Transactions of the Geological Society of South Africa, 1, 12-50
I intend in the following pages to lay before you the leading features only of the Primary Systems of South Africa, leaving the details to be worked out at some future date. In the map of South Africa attached to this paper you will notice that the shaded portion extends in a narrow strip roughly parallel to the coast line, from the mouth of the St. John's River, through the north-eastern portion of Pondoland, Natal, Zululand, and Swaziland, to the 26th deg. parallel to south latitude, from which point it stretches northward beyond the Limpopo and westward across the continent to the shores of the Atlantic Ocean, occupying the greater portion of the Transvaal, the whole of British Bechuanaland, the southern portion of the Kalahari Desert, and then extends south into the Cape Colony, through the western districts of Namaqualand, Clanwilliam, Tulbagh, Malmesbury, Wellington, and Wynberg, and the southern districts, of Caledon, Swellendam, Riversdale, Oudtshoorn, George, of the Koonap River. This represents the geographical position of the Primary Systems and the crystalline rocks upon which they were deposited. With the exception of a short distance between the Koonap and St. John's Rivers, they completely surround the Secondary Systems, which are situated in that portion of the map left blank.
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Transactions of the Geological Society of South Africa, 1, 129-141
The glacial and pseudo-glacial phenomena which I intend to describe more particularly in the following paper occur in the regions of the so-called "Karoo formations" in South Africa. This is a system of shales, sandstones, and diabase rock, reaching, according to age, from the Carboniferous to the Upper Trias, and exhibiting very different features from contemporary measures in Europe, but showing in its whole construction an extraordinary similitude to the series of deposits which are known in India as the "Gondwana System", and also with anologous formations in Australia.
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Transactions of the Geological Society of South Africa, 1, 90-112
I intend to deal with that unique and most interesting rock, known in South African geology as the Dwyka Conglomerate, and in order to give you a clearer idea than I can do in words of its principal features, I have placed a few specimens, taken from different parts of the country, on the table, and also some microscopic slides, and I intend to further illustrate my paper by lime-light views of sections of this rock. My object this evening is to place before you, in a concise form, the principal points in the writings of those who have studied this system, and to add a few details which I have thought worth noting during my investigations of the geology of South-Eastern Africa.
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Transactions of the Geological Society of South Africa, 10, 1-5
I am having analyses made of a series of specimens of Kimberley Slates and Main Reef Footwall Slates from boreholes in the Far East Rand to assist me in following out a comparative study of the two slate occurrences on lines suggested by Dr. Hatch's "Notes on the Witwatersrand Gold Deposits and their Associated Rocks". The results are not yet all to hand, but in the notes submitted I wish mainly to bring to your attention, as offering several special points of interest, the analysis, by Professor Reinisch, of Leipsic, of a section of Kimberley Basement Slates from Daggafontain Borehole No. 6 at 2,025 feet.
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Transactions of the Geological Society of South Africa, 10, 6-9
The rocks which occur in this district may be classified into: - (1) Granite and allied rocks (the rocks of Craighall Ridge). (2) Basic intrusions. (3) Acid intrusions. I propose dealing with them in the order given.
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Transactions of the Geological Society of South Africa, 10, 17-30
The following notes on the "banket", which I hope to continue later, are based on a study of specimens taken from the mines at intervals along the "reef", from the West to the East Rand. I have examined about one hundred and fifty microscopic sections of the rock. Allogenic constituents. Authigenic minerals: silica, chloritoid, pyrite, pyrrhotite, gold, gold telluride, calcite, chlorite, solution of quartz. Recapitulation.
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Transactions of the Geological Society of South Africa, 10, 31-35
It is only recently that the sandstones of Buiskop, near Warmbaths, and the Springbok Flats have been described in detail, and recognised as belonging to the upper portion of the Karroo System, as developed in the Transvaal. The same sandstones were also found above the Coal-measure Series at Komati Poort and in the Bushveld. For this succession of red marls, shales, and the overlying fine-grained sandstones, the term Bushveld Sandstone Series was adopted. This series is overlain by the amygdaloidal basalts of the Springbok Flats and Komati Poort, and vaires in approximate thickness from 300 feet in the Eastern Low Veld to at least 800 feet in the Central Transvaal. It constitutes a distinct and important member of the Karroo System.
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Transactions of the Geological Society of South Africa, 10, 44-50
Recent survey work in the Middelburg district has brought out very clearly the character and relationships of the various divisions of the Waterberg System, and has afforded a very interesting example in tectonic geology, which gives a key to the structure of a very large part of the Middelburg district and a portion of the adjoining district of Pretoria. In particular, the extensive series of volcanic rocks forming the lower portion of the Waterberg System, to which attention was drawn by the writer in a previous paper, has been more fully worked out, and it is now possible to give an approximate estimate of the thickness of these lower beds, and to explain their relationship to the upper part of the system.
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Transactions of the Geological Society of South Africa, 10, 51-61
During part of November and December of last year I was engaged upon the mapping of the southern portion of the area occupied by the granite north of Johannesburg. In the course of the work special attention was given to the southern and south-western boundary of the granite, and to the collection of all available evidence bearing upon the relations between this extensive igneous mass and the various rocks with which it is found in contact, and it is this question which I propose to deal with in the present communication.
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Transactions of the Geological Society of South Africa, 10, 62-64
This quartzite is generally known as the "Speckled Bed", a name first given to it by Mr. D. Draper, on account of the numerous yellow and brown spots, due to alteration of the felspars, which it generally shows at the outcrop. These spots, however, are sometimes few or entirely absent. This is owing to the grey felspar in the rock remaining at places, as at Auckland Park, comparatively fresh, or to the manner in which the felspars have been replaced, as described below. Sometimes the felspars are reddish in tint, through the infiltration of ferric oxide along some of the cleavage cracks. The brown or yellow colour of the altered felspars is due to the presence of similar oxides.
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Transactions of the Geological Society of South Africa, 10, 65-68
In the two years during which the Roberts Victor Mine, on the farm Damplaats, Boshof, Orange River Colony, has now been opened, many so-called "eclogite boulders" have been found in the yellow pyroxene, with which, in many cases, kyanite is associated. The minerals are arranged either in true granitic structure (Körnige Structur), or occasionally they are in layers as in a typical granulite. The nodules which I have seen are in layers as in a typical granulite. The nodules which I have seen are either spheroidal or ellipsoidal in shape, many, however, being incomplete, having obviously been broken across. On a recent visit to the mine I was shown by Mr. J.L. van Eyssen, the Manager, such a nodule which had, on careful examination, been noticed to have on the outside no fewer than eight diamonds, some of them quite minute splints, but one or two well shaped octahedra of approximately one-fifth to one-sixth of a carat. The piece of rock as originally found was a broken portion about 3 inches by 5 inches by 1 3/4 inches of a flattened ellipsoid. On the outside of the nodule the pyroxene appears of a light yellowish-green colour, in some places almost white, and quite amorphous, having weathered into a soft powdery material in which the dark red garnets appear set like currants in a cake. The garnets are generally more or less rounded. Though in the majority of cases they occur as separate individuals, they show little evidence of dodecahedral or other crystal outline. Their outer surface has a curious appearance, as if the individual crystals had been flattened or hammered out while in a plastic condition.
