probably represents the oldest acid lava on earth still preserved in a relatively unaltered condition. A rock sample of the quartz porphyry from the farm Geluk 71, district of Barberton, Transvaal, yielded minute but sufficient quantities of Cu/Fe/As sulphides and zircon for reliable determinations of their age. The similarity of the ages established for the two mineral types confirms their contemporaneous crystallisation from the acid magma 3.36 (±.1) x 10(9) years ago. This age determination is the highest yet obtained for a rock in South Africa by the U-Pb method of radiometric dating.

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Proceedings of the Geological Society of South Africa, 72, xxviii-xxxii

Biographical memoir. Bibliography of publications by L.T. Nel.

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Proceedings of the Geological Society of South Africa, 72, xxxiii-xxxvi

Biographical memoir. Bibliography of publications by F. Walker.

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Transactions of the Geological Society of South Africa, 73, 1-16

The hypothesis is presented that the Mozambique Channel originated as Madagascar drifted away from the African continent, thus widening a rift that had started to open in pre-Karroo times. In support of this suggested origin a reconstruction in several stages is attempted, based on stratigraphical and structural evidence collected in western Madagascar and on the coastal area of Mozambique and Natal. In particular, the peak of rifting is shown to coincide with the outpourings of lavas at the end of the Karroo on the African side, and a comparison of the stratigraphy on either side of the channel 'through time' is discussed, which supports the reconstructions presented. The presence of mid-Channel volcanics is explained as connected with the zone of crustal instability still active in the Channel area.

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Transactions of the Geological Society of South Africa, 73, 107-150

The Ancient Gneiss Complex consists of a suite of metamorphic including kinzigites, quartzites, taconites, amphibolites and siliceous diopside-bearing granulites. Following the imposition of regional metamorphism, the metamorphites of appropriate composition were extensively granitized. The rocks of more extreme composition were preserved and from these it has been possible to reconstruct the metamorphic grade prior to granitization. It is concluded that metamorphism took place at temperatures between 550° and 650°C at pressures of around 3,000 bars. This places the metamorphism in the higher grades of the amphibolites facies (Abukuma type). From the field and petrological evidence it is concluded that the granitization was accomplished by migrating, superheated aqueous solutions. The correlation of the Ancient Gneiss Complex is discussed. It is apparent that the Complex represents a period of deposition of supracrustal material in an area of rapid erosion, transport and deposition accompanied by the extrusion of ultrabasic and basic magma. In this regard the Complex resembles the Swaziland System. Structural data indicates a very systematic north-easterly trend which is superposed. The presence of Swaziland System rocks metamorphosed in the middle greenschist facies in faulted juxtaposition to the complex together with the structural data is taken as evidence that the period of deposition represented by the Ancient Gneiss Complex pre-dated the Swaziland System. Whatever the correlation of the Complex, no evidence of the floor on which deposition took place was found.

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Transactions of the Geological Society of South Africa, 73, 151-157

The classic geological section of Tertiary rocks at Uloa on the lower Umfolozi River has been partly obscured by bulldozing for a new road. A concise authoritative statement on the formations present, their ages and unconformities, and their relationships with the denudational episodes present in the coastal hinterland is, therefore, assembled by the author, who was the first to work at the site in 1951 and has been associated with it ever since. Coastal Hinterland:
Monoclinal tilting, with incision of river valleys;
Pliocene Basin Plains; tilt, with uplift and erosion;
"Post-African" cyclic land surface;
Uplift and erosion;
"African (early Teriary) lateritized landsurface
- Zululand Coastal Plain :
Monoclinal tilting and retreat of Pliocene sea.
Z.C.P. exposed Zululand Coastal Plain (marine cut);
Tilt, with Pliocene transgression;
Miocene-Pliocene unconformity;
Lower Miocene beds (with detrital laterite);
Cretaceous-Miocene unconformity.

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Transactions of the Geological Society of South Africa, 73, 159-171

The course of the Steelpoort River can be divided into three sections:
(i) the upper section which may represent the captured headwaters of the Blood River,
(ii) the section from Laersdrif, flow ing northwards, which may be regarded as the captured headwaters of the, Sekwati River, and
(iii) the lower section, which forms a north-east-striking valley and follows a fault-zone.
This last section of the river cuts obliquely across an older north-flowing drainage-pattern, which followed the strike of the igneous and the sedimentary rocks, the result being an asymmetrical drainage- pattern of the Steelpoort River. The tributaries of the Steelpoort River from the north are short and steep, whereas those from the south are much longer with more gentle profiles. The Klip River and the Mosohlotsi Spruit developed along the same strike-fault. Near their junctions the larger, north-flowing tributaries of the Steelpoort River are characterized by a sharp turn towards the west. In each case this is ascribed to river-capture, in such a way that a small upstream tributary which has a rectangu lar junction with the main stream beheads the lower, larger tribu tary which has an acute junction with the main river. An acute junction between a main stream and its tributary is apparently not in equilibrium, because it causes a competition in their attempts to enlarge their valleys. This is evidently not so in the case of rectangular junctions. Many cases of river-capture from the upper courses of the tributaries of the Steelpoort River are reported. Several U-shaped valleys are also described; however it was found that they are asymmetrical in shape, and were probably not caused by glaciers, but seem to be typical of the drainage systems in gabbroic rocks. No evidence could be found that the Steel poort River is a superimposed river. The present drainage system of the Steelpoort River is largely controlled by the existing formations, structures and normal erosion processes, existing formations, structures and normal erosion processes, in which river-capture plays a prominent role.

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Transactions of the Geological Society of South Africa, 73, 17-28

A reconnaissance seismic-reflection traverse running N-S past Beaufort West was shot for Southern Oil Exploration Corporation (Pty.) Limited, between November 1965 and February 1966. The field-techniques that were used are described, with a description of the results, and an interpretative depth-section is presented together with a possible geological interpretation.

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Proceedings of the Geological Society of South Africa, 73, xx-xlii

The foundation, history, and activities of the Geological Society of South Africa have on several occasions been the subject of presidential and other addresses by former presidents of our Society. Apart from the three consecutive addresses in 1895, 1897, and 1898 by our first president, Dr. Hugh Exton, which dealt mainly with current Society affairs, the first extensive review of our Society's history was the presidential address by the date Prof. R. B. Young in 1927. Eight years later, in 1935, our Society's most senior member, Brig. R. S. G. Stokes, delivered a presidential address entitled "The Geological Surveys and Societies of the World" to mark the fortieth anniversary of the foundation of the Geological Society of South Africa and of the Geological Commission of the Cape of Good Hope. In 1939 the late Dr. H. S. Harger presented some historical notes on the Geological Society of South Africa at a monthly meeting held in Kelvin House. Here it may also be noted that many interesting facts about our Society are contained in the very extensive review of the history of the Associated Scientific and Technical Societies of South Africa which was given as a presidential address by the late Prof. John Orr in 1937. The fiftieth anniversary of our Society was commemorated in a rather special manner by the institution of the Jubilee Medal to be awarded annually for a paper of particular merit. The Transactions and Proceedings for 1945 (Volume 48) contain a preface by Prof. E. Mendelssohn in which reference is made to the foundation of the Society as well as contributions by the late Drs. H. S. Harger, R. B. Young, and A. L. du Toit in which they recall some of the more interesting aspects of the early history of the Society.
The following year the president, Prof. D. L. Scholtz, gave a review of the activities of the Society during the first fifty years of its existence and made some suggestions regarding its future. This review was illustrated with several graphs showing variations for the first fifty years in: the total, ordinary, and student membership; the size of the Transactions and the papers published therein; the total number of contributions and the number of contributions made by the Geological Survey, the universities, and the mining groups; and lastly also income, publication costs, donations, fees, and sales. In 1954 Prof.; E. Mendelssohn chose the work and activities of the Geological Society of South Africa as the subject for his presidential address to mark the sixtieth anniversary of the Society in 1955. This year we are celebrating the seventy-fifth anniversary of the foundation of our Society.
It is also seventy-five years since the first chair of geology in South Africa was established at the South African College in Cape Town with the appointment of the late Dr. G. S. Corstorphine as the first professor of geology in this country. It was also in 1895 that the Government of the Cape of Good Hope appointed a geological commission to organize the first geological survey in South Africa with Prof. Corstorphine as the geologist in charge and the late Drs. A. W. Rogers and E. H. L. Schwarz as his assistants. The year 1970 therefore marks the passage of seventy-five years since the beginning of organized geological activities in the fields of scientific association and communication, teaching, and regional mapping in South Africa. With a view to observing this undoubtedly important anniversary, I have decided to speak to you this afternoon on the progress of our Society during the past seventy-five years and the trends that become apparent when an attempt is made to portray this graphically.
I do not, however, propose to deal specifically with the history of our Society as this has already been adequately accomplished by several of our past presidents as was indicated previously. I will, in fact, confine myself to those three aspects which I feel are most important for the growth and development of our Society, namely membership, publications, and finances. In a study of this nature one has to rely on information contained in the Trans actions and Proceedings and the minutes of annual and ordinary general meetings of the Society. In an attempt to find a suitable way in which data of this sort can be presented, with a view to showing our present position and the trends during the past, I have constructed various simple diagrams. These diagrams are not intended to be specifically accurate but will be used only for illustrative purposes in connection with what I have to say this afternoon. My colleague, Dr. A. A. Bisschoff has kindly prepared the slides which I will use during this address.

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Transactions of the Geological Society of South Africa, 73, 29-48

Pyrite constitutes generally more than 90% of the ore-minerals in the Basal Reef of the Witwatersrand System, and is present in a variety of forms. In this paper a descriptive classification of the different forms of pyrite is attempted and the following three main types are distinguished: rounded pyrite, idiomorphic to hyidiomorphic pyrite and xenomorphic pyrite. The rounded pyrite is subdivided into a compact variety, a porous variety, a variety that is pseudomorphous after black sand and formed from it by pyritization, concretionary pyrite, and pyrite nodules containing different microspherical structures of the "mineralized bacteria" type. The idiomorphic to hypidiomorphic pyrite is found as compact and porous varieties and also as encrustations. The xenomorphic pyrite is present as veinlets and fracture fillings. The relative abundance of different microspherical structures is a striking feature of the portion of the Basal Reef studied. The possibility of an anaerobic environment in the Witwatersrand basin, during and just after the deposition of the conglomerates, is discussed, and found to be feasible. It is believed that in these anaerobic environments sulphatereducing H2S-generating microbes existed. Environments suitable for the existence of H2S-forming bacteria, however, prevailead konly in small areas and it is pointed out that the Basal Reef in parts of the Free State Geduld area might represent such a "pocket".

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Transactions of the Geological Society of South Africa, 73, 49-63

The carbonate components of South African Coastal limestones and Agulhas Bank limestones consist of carbonate grains and an intergranular fabric. Carbonate grains in these limestones are intraclasts, ooliths, pellets, and fossils, Five types of inter granular fabric are found in South African limestones: drusy calcite, fibrous calcite, micrite, microspar, and syntaxial over growths. Drusy calcite is the dominant intergranular fabric of the Coastal limestones and was formed by dissolution of skeletal aragonite. Numerous micrite envelopes remain as evidence of the dissolution of skeletal material. Micrite is the dominant intergranular fabric of the Agulhas Bank limestones. At least some of this micrite has been generated by skeletal disintegration due to boring action of organisms. Micrite has occasionally recrystallized to microspar in both the Agulhas Bank limestones and the Coastal limestones. Microspar preferentially recrystallizes from an intergranular fabric of micrite, but only rarely from micritic carbonate grains. The Coastal limestones were originally a sediment of mixed carbonate mineralogy, but the unstable carbonate minerals have now altered to their stable state, low-magnesium calcite. Agulhas Bank limestones still have a mixed carbonate mineralogy consisting of aragonite, high-magnesium calcite and low-magnesium calcite, and have therefore not undergone the mineralogical changes that have altered the Coastal limestones. Most of the Coastal limestones are classified as skeletal lime grain stones or skeletal lime packstones. Three separate limestone facies have been dredged from the Agulhas Bank: (1) a coquinite lime packstone facies, (2) a quart zose lime packstone facies, and (3) a foraminiferal-bryozoan lime packstone facies.

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Transactions of the Geological Society of South Africa, 73, 65-88

The location and the distribution of previously unrecognised volcanic vents below the Royal Society Range, Antarctica, is described and discussed. The mineralogy, petrology and chemistry of basalt and associated ultrabasic inclusions from one vent, the Brandau Vent, are described in some detail. Evidence is presented to indicate that ultrabasic inclusions present in the lavas include both cumulates and mantle derived materials.

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Transactions of the Geological Society of South Africa, 73, 89-98

It is evident from published information and personal experience that the Bankets of the Witwatersrand System are essentially gold-bearing conglomerates. The size distribution of the particles comprising these conglomerates is bimodal and the detrital heavy minerals are hydraulically equivalent in size to the sand-sized mode. The high density of pebble packing in these conglomerates means that they were open-work gravels which were subsequently filled with sand and heavy minerals. Flume experiments have shown that deposition of sand in a gravel bed is controlled by the surface layer of pebbles and that the sizes of the sand particles are not independent of the pebble sizes. They also indicate that gravel beds thinner than one and a half pebble diameters accumulate fine-grained sediment much more slowly than thicker gravel beds. Rudimentary flume experiments described in this paper demonstrate the above relationships between gravel and sand. Provided that the pebbles are nineteen times coarser than the sand their size does not influence the deposition of sand. Magnetite was added to the sand to analogize the behaviour of detrital gold and it was found that its concentration in sand deposited in a thin gravel bed was a little less than in the bed-load supplied. However its concentration in a thicker gravel-bed was considerably lower than in the bed-load supplied. Consequently the concentration of magnetite in the bed-load increased during passage across gravel beds and the concentrationd eposited in gravel beds became progressively greater downstream. This might be one reason why the midfan part of an alluvial fan has a greater potential for economic concentration of gold. Pebble size the therefore indicates the geographical position of a location within a Banket deposit but is not directly related to the gold content.

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Transactions of the Geological Society of South Africa, 73, 99-106

A widespread, thin blanket of soil sediments covers the south- western Transvaal. The appearance, lithology and the intimate association of these sediments with typical glacial landscape features lead to the conclusion that they are of glacial origin. Associated landscape features typical of a glacial topography, including striated pave ments, mammillated surfaces and roches mountonnees are described from an area west of Klerksdorp. The direction of ice movement, as deter mined from various glacial features, was from north to south in the Bloemhof-Schweizer Reneke area; in the region west of Klerksdorp two directions were found, north-west to south-east and north. east to south-west. Intrusion by Karroo dolerite sills and dykes indicates these sediments to be older; they are therefore probably of Dwyka age. The glaciated topography of Dwyka times can be found in var ious stages of resurrection throughout the south-western Transvaal. Large polished boulders, some standing vertically on their long axis, form an unusual feature of the landscape. A glacial origin is suggested. The evidence indicates that large areas of the south- western Transvaal are still covered by Dwyka sediments. This knowledge enables a better understanding of the geology and the geomorphology of this area.

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Transactions of the Geological Society of South Africa, 74, 1-24

A series of volcanic and sedimentary rocks occurring within Botswana territory and lying below the Transvaal System is correlated with the Ventersdorp System. The succession is divided into three lithostratigraphic units. The Lower volcanic Assemblage consists of siliceous and potash-rich igneous rocks both of pyroclastic and flow origin. The Mogobane Assemblage is made up of argillaceous sedimentary rocks and the Upper Volcanic Assemblage mainly contains andesitic lavas. The nature of the volcanic phenomena associated with the formation of the rocks belonging to the Lower Volcanic Assemblage is considered in some detail. The petrogenesis of the rocks of the Lower Volcanic Assemblage is also discussed at length. Finally, a review is given of the stratigraphic and tectogenetic problems that arise when the rocks of the Ventersdorp System of the Lobatse and Ramotswa areas are considered in their regional context.

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Transactions of the Geological Society of South Africa, 74, 103-105

The discovery of a reptilian tooth from the Cretaceous limestone (Lower Quarry) at Needs Camp, South Africa, is recorded. New work on the associated microfossils suggest an Upper Senonian (Campanian) to Maestrichtian age.

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Transactions of the Geological Society of South Africa, 74, 107-108

I was most interested to read Von Gottberg's account of the work he did in connection with the Dwyka glaciation in the south-western Transvaal, but I feel that certain parts of his paper call for comment. One of Von Gottberg's directions of ice flow in the Klerksdorp district is from north-west to south-east which is a new paleo-ice flow direction for this area, and as such is a valuable discovery. Does Von Gottberg consider that this direction of flow might be related to the deep and prominent glacial valley discovered in the Odendaalsrus area by Cousins (1950) the size of which was subsequently extended (Stratten, 1968 and 1970)? In his conclusions Von Gottberg should have related his direction of ice flow to the known source areas that produced the ice sheets which covered the area (Du Toit, 1921). The most prominent ice sheet here was the Transvaal Ice Sheet and its general direction of flow, in this area, was towards the south-west (Du Toit, 1921; Von Backström, et al., 1953; Stratten 1967), subsequent till fabric work on the Dwyka Tillite at the Oppermansdrift Dam site supported this direction of flow (S 68° W). The Griqualand-Witwatesrand arch, which was slightly higher than the surrounding country, stretched from the Kaap Plateau to the Transvaal Highlands (Stratten, 1968 and 1970). Judging from Von Gottberg's paleo-ice flow directions this highland arch apparently shed considerable material. However, the most prominent highland mass which acted as a source area for the ice was the central Transvaal. This has often been remarked upon (e.g. Dn Toit, 1921 and 19i4; Stratten, 1967; Truswell, 1970), and can be determined by the composition of the pebbles found in the veld and by the clasts held in the tillite. There are two more points to be raised in connection with this paper. Firstly the introduction of new names such as clay-tillite, gravel-tillite, tillite-breccia and rubble-tillite is unnecessary. Tillite is a sedimentary rock composed of cemented or compact

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Transactions of the Geological Society of South Africa, 74, 109-110

I wish to thank the author for his very interesting and important paper. I think he has put forward a very plausible theory to explain the origin of the Mozambique channel. His idea of a north-easterly striking dextral transcurrent fault is supported by evidence in the Soutpansberg and Eastern Botswana areas. In the latter area Mason (1969) describes a dextral transcurrent movement of 80 km along the Letlakane fault. I have analysed the faults in the Soutpansberg and other areas in a paper that is in preparation and some of my conclusions have a bearing on those of the author. There are three directions of post-Waterberg but pre-Karroo faulting in the Soutpansberg area. The one direction, viz. east-north-east, is more or less parallel to the Letlakane fault in Botswana and the Messina and Dowe-Tokwe faults north of the Soutpansberg. This is a direction of dextral transcurrent movement. Another direction is north-west south-east and is represented by, e.g., the Siloam fault in the Soutpansberg and Lechwana fault in Botswana. It is a direction of sinistral transcurrent movement. These faults indicate that the maximum pressure was east-west and the minimum pressure north-south when they were formed. Another direction is north of north-east but the faults of this direction are normal faults with the downthrow side to the east. ln post-Karoo times normal faulting occurred along the transcurrent faults of both directions. There is no evidence of movement along the faults between the periods of deformation. From regional evidence in South Africa it would appear that the transcurrent faults are about 1100 m.y. old, i.e. of he same age as the Namaqualand-Natal period of metamorphism and granitisation. The mechanics envisaged by Hardie (1962) for the formation of the Natal fault system is untenable on theoretical grounds. There is enough evidence in the literature for a view that the post-Karroo movement along the faults in Natal occurred along older faults as is the case in

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Transactions of the Geological Society of South Africa, 74, 111-131

The National Committee for Geological Sciences has accepted in principle the recommendations of the International Subcommittee on Stratigraphic Classification. On the 26th March, 1971, the National Committee formed the South African Committee for Stratigraphy (SACS). The same committee was also appointed by the South African Scientific Committee for the International Union of Geological Sciences (IUGS) of the C.S.I.R. SACS decided on the 14th June, 1971, to draft a South African Stratigraphic Code broadly related to the ISSC proposals. This Code has leaned heavily on circulars 26, 27, 29, 31 and 34 of the ISSC, and on an article by F.W.B. van Eysinga (1970. Stratigraphic terminology and nomenclature; a guide for editors and authors. Earth-Sci. Rev., 6, 267-288). Naturally this Code will be modified with time, and the SACS invites and welcomes comments on it. The membership of SACS, and of the working groups to which this code is now being referred, are given in an appendix to this code.

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Transactions of the Geological Society of South Africa, 74, 133-147

The Deweras Group between the Umfuli and Umniati rivers consists of an upper sequence of arkoses and argillites, the Arenaceous Formation; a middle sequence of tholeiitic basalt, the Volcanic Formation and a lower discontinuous sequence of quartzite and conglomerate, the Basal Sedimentary Formation. The succession is interpreted as being deposited in a variable shallow water to continental environment, which in this instance is believed to be associated with a step-faulted or graben structure. The Deweras Group unconformably overlies Archaean rocks and is unconformably overlain by the Lomag undi Group, the basal beds of which represent a stable shelf facies of deposition. The possibility of a thrust between the Deweras Group and the Lomagundi Group is considered. It is suggested that the Deweras Group should not be regarded as the basal portion of the Lomagundi Group. There is not only a difference in depositional environment between the two, but also evidence of a time gap between the top of the Deweras Group and the bottom of the Lomagundi.

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Transactions of the Geological Society of South Africa, 74, 149-171

Aerial photography is finding ever-increasing uses in many fields of geological research and application, including regional mapping, the search for mineral deposits, fracture analysis, structural analysis, engineering geology and hydrology, and recent literature in these subjects is reviewed. The range of material available is now much more extensive, including colour and multiband photography, infra-red photography and thermal imagery, radar, and orbital photography. The principles of these newer techniques are briefly discussed and their application to geological problems examined. It is concluded that although many of these techniques have important roles to play in particular circumstances, the ordinary black and white photography will remain the most generally used tool for some time to come, and one of the main aims of the paper is to show just how useful it can be to the earth scientist.

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Transactions of the Geological Society of South Africa, 74, 173-186

Three major Tertiary transgressions have been identified from a study of seismic profiles across the continental shelf off the south and west coasts of the Cape Province. These are dated as: early Tertiary (Palaeocene/Eocene); mid-Tertiary (Miocene); and late Tertiary (Pliocene). The west coast Tertiary history is controlled by a relatively complex sequence of events in an obviously epeirogenically unstable area; whereas the south coast appears to have remained more stable, or at least the effects of earth movements are less well displayed. Altogether, four main sedimentary sequences are recorded on the west coast, which can be correlated with two well-defined units off the south coast. The onshore evidence for Tertiary movements of sea level is discussed and found to be in good accord with the offshore data. The history of the Cape Canyon can be fitted into the general picture of erosive and depositional periods.

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Transactions of the Geological Society of South Africa, 74, 187-199

The sporadic outcrops of diamictite in the Northern Cape Province and in the Transvaal were investigated to establish a model for glacial sedimentation in the Transvaal Supergroup. Seven sections were measured and the data analyzed. The outcrops in the Northern Cape Basin consist of diamictite, conglomerate, pebbly sandstone, siltstone, varved shale and mudstone. Evidence of glacial action include striated pebbles, rafted stones and remnants of an eroded glacial pavement. The rock-types are interpreted as tillite, fluvioglacial and glacio-marine sediments. The outcrops in the Transvaal Basin consist of diamictite, conglomerate lenses, clayey sandstone, siltstone and shale. Deposition of these rock-types took place offshore on a relatively steep slope. These sediments are considered glaciomarine in origin. The glaciation was limited and probably centred over the Vryburg Rise. A mountain ice-sheet with piedmont glaciers reaching down to sea-level, is visualised. Nearly all the sediments were derived intrabasinally by glacial erosion of the underlying formations of the Transvaal Supergroup. In the central area the glacial material was deposited on land as moraines, part of which was reworked by streams and laid down as fluvioglacial sediments towards the south. Mainly glaciomarine deposits formed where the floating ice entered part of the Northern Cape Basin towards the west and the Transvaal Basin towards the east. Part of this material was transported deeper into the basin by slumps and turbidity currents. Extensive erosion before the outflow of the Ongeluk lava outflow of the Ongeluk lava removed some of the glacial sediments over large areas.

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Transactions of the Geological Society of South Africa, 74, 201-210

Within the Pretoria Group of the Transvaal Sequence (1,950-2,300 mil lion years old), six separate algal stromatolite-bearing horizons are described. These organo-sedimentary structures occur in cherts and carbonate rocks associated with the argillaceous phases of the Pretoria Groups. The stromatolites conform in their geometry to the class of lateral linked hemispheroids described by logan and others. Consequently, the stromatolites and their enclosing shaly sediments probably formed on widespread intertidal mud flats. Since algae photosynthesize carbon dioxide to yield oxygen, the atmosphere during Transvaal times must have been at least partially oxygenic. The algae which existed during this period could have been directly or indirectly responsible for the formation of carbonate sediments.