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Transactions of the Geological Society of South Africa, 10, 69-74
It is now an established fact among South African geologists that all pipes are connected with fissure veins, as the popular expression runs, or in other words that we find the pipes along lines of fissure. From a geological point of view the so-called fissure veins are nothing but true dykes which, in their strike, follow the general lines of weakness or the tectonic tendency of the country. In most cases they do not run singly, but several of them can be followed, parallel to each other, for miles. They are sometimes continuous, sometimes they are inclined to pinch out; and in this lenticular character in strike as well as dip they resemble true dykes.
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Transactions of the Geological Society of South Africa, 10, 75-80
When formulating any hypothesis on the origin of the diamond we have to consider two points: (1) The mode of occurrence of the diamond. (2) The manner in which it can be produced artificially. This paper deals only with the origin of the diamond in the pipes, and I do not, therefore, touch on the question of the origin of diamonds which are found in rocks of older horizons, such as itacolumite in Brazil and in the Witwatersrand Beds near Klerksdorp, in the Transvaal. With the exception of the occurrence in meteorites, which will be dealt with later on, kimberlite is the only rock in which the diamond has been found as a primary constituent.
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Transactions of the Geological Society of South Africa, 10, 81-89
The material which forms the subject of these notes was sent to me a considerable time ago by Mr. Anderson, the Government Geologist of Natal. The specimens were obtained from the following localities: - i. St. Lucia (Somkele) Coal-Field, Zululand; from the first tributary of the Enseleni River, north-west of the Main Northern road. ii. St. Lucia (Somkele) Coal-Field; from a locality south of Ingula Hill. iii. Umlalaas Coal-Field, Zululand; from Inyezane Creek. iv. Umlalaas Coal-Field; borehole. v. Ramsay Colliery, Newcastle District. A comparatively small number of species have been recognised. As frequently happens in the plant-bearing rocks of South Africa, and other regions of Gondwanaland, the genus Glossopteris is represented by a great number of specimens, but by few distinct forms.
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Transactions of the Geological Society of South Africa, 10, 90-94
In my papers on this subject and the subsequent discussions, published in the Transactions of this Society on September 4th, October 30th, and November 20th, 1905, I maintained that large areas of gneissoid rocks on both sides of the Limpopo River cannot be classed with the granites intrusive in the Swaziland Series, or with the latter formation itself. The question at issue is: Are these gneissoid rocks on the Limpopo simply foliated varieties and segregations of the intrusive granites, and therefore of the same age, or do they constitute a separate and older formation?
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Transactions of the Geological Society of South Africa, 10, 101-106
No abstract. Description of rocks. Eluvial diamond deposits.
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Transactions of the Geological Society of South Africa, 10, 107-111
About eight months ago I had an opportunity of inspecting certain places on the Vaal River, in the neighbourhood of Windsorton and Barkly West. It was then that I arrived at the opinion that the origin of the river stones was not to be sought for in undiscovered occurrences of kimberlite, but in the diabasic rocks so widespread in that part of the country.
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Transactions of the Geological Society of South Africa, 10, 112-114
In view of the valuable confirmation of the occurrence of diamonds in the ecologite boulders found in the South African diamond-bearing rock, brought forward at the last meeting of the Society by Dr. Corstorphine, the following notes on the lherzolite and eclogite boulders of the Roberts Victor Mine may be of interest.
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Transactions of the Geological Society of South Africa, 10, 115-119
The tin, molybdenum and lead occurrences herein described belong to that interesting type of metasomatic ore-body to which the term pneumatolytic has been applied. Though genetically the same, they each present a distinct facies. The country rock is granite.
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Transactions of the Geological Society of South Africa, 10, xix-xxvii
The relationship between the scenery and the geological phenomena prevailing throughout South Africa is a subject which affords scope for much fascinating study, and it will be my endeavour tonight to try to lay before you some of the more outstanding features, though this aspect of South African geology, like many others, cannot be dealt with exhaustively. Still, in travelling about the country, one has opportunity for comparing and contrasting the effects produced in the landscape by the same or different geological structures and formations, and no more attractive means can be found of relieving the tedium we all at times endure in journeying across the veld. No country affords readier facility for the observation of the geological causes of scenery, though we may regret the fact that the facility owes its existence largely to the deplorable destruction of a former vegetation. South African scenery is striking in its very monotony. Over hundreds, or rather thousands, of square miles there is a sameness which becomes oppressive, and a want of variety of feature which exceeds all imagining. There is nothing stimulating in the landscape but its immensity, yet, owing to the limited horizon, that immensity is not a characteristic immediately appreciated. The fascination of the veld is subtle and elusive, probably because, more there than anywhere else, is the charm due to conditions of sunshine and atmosphere, factors as essential to the final effect of a landscape as the configuration of the earth's surface. The geological constitution and structure are the fundamental conditions on which the scenery of a country depends, and the resulting landscape is the outcome of the work done by the agents of denudation, which are themselves mainly due to the prevailing climatic conditions. Denudation working on the original structure, finding out the weak spots and gradually carving away even the hardest rocks, is the great factor in the evolution of a landscape. Whether that denudation is of one type or another, whether its weapons are rain, running water, snow and ice, or whether extremes of temperature aided by torrential tropical rains are the main modifying influences, depends on the climatic conditions. Similar geological conditions in regions enjoying different climates are subjected to different denuding forces, with the result that varied types of scenery are produced. In a region such as South Africa, where the same geological formations extend from the Atlantic to the Indian Ocean, and from Agulhas to the retreating boundary of "Darkest Africa", the resemblances in the scenery are produced by the prevailing geological uniformity, and the differences are due to the variations in the climate. It is to the action of long continued sub-aerial denudation that South African scenery owes most of its characteristic features. Geological investigation reveals the fact that long ages have elapsed since the main geological structures originated, and that even
the present land surface has an antiquity for which any possible equivalent in years would convey no meaning to the human understanding, for since the upper beds of the Karroo System were deposited only a small portion of the coastal region has undergone submergence. The present surface, here as elsewhere, is the last expression of the interaction of various geological forces, some of which are as active today as they probably ever were, while others have in these days no share in the sculpturing of this landscape. Changes of temperature, wind and rain, surface and underground water, are probably not much less active in South Africa today than in past ages; whereas extreme glacial conditions have played no part in modifying the surface since the beginning of the Karroo Age, nor have volcanic agencies been at work since the eruption of the rocks of the Drakensbergen and the Lebombo Range.
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Transactions of the Geological Society of South Africa, 11, 1-24
The presence of numerous intrusive bodies in the Transvaal System, particularly in the Pretoria Series, is well known, and in the majority of cases the relationship of such igneous masses can be established by their influence on the enclosing sedimentary strata. While in the Pretoria District this alteration is usually very slight, rarely producing more than local hardening of the shales, in the Lydenburg and Zoutpansberg Districts it becomes so intense, as to completely destroy the original characters of the older beds and give rise to contact rocks, the true nature of which can only be demonstrated by detailed petrographical work. It is therefore hoped that the following account of these rocks may not be without interest.
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Transactions of the Geological Society of South Africa, 11, 107-115
Some time ago Mr. J.W. Woods, of East London, obtained from Need's Camp, near East London, some fossils which he sent to the South African Museum. These have now been determined, and all of them have a time distribution within the Cretaceous period. The Polyzoa have been identified by W.D. Lang, of the British Museum, and the mollusca and brachiopods by H. Woods, of Cambridge. From the evidence afforded by the Polyzoa, which are the only organisms satisfactorily preserved, Lang came to the conclusion that the age of the deposit is either Senonian or Danian, that is to say, later than the Pondoland Cretaceous beds and equivalent ones from Natal.