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Transactions of the Geological Society of South Africa, 74, 211-235

The structural geology of the later Precambrian formations of south eastern Botswana is reviewed. It is suggested that major differences that exist in the tectogenetic evolution of different parts of the region are due to the simultaneous existence of mobile basin zones and relatively more stable platform zones. This distinction seems to have been in existence already by the end of Transvaal System time. Following the cessation of Transvaal System sedimentation isolated areas of major structural complexity arose in at least two different localities along the boundaries between basins and platforms. The hypothesis is developed that in both of these areas the complicated structural pattern is the result of the gravity sliding of large masses of Pretoria Series rocks moving down slopes linking a platform zone with a newly subsided basin floor. From the beginning of Waterberg System time onward, a notable feature of the tectonic pattern of the region is the existence of several major "lineaments" running mostly in an east-northeast direction for hundreds of kilometres across country. These may have been initiated as transcurrent fractures at some uncertain period. During post-Waterberg System time differential up and down movement of crustal segments either side of these lineaments resulted in the formation of monoclines in Waterberg System rocks and crush zones in pre-Ventersdorp System crystalline rocks. Igneous intrusions of vari ous kinds were emplaced along these lineaments. Notable among these is the Moshaneng Granite whose emplacement caused considerable dis location of the surrounding country rocks. The paper emphasises that the later Precambrian tectonic events of southeastern Botswana cannot be ascribed to tangential forces originating out of any orogenic cycle but, on the contrary, appear to be vertical tectonic phenomena perhaps associated with events in the planetary mantle.

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Transactions of the Geological Society of South Africa, 74, 237-238

The yellow powdery material occurring as a coating on a great variety of rocks, consists in most cases of a ferric sulphate belonging to the jarosite series. X- ray powder data and a electron-photomicrograph are provided.

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Transactions of the Geological Society of South Africa, 74, 25-31

The use of a new analysing technique has made it possible to reevaluate the differentiation pattern found in the Losberg Intrusion. The results demonstrate that the rhythmic, phase- and cryptic layering present can be ascribed to the fractional crystallization of olivine and orthopyroxene from a single magma. Furthermore, there is no evidence of large-scale assimilation of country-rocks.

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Transactions of the Geological Society of South Africa, 74, 33-43

In areas where the formations above the solid bedrock consist of unconsolidated sands and alluvium the seismic refraction method can often be applied with a large measure of success to determine the thickness of the recent formations. In particular the watertable may be identified since the water-bearing zone generally occurs as a definite seismic horizon. From the seismic velocity and the depth of the water-bearing layer, its porosity can be deduced which provides a means of estimating the storage capacity of an aquifer since the surface area over which it extends and its average thickness is generally known from the seismic survey. It is also shown that in cases where the time-distance curves are complicated the study of secondary arrivals is a great help in interpretation. The recording system used for refraction surveys is described and mention is made of a specially developed portable sand drill for drilling shallow shot holes in loose sand. The results are illustrated by means of a field example.

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Transactions of the Geological Society of South Africa, 74, 45-55

A rock containing forsterite phenocrysts in a monticellite- nepheline-olivine groundmass which occurs on the southern slopes of the Brukkaros carbonatite mountain, South West Africa, is described and compared to similar rocks in Yakutia, U.S.S.R., and North America. These rocks are considered to be the volatile- poor fractions of kimberlite-carbonatite magmas.

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Transactions of the Geological Society of South Africa, 74, 57-68

Detailed field and laboratory studies of the Basement Complex around Mapumulo, Natal, revealed two intrusive potassic granites that are younger than the regional metamorphism and migmatization of the Tugela Formation. The older of the two, named the Mati Granite, occurs as narrow sheets intrusive into the Tugela Formation north of Mapumulo whereas the younger, named the Mvoti Granite, forms larger bodies to the south of Mapumulo. Granite gneiss, a third granitic rock type, crops out over much of the area and is demonstrably older than the Mvoti Granite; the Mati Granite was nowhere found in intrusive contact with it. This granite gneiss is interpreted as grading from an autochthonous granite in the south to paraautochthonous in the north. Statistical studies of parameters of zircon crystals confirm that the Mvoti and Mati Granites are distinct from one another and are genetically unrelated. Similarity of zircon populations between the Mati Granite and granite gneiss, coupled with field evidence of consanguinity, indicates that the intrusive sheets of Mati Granite were derived from interstitial melt in the subjacent body of granite gneiss. Metasomatism of the Tugela Forma tion was initially sodic but later predominantly potassic and the granite gneiss and Mati Granite north of Mapumulo represent the final magmatic phase of this event. The Mvoti Granite is interpreted as belonging to a later and probably unrelated orogenic episode affecting the Basement Complex.

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Transactions of the Geological Society of South Africa, 74, 69-74

The boundary between the Numees Formation and the Nama System at the Orange River on the farm Aussenkjer 147 in South West Africa has been re-defined because previous interpretations were found to be incorrect. Nama sediments overlie the Numees beds with an angular unconformity indicating a hiatus between the two successions. Another hiatus was found between the Kuibis Series and the Schwarzrand Series of the Nama System. It is suggested that the Numees Formation be omitted from the Nama System.

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Transactions of the Geological Society of South Africa, 74, 75-102

The structural relationships, petrology and mineralogy of kimberlite dykes and "blows" (i.e. pipe-like swellings) occurring about 40 miles north-northwest of Barkly West were investigated with a view to obtaining information on the origin of kimberlite and its associated minerals. Petrographic data indicate that the kimberlite is a phlogopite-carbonate rock rather than a peridotite. It is composed essentially of phlogopite and calcite, with accessory apatite, erovskite, and ilmenite. These minerals form a matrix for a variable amount of inclusions such as xenolithic nodules of peridotite and griquaite and xenocrysts of olivine, phlogopite garnet, chrome-diopside and diamond. The xenocrysts and nodular xenoliths are considered to have been derived from the upper mantle by magmatic disruption and incorporation in kimberlitic fluid. The textural and structural features of the kimberlite, and the absence of thermal metamorphism in the xenoliths and country rock, indicate that emplacement was effected at low temperature and in a fluid condition. The textural, structural, and mineralogical features are best explained by assuming that kimberlite, consisting of a fluid and solid, was emplaced along preexisting zones of weakness, as a super-critical two-phase system. The various hypotheses proposed for the origin of the primary kimberlitic fluid are in a speculative state; however, if it can be proved that differential or fractional melting of peridotite or griquaite in the upper mantle could generate a fluid from which phlogopite can crystallize, and if the carbonate in the matrix of the kimberlite is accepted as being of magmatic origin, as in the case of carbonatites, then a generally acceptable hypothesis for the origin of kimberlite could be propounded.

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Transactions of the Geological Society of South Africa, 75, 1-3

Deposits of Upper Cretaceous marine limestones crop out in two quarries at Needs Camp hinterland of East London. Eight miles dis tant from the sea, the limestones now stand at ele-vations of 1 100 to nearly 1 200 feet above sea-level. What significance have these limestones, in the geomorphic evolution of the region? The unconfor mity below them must on the above da-ting be a relict of the post- Gondwana cyclic landscape of Southern Africa. Later cyclic Sur-faces of denudation Stand at appropriate le-vels: the early Tertiary plana tion cuts across the limestones and forms the Plateau on which they are revealed; small remnants of late Ter-tiary planation exist at lower elevations on minor interfluves in the area; a coastal (pre sumed Pliocene) truncates interfluves below 600 feet towards) trun cates interfluves below Valley forms belong to Quaternary incision of the drainage. Monoclinal tilting of the cyclic land surfaces towards the sea during Tertiary and Quaternary time is indicated.

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Transactions of the Geological Society of South Africa, 75, 11-21

Statistical analysis of available chemical data from the Karoo basaltic province shows significant patterns of regional geochemical variation. The non-parametric Mann-Whitney U-test was used to test for equility of means between selected areas in southern Africa and results show statistically significant differences between an elliptical central area and areas marginal to it. These results were confirmed by applying the tecnique of polynomial trend-surface analysis to demonstrate regional variations in individual oxides. The distinction between northern and southern subprovinces suggest by various workers does not adequately describe regional geochemical trends in the Karoo province. The central area illustsrated by trend surfaces corresponds to the configuration of the central Karroo structural basin indicating strong tectonic control over geochemical variation of the basaltic rocks. Tholeiites from this central basin are higher in Si, Al. Mg and Ca, and lower in Fe, Na, K, Ti and P relative to basaltic rocks from the basin margins. Results are consistent with recent experimentalk studies on the margin of basalts, indicating low-pressure fractionation of basaltic rocsk from the central basin compared with high-pressure fractionation in marginal areas. Trend surfaces also show tectonic control over geochemistry of the basaltic rocks by the continental-margin Lebombo monocline. These patterns of geochemical variation are related to regional tectonics that prevailed during late Karoo time and are independent of Pre-existing structural features in the Precambrian Basement-complex.

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Transactions of the Geological Society of South Africa, 75, 111-119

A sandstone succession, about 194 m thick, occurs between the granite-gneiss of the Basement Complex and the overlying Dwyka tillite. About 80% of the beds consist of medium-grained well-sorted orthosandstone and ortho-quartzite with some scattered pebbles, while fine- to coarse-grained protosandstone and protoquartzite and thin shale beds occurring interbedded in the mature sandstones constitute the rest of the succession. The grain-size distribution of two samples were interpreted as consisting mainly of two saltation-populations and a subordinate traction-population, possibly indicating deposition on a beach. A further analysis probably points to deposition in a shallow marine environment. The nonopaque heavy minerals consist mainly of stable species (zircon, tourmaline, rutile) with minor amounts of apatite, garnet and pyroxene. A sharp change in the heavy-mineral suite occurs about two-thirds up in the succession and this coincides with the appearance of chert grains in the rock. Sedimentary structures are poorly developed and consist mainly of normal bedding and current-ripple lamination. The beds were deposited probably as five transgressive cycles in a marine environment. The lower part of each cycle which consists of alternating coarse-and medium-grained beds, was deposited during a transgressive phase in environments ranging probably from a beach to shallow marine (depth of water less than 10 m). The upper part of the cycle which consists of homogeneous massive sandstone, was deposited during stable periods probably as shore bars. The source-areas of the sediments consisted mainly of metamorphic rocks belonging to the Basement Complex, although the Transvaal Supergroup in Griqualand West later on also supplied material to the depositional area. The sandstone succession depositional area. The sandstone succession is tentatively correlated with the Table Mountain Group by reason of the correspondence in the environment of deposition.

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Transactions of the Geological Society of South Africa, 75, 121-134

The roof-rocks of the Bushveld Igneous Complex in the area between Tauteshoogte and Paardekop consist of highly metamorphosed felsite, generally referred to as leptite, relatively unaltered felsite and granophyre which occurs as a thick sill between the leptite and the felsite. The leptite in this area is traversed by numerous veins of granodiorite and fine-grained granite. It is envisaged that the veins of fine-grained granite owe their origin to the melting of the leptite, caused by the intrusion of basaltic magma which gave rise to the Layered Sequence of the Bushveld Complex. The coalescence of these products of melting probably gave rise to the thick sill of granophyre. As a result of fractional crystallization of the basaltic magma, the volatile content of the remaining magma was gradually increased. Some of these water-rich residual liquids apparently intruded the overlying leptite, causing additional melting of the latter and the formation of irregularly shaped veins and pockets of granodiorite. From published experimental work on melting relations of granitic rocks and crystallization temperatures of basaltic magmas it may be concluded that the difference in temperature between crystallization of the magma which gave rise to the Layered Sequence and that necessary to start melting of the overlying felsite, could have been as much as 400°C.

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Transactions of the Geological Society of South Africa, 75, 135-144

The existing classification of the Bushveld granites in the Zaaiplaats area is revised in the light of newly collected data. Petrological and field data indicate that the so-called Main Granite originated through metamorphism of the basal portion of the Epicrustal Phase of the Bushveld Igneous Complex. The agents responsible for this metamorphism are the rocks of the Layered Mafic Sequence and, to a minor extent, probably also the Bobbejaankop Granite. The Lease Granite appears to represent highly metamorphosed and metsomatised Main granophyre.

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Transactions of the Geological Society of South Africa, 75, 149-158

This Presidential Address is a brief review of the history and development of palaeontological studies, from 1901 onwards, of materials from rocks of varying ages in Rhodesia. The "milestones" dealt with are 10 in number.
Milestone 1 was reached in 1901 when A.J.C. Molyneux lectured on discoveries of fossil fish, lamellibranchs and plants made by him in the course of investigations in the coal-fields in the Limpopo and Zambezi valleys. He indicated the palaeontological significance of these finds, which subsequent studies have amplified and refined. The position of their containing beds in the stratigraphic succession is now well established.
Milestone 2 was the discovery by B. Lightfoot of the first indications of the "Wankie flora", on which many papers have subsequently appeared. Many species have been described and, together with detailed stratigraphic studies, there has resulted a detailed correlation of the succession with sediments beyond the bounds of Rhodesia.
Milestone 3 is considered to be the first recording by Maufe and Haughton (1916) of fragmentary dinosaur bones from the Forest Sandstone.
Progress in the study of Upper Karoo reptiles was slow until 1952, but its rate increased from then onwards, and a wealth of material is now under study.
Milestone 4 was the discovery of a Molteno plant flora (the Dicroidium flora) at Somabula, described for the first time in 1921 by Seward and Holttum, and subsequently found more abundantly in the Zambezi valley.
Milestone 5 was reached by A.M. Macgregor in 1935 when he discovered algal stromatolites of Bulawayan age in rocks that are now regarded as having an age of at least 3 000 my.
Milestone 6 was also reached by Macgregor in 1938 when by Macgregor in 1938 when he rediscovered a locality which yielded dinocephalian skulls and other bonest subsequently assigned to the genus Criocephalus, that proved the existence of beds of Tainocephalus-zone age in the Sebungwe district (Madumabisa mudstones). Since then more reptilian remains have come from the Zambezi valley, and Cistecephalus-zone genera have been identified.
Milestone 7 is considered to be the discovery of dinosaurian bones lying between the Karoo basalts and the base of the Kalahari beds in the Gokwe Formation, as it is now called, and possibly of Upper Jurassic age.
Milestone 8 was reached in 1962 and was the discovery of very large vertebral centra and some fossil wood in the Zambezi valley north of Sipolilo. The area has since been shown to be rich in large reptilian bones that are comparable with the "giants" of Tendaguru in Tanzania.
Milestone 9 was reached by the filling of the Kariba dam and the subsequent exposure of rock along the shores of the lake and of the islands within it by wave-action. On one of these islands bones were eroded out, and Raath and Willborg excavated the site, collecting the articulated hinder half of a dinosaur embedded in a current-bedded gritty sand stone immediately below a porphyritic basalt. The bed appears to be of lower Jurassic age. This age is a vital one in dinosaur evolution.
Milestone 10 was the discovery by Mrs. R. Falcon of spores in material that had penetrated lower Karoo sediments on the Matabola Flats. Thus began the study of palynology in Rhodesian Karoo sediments.

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Transactions of the Geological Society of South Africa, 75, 159-160

Pliocene marine microfossils have been identified in samples from localities near Paterson, C.P., by Dr. L.R. Nolten, previously of Royal Dutch Shell at the Hague. These fossils are now at 1 000 feet above sea-level, and they attest to: (a) the occurrence of a Wide Pliocene transgression of the seal and (b) differential monoclinal tilting towards the sea amounting to hundreds of feet in post-Pliocene time.

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Transactions of the Geological Society of South Africa, 75, 161-163

Dr. Crockett has given a valuable contribution on the structural geology of south-eastern Botswana, an area adjacent to the north-western Transvaal, where stratigraphical and structural problems are being investigated at present by members of the Geological Survey. During the course of a detailed survey of the Waterberg area, certain conclusions have been drawn, which differ fundamentally from Dr. Cockett's interpretation of Waterberg tectonics. I regret that most of the recent data have not yet been published with the exception of two papers by W. C. P. de Vries and H. Jansen in the Annals of the Geological Survey of South Africa 1968-1969. More contributions on Waterberg tectonics and volcanism will appear in the following Annals. My comments mainly deal with the origin of the monoclines and the Tletlesi thrust. The Tletlesi thrust bears some resemblance to the - I presume better exposed Gatkop overthrust east of Thabazimbi, which has been recently mapped in great detail. At Gatkop, overthrusting is attributed to horizontal stresses operating in the belt of deformation between Thabazimbi and Naboomspruit during post-Waterberg times. These stresses bear no relationship at all to lateral compression effected by post-Waterberg intrusions. The latter are cross-cutting bodies without any "mushrooming effect", which is particularly well illustrated by a well exposed granophyric gabbro-granophyre intrusion south of Kransberg. Post-Waterberg diabase dykes intersect belts of steeply-dipping to overturned Waterberg beds and are due to tensional relief subsequent to deformation.

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Transactions of the Geological Society of South Africa, 75, 165-175

X-ray investigation of the alkali feldspar phase of the Concordia granite gneiss and the Nababeep gneiss wall-rocks of the Homeep East mafic rocks, Namaqualand, indicates that this phase has been subjected to a thermal influence hitherto unsuspected. A microcline-orthoclase transition, homogenization and a slight decrease in triclinicity are features ascribed to adjustments of the feldspar structure under higher temperatures next to the contact. The existence of this thermal aureole lends support to the idea that the Namaqualand mafic rocks are of magmatic origin.

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Transactions of the Geological Society of South Africa, 75, 177-185

The Alexandria Formation, the Bredasdorp Formation and the Dorcasia Limestone are considered to be one lithostratigraphic unit, herein informally termed the Coastal limestones. This unit consists mostly of fragments of littoral and nearshore organisms and terrigenous grains cemented by pseudospar and sparry calcite. The rocks are wholly low-Mg calcite, have a high Ca/Mg ratio (mean of 76,0) and a low Sr/Ca x 10-3 ratio (mean of 2,3), and have negative C13 and O18 values. The Coastal limestones originated in response to regressive seas. Shells comminuted in the surf zone were mixed with terrigenous and other grains and left as stranded beach and dune deposits as seas regressed. These deposits were reworked during periodic marine transgressions, and the derived sediments preserved as new beach-dune deposits during subsequent regressions. Tertiary seas transgressed coastal South Africa in early Palaeogene, early Neogene, and late Neogene times, so that the above process was repeated several times. Neomorphism, especially to pseudospars partially obliterated the original components of many rocks during lithification. Subaerial exposure during regressive phases allowed lithification to be completed by solution of aragonitic skeletons and reprecipitation of the solute as low-Mg sparry calcite. Electron photomicrographs of quartz grain surfaces show three diagenetic features: solution surfaces, striations, and crystal growths.

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Transactions of the Geological Society of South Africa, 75, 187-196

Mesoscopic structures, particularly folds, faults, joints and cleavage, within Hospital Hill sediments in the Johannesburg area have been examined. There is a strong spatial and geometric control on the folds in the Contorted Bed, which are predominantly of the "flattened-flexural" class. The adjacent argillaceous rocks, in which the ductility contrast between layers is much smaller than that in the banded ironstones, do not exhibit the same style of deformation but instead kink bands, conjugate folds and chevron folds are present. The attitude of cleavage, axial surfaces and brittle structures within the Hospital Hill sediments suggest that the folds formed under the influence of a north-south compressive stress, after lithification. Initial buckles, which may have formed when the sediments were in a more ductile condition, provided the mechanical instabilities necessary for further deformation. The orientation, along strike, of high-angle ductile fautls, tension-joints and injective shale dykes suggest an earlier north-south tensional stress which was possibly related to basin-edge activity on the north-central margin of the Witwatersrand Basin. The exposure of Contorted Bed rocks in Jan Smuts Avenue represents a natural laboratory for undergraduate students of structural geology.

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Transactions of the Geological Society of South Africa, 75, 197-224

That ground-water can give rise to costly problems in major civil engineering construction was emphasised, in the Orange-Fish Tunnel Project, by the flooding of the Shaft 2 tunnel headings.
An abnormal, and for the Karoo area, most unusual fissure-zone was intersected during blasting in an area already grouted and sealed by means of pilot boreholes drilled ahead of the advancing tunnel face. The calculated initial inflow as 680 000 g.p.h. (3 090 M³/h.) under a hydrostatic head of 285 feet (87 m). The sedimentary rocks intersected by the tunnel have been assigned to the Middle Stage of the Beaufort Series. They consist of horizontally-bedded layers of sandstones, siltstones and mudstones. In the Shaft 2 area the majority of these rocks are covered by alluvium. The presence of this material and the wide spacing of the exploratory boreholes drilled during the site-investigation stage, rendered prior recognition of the abnormal hydrological conditions to the south of Shaft 2 impossible. The sedimentary rocks have been intruded by an interconnected network of post-Karoo dolerites, which tend to divide the area into different ground-water compartments. Owing to the inherent imperviousness of the unweathered sedimentary rocks, ground-water is stored mainly in the upper weathered and jointed rock below the alluvium and, to a lesser extent, in the various highly-permeable but narrow Contact-Zones of indurated sedimentary rock along the dolerite dykes. The permeability of the contact-zones decreases with depth and in the "notmal" tunnel area the majority of the dolerite dykes encountered to date at tunnel level, were either dry or very low-yielding.
The prominent east-west-trending dykes in the immediate immediate vicinity of Shaft 2 have, however, proved to be exceptionally vicinity of Shaft 2 have, however, proved to be exceptionally permeable down to at least tunnel level. Yields of up to 60 000 g.p.h. (270 m³/h.) have been encountered during excavation in this "abnormal" area. In the area approximately 6 000 feet (1 800 m) to the east of the tunnel route, thermal springs, with water temperatures of up to 31°C indicating deep circulation of ground-water, are associated with one of these dykes.
Geohydrological investigations by means of diamond-drill and percussion boreholes, geophysical surveys and detection of ground-water movement, were carried out from the surface in the immediate vicinity of the flooding point and in other selected areas. The object of these investigations was to determine the structure and the extent of the main fissure-zone and to plan the correct grouting operations to seal off the inflow of water into the tunnel.
It was deduced that the tunnel was flooded by an east-west-trending fissure-zone which can be compared with a diastropic joint-system extending to abnormal depths and which is not associated with any dolerite intrusion. With an estimated minimum lateral width of 1200 feet (365 m), this zone consists of numerous open, highly permeable joints, varying in width from hair-line to a maximum of 3 inches (7,6 cm), at the flooding point itself. The dip of these joints varies from 75°S to vertical. Water-level recordings carried out in various boreholes in the Shaft 2 area, have indicated that the levels in recording boreholes fluctuate as a result of recharge by rain-water and local pumping by farmers. The levels also varied as result of earth-tides and earthquakes. The flooding event itself, the subsequent draw-down tests from the inclined shaft and the final dewatering of the tunnel from the inclined shaft and the final dewatering of the tunnel also caused fluctuation. A total volume of 350 million gallons (1,6 x 10 6 m³) was drained from the area during a period of 15 months; this resulted in only a fairly limited lowering of water-levels in some of the recording bore-holes. The water-levels recovered fully within a period of 7 months, indicating a very large storage capacity of the aquifer-system. Chemical analyses of water samples, collected from various geohydrological environments, indicated that different types, and thus different bodies, of water are present.
The quality of the water varied from slightly saline, chloride to alkaline, soda-carbonate. Carbon-14 and tritium age-determinations of selected samples indicated the age of the ground-water to vary from zero to approximately 4 000 years.
The results of these analyses, in the light of a possible theoretical model for the aquifer-system, are discussed in detail. The very large earth-tidal fluctuations (37 cm maximum) observed in some of the recording boreholes and the abnormally high response of the water-levels to the Ceres-Tulbagh earthquakes, suggests the possible existence of a planar zone of crustal disturbance in the vicinity of Shaft 2.
An arcuate belt of gravity highs (for particularly the Bouguer anomaly) extending from the Doringberg fault near Prieska to the post-Karoo faults in Lesotho, suggests the possible existence of a major fault-system of pre-Karoo age which has been reactivated during post-dolerite times. It is postulated that the abnormal fissure-zone at Shaft 29 the thermal springs on the farm Roodewal, west of the tunnel route, and those on the farm Badsfontein near Shaft 2 together with the springs at Aliwal North and, farther east, on the farm Badsfontein are associated with this deep-seated zone of crustal disturbance.

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Transactions of the Geological Society of South Africa, 75, 225-264

The Jamestown Hills areas known also as the Jamestown Schist Belt, constitutes the largest of a number of narrow, tapering, generally arcuate, schist belt remnants which trend in various directions away from the main east-north-east- trending grain of the Barberton Mountain Land. The Schist Belt, which has a strike length of approximately 35 kilometres, occurs on the north-west flank of the Barberton greenstone belt, wedged between the Nelspruit migmatite gneiss terrain in the north and the Kaap Valley Granite diapiric pluton in the south.
The rocks of the Jamestown Schist Belt are composed mainly of a variety of mafic and ultramafic assemblages that constitute part of the Lower Ultramafic Unit of the Onverwacht Group of the Swaziland Sequence. Interlayered with the mafic and ultramafic horizons, which include also a wide variety of amphibole, chlorite, talc, and carbonate schists are a number of distinctive, generally aluminous, siliceous schist and cherty sedimentary horizons. These rock assemblages are correlated with the Theespruit Formation as defined by Viljoen and Viljoen from the type-area on the southern side of the Barberton Mountain Land. Mafic and ultramafic assemblages, together with intrusive soda-rich felsic porphyry bodies, occupy the central core of the Jamestown Schist Belt and are correlated with rocks of the Komati Formation also defined by Viljoen and Viljoen.
Whereas the mafic and ultramafic rocks in the type-area are mainly of extrusive origin, those in the Jamestown Schist Belt appear to have been emplaced as penecontemporaneos near-surface sill-like bodies that underwent processes of differentiation to form cyclically layered successions of alternating dunite, peridotitel pyroxenite, and gabbro. The onverwacht formations in the eastern part of the Schist Belt are overlain mainly by the sedimentary rocks of the Fig-tree and Moodies Groups. These successions are intensely deformed in the area of the New Consort Gold-mine and constitute part of the western closure of the Lily Syncline. The rocks of the Jamestown Schist Belt have been complexly deformed and metamorphosed. An attempt is made in this paper to describe the structure of the Schist Belt and to relate the gold and other mineralization to the tectonic history of the area. Aspects relating to the petrology, metamorphisms and geochemistry of the Swaziland Sequence rocks are also described and discussed.
Finally, a brief account is given of the gold, chrysotile asbestos, talc, magnesitel nickel, and verdite-buddstone mineralization occurring in the area. Available gold production data from 32 workings, and dating back to 1882, is tabled.