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Transactions of the Geological Society of South Africa, 11, 25-42
In consideration of the great number of lay members of this Society whose warm interest in our doings is a constant source of satisfaction to us, and further in consideration of criticism of the theory as to the genesis of tin deposits which my observations in the Bushveld tin fields supply, I shall first give a brief sketch of our present day knowledge of tin deposits and their genesis.
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Transactions of the Geological Society of South Africa, 11, 43-44
With reference to the remarks of Dr. Corstorphine at the meeting of the Society held on December 17th last regarding the geological features of the Rhodesian diamond fields, the following brief notes on the subject may not be out of place.
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Transactions of the Geological Society of South Africa, 11, 45-46
On the farm Weltevreden No. 18, situated on the north-east boundary of the Potchefstroom District, there is an occurrence of yellow and red ochre, which is of interest not only commercially, but also on account of the clear indications that it is the result of the extreme decomposition of an igneous rock.
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Transactions of the Geological Society of South Africa, 11, 47-54
The object of the following remarks is to call attention to the presence in the Pretoria Series of igneous masses of contemporaneous rocks, occurring along certain horizons in the Eastern Transvaal as well as in the Rustenburg district. In a paper communicated to this Society in December 1905, Mr. Holmes was the first to suggest a contemporaneous origin for a thick bed of dolerite overlying one of the quartzites of the Pretoria Series in the Marico district. Igneous rocks in the Pretoria Series of undoubted contemporaneous character first came to the writer's notice, while mapping in the neighbourhood of Schoeman's Kloof, S. of Lydenburg in the winter months of 1905. Since that date further work in the same part of the Eastern Transvaal has brought to light several occurrences of similar rocks, for the contemporaneous character of which there is good evidence.
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Transactions of the Geological Society of South Africa, 11, 55-68
The stratigraphy of Zwartkop having been dealt with by Mr. A.L. Hall in the Annual Report of the Geological Survey for 1905, as well as in a joint paper to this Society by Messrs. Hall and Humphrey, and the results of both authors having been confirmed by the Director, Mr. Kynaston, in the Report for 1906, and presented to the world on Sheet 1 of the official geological maps of the country, some explanation of the origin of the present paper appears needful. One of the authors, having occasion to study the question of the stratigraphy of Zwartkop and having but a slight acquintance with the locality, read carefully the descriptions of the rocks and the reasons given by the Survey for placing them in the Swaziland System. Since the arguments appeared inconclusive, or were at any rate unconvincing, he stated the problem to his co-author, but, as naturally might be expected, discussion made obious the fact that the solution was to be reached only by an examination of the ground. Our visits have led us to a decision entirely opposed to that of the Survey, and, in presenting our views to the Society, we are aware that correctness in our main conclusion can be the only justification for this further word on the geology of Zwartkop (82).
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Transactions of the Geological Society of South Africa, 11, 69-77
Apparently the first reference to an occurrence of chromite in this Colony is found in the Report of the State Geologist for the year 1898, in which Prof. Molengraaff mentions the presence of chrome iron ore as basic secretions in serpentinised norite north-west of M'Zilikat's Nek in the Magaliesberg. Since then numerous occurrences have been found in many localities along the margin of the Bushveld Plutonic Complex, notably in the Rustenburg and Lydenburg Districts. In the following notes we propose to give a more detailed account of the nature and distribution of this ore.
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Transactions of the Geological Society of South Africa, 11, 78-82
My name having been mentioned by both Messrs. Corstorphine and Jorissen, and the Director of the Geological Survey, in their papers read before this Society, on the 13th April and 18th May respectively, with reference to the geology of the Zwartkop area, I beg permission this evening to state my views on this most interesting subject. In 1894 I examined the Zwartkop, and then came to the conclusion that the sedimentary beds, forming both the kop and the range north of the Crocodile River, belonged to the Lower Witwatersrand Series, and subsequent visits in 1904 and twice recently served to strengthen this determination.
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Transactions of the Geological Society of South Africa, 11, 83-106
The object of this paper is to draw the attention of the Society to a district hitherto undescribed, which, on account of its variety of ore deposits and of the unusual, often unique, features of the individual deposits, is of the greatest scientific interest, and which, at the same time, promises to become a very important district economically. Although acquainted with the district and some of its deposits for nearly three years, I have hesitated until now to publish my observations, hoping that new facts being revealed almost weekly, by the development work going on there, would solve some of the many problems and enable me to give a clear description and explanation of the facts observed. The consciousness growing upon me that even now we are only in the beginning of our knowledge, and that for years to come new facts will be revealed, solving some old problems, and presenting new ones instead, has prompted me to collect my data and present them to the Society at the present moment. Any interesting new development of the deposits known at present, or any new discoveries I shall bring to the notice of the Society in due time.
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Transactions of the Geological Society of South Africa, 12, 1-7
Since the uppermost portion of the Transvaal System is everywhere made up of a great succession of shales and quartzites, the occurrence of calcareous bands, of which one at least attains a considerable thickness, is of particular interest. The first reference to a local change of this kind is contained in the Report of the State Geologist for 1897, in which Professor Molengraaff refers to the occurrence of a belt of limestone immediately underlying a coarse diabase, which forms the summit of Van Lennops Kopje close to Waterval Boven on the Eastern Line. This band consists of a pale geyish impure limestone; its position between the Magaliesberg and Daspoort Quartzite roughly corresponds with that of the principal occurrences east of Potgietersrust.
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Transactions of the Geological Society of South Africa, 12, 102-111
The tin deposits, which have so far been discovered in the vicinity of Capetown, are all, as is shewn on the accompanying map, confined to a hilly belt of country stretching in a north-westerly direction from the foot of the Helderberg in the south to farm Hoogekraal in the north, a distance of about 24 miles. This belt of country is composed entirely of rocks belonging to the Malmesbury Series and of granite, the latter rock being intrusive into the former. Within this area the following types of deposits may be distinguished: - (1) Veins and associated impregnations in granite. (2) Veins and associated impregnations in rocks belonging to the Malmesbury Series. (3) Detrital deposits resulting from the destruction of the two previous types.
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Transactions of the Geological Society of South Africa, 12, 112-118
Through the courtesy of Mr. G. Bryant, of Port Elizabeth, and Mr. J. Farquhar, of Grahamstown, the Albany Museum has secured a collection of the shells from the raised beaches and old filled-in alluvial basins of Port Elizabeth and Zwartkops. These were named by Dr. H. Becker and Mr. Farquhar; in the case of a few doubtful species, Mr. A.E. Smith, of the British Museum, was referred to, and very kindly reported on them. The list published below with the help of these gentlemen is not a long one, but it is a beginning, and it is hoped to enlarge it as opportunities for collecting an investigation offer.
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Transactions of the Geological Society of South Africa, 12, 119-138
The following remarks deal with the nature and distribution of the many varieties of metamorphic rocks occurring in the Transvaal System, from the top of the Magaliesberg Quartzite to the uppermost beds of the Dolomite, as developed from the Capital westwards to beyond Zeerust. Since the detailed examination of this belt of country is now completed, it is possible to review the phenomena more fully, and to compare them with similar experiences in the Eastern Transvaal. In the Lydenburg and Zoutpansberg Districts the Pretoria Series is profoundly metamorphosed, both by the main body of the Bushveld Plutonic Complex as well as by numerous sheets intrusive in some detail in a paper contributed to this Society last year. Since in both areas the altered rocks represent shales, quartzites, and greywackes, while the agents are also essentially the same, a general resemblance between the leading types of metamorphic rocks is to be expected. There are, however, important and instructive differences, both structurally and mineralogically, while certain more general questions, such as the respective metamorphic influence of intrusive sheets and the main body of the Plutonic basin, or the width of the contact aureole of the latter, can be better answered from the distribution of the altered rocks in the Rustenburg and Marico Districts.