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Transactions of the Geological Society of South Africa, 75, 23-30

Two suites of igneous rocks synchronous with the igneous activity in the Bushveld Complex include the most important igneous rocks in the Vredefort Dome and the adjoining Potchefstroom Synclinorium. The older is a tholeiitic suite which forms sills, mainly in the sedimentary collar of the Dome. These sills are composed of dolerite, hyperite, and norite. Variation in mineralogical composition of these sills shows a gravitational concentration of ferromagnesian minerals towards the stratigraphic base. This is regarded as proof that these sills were emplaced before the strata attained a vertical attitude during their overturning. The average mineralogical compositions of some of these sills were determined and they were found to contain between 45 and 80% of pyroxene, whereas a chilled dolerite of one of these sills contains only 52% of pyroxene. This variation in the average composition of the different sills is interpreted as the result of separation of magma at different stages and levels from a larger differentiating pluton, consequently these sills are considered to represent satellites of an unexposed pluton in the central part of the Vredefort Dome.

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Transactions of the Geological Society of South Africa, 75, 265-274

In the Schmidtsdrif area, Northern Cape Province, the contact between the Black Reef and the Dolomite Series is transitional. A detailed measured section across the succession makes it possible to subdivide the transition beds into three members: the lower one is composed of alternating limestone, dolomite, calcarenite, shale, siltstone and quartzite; the middle one consists essentially of shale with very subordinate thin beds of dolomite and flat-pebble conglomerate; while the upper one comprises alternating dolomites chert, shale, siltstone and quartzite. The carbonate beds are partly clastic and partly biogenetic in origin. The latter contains abundant cryptalgal structures like domal and columnar stromatolites, flat cryptalgalaminae, oolites, pisolites and bioherms. Sedimentary structures in the clastic deposits include both planar and trough cross-bedding, current lineation, ripple marks, sole marks, tidal current ridges and graded bedding. Facies analysis indicates that deposition took place mainly in the intertidal to subtidal environments on a tidal flat, while some off-shore, lagoonal and supratidal deposits were also present. These environments of deposition were partly controlled by the rate of transgression of a stable land area by a shallow sea, probably from the north-east. Local factors like storms and off-shore bars, however, influenced the environments and played a vital role in the establishment and growth of the blue-green algae which gave rise to the cyclic carbonate deposits. As the transition beds constitute a separate lithological unit a formational status was assigned to the sequence. The name Schmidtsdrif Formation which consists of three members, viz. the Boomplaas Member, the Clearwater Shale Member and the Monteville Member, is proposed.

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Transactions of the Geological Society of South Africa, 75, 275-291

Rocks equivalent to the Transvaal System of the Republic of South Africa are widely distributed in south-eastern Botswana. A brief review is given of the stratigraphy of the Transvaal System within the main areas of occurrence. The hypothesis is developed that the characteristic palaeogeographic, stratigraphic, sedimentological and volcanological nature of the Transvaal System is the result of this formation having been laid down in a number of basins whose floors showed a continuing tendency to subside. Some speculation is made as to the geotectonic environment in which this subsidence of the basins occurred; it is stressed that the phenomenon does not appear to be part of a conventional orogenic cycle. The special problems of the origin of chert breccias associated with the Transvaal System at certain localities and the question of the correlation of the Shoshong Series of east-central Botswana with the Transvaal System are discussed.

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Transactions of the Geological Society of South Africa, 75, 293-294

The biotites are derived from metamorphic and plutonic rocks in the Precambrian at 5 localities in Swaziland. The chemical analyses and structural formulae together with indices of refraction and ratios of elements are given in tabular form. The results are discussed in the light of similar investigations elsewhere.

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Transactions of the Geological Society of South Africa, 75, 295-298

The South African Coastal limestones are composed of aeolian and marine facies that are often difficult to distinguish in isolated outcrops where field-relationships are obscured. Normal Petrographic investigation of compositional and textural aspects of the rocks is environmentally suggestive, but the study of quartz grain surface textures by electron microscopy provides much firmer evidence. Although this is a well-known technique in sediment studies, relatively infrequent application has been made to lithified rocks, presumably because of diagenetic problems. This study indicates that electron microscopy is useful for determining the depositional environments of these, and perhaps other, well-lithified Tertiary carbonate-rocks.

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Transactions of the Geological Society of South Africa, 75, 299-300

A classification of bedding plane spacing is proposed in terms of frequency per metre of sediment. It is suggested that the term "lamination" be discarded from bedding plane terminology as such, and be retained where closely spaced bedding exhibits a fissility.

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Transactions of the Geological Society of South Africa, 75, 301-306

A small glacial pavement about 40 km north of Christiana gives a paleo-ice-flow direction for the Dwyka glaciation which differs from the general paleo-ice-flow directions of that area. The regional paleo-ice-flow directions are towards the south, south-west and west caused by the Transvaal Ice Sheet. This glacial pavement gives two directions of ice flows, one towards W11N, the other towards N23W. Two possible explanations are presented for this deviation from the regional paleo-ice-flow direction. The one is that this was caused by an expanding ice lobe which flowed towards the south-west and expanded towards the north-west, and south-east prior to the whole area being covered by the Transvaal Ice Sheet. On the other hand if extrapolated back along their direction of paleo-ice-flow it would appear that the ice which engraved this pavement might have originated from the elevated or "dome" areas, one in the eastern Orange Free State and the other between Kimberley and Bloemfontein in the western Orange Free State.

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Transactions of the Geological Society of South Africa, 75, 307-309

Whilst engaged in regional mapping connected with mineral exploration in South West Africa, the author came across a small exposure of "nodular" limestone, subsequent examination of which showed the rock to contain the rare calcium borosilicate danburite, CaO.B2O3.2SiO2. The area under consideration lies some 120 Km eat of Windhoek, between the small centres of Omitara and Witvlei, and is underlain by strata of the late-Precambrian Damara System. North of the White Nossob River, on the farm Entracht 118, a thick zone of limestone, assigned to the Hakos Series of the Damara System, forms the prominent Vierkuppenberg range. The exposure occurs at the extreme south-western end of these hills, 0,75 Km south-east of the boundary between the farms Eintracht 118 and Diana 117, and 1 Km north-east of the Windhoek-Gobabis railway line. Here, over a very limited area, the fine-grained, blue-grey limestone contains numerous inclusions, 2-3 mm across, which stand out on weathered surfaces. Under the hand-lens these nodules, usually rounded to elongated, are seen to be finely layered. This layering does not necessarily correspond to the bedding of the host-rock.

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Transactions of the Geological Society of South Africa, 75, 31-45

Magma, which produced a consanguineous group of igneous rocks, was extruded and intruded into the pre-Karoo rocks after or, possibly, during the late stages of the main tectonic event which led to the formation of the Vredefort Dome and its surrounding synclinorium. Only the dioritic group is treated in this paper. It comprises the Lindequesdrift intrusion, the Roodekraal complex and the bronzite granophyre. The Lindequesdrift intrusion is composed mainly of spessartite and syenodiorite. The Roodekraal complex represents an old andesitic volcano into which dioritic magma was intruded. The rocks of this complex were hydrothermally altered to albite-amphibole-bearing rocks and in the final stages of igneous activity copper sulphides were introduced mainly in the lava. The bronzite granophyre forms dykes in the core of the Vredefort Dome, and they are the youngest (undoubtedly post-tectonic) intrusions of this group. The bronzite granophyre is believed to have originated from a contaminated dioritic magma.

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Transactions of the Geological Society of South Africa, 75, 311-312

Shark teeth of Teriary age are confined to the fossiliferous Pecten Bed occurrences that are scattered between Uloa and Hell's Gates in Zululand. The shark fauna is at least of Upper Miocene or even of Pliocene age. No teeth have been recorded from the limestone-calcarenite succession that overlies Pecten Bed occurrences in Zululand.

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Transactions of the Geological Society of South Africa, 75, 313-315

The petrology, Mineralogy, and chemical composition of a hornblendite dykelet from Bon Accord are presented. The composition of tile hornblendite is compared with members of the Caledonian appinite suite, and the similarity of the latter with the basaltic komatiites from Barberton is noted.

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Transactions of the Geological Society of South Africa, 75, 47-54

The Stinkfontein Formation extends from the Richtersveld southwards to Kleinzee and can be divided into a lower orthoquartzite succession with a basal conglomerate, and an upper part consisting of feldspathic quartzites, arkoses and intercalated volcanics. Mafic rocks and a granite intruded the sediments and these magmatic events may be related to the Richtersveld Granite farther north. The Stinkfontein beds have been subjected to four recognisable phases of deformation which can also be detected in the underlying Basement-gneisses. The first two of these tectonic episodes gave rise to basement shearing with subsequent gravity-sliding of the cover-rocks into the troughs formed. Episodes Fl to F3 appear to be of pre-Nama age and may therefore be attributable to a pre-Damaran tectonic event where phase F4 probably reflects the Damaran orogeny. Some of the Stinkfontein beds are selectively granitized along the coast, probably during F2, and this phenomenon is ascribed to isochemical metamorphism at high crustal level so the Stinkfontein Formation is conformably overlain by the Holgat Formation along the coast and by the Hilda Formation in the interior of the area surveyed.

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Transactions of the Geological Society of South Africa, 75, 5-10

The current status of radioactive isotopes in the ground-water research programme in Rhodesia is described. The single-well Point-Dilution technique utilising gamma-emitting radiotracers for flow rate determination is discussed and compared with the classical time/distance tracer method. Single bore-hole ground-water direction measurement techniques are also highlighted. Brief mention is made of the use of artificial radio-isotopes in the measurement of effective porosity and the delineation of the major zones of flow in bore-holes sited in the crystalline rocks. Regional ground-water flow rates and direction measurements with the aid of the radioactive hydrogen isotope, tritium, are described. Tritium, which is injected into ground-water regimes by the atmosphere, allows the geohydrologist at times to "date", underground water and with supplementary hydrological data, useful information on flow rate, direction of flow and turnover times can be obtained.

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Transactions of the Geological Society of South Africa, 75, 55-66

The Molteno sandstone contains secondary silica in the form of: (1) quartz overgrowths in optical continuity with the detrital parent grains and (2) a local interstitial cement filling the pore spaces and cavities in the rock. These cavity-fill deposits occur as microcrystalline quartz, chalcedony, and megaquartz and are believed to be related in origin to the quartz overgrowths. A petrographic study of the sandstones and grits in the sequence between Aliwal North and Burgersdorp in the north-east Cape Province provides evidence of the origin of the silica and the chemical environment of deposition. Conditions were predominantly acid but with local pools of alkalinity Where time and the delicate balance of the PH determined whether carbonate or silica were precipitated. Fluctuations in the concentration and supply of silica to the reaction site are believed to be responsible for the many deviations from the normal crystallisation sequence of microcrystalline quartz-chalcedony-megaquartz.

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Transactions of the Geological Society of South Africa, 75, 67-70

"This technique ..... has frequently yielded information of environmental significance in rocks wherein the structure was either poorly displayed or not apparent ....... When X-rays are transmitted through a rock slice variations in composition, fabric etc. within it may result in differences in absorption that can then be recorded on photographic film". The technique has been applied to South African stromatolites, sandstones and andesite. Resultant photos are shown.

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Transactions of the Geological Society of South Africa, 75, 71-75

Dolerite sheets were found to degrade seismic reflection records in three ways. Firstly, when the shot was located in dolerite, there was poor energy transfer to the formation. Secondly, the seismic pulse produced when the shot was located in dolerite consisted mainly of high frequencies, which were not well suited to producing deep reflections. Thirdly, dolerite sheets deeper in the sedimentary section reflected back much of the incident energy, reducing the amplitude of the deeper reflections. By the use of multiple geophone patterns and CDP stacking, the signal-to-noise ratio of the deeper reflections could be improved to such an extent that reflection seismic profiling could be used successfully for mapping structure in most of the Karroo Basin. Some dolerite sheets could be mapped very precisely by seismic reflection work. Usually they were observed to follow the sedimentary bedding, but in some places they transgressed sharply across it.

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Transactions of the Geological Society of South Africa, 75, 77-84

Revision of Mellor's official Witwatersrand nomenclature has become necessary as it no longer conforms with currently accepted stratigraphic codes. The suggested lithostratigraphic classification and nomenclature is in accordance with the recommendations of the International Subcommission on Stratigraphic Classification. Mellor's nomenclature of 1917 is modified no more and no less than required to bring it into line with the recommendations of the I.S.S.C. Circular No. 26 (1970).

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Transactions of the Geological Society of South Africa, 75, 85-95

A stratigraphic column for the Malmani Dolomite has been constructed through the recognition in bore-hole cores and quantitative logging of seven macroscopic parameters, namely, coarse clastics, carbonaceous shale, finely-laminated to massive dark dolomite, columnar stromatolites, domical stromatolites, oolites, and chert. Overlying the predominantly clastic Kromdraai Member at the base, ten zones have been outlined, consisting almost wholly of non-clastic or autochthonous sedimentary rocks. Three depositional environments have been recognized in the Malmani Dolomite, namely, supratidal, intertidal and subtidal, each being characterised by certain macroscopic parameters. The nature of the stratigraphic succession in the Malmani Dolomite resulted from facies sedimentation accompanied by migrations of the shoreline. One complete transgressive-regressive cycle of deposition is recognizable as well as portion of a second. Much evidence for chertification has been noted, this process being largely dependent on the pH of the environment, and on the availability of silica in solution. On account of the highly alkaline nature of the environment, supratidal rock-types are devoid of chert. Silica was precipitated under lower pH conditions in the intertidal and subtidal environments, particularly so in the highly porous oolite zones, in which most of the silica was taken up.

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Transactions of the Geological Society of South Africa, 75, 99-110

Stromatolites in the Transvaal Dolomite from an area north-west of Johannesburg have been classified and their morphology described. Domical forms are either symmetrical or elongate in plan. Oncolitic and "biscuit-like" encapsulated structures have been distinguished. Tabular stromatolites are either columnar or non-columnar. The former are differentiated on their growth form or, where appropriate, the nature of their branching. Laminated stromatolitic and "crinkled" types are the two non-columnar forms recognised.

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Transactions of the Geological Society of South Africa, 76, 1-7

The fossiliferous limestones at Needs Camp, near East London, are briefly described and the history of their investigation outlined. It has been generally accepted, for many years, that the lower quarry contains upper Cretaceous limestones, while those in the upper quarry are of Tertiary age. King has recently proposed that both deposits are of late Cretaceous age; the evidence for this view is here examined and rejected.

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Transactions of the Geological Society of South Africa, 76, 113-133

Part of the east-west-trending Zambezi orogenic belt in Rhodesia is described in detail for the first time. The area was chosen because of its geological simplicity after an interpretation of air-photographs covering the entire belt in Rhodesia. The cover-sequence consists of generally well sorted sediment which was deposited to the north of, and overstepped a positive stable block of crystalline basement which is divisible into two main units. If, as suggested by Vail (1965), and assumed in this report, the cover-sequence belongs to the Umkondo System (< 2 000 > 1 780 m.y.) then it may have remained undeformed for a very long time for the date of the Zambezi orogeny is generally taken to be about 500 m.y. Both the metamorphism and the strain were strongly progressive from the earliest recorded stage of the orogeny and continued so through both main phases, until the final cooling and uplift. The first major phase was characterised by a Barrovian metamorphism in the upper amphibolite facies during the development of a complex pattern of elongate domes and basins with axial surfaces which now strike roughly east-north-east - west-south-west and dip to the south at about 40°. During the hotter, regional Abukuma metamorphism of the second major phase, also in the upper amphibolite facies, large rounded domes formed in the interface between the metasedimentary cover sequence and its basement. The earlier fold pattern was either intensified and refolded (away from the mantled gneiss domes) or incorporated into rim-synclines around the domes. Various stages in the transformation to potassic granites of the acid volcanic sequence in the basement-rocks is thought to be recorded in the basement-domes of the region. The underlying basement-paragneisses (of unknown age) were probably being migmatised throughout the orogeny and the originally psammitic units are sodic granites in restricted areas.

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Transactions of the Geological Society of South Africa, 76, 135-143

The term morphometry is briefly explained and it is indicated that in geomorphology a careful selection of statistical techniques is necessary in order to reach meaningful conclusions. The importance of the use of large-scale maps and aerial photographs for morphometric analysis is stressed, and the techniques of compiling the drainage map, and sampling of first order stream segments are dis cussed. The various geological formations that outcrop in the Umbilo River drainage basin are represented by the Table Mountain Series, the Dwyka Series, the Ecca Series and the Red Berea Sand, which are shown on a generalized geological map of the area. The morphometric properties that have been investigated include the number of stream segments, bifurcation ratios, length ratios and frequency distribution of stream lengths. Finally it is concluded that the mathematical relationships in the basin conform with Horton's laws; the lithology does not influence the development of the drainage directly; and that permeability of the superficial material and topography may be the most significant factors in drainage development in the Umbilo River drainage basin.

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Transactions of the Geological Society of South Africa, 76, 145-152

The Cape Fold-belt shows several anomalous features if it is interpreted as the result of "conventional" geosynclinal or plate tectonic processes, including a complete lack of igneous and metamorphic phenomena, and a 90 degrees change of direction. A literature survey and a study of aerial photographs yields evidence which can be most satisfactorily explained in terms of gravitational tectonics, e.g. the presence of a regional slope, disharmonic and cascade-folding with downslope asymmetry, and evidence of soft-sediment deformation. A model for the Cape Fold-belt is proposed in which the initial regional slope was increased by uplift, probably aided by faulting, which resulted in wholesale northward sliding towards the axis of the trough. A similar but gentler movement in the western branch of the trough led to interference of the two sets of folds in the south-western Cape and resulted in a south-westerly trend. Late-stage brittle deformation in the form of thrusts occurred in places. Subsequent deformation has been by faulting of a tensional nature, associated with the break-up of Gondwanaland.

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Transactions of the Geological Society of South Africa, 76, 15-25

The depositional history of the Wolkberg Group and of the Black Reef Quartzite in the eastern and northern Transvaal is outlined. In the early stages of Wolkberg sedimentation, irregularities in the basin floor had a profound effect on the thickness and the distribution of stratigraphic units. Subsequently, deposition took place on a smoothed surface, and formations varied much more gradually in thickness in response to regional tectonic controls. The angular unconformity between the Black Reef Quartzite and the underlying Wolkberg Group is of local significance only, these units being perfectly conformable and gradational into one another over the majority of their outcrop extent. The Wolkberg Group represents the initial or proto-basinal stage of Transvaal sedimentation, and cannot logically be equated with the earlier Dominion Reef and Witwatersrand events.

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Transactions of the Geological Society of South Africa, 76, 153-163

Petrochemical fields and trends of the exposed part of the Still water Igneous Complex are established using sixty-one new major and trace-element rock analyses and eight major-element rock analyses from the literature. The fields and trends of these crystal cumulates Preresent variations along solidus curves, not continuous variation along some liquidus. The variation diagrams show enrichment in alkalis and a decrease in the Mg/total Fe ratio for rocks progressively higher in the complex and significant changes in petrochemical trends with the first appearance of cumulus plagioclase. These fields and trends form a basis for comparison with other stratiform complexes. As more petrochemical data become available, such fields and trends may form a basis for discriminating among the many kinds of basic and ultrabasic rock associations.

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Transactions of the Geological Society of South Africa, 76, 165-167

Biographical memoir.

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Transactions of the Geological Society of South Africa, 76, 169-171

An examination of fine-scale sedimentary structures from the Middle Ecca near Grahamstown suggests that some, at least, of the fine-grained rocks from this formation were deposited as turbidites.

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Transactions of the Geological Society of South Africa, 76, 175-177

D. H. Lenthall: Dr. De Waal has presented in his paper a new and highly original theory on the origin of the Bushveld granites in the Zaaiplaats area. His thesis that the Bushveld granites, excluding the intrusive Foothills and Bobbejaankop granites, represent epicrustal material that has been metamorphosed by the Mafic Assemblage of the Bushveld Complex, and hence termed by him the "Main Suite", is based essentially upon three considerations: (i) an observed systematic variation of the granularity of the granites, (ii) the uncertainty of the age relationships between the granites and the Mafic Assemblage of the Bushveld Complex, and (iii) an apparent systematic variation in the mineralogy of the "Main Suite" that conforms very closely with the systematic variations of granularity, which, together, are taken to suggest an increase in the grade of metamorphism as the rocks of the mafic assemblage are approached. Prior to discussing the merits of the paper it is necessary to comment upon the nomenclature which has been used. As Dr. De Waal has gone to the trouble of explaining the reasons for his choice of the term "Main Suite" instead of Main granite one wonders why the term granulite has been used so loosely and out of context in describing the Bushveld granite. Undoubtedly some of the metasediments of the Transvaal Sequence, wedged along the contact of the Bushveld granites and the Mafic Assemblage, may be described as pyroxene hornfelses, but to use the term granulite for the coarse-grained and granophyric granites which are composed of perthite, antiperthite, sodic plagioclase, locally micropegmatite, hornblende, biotite, chlorite, quartz, and accessory magnetite, ilmenite, sphene and epidote, is certainly unjustified.

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Transactions of the Geological Society of South Africa, 76, 177-179

Reply to D. H. Lenthall: To begin with I would like to thank Mr. Lenthall for the time he has taken to comment on my paper. Coming from a person who has done a large amount of work in the Zaaiplaats area it is even more appreciated. However, it is obvious that our ideas on the Zaaiplaats granites differ considerably and I will discuss Mr. Lenthall's comments, where possible, in the order he made them. a) The term granulite. b) Variation in the granularity of the Main Suite rocks. c) A marked difference exists between the trace-element geochemistry of the Rooiberg felsites and the Main granite. d) Age relationships of the Bushveld granites. e) The textural nature of the dark minerals. f) Regional distribution of the dark minerals. Reply to P. Ianello: I thank Mr. Iannello for his contribution. I am fully aware of his work in the Rooiberg area. Unfortunately I have not had the opportunity to visit that area and in view of our past experience with eye-ball correlations I have little to comment on Mr. Iannello's ideas. However, one thing is certain and that is that there is much confusion about what is Main granite in areas of the Bushveld other than Zaaiplaats. If my contention is correct that the Main in its type-area is not a true magmatic granite, but a metamorphosed portion of the Epicrustal Phase, then there is a lot or reconsideration to be done.

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Transactions of the Geological Society of South Africa, 76, 181-182

Comments on the choice of names to replace the present nomenclature of the Witwatersrand formations must obviously await a more formal and authoritative revision. However, I would like to voice a criticism of his choice of "Hamberg" for the currently named "Government Reef Series". Hamberg township and railway station are both underlain entirely by beds of the Jeppestown Series. The Government Reef beds lie to the north, underlying the suburb of Discovery. The author makes a regrettable mistake on page 83, when discussing the Jeppestown lava. Here he states that this formation "does not occur in the type-area". While it is true that the succession figured by Mellor (1911) and copied by Pretorius (1964) omits the lava, it must be realised that Mellor was handicapped severely in his field mapping by the lack of exposures in the wide, flat valley which follows the Jeppestown beds from Johannesburg to Roodepoort. Vertical shafts on certain gold mines indicate its persistence into the Central Rand area (Cousins, 1965). A subvertical shaft (No. 16A) on Crown Mines and the subvertical shaft at the Van Dyk mine, east of Boksburg, cut excellent sections of the Jeppestown Series, including the Jeppestown lava. It is also exposed, on surface in the deep railway cuttings lying between Langlaagte railway station and the Main Reef road, and is exposed in a trench near the South Roodepoort mine The Jeppestown lava has been intersected in bore-holes at intervals around the entire Witwatersrand basin including the East Rand and is exposed on outcrop in the Vredefort Dome, where it was incorrectly correlated as Bird lava by Nel (1927). The Jeppestown lava, in spite of its thinness, (˜30 m), apparently extends as a sheet over 25 000 sq km, a remarkable indication of its mobility and suggesting that it must have been extruded from well distributed feeder-fissures. I support the author in this division point between the Upper and the Lower stages. I suggested this in an earlier paper (Cousins, 1965). If the author wishes to divide the Lower Witwatersrand beds into stages of similar sedimentary patterns in accordance with I.S.S.C. rulings, a much more radical revision of Mellor's (1911) succession is required. (a) The Jeppestown beds above the lava are very fine-grained shales and fine-grained argillaceous quartzites. Below the amygdaloid they are coarser quartzite with pebble-beds and a magnetic shale. These lower beds are virtually indistinguishable from the upper beds of the Government Reef Series (See Fig.2). (b) The Coronation beds include beds of tillite. These underlie the West Rand shale, which closely resembles a varved shale, and, in its environments this is probably a correct interpretation. (c) The Promise beds are again non-glacial and resemble the upper beds of the series. There is therefore a very strong case for subdividing the Government Reef beds into three separate stages and for including the lower part of the Jeppestown series in the uppermost of these. Reply to Mr. C. A. Cousins. I wish to thank Mr. Cousins for his comments. His authoritative contributions regarding the distribution and lithologic character of certain stratigraphic units will no doubt be welcomed by the Witwatersrand Triad Subcommittee of the South African Committee for Stratigraphy. My statement that the lava unit is absent from the Jeppestown Formation of the Central Rand, is indeed a regrettable mistake, the more so as I have personally seen an excellent exposure of this unit in a deep foot-wall cross-cut in the E.R.P.M. mine. However, the mistake has been rendered less regrettable by the resulting wealth of information on the unit that Mr. Cousins has recorded in his discussion. Since the publication of the very lucid South African Code of Stratigraphic Terminology and Nomenclature, which appeared while my paper was in the press stratigraphic terms should no longer be used in a loose and essentially incorrect way. Such usage of the term stage in the contribution under discussion is therefore unfortunate.