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Transactions of the Geological Society of South Africa, 12, 13-23
It was during the first half of last year that reports reached Johannesburg of the discovery of diamonds at Lüderitz Bay in German South-West Africa. At first only very scanty news filtered through; even later on, when more reliable information was obtainable, no great interest was taken in these discoveries, as it was stated that the diamonds occurred in an alluvial deposit, which, as experience proved in Brazil, Borneo, India and along the Vaal River, has never yet formed the basis for any enterprise on a large scale. However, interest was aroused amongst those connected with the diamond industry, when last December the surprising information was cabled from Berlin that, according to official statements, the new diamond fields were so enormously rich that a daily production of 5,000 carats could be relied upon, equalling an annual output of 1+ million caracts.
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Transactions of the Geological Society of South Africa, 12, 139-158
About nine months ago I had occasion to examine a considerable area of country between the town of Barkly West (C.C.) and Klipdam, occupied largely by the so-called Vaal River Diamond Diggings, and I think some observations made at that time are sufficiently interesting to be placed before this Society. For forty years the gravel beds in the Vaal River and its vicinity have been worked for diamonds, but no indisputable evidence relating to the origin of those diamonds has up till now been recorded. Several theories have been formulated but have necessarily borne a strong impress of the hypothetical, owing to the absence of convincing facts. These facts, or rather proofs, I am pleased to say are at last in our possession; and together with a few geological observations will, I hope, somewhat clear the hitherto obscured horizon surrounding this most interesting subject.
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Transactions of the Geological Society of South Africa, 12, 159-167
The Katanga copper belt is situated to the north of the Congo-Zambesi divide in the southern portion of the Katanga district of the Belgian Congo, between latitudes 10x and 13xS., and some 400 to 450 miles to the north of the Zambesi River. The main portion of the belt is about 250 miles in length, and varies from 30 to 60 miles in width. The general character of the country is undulating, varying from 3,500 to 5,000 feet above sea-level; in the vicinity of the copper deposits the country is often hilly, but the hills seldom exceed 400 to 500 feet in height. Many of the deposits are, however, situated in comparatively flat areas. The country is generally covered by thin forest and is extremely well watered by the numerous tributaries of the Luapula, Lufira, and Lualaba rivers, which form the head waters of the Congo. The climate is sub-tropical and healthy, with an annual rainfall of from 50 to 60 inches, practically all within the six months November to April.
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Transactions of the Geological Society of South Africa, 12, 168-202
The views expressed in the following paper on the origin of the South African tin deposits differ considerably from those held by the various authors who have written on the subject and also by the authorities on ore deposits generally. In order to facilitate discussion and to present the author's views in relation to a number of general principles involved, the paper will present in Part I, a criticism of the acknowledged theory of the origin of tin deposits and in Part II, an exposition of certain important subjects, which have been either neglected in previous discussions or the full bearing of which has not been recognised. Part III, will contain the author's view on the subject of the paper proper.
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Transactions of the Geological Society of South Africa, 12, 203-204
Some time ago I made the following observations in the Lace Diamond Mine, which is situated about 20 miles to the north-west of Kroonstad, Orange River Colony. On the first and second levels of this mine there occur masses of floating reef consisting of a fine to medium grained arkose sandstone, buff or light purplish in colour. These masses are in some places quite free from inclusions, but in others are full of rounded and angular fragments of all kinds of rocks, especially dolerite, andesitic rocks, shale and quartzite. Closer examination revealed the interesting fact that these rock fragments correspond exactly to those found in the blue ground, and even the proportions of the foreign inclusions are approximatley the same. We have, therefore, to deal here with two breccias, in which the fragments are in the one case cemented by sandstone and in the other by blue ground.
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Transactions of the Geological Society of South Africa, 12, 205-212
From a study of the Roberts Victor Diamond Mine, it appears to me that considerable light can be thrown upon the interesting questions of the origin of Kimberlite and the contained diamonds, the relation of fissure- or dike-kimberlite to that characteristic of a pipe or true mine, as well as the variations which may occur in the mine kimberlite itself. The results of my various investigations into the Roberts Victor Mine are embodied in the accompanying plan and seven sections of the mine, which is situated on the farm Damplaats, about 20 miles east of Boshof, Orange River Colony (longitude 25x33'40" East, and latitude 28x28'43" South, according to the Surveyor-General's Degree Sheets). The work was finished in January, 1909, and included: - (1) Occasional surveys since the discovery of the mine in August, 1905; (2) observations made and photographs taken during periodic visits to the mine; (3) information obtained from several boreholes sunk to various depths; and (4) a detailed survey made by me last January for the Company's 1908 Report.
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Transactions of the Geological Society of South Africa, 12, 24-31
Some time ago, in the course of a journey westwards from Lourenco Marques into Swaziland, when crossing the lava flows that constitute the Lebombo Range, I collected a few specimens of some of the different types of acid and basic lavas encountered. The object of the present note is to submit the results of a detailed microscopical examination, together with an analysis of some of these rock specimens, carried out for me by Professor Reinisch of Leipsic, as it seemed that such might prove a not unwelcome addition to the Society's collection of petrographical data. Before proceeding to the description of the individual specimens, I will indicate briefly the general geological characteristics of the country traversed, as far as these can be delineated by occasional notes taken on what was of necessity a hurried journey.
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Transactions of the Geological Society of South Africa, 12, 32-53
The subject of the present paper is one of considerable importance in the Geology of the Transvaal, for it is closely associated with the origin and definition of the term Swaziland Series, as at present generally understood. While we possess a certain amount of detailed information regarding the petrographical characters of the rocks making up the sequence of Mount Maré, our knowledge of the succession and relationships of the leading rock types is still incomplete. It is therefore hoped that further information on these points may be acceptable to members.
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Transactions of the Geological Society of South Africa, 12, 54-66
We are indebted for our introduction to the interesting series of caves herein described, to Dr. H. Lyster Jameson, late Professor of Biology in the Transvaal University College, who, while investigating the mammalian fauna of the district, incidentally discovered the presence of human and other mammalian remains in the floor-debris of these caves. Unfortunately, the osteological collection has not yet been described, but we believe that the human remains, which may prove to be those of Bushmen, are in the hands of a specialist at home, so that we may look forward shortly to their description.
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Transactions of the Geological Society of South Africa, 12, 67-77
In current accounts of igneous rocks in the Witwatersrand system, in the Witwatersrand area, it is invariably stated, that the rocks are all of basic or intermediate composition, but I have observed occurrences of intrusive rocks of a distinctly acid character in the following places: - I. In the Rand Deep Level bore hole, situate about 300 feet from the northern beacon and about 30 feet from the northern boundary of the Rand Deep G.M., Ltd., property. II. In the Cinderella Deep G.M. where it lies below the Reef at the 4,000 ft. level, and above the Reef at other depths. III. In the Turf Club East bore hole at a depth of 3,265 ft., between the Bird Reef and the South Reef. IV. On the farm Waterfall (74) and on the farm Witfontein (29), both situate on the West Rand. V. In the Roodepoort Deep G.M. I shall now give an account, mainly petrological, of each of these in turn.