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Transactions of the Geological Society of South Africa, 76, 183-194

The present drainage patterns of the Harts and Molopo Rivers have developed in consequence of crustal movements associated with the initiation of the Griqualand-Transvaal Axis of uplift towards the end of the Tertiary Period. The development of this axis along a north-east-south-west Precambrian lineament which now forms the divide between the Harts River and the Skoonspruit drainage and the Vaal River, caused disruption of the paleo-Nossob, the paleo-Dry Harts, and the paleo-Harts Rivers. The disruption of these rivers, which were southward-draining tributaries of the Vaal River during the Tertiary, culminated in the evolution of the present physiographic features of the area lying to the north-west of the Vaal River between Klerksdorp and Barkly West. Tectonic movements also resulted in a significant reduction of the volume of water draining into the Vaal River from the north. This fact, coupled with the diastrophic steepening of the slope of the pre-Karoo surface on which the Vaal River was shifting towards the south-east, contributed to the formation of the "order" the glauconite in the deltaic Coal Measures of the Ecca in the northern part of the basin. It is possible then that the fossiliferous marine shales near Kimberley accumulated as a fine-grained offshore facies of the Ecca deltaic sequence.

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Transactions of the Geological Society of South Africa, 76, 195-200

Two intergrowths of orthopyroxene and ilmenite from Frank Smith Mine were investigated mineralogically, petrologically, and chemically. Five new chemical analyses are reported, together with the optical data for the orthopyroxene and the cell dimensions of the ilmenite. These intergrowths are compared with the intergrowths of clinopyroxene and ilmenite investigated by Williams, by Ringwood and Lovering, and by Dawson and Reid. The data indicate that neither the explanations offered by Williams, nor those proposed by Ringwood and Lovering and by Dawson and Reid account for the origin of these intergrowths. It appears that these intergrowths resulted from cotectic crystallization, with the ilmenite representing skeletal crystals. This inclusion points to the existence of a stage of crystallization of ilmenite and pyroxene prior to the eruption of the kimberlite magma. This appears to be the last stage prior to eruption, and it seems to be an important phase in the evolution of the kimberlite magma, because it is during this stage that the kimberlite magma changes from a magma from which silicates, such as garnet, olivine, orthopyroxene and clinopyroxene crystallize, to a magma from which carbonates and oxides, such as calcite, perofskite, magnetite and apatite crystallize.

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Transactions of the Geological Society of South Africa, 76, 201-206

It is shown that when a land-mass is moving towards a pole, glacial beds should be stratigraphically higher than aeolian beds, but that aeolian beds should succeed glacial beds if the movement is away from a pole. The direction of ageing of these beds should be in the direction of movement of the land-mass whether towards or away from a pole. Evidence is presented that the northern Ecca is the equivalent of the Upper Dwyka in South West Africa. The coal-measures of the so-called Middle Ecca are shown to thin in a south-westerly direction and to die out in a cut-off zone that stretches from near Scottburgh on the east coast of the Republic of South Africa to Mariental in South West Africa. This zone is also the north-eastern limit of the White Band at the top of the Dwyka Series. Lithologically nearly all the Karroo beds between the Dwyka and the Cave sandstone are different on the opposite sides of the cut-off zone and chronostratigraphically they cannot as yet be correlated with one another with any degree of certainty.

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Transactions of the Geological Society of South Africa, 76, 207-227

The rocks of the Main and Upper Zones are described and subdivided into various subzones on the basis of characteristic rock-types and marker horizons. The composition of orthopyroxene, plagioclase and olivine was obtained from a large numbr of samples by routine optical and X-ray diffraction methods, in order to determine the crystallization trends of these minerals. Comparison of these results with those given by Groeneveld (1970) for the area to the south, as well as additional mapping in the valley of the Blood River, has revealed the existence of pronounced lateral variation in the composition of the cumulus minerals and in the rock-types of the Upper Zone. It is suggested that towards the outer margins of the Complex, as in the Stoffberg area, the heat loss was more effective, causing lower-temperature phases to crystallize simultaneously with higher-temperature phases in the central portion of the magma chamber. Crystallization of the lower temperature phases of the ferromagnesian minerals extracted more iron from the fractionating magma where the thickness of the chamber was less, with the result that the magma was depleted in iron, relative to that in the central portions, and prevented the formation of the magnetite layers of Subzone D of the Upper Zone in the south. Apatite is an important cumulus mineral in the olivine-bearing diorites of Subzone D of the Upper Zone. It is considered that the magma reached saturation in phosphorus at the base of Subzone D and that subsequent crystallization of apatite was responsible for sufficient extraction of Ca from the magma so that the coexisting plagioclase is an andesine and the rocks are therefore dioritic in composition. There is a pronounced compositional break at the base of the Pyroxenite Marker of the Main Zone. This is probably due to the influx of fresh, undifferentiated magma into the magma chamber. It was possible to calculate that this addition of fresh magma must have been at least ten% of the tot

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Transactions of the Geological Society of South Africa, 76, 229-247

A systematic study of the Malmani Dolomite stratigraphy in the eastern and north-eastern Transvaal has resulted in the recognition of five regionally persistent lithological units. The units are recognized on the basis of dolomite colour and on the proportion of chert, limestone, banded iron formation, mudstone and quartzite interbedded with the carbonates. Three major depositional cycles are recognizable and are separated by two intraformational disconformities. The surfaces of disconformity are capped by thin bodies of chert-in-shale breccia. The geographic distribution of the five units within the dolomite is controlled primarily by the pre-Pretoria Group unconformity. The Pretoria Group comes to rest upon successively lower units within the dolomite when followed in a southerly direction. Very extensive deposits of primary limestone, hitherto unrecorded in the Transvaal, are described. These bodies represent remnants of a primary limestone which has been largely obliterated by the dolomitization process. The limestone deposits are very similar in their stratigraphic setting and in their stratigraphic relationships to the economically exploited deposits of the north-western Cape Province.

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Transactions of the Geological Society of South Africa, 76, 249-270

The Pilanesberg alkaline province is an area in which major magmatic activity has taken place, commencing in the Precambrian and reactivated as recently as the Upper Jurassic. The province comprises swarms of narrow dikes of essentially subalkaline and femic character, whereas the intrusive rocks of the passively emplaced central bodies generally post-date the dikes and faults and, are almost exclusively salic and alkaline. Abundant kimberlite and carbonatite occurrences demonstrate forceful intrusion. The main site of igneous activity is controlled by north-west-trending anticlinal flexures that manifested themselves in pre-Pilanesberg times. The location of central intrusions appears to be determined by the intersection of north-west and east-west-trending fault-zones. In keeping with other major continental alkaline provinces the most abundant magma types are nepheline syenite and potassic tristanite. The femic rocks are generally dike-rocks and are subalkaline froleiites and andesites, making up a small volume percentage of the rocks present in the province. The major element analyses occupy mean positions relative to trends in other alkaline provinces. The limited trace-element data show a covariance between Ba and K, Ba and Si, Sr and Al and Ga, Zr and Hf and Nb and Ta, and most of the rocks show Rb enrichment relative to K. It is concluded that the dense femic magmas could only be emplaced at high levels in the crust during tensional conditions whereas the salic magmas, owing to their marked buoyancy were able to rise through the crust during static conditions by a passive stoping mechanism. Kimberlites and carbonatites carbonatites demonstrate forceful intrusion, probably as a result of gas-fluidization emplacement.

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Transactions of the Geological Society of South Africa, 76, 27-52

The Rietfontein Complex and the alkali granite plutons are members of a larger group of comagmatic intrusions which were emplaced during the late stages of the development of the Vredefort Dome. The mafic portion of the Rietfontein Complex is a layered intrusion which is composed of a wehrlite-olivine gabbro series and a troctolite-picrogabbro series. A pluton of amphibole-bearing hypersolvus alkali granite is intrusive into the layered intrusion. The two plutons of "alkali granite" along the Vaal River in the Vredefort Dome are composed of amphibole and pyroxene-bearing subsolvus alkali granite and alkali syenite. The alkali granite originated from an alkali syenitic magma by the assimilation of quartz-rich country-rocks. Dykes of mariupolite which are genetically related to the subsolvus "alkali granite" were emplaced in the roof and the hood-zone of these two plutons and originated by desilication of the alkali syenite under conditions of high PH2O.

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Transactions of the Geological Society of South Africa, 76, 271-277

An unconsolidated, phosphatic, lag-placer deposit containing up to 10% P2O5 is widespread on the Agulhas Bank off the southern tip of Africa. The phosphate is concentrated in the sand and gravel fraction of the sediment in the form of grains of phophorite and glauconite eroded from outcropping Tertiary phosphorites during late Teriary and Pleistocene regressions. Some modern phosphate mineralisation may be taking place within faecal pellets in organic-rich muds on the western Agulhas Bank. The grade of parts of the lag-deposit can be beneficiated by screening, probably to a level of about 16% P2O5. The deposit may containa bout 1,4 x 10(8) metric tons of P2O5, and constitutes a marginal phosphate resource.

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Transactions of the Geological Society of South Africa, 76, 279-299

This investigation deals with the mineralogy and petrology of the copper-bearing formations in the Witvlei area, South West Africa. These copper-bearing formations occur in a zone extending through central South West Africa into neighbouring north-western Botswana - the mineralization having thus far been established at intervals over a length of strike of more than 800 km. The mineralogy and the petrology of the copper ores have been studied with the aid of thin and polished sections, and a full description of all the mineral species and rock-types observed in the area are given. The main ore-mineral was found to be chalcocite, occurring together with lesser amounts of digenite, bornite, chalcopyrite, covellite, pyrite, curite, native copper, malachite, azurite, chrysocolla, and iron ore. Although silver is consistently reflected in assays of the ore, no silver mineral could be detected using an ore-microscope. Electron-microprobe tests showed that the silver occurs as trace-amounts in solid solution in the sulphides. The ore-minerals display evidence of progressive enrichment in copper from pyrite, through chalcocite, to native copper. The grain-size characteris tics of the Witvlei ores were investigated, and cumulative frequency curves, representative of the grain-size of sulphides were constructed. The ore particles vary in size from less than one micron to a maximum of 125 microns, the median grain-size being of the order 4-8 microns. Specific gravity determinations yielded a mean value of 2,71 for the argillaceous copper-bearing sediments. A geochemical study of the Witvlei ores revealed that only copper and silver are concentrated ores revealed that only copper and silver are concentrated in amounts of possible economic importance. Correlations between the various chemical and physical properties of the ore were sought using computer techniques. Good correlation was obtained between copper and silver content and between copper samples between copper samples taken from varying widths in the ore horizons. A comparison is made between the Witvlei deposits and stratabound sulphide ore-bodies elsewhere in the world. It is concluded that similarities exist between the South West African occurrence and the Kupferschiefer of Europe, the Nonesuch Shale in Michigan, U.S.A. and the Zambian Copper-belt. Finally, it is possible that the ultimate source of the copper found in the Witvlei stratiform ore-bodies could have been the underlying volcanic succession.

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Transactions of the Geological Society of South Africa, 76, 301-307

The zinc contents of a large number of kimberlites and their xenoliths (peridotites and eclogites), olivine melilitites and basalts are presented and discussed. Zinc was also determined in some rocks from the Bushveld Igneous Complex, the Messum Complex, O'okiep "metamafics" and granites, as well as some mineral separates. An X-ray fluorescence method was used to obtain the data. The main observations are: (i) The zinc concentration is remarkably uniform in kimberlites, peridotites, olivine melilitites and basalts, but not in eclogites, for which the range is 13 to 77 ppm Zn. (ii) The zinc distribution in each of these rocks is discrete (no overlap) with the exception of eclogite. Average Zn values are: peridotite -35 ppm; kimberlite -55 ppm; and basalt plus olivine melilitite -00-110 ppm. (iii) The nature of the Zn distribution in ultramafic rocks appears to have a bearing on hypotheses concerning the origin of ultramafic rocks and basalts.