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Transactions of the Geological Society of South Africa, 12, 78-81
The ever-increasing importance of the ore deposits contained in the dolomites of Pilgrims Rest has prompted the Government to commission the Geological Survey with the preparation of a monograph of these fields; some, perhaps many, engineers and geologists may visit now, or in future, these or other parts of the Transvaal where dolomites prevail. It is in the hope of soliciting their interest that I draw once more your attention to these perculiar rocks.
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Transactions of the Geological Society of South Africa, 12, 8-12
Wherever the basic margin of the Bushveld Plutonic Series has been examined in detail, whether in the central Transvaal from Pretoria westwards, or in the eastern part of the Colony from near Lydenburg northwards through Secoecoeniland to near Potgietersrust, the norite and to a lesser extent the Red Granite adjoining it, show a more or less pronounced tendency to assume an oriented structure. A similar schistose or gneissic habit is also noticeable in the upper horizons of the Pretoria Series, especially in Secoecoeniland and the southern portion of the Haenertsburg Goldfields, where the shales have been converted into holocrystalline rocks. In the Western Transvaal (Rustenburg and Marico Districts) this tendency is only feebly developed in the Pretoria Series, for reasons given later. In the following remarks an explanation is suggested for the distribution and origin of these structures; though both the igneous and sedimentary rocks have acquired their distinctive features through the same cause, it will be convenient for practical reasons to treat them separately.
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Transactions of the Geological Society of South Africa, 12, 82-101
The following notes are supplementary to those contained in a paper read by me before this Society in March, 1907, and are the result of the examination of a large amount of material, taken form all parts of the Rand.
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Transactions of the Geological Society of South Africa, 12, xxi-xxx
I propose in what follows to make a few remarks upon the so-called Red Granite of the Bushveld, my object being more especially to draw attention to some of the problems connected with its intrusion, and to discuss briefly its relationship to mineral deposits - in short, to give a sort of general summary of what we know and of what we do not know concerning this interesting and complex intrusion, which has played such an important role in the geological history of the Transvaal.
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Transactions of the Geological Society of South Africa, 13, 1-9, 1 pl
In view of the increasing interest which the country adjoining United South Africa now enjoys, I believe I meet a desire of the Geological Society in presenting a summary of the results of my investigations in the southern portion of German South-West Africa. This paper is essentially an expansion of one which I published in the Monatsberichte der Deutschen Geologischen Gesellschaft, 1909, No. 3. While several alterations and additions have been necessary, my later investigations have confirmed the geological outline which I originally published. I have continued the section to the eastern boundary and it now joins up with Rogers' valuable work. Since the paper mentioned above was written I have had the advantage of a short visit to the Cape and the Transvaal Colonies, and I have attempted to correlate the formations of German South-West Africa with those of the above territories.
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Transactions of the Geological Society of South Africa, 13, 10-16
It is well known, that the various rocks which make up the Plutonic Complex of the Bushveld range between wide limits as regards their silica percentage, and can be arranged into two broad groups, represented by granite as the acid, and norite as the basic phase. It is furthermore agreed, that these rocks have a common origin as the result of magmatic differentiation from a single parent magma, either directly, or perhaps through the intermediate stages of partial magmas ("Spaltmagma"). The statement is commonly made that the granitic rooks occupy the central portion, while the norite and other basic varieties are arranged round the periphery of the complex, there being a general increase of basicity from the centre outwards. This view is broadly speaking correct, but requires modification when tested in detail. The object of the following note is to call attention to the existence of a well-defined and persistent zone of highly quartzose rocks, the character and disposition of which form a striking exception to the simple rule above stated, since the silica percentage is considerably higher than that usually found in granite, while the rocks are only met with close to the norite-granite boundary, that is, far removed from the centre of the Bushveld Complex.
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Transactions of the Geological Society of South Africa, 13, 105-106
The carbon in the banket occurs chiefly in the matrix of the rock and only very rarely in the pebbles. In the matrix it is common to find the relations of the carbon to the quartz such as to suggest that the latter has been partially replaced by the former. However, the quartz in the matrix has almost invariably undergone a certain degree of recrystallisation, and as this may have been brought about subsequent to the inclusion of the carbon in the rock, no reliable conclusions can be drawn from the relations of these minerals. It is not so when the carbon occurs in the pebbles. The writer has observed carbon in the pebbles in specimens of banket from the Meyer and Charlton G.M. and the Bon Accord G.M. In both cases the matrix contained an unusual amount of carbon mostly in the form of small somewhat rounded grains of the ordinary size. In the specimen from the Meyer and Charlton G.M. only a few grains of carbon are noticeable in the pebbles, which are of white vein-quartz. In the specimens from the Bon Accord G.M. carbon is conspicuous on the fractured surfaces of quite a number of the pebbles, mostly in the cherty pebbles (fine-grained quartzites) which are sometimes banded, but also in a few of the white vein-quartz pebbles. The carbon principally occurs as rounded particles which are imbedded in the material of the pebbles, generally in the neighbourhood of the minute cracks which traverse all the pebbles of the banket. The material can be picked out of the pebbles, leaving behind distinct pits, and is not a filling of the cracks.
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Transactions of the Geological Society of South Africa, 13, 107-128, 3 pl
The Grootfontein District embraces a considerable area of country in the north-eastern corner of German South-West Africa, being bounded on the north by the Okavango River and Southern Angola, and on the east by the Caprivi Belt and British Bechuanaland. Lying well within the Tropics and at a mean elevation of considerably over three thousand five hundred feet above sea-level, this portion of the German Colony possesses a climate which is similar on the whole to that of Southern Rhodesia. It was first occupied by white men in 1885, when "trek" Boers, under the leadership of a certain Jordan, attracted no doubt by the "High Veld" conditions there prevailing, established the Republic of Upingtonia, on the site of the present Grootfontein. This Republic was, however, doomed to be very short-lived, for in the following year Jordan was treacherously murdered by natives, and his hardy band of followers were forced to seek the assistance of the German Government; which towards the end of 1886 established a Protectorate over tho whole territory. Since this date there have been several further "treks", but on the whole the Boer population has diminished, rather than increased, under the German regime. The existence of rich deposits of copper ore in the Otavi Range has been known since the publication, in 1852, of Sir Francis Galton's well-known work, " Travels in Tropical Africa", in which he describes a journey from Walfisch Bay into Ovamboland. It appears that for generations prior to the advent of the white man these ores were mined by Bushmen, and then conveyed by Ovambo caravans to Ondonga, distant about one hundred and thirty miles from the copper workings, where they were smelted by Omudonga, a native tribe especially skilled in metallurgical work; the latter in turn bartering the copper thus produced for other commodities. In order to render possible the systematic exploitation of these deposits, they were in 1906 linked up with Swakopmund by means of a narrow gauge railway. Since the completion of the latter the different mines have been worked on a very considerable scale, as may be gauged from the fact that during the last financial year they yielded copper and lead ores to the value of over £400,000. In addition to its mineral wealth the southern portion of the district appears to be well adapted for the culture of maize and for cattle ranching; and, it ought to play an important part in the development of German South-West Africa. Very little has been written on the geology of this part of the country. In 1904 Passarge gave an excellent summary of the observations which had been recorded to that date by different travellers; and despite the fact that he had never visited the area in question drew, from these observations, conclusions which are in the main quite correct. More recently the publications of Kuntz, Range, and Hermann have added to our knowledge on the subject. My own investigations took the form of a preliminary reconnaissance,
rather than of systematic survey work, but I hope, nevertheless, that the information embodied in the present paper will prove of interest and utility.
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Transactions of the Geological Society of South Africa, 13, 129-139
The red granite of Balmoral: This rock is primarily composed of quartz, orthoclase, albite, anorthite and microcline, together with some muscovite or sericite, apatite, fluorspar and haematite. It is a highly alkaline muscovite granite closely approaching, or at any rate forming a link which connects typical muscovite granites very intimately with true aplites and pegmatites. Graphic and micrographic structures are common. Perthitic intergrowths between felspars of different composition are abundant, whilst the clastic condition of much of the material is distinct evidence of the crushing forces to which the rock has been subjected.
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Transactions of the Geological Society of South Africa, 13, 140-146, 1 pl
Dr. Rogers, in his paper on the Kheis series, refers with apparent surprise to my having recently repeated my assertion that this series is but a metamorphosed portion of the Transvaal system. For some years I have been aware that Dr. Rogers has combated this view, and I have urged that some satisfactory reason should be given for this, but up till now I have not seen any, either in the geological reports issued by the Cape Survey or in the paper recently read before this Society, and consequently I can see nothing remarkable in my retaining the correlation which appears to me to be the only reasonable one. The stratigraphy of the portion of the country round Prieska which I surveyed in conjunction with Dr. Rogers and the part to the north surveyed after I left the Survey, show clearly that there are sharp zones of metamorphism: up to a certain line the beds lie undisturbed; beyond they are intensely folded, so that if the Transvaal system, with its quartzite, dolomite and ironstone series, occurs in the one area it would occur in the other with considerable alteration. We know what would happen to rocks such as occur in the Transvaal system - indeed, as we shall see, the process can actually be traced in the area in question along the strike of the beds - and if we therefore find such metamorphosed equivalents in the intensely folded area, the rational interpretation would he that the two are one and the same stratigraphically. Against this Dr. Rogers maintains that there are dykes of granite in the Kheis series and none in the Transvaal system as represented in the area, though there are syenite dykes. The dykes of granite that I have seen in the Kheis beds are all folded in with the quartzites, and the sections through this area prepared by Dr. Rogers show this very clearly. The folds in the metamorphosed areas are so sharp that the granite on which the Kheis beds rests has been folded with them in long narrow strips, which appear as dykes when the crests of the anticlines are exposed by denudation. I have looked earnestly for any case adduced by Dr. Rogers where the granite strips might legitimately be taken to be intrusive dykes, and I have failed to discover any. His statement (loc. cit. p. 104) that transgressive intrusions do occur in the Kheis series should surely be substantiated by reference to some actual occurrence, but where the matter is discussed in detail, with plans, in the Reports of the Geological Commission, for instance in the 12th Annual Report, pp. 33, the so-called granite intrusions are drawn and described so that an impartial reader would take them to be folded-in masses. I cannot therefore see any justification for considering the Kheis series to be an earlier formation than the Transvaal system. I will take the objections to the Kheis Formation being older than the Transvaal Formation one by one, under three heads: 1st, the nature of the metamorphism; 2nd, the question of the granite dykes; and 3rd, the
stratigraphical position of the two.
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Transactions of the Geological Society of South Africa, 13, 17-25
Little has yet been written on the geology of this part of the Transvaal, owing, no doubt, to the fact that few geologists have made any extended examinations of the area. The latest and principal papers were read by Mr. G. G. Holmes, before the Geological Society of South Africa in 1904, and 1905. In these papers Mr. Holmes gives a generalised sketch of the main geological features, over a wide area of the north-western Transvaal. Previous to Mr. Holmes' papers a sketch map of the area was given by Professor Molengraaff in his geological map of the Transvaal, published in 1902. Up to the present time, little or nothing has been done in the way of extended accurate mapping. I am sorry to say that during my hurried trip through this district it was impossible to do anything in the way of systematic mapping, except in the case of more or less small local areas, which had to be thoroughly examined because of their mineral possibilities. The rest and by far the larger portion of the area was passed over too hurriedly for any but a most cursory examination; while large areas of the flat country immediately south of the Limpopo river had to be quickly dealt with, owing to the almost entire absence of surface water, except in widely separated pans, most of which are not permanent, and occasional filthy mud-holes which furnish too substantial a water supply to be wholesome or desirable. Nevertheless the observations embodied in the following notes may prove of some interest and utility.
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Transactions of the Geological Society of South Africa, 13, 26-28
The country between Krugersdorp and Randfontein is dotted with pans most of which, unlike those of western Orangia, but like those of the Lake Chrissie district, hold water all the year round. In connection with the great construction works now being undertaken at the Randfontein Central mines, one of these pans, situated north of Robinson, has been drained, and a pit has been sunk in it for the supply of brick earth. The section exposed shows bluish-black carbonaceous soil passing downwards, at a depth of about eight feet, into yellowish-brown loam. At four feet from the surface there is a well-defined line of stones, and at eight feet there is another but less persistent layer. Isolated stones occur to the depth at present reached, namely, twelve feet. The pit is situated in the flat bottom of the pan but towards the side. A large number of Acheulic amygdaliths and axe-heads, in different stages of manufacture, have been obtained from this pit, but the exact horizon from which they mostly come is uncertain. They were not noticed till the pit had nearly reached its present depth, which would seem to indicate that they chiefly came from low down in the section, but one of the foremen on the other hand thinks they mostly came from the four feet horizon. I myself saw worked stones in situ at both the four feet and the eight feet levels. The condition of the specimens shows that none have come from the surface. The implements are mostly of quartzite of both fine and coarse texture-several are of chert while three are of white quartz. All are of local material. There can be no doubt that they are close to the site of manufacture.
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Transactions of the Geological Society of South Africa, 13, 29-55
The object of this paper is to place on record the results of the analyses of some typical Transvaal rocks, together with certain notes and conclusions based on these analyses; and, at the same time, to add a few notes with regard to their petrographical features and the area covered by the formations to which they belong. The analyses were made more than five years ago but, with much of the substance of the following notes, were, at the time, published only for private circulation. A few have since been published by the writer, but no apology is made for quoting them as by so doing all are brought together in convenient form for reference. Several other analyses are also quoted for comparison. Contents: The dolomite. Carbonaceous shales in the dolomite. The Black Reef Series. The Klipriversberg amygdaloidal diabase. Some slates and quartzites of the Witwatersrand Formation. Granites. Granophyres and tonalite.
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Transactions of the Geological Society of South Africa, 13, 56-60, 1 pl
Owing to their ever increasing production the German South-West African diamond fields are attracting more and more attention, and the question of the source of the diamonds has become one of the most important geological problems which has arisen in recent years. In the present contribution I do not propose to enter upon a discussion of the different theories of origin which have already been propounded, but merely wish to place on record certain observations, which, as I shall endeavour to show, have a very important bearing upon the subject. In the first place brief reference must be made to the geographical boundaries of the deposits, and to the size and distribution of the diamonds within these.
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Transactions of the Geological Society of South Africa, 13, 61-64
With the advent of Dr. Wagner's paper the occurrence of diamonds in German South-West Africa has been brought to the notice of this Society for the second time; reference to his paper, however, will show that leading German geologists have given the matter attention in several publications. I believe it will be of importance to our members, before the subject is referred to or discussed at length, to have the views of our neighbouring colleagues placed before them in a brief form, the more so since they are men who have spent years in Damaraland as State geologists, and have been able in their official capacities to give the diamond fields full attention.
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Transactions of the Geological Society of South Africa, 13, 65-92, 8 pl
Attention has previously been called to the presence of carbonaceous or graphitic matter in the Witwatersrand conglomerates, and it has been suggested that this may have acted as a precipitating agent for the gold. Dr. F. W. Voit speaks of it as organic matter which was converted into coal during the sedimentation of the strata and directly precipitated the gold. Professor J. W. Gregory, after stating that Drs. Hatch and Corstorphine suggest that the precipitant for the gold may have been organic matter, remarks "although the Rand beds may be pre-Cambrian in age, they probably originally contained some organic matter, as it is not likely that the sea, beside which they were deposited, was lifeless; but it is difficult to see how organic matter in a series of shore deposits should be present in beds of coarse well-rolled pebbles, and absent from the finer and more angular shingle and from beds of sand. The natural expectations would be for organic matter to collect more in the bastard reef than in such a layer as the Main Reef Leader". Drs. Hatch and Corstorphine speak of carbonaceous matter, but I can find no record of them referring to it as organic. The only detailed account of its mode of occurrence, so far published, is that by Prof. R. B. Young, who describes it as usually occurring in small, black, opaque nodular grains, having a somewhat warty, dull surface, and ranging in diameter from one millimetre downwards; and, sometimes blending together into a compact mass of anthracitic appearance. Further, he mentions that at the Rietfontein mines it occurs not only in nodular grains but also in veinlets, up to two millimetres thick, with a columnar structure, the columns being perpendicular to the walls; and between the columns, very thin films of sericite are generally present. He states that in his specimens the carbon lies along, or close to, a parting, generally a bedding plane, but in some cases a crack oblique to the bedding plane, and that the carbon is frequently wholly or partially embedded in secondary quartz; and after calling attention to the association of gold with carbon, remarks "there are features in the distribution of carbon in the bankets and associated quartzites which suggest that it may not have been an original constituent of the rocks in which it is found, but was introduced at a later date. This however requires a fuller investigation than I have been able to give it". He then concludes "the association of graphite with gold in some of the Australian gold fields is well known. In the Croydon Goldfield in Queensland the auriferous quartz veins are found in a much disturbed and altered zone of granite containing graphite". Carbon can be occasionally detected in the pay reefs, in, perhaps, most of the mines along the Rand but only in a few is it sufficiently in evidence to be a characteristic feature. These are the Rietfontein mines on the Du Preez series on the East Rand and the Randfontein mines on the far West Rand;
and, it also occurs in noticeable quantity at the Buffelsdoorn mine near Klerksdorp.
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Transactions of the Geological Society of South Africa, 13, 93-104, 2 pl
In a paper published in 1905 Prof. Schwarz correlated the Kheis quartzites and schists with the quartzites (Black Reef) at the base of the dolomites on the flanks of the Doornberg, and he attributed the intimate connection of the Kheis rocks in the Brakbosch Poort ridge with the granite and gneiss to folding; at the same time he said that there was at places evidence of intrusion of acid igneous rooks posterior to that folding. The correlation of the Kheis beds and the Black Reef quartzites is adhered to by Prof. Schwarz in a later publication. The reasons why this correlation cannot be accepted are, firstly, the great differences between the two groups in character, thickness, and stratigraphical relation to the neighbouring sedimentary and volcanic rocks; and secondly, the fact that while the granitic rocks of Prieska, Kenhardt and Gordonia are intrusive as regards the Kheis beds, they are not known to be intrusive in the Black Reef or higher beds of Prieska, Griqualand West and Bechuanaland. A statement in the Annual Report for 1899 (p. 72) that a dyke of granite traverses the rocks of Doornberg was based on the mistaken identity of the igneous rock, which had not at that time been examined under the microscope; at a later date other dykes of similar nature were found in the Doornbergen, and both they and the dyke found in 1899 proved to be related to the syenites and to be of quite a different nature from that of the granite and gneiss to the west.
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Transactions of the Geological Society of South Africa, 13, xxi-xxxiv
No abstract. Discussions on gold, diamonds, tin, copper, dolomite, contact metamorphism, iron, Karoo System, Bushveld Igneous Complex, Potchefstroom System, Witwatersrand, Swaziland, magnetite, haematite, Glossopteris browniana.
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Transactions of the Geological Society of South Africa, 14, 1-7
Among the ancient metamorphosed sedimentary rocks of Southern Rhodesia, which occupy considerable areas between the huge granite masses intrusive in them, are extensive and thick series of hornblende and chloritic rocks, many of which represent original basic eruptives. These rocks, as mentioned by Mr. F. P. Mennell ("The Geological Structure of Southern Rhodesia", Quarterly Journal of the Geological Society, vol. lxvi., No 263, p. 354), "constitute one of the most striking features of the greater part of the metamorphic areas". They make their appearance in many parts of Southern Rhodesia and adjoining territories, and comprise several forms and varieties according to their original nature or subsequent metamorphism. Mr. Mennell apparently regards most of them as being of intrusive origin (ibid p. 355). The present writer will endeavour to show in this communication that extrusives occur among the series, and it is to be expected that further work will prove a very considerable proportion are of this origin - an important point in elucidating their age relative to the rocks with which they are associated. The purpose of the present note is to give a description of one of these varieties of hornblende rocks, a variety which is of more than usual interest, namely, the amygdaloidal epidiorites as developed at Bulawayo. From specimens and information received from time to time the same rock appears to occur e:rtensively in other localities in Rhodesia, for example the Gwanda district and elsewhere. Upon a future occasion it is the desire of the author to describe the other rocks of this hornblendic series, namely, those which retain the massive form and ophitic structure of the dolerites (mentioned by Mr. Mennell, ibid p. 355), those which have the form of "pillow lavas", those which have been impressed with a schistose structure-hornblende and chlorite schists, and those which by contact with, and absorption in, granite have become hornblende granulites. All these are more or less well seen at and in the immediate vicinity of Bulawayo.
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Transactions of the Geological Society of South Africa, 14, xxi-xxx
Since ever the Witwatersrand and goldfields were discovered, the banket, and especially the origin of the gold it contains, has been a subject of discussion - a discussion of which some people are doubtless very weary. Indeed, as far back as 1895, the first year of this Society's existence, a prominent member remarked that the question of the origin of the gold had already been debated ad nauseam. It is not so much my intention this evening to renew this debate as to review our present knowledge of the banket, which is largely the fruits of the discussion, and to consider towards what solution of the central problem that the banket presents, opinion appears to be trending. It is now generally agreed that the banket is a littoral marine deposit. The Witwatersrand System was laid down in an area in which the general movement was one of subsidence, with a gradual encroachment of the sea on the land. The bands of quartzite, which are usually ripple-marked at places, and the beds of conglomerate indicate periods of pronounced shallow-water conditions. There are at places signs of contemporaneous erosion, and these apparently form the grounds on which is based the opinion, which one occasionally hears expressed, that an unconformity exists in the System. It follows from the fact that the conglomerates of the Main Reef Series are underlain conformably by sediments several miles thick, that these beds, where they are now being worked, must have been distant many miles from the ancient land from which their material was originally derived, and the term "beach-deposits" sometimes applied to them, is probably misplaced. The precise conditions under which the Main Reef Series was laid down are difficult to reconstruct in imagination, but this may be safely left to the members of the Geological Survey, who are at present engaged on the Witwatersrand area. Of the rocks that formed the land in Witwatersrand times we can form some notion from the composition of the banket and other rocks of the Witwatersrand, without drawing upon our direct knowledge of the Swaziland System. It is evident from the pebbles of the banket that they comprised quartzites, banded slates and schists - for schist pebbles, though rare, do occasionally occur. Quartz grains, in the matrix, enclosing apatite and other minerals spear; of igneous rocks, while pebbles of vein-quartz and quartzite containing abundant tourmaline, and others composed entirely of that mineral suggest acid intrusions. Here I may mention that pebbles of what appear to be altered quartz-porphyry, though no one has hitherto referred to their presence, are common in some portions of the "reefs." The abundance of microcline, orthoclase and acid plagioclase felspars in the "speckled bed" is evidently derived from the disintegration of granite. The widespread occurrence of chromite in the matrix of the banket suggests basic igneous rocks. The commoner pebbles inform us that the country was intersected by numerous quartz veins. From the base of the System upwards the same types of vein-quartz pebbles occur, and the variations that can be observed in the other pebbles indicate the varying character of the rocks coming successively within reach of the ever-encroaching sea It can be inferred from the nature of the rocks that formed this ancient land, and the different degrees in which they resist disintegrating agents, that the land presented a diversity of feature in some degree comparable to what can be seen at the present day in areas occupied by rocks of the Swaziland System.
Transactions of the Geological Society of South Africa, 15, 93-99
The Witwatersrand Strata exposed on the East Rand. The plan and section attached to this paper are based on the more detailed map (exhibited during the meeting), which embodies the result of field work commenced during my official connection with the Van Ryn Mine in 1904, and lately brought to a close. The plot being on a fairly large scale will, I trust, he found sufficiently explanatory to make any lengthy description from me unnecessary. The geological and topographic features are shown as they present themselves to the field observer, and it is left to the reader to draw his own conclusions, particularly with regard to the location of faults other than those inserted. The area mapped-out borders on ground with which members of this Society have become familiar during recent discussions, and some of the points then advanced will perhaps appear in a clearer light now that the localities, separately or casually alluded to, have been connected-up by a comprehensive survey. A prominent feature brought out by the survey is the variable width of the belt occupied by the rocks of the Lower Witwatersrand System. On the meridian of the Glencairn mine the horizontal distance between the base and, the top of the system is 9,200 feet; six miles further east (about Benoni) it has increased to 28,000 feet; while at the Van Ryn mine it is 16,400 feet. The expansion of the belt is not attended by a corresponding flattening of the dip; on the contrary, throughout the greater part of the farm Kleinfontein the bassets are inclined 70 to 85° south, and in places even tilted to 80° north. The widening of the belt is no doubt due to the reduplication of strata, but while there is indirect evidence of the effect of faulting and anticlinal folding, it is not, as a rule, practicable to locate the axes of displacement, mainly on account of the cappings of younger sediments (Karroo and local drift), which cover most of the table-land. A knowledge of the broad structure of the field can, of course, be obtained without attempting to trace the actual lines of displacement with such precision as would satisfy the mining engineer. Thus at the trig-station on farm Kleinfontein the Hospital Hill quartzites dip 80° N.; following their strike to the south-west they stand vertical; further on they dip 77°S., and then terminate on a strike fault (shown on the plan), which apparently extends along the valley of the Klipfontein Spruit, through or south of Knights Pan, and thence to the Bezuidenhout Valley, near the south-west corner of Rietfontein Estate. Another main strike fault is traceable from the Van Ryn Estate in a north easterly direction, the strata on the right (including the Main Reef series) dipping 20° to 30° south, while those on the left (including the Government Reef) dip 65° to 85° to the north-west. It will be noted that the heft of Lower Witwatersrand strata, apart from the above-mentioned variations in width, has its northern and southern margins approximately
parallel. It is of importance to bear in mind that such parallelism must necessarily be shared by the intermediate zone, comprising the Government, Coronation, and Promise Reefs. This zone is exposed from the meridian of the Glencairn Mine eastward - for about two miles, thence for a distance of 4¼ miles is masked by a basalt flow and Ecca sediments; reappears for a short distance in the valley of the Boksburg Spruit ,on farm Klipfontein, and is for the next 1½ miles for the most part hidden under the Ecca deposits, leaving, however, the Lower Coronation quartzites prominently bare in the large pan east of the Benoni Race-course. The strata have now assumed a north-easterly strike, which they maintain for the next six miles before they finally disappear under the Karroo beds.
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Transactions of the Geological Society of South Africa, 15, xxi-xxxiv
No abstract. Nature of geological work in a new country. Advantages of scientific and technical discussion. Sampling. Shaft and borehole records. Correlation of geological data. Johannesburg and geology. South African geology as a field for scientific observation.
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Transactions of the Geological Society of South Africa, 16, 1-32
I. INTRODUCTION - (p. 1).
II. COMPARISON OF SECTIONS - Lower Witwatersrand (p. 3). Upper Witwatersrand (p. 4).
III. STRUCTURAL FEATURES - The Dolomite and Black Reef Series (p. 5) Witwatersrand System, Order of Treatment (p. 7). The Witpoortjie Fault (p. 8). Country north of the Witpoortjie Fault (p. 9). Continuation of the Rietfontein Fault (p. 9). Country north of Krugersdorp, Alexandra Estate Reef (p. 11). The Government Reef west of Krugersdorp (p. 11). Correspondence of Botha's and Main Reef horizons (p. 12). Country South of Witpoortjie Fault (p. 13). The Witpoortjie Fault (p. 14). Dolomite basin on Vlakfontein (p. 15). Folding about Doornkop (p. 15). Extension of Upper Witwatersrand System west of Roodepoort (p. 16). The Roodepoort Fault (p. 16). The Saxton Fault (p. 19). Broken country between the Roodepoort and Saxon Faults (p. 20). Continuance of Main Reef horizon south-west of Roodepoort (p. 22). History of the Faulting on the Witwatersrand (p. 23). Conglomerate on Rietvlei (p. 25). Country west of Randfontein and the West Rand Fault (p. 25). The Middelvlei Inlier (p. 28). Extreme Western Rand (p. 30).
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Transactions of the Geological Society of South Africa, 16, 142-146
The tin deposits of Swaziland are of exceptional interest to the geologist, since their mode of occurrence, notably that of Forbes Reef presents certain novel features, unlike those usually met with among the better known South African deposits. Two main tin-bearing districts can be recognised in north-western Swaziland; the one consists entirely of alluvial occurrences and embraces Embabaan with the surrounding country, including the lower-lying district round McCreedy's Tins, some 10 miles further south; in this belt of country the tin is associated with granite only. The other district lies on the eastern side of the Ingwenya Range, round Forbes Reef, and comprises occurrences associated both with granite and with schists.
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Transactions of the Geological Society of South Africa, 16, 147-155
Stellenbosch stands on a wide gravel flat, almost completely surrounded by hills. Upon this flat there debouch three large valleys - Jonker's Hoek on the south-east, Ida's Valley on the north, and the valley of the; Plankenberg River on the north-west - besides numerous ravines and gorges. The whole of the drainage ultimately finds its way into Eerste River, either directly or by way of Kromme River and Plankenberg River, and these three are the only perennial streams in the area under consideration. The headwaters of Eerste River rise in the mountains at the south-east end of Jonker's Hoek, and the river has already accomplished nine miles of its course when it emerges from the valley on to the Stellenbosch flats. So