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Transactions of the Geological Society of South Africa, 76, 309-318

The Middle Ecca of the Muden and Tugela Ferry areas is subdivided into upward-coarsening sequences which grade from horizontally-laminated siltstone or interbedded siltstone and sandstone at the base, through a horizontally-laminated and cross-laminated sandstone, into cross-bedded and massive sandstones, which are commonly channelled and pebbly in their upper parts. These sequences are interpreted as representing delta complexes which prograded south to south-west over a muddy platform, and which were subsequently cut through and modified by the associated river systems to landward. The locus of major coarse-grained deltaic deposition was in the immediate vicinity of the distributary mouths. Finer sediments accumulated farther basinward and in the interdistributary areas, and in certain places these can be seen to interfinger laterally with the major sandstone units. Other sandstones are laterally very persistent, and are the product of coalescing of adjacent distributary mouth bars. Thinner sands extended laterally into interdistributary embayments, and were probably deposited following crevassing of the levees. Waves and basinal currents were ineffective, and there is no evidence of significant reworking of the outer delta margins by shoreline processes.

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Transactions of the Geological Society of South Africa, 76, 319-320

The paper gives a brief account of the discovery of a mineral bearing a very close similarity to that of metazeunerite found in the St. Anton Mine in Germany. This mineral is very uncommon and the author believes this identification to be the first made of a metazeunerite type mineral in South Africa. The paper sets out to give a physical, chemical, and crystallographic description of the mineral.

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Transactions of the Geological Society of South Africa, 76, 53-61

Two parameters of differentiation for layered intrusions are proposed, viz. a modified version of the differentiation index and a modified version of the crystallization index. Both these indices are calculated from the norm in such a way that they are practically independent of the concentration of particular minerals or oxides present in the analysed rock. The two indices are used to illustrate the differentiation trend in the Layered Sequence of the Bushveld Complex. From these diagrams it may be concluded that the modified differentiation index (MDI) is more useful for intrusions such as the Bushveld Complex where relatively few ultramafic rocks are developed, whereas the modified crystallization index (MCI) seems more useful for intrusions with a considerable development of ultramafic rocks.

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Transactions of the Geological Society of South Africa, 76, 63-73

The mode of occurrence of potassium feldspars is described. Measurements of the spacing of the (131) and (131) lines of 38 samples of feldspar show that all have high obliquity values (lowest 0,82; mean 0,94). Potassium feldspars embay and replace plagioclase grains, but only highly ordered microcline affects this replacement. It is concluded that the development of microcline is coincident with the act of replacement, and that its structural state has been influenced by the associated feldspars. Microclines with high obliquity are found in the contact-zone of the Homogeneous Granite and in the tonalitic gneisses of the Ancient Gneiss Complex showing no evidence of replacement. It is concluded that these microclines achieved a high degree of ordering as a result of crystallization in the presence of volatiles. Myrmekite, microperthite, and mantling by oligoclase are described and their origin discussed. Tin and tantalum mineralization is located in a linear zone extending across the Homogeneous Granite associated with albitization efdfects. By contrast columbium minerals are apparently related to a more potassic variety of the Homogeneous Granite lying on the north-eastern flank of the Tin Belt in the vicinity of Forbes Reef.

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Transactions of the Geological Society of South Africa, 76, 7-14

A mineralogical, a petrological and a petrochemical investigation of the rocks from the chilled margin of the Bushveld Complex, and from the "Sill Phase" were made. The investigation indicated that two rock-types comprise the "Sill Phase". An older dioritic type, which has calc-alkaline affinities and a younger tholeiitic type. The andesite in the Pretoria Series also shows calc-alkaline affinities and has almost the same composition as the diorites. Geological evidence also indicates that some diorites are older, and others younger, than the andesites. It is therefore concluded that the diorites and the andesites represent the same phase of magmatic activity, called the Sill-phase.
The fine-grained chilled margin of the Bushveld Complex and the dolerite sills have a tholeiitic composition, and plot along the same variation trend on the AFM-variation diagram. Geological evidence also indicates that both are younger than the diorites and the andesites; they have therefore been grouped together as the Chill-zone.
The variations in the composition of the chilled margin of the Bushveld Complex indicate that the middle to lower portion of the Critical Zone formed from a more mafic magma than the upper portion of the Critical Zone and the lower portion of the Main Zone. The compositions of the chilled margins of the dolerite sills indicate that the compositions of the magmas which gave rise to the Chill-zone of the Bushveld Complex varied significantly.
The presence of the two trends does not necessarily contradict the contention of Willemse that the Dullstroom Lava represents the first stage in the evolution of the Bushveld Complex, because calc-alkaline and tholeiitic magmas are known to coexist in the same magmatic province, and even in the same volcano. It does, however, indicate that the magma from which the layered portion of the Bushveld Complex crystallized was essentially tholeiitic in composition.

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Transactions of the Geological Society of South Africa, 76, 75-76

The author reviews the work of previous investigators on the origin and genesis of granophyres associated with the Bushveld Igneous Complex and points to inconsistencies in the nomenclature used by them. Following his own investigation, he now proposes a system of nomenclature in which the term granophyre follows the names of the type areas, which are 7 in number: Waterval, Paardekop, Sterk River, Blinkwater, Groenfontein, Welgevonden and Stavoren.

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Transactions of the Geological Society of South Africa, 76, 77-81

Geochemists appear to have been misled on the geochemistry of platinum group elements by over-emphasis on the chemical inertness of these elements and by the preponderance of metals and alloys in the samples of platinoid minerals available to them in the earlier years of the present century. Major production up to that time was from alluvial deposits, which were mainly uncombined metals, and show a marked contrast to the largely combined platinum group minerals present in primary deposits of these elements. Present evidence indicates that the platinoid elements are strongly chalcophile and only subordinately siderophile. Differences in the mineralogy between primary and alluvial ore are considered to be the result of chemical attack during weathering and transportation and not caused by differences in the primary mineralogy.

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Transactions of the Geological Society of South Africa, 76, 83-84

C.A. Cousins: The author has chosen a fascinating and valuable study of one of the problematical aspects of the Bushveld Complex. From reading this paper, it appears that the author considers that the felsic "roof-rocks" are of pre-mafic age. The evidence for this view, although shared by many distinguished students of the Bushveld, is not entirely convincing. A major problem is the distribution of the felsic rocks, which overlie the layered mafic rocks, while at the same time are absent from undisturbed successions of the Pretoria Series, even in places, such as near Dullstroom, where the succession appears almost complete. Felsic rocks of closely similar chemical composition and similar lithology, overlie other layered complexes. Sudbury and Muskox in Canada, the buried Trompsburg Complex in the Orange Free State are all examples showing this feature. P. Ianello: Dr. von Gruenewaldt has presented a very interesting and stimulating paper on the problem of the origin of the roof-rocks of the Bushveld Igneous Complex. After reading the paper, I found it rather gratifying to see that Dr. von Gruenewaldt has somewhat changed his ideas about the origin of the roof-rocks. In 1968 (p. 156) he stated that the leptite was "highly metamorphosed, recrystallized felsite, whereas the microgranophyre and granophyre are palingenetic products of the felsite" without any mention of gradational sequence whatsoever. Now (1972, p. 126) he suggests that "the emplacement of the gabbroic magma caused a gradual increase of the temperature of the overlying felsite which resulted in the recrystallization" of the felsite "to micrographic felsite and leptite" and, as a result of the continuation of the process, to granophyre. This new statement implies, of course, a gradational process.

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Transactions of the Geological Society of South Africa, 76, 85-94

The occurrence of the magnesium ilmenite in kimberlite and in the associated garnet peridotite and griquaite inclusions is discussed. The ilmenite in the garnet peridotite occurs in veins of serpentine, ilmenite is the same as that in the kimberlite, and it is explained as secondary replacements of ilmenite in the garnet peridotite. Ilmenite is seldom present in the griquaite xenoliths, and usually occurs as replacements in and around rutile grains. This ilmenite is more iron-rich than those in the kimberlite. The ilmenite in the griquaite is explained as a reaction product between the rutile grains and the melt derived from the partial melting of the griquaite. The ilmenite inclusions in the kimberlite show a variation of granulitic textures, ranging from inequigranular polygonal amoeboid to equigranular polygonal interlobate (after the nomenclature of Moore, 1970). Both single crystal and polycrystalline inclusions are present, and the single crystal inclusions show a variety of deformation textures such as undulose extinction, kink banding and deformation twinning. The polycrystalline ilmenite inclusions are recrystallized, showing the granulitic textures mentioned above. A variation curve showing the mol. per cent of MgTiO3, FeTiO3 and Fe2O3 as a function of the ao and density values of the kimberlitic ilmenites is presented. This diagram provides a cheap, but accurate method for the identification of kimberlitic ilmenites. The chemical, mineralogical and petrological data presented indicate that the following conclusions regarding the kimberlitic ilmenites can be made:
1. The kimberlitic ilmenites display a geikielite-hematite variation trend, which could be ascribed to the process of ilmenite fractionation from a kimberlitic magma.
2. The high hematite content in solid solution in the kimberlitic ilmenites is due not only to the rapid decrease in temperature of the kimberlitic magma during emplacement, but is also a function of the prevailing pressure during ilmenite fractionation, and the rapid decrease in pressure during emplacement of the kimberlite.
3. The presence of the reaction rims of perovskite around the ilmenite inclusions is a consequence of the reaction between the magmatic carbonates in the kimberlite magma and the ilmenite inclusions.
4. The spene forms during the late-stage reaction between the perovskite and the free silica, which was liberated during the serpentinization of the olivine in the kimberlite.
5. The ilmenite in the kimberlites crystallized intratellurically under high confining pressure in cotectic relationship with orthopyroxene and clinopyroxene. This takes place from a silicate magma, and after the ilmentie fractionation (during emplacement), the magma changed to a kimberlite magma which contains large amounts of magmatic carbonates.

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Transactions of the Geological Society of South Africa, 76, 95-111

Two faunas from excavations into the subsurface Cretaceous deposits at Durban (Natal) contain elements of both Santonian and Campanian age. The principal groups represented are ammonites and bivalves, with subsidiary gastropods, serpulid polychaetes, an ahermatypic coral and a single echinoid. Important elements in the fauna are Anagaudryceras subsacya (Marshall), Hoplitoplacenticeras plasticum (Paulcke) and a series of inoceramid bivalves, previously not recorded from South Africa. These occur with species such as Texanites (Plesiotexanites) stangeri (Baily), Submortoniceras woodsi (Spath), Hauericeras cf. gardeni (Baily) and Kossmaticeras (Natalites) cf. acuticostatus (Spath) already known from South Africa. The collections thus form a biostratigraphic link between faunas known from surface exposures in Zululand to the north and Pondoland to the south. Ammonites and inoceramid bivalves provide a basis for dating and regional correlation of the faunas.

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Transactions of the Geological Society of South Africa, 76, p173

The author is to be congratulated on an excellent and interesting paper. Presumably the graphical plots of the parameters used to subdivide and theorise on the mode of formation of the Series, are composites of all the bore-hole sections studied. However, a succession of the Pretoria Series is figured (in Table I) in which an important formation appears to have been omitted. I refer to the glacial stage, which lies a short distance below the Ongeluk lava. This is well developed in bore-hole K1 on Kalbasfontein 365 I.Q. The writer made a study of the Transvaal System in area covering the Western Areas and Elsburg gold mines (Cousins, 1962). In the course of this study generous cooperation was received from those mining groups whose bore-holes penetrated this system. In many of these bore-holes excellent successions of Pretoria beds could be studied. When borehole DP 2 (on Doornpoort 347 IQ) was drilled, the dolomite was sampled at approximately 12 metre intervals. The chert breccia and a layer of quartzite (from 940-948 m) were omitted from the samples used for chemical analysis. The dolomite, 1 230 metres of core, provided 105 samples. The density of each sample was measured and a chemical analysis of the composite of these samples was carried out by the J.C.I. Research Laboratory. Fig. 1 indicates the density sampling, graphically, and the geological section of the dolomite. The low values represent chert- or shale-rich samples. Table I records the chemical analysis and a chemical synthesis of the rock, which indicates that the dolomite is the double carbonate of calcium and magnesium, with iron and manganese substituting for magnesium. Study of published literature has not indicated that any other sections of the complete Malmani dolomite have been sampled and analysed. The presence of what appears to be organic carbon is illuminating.

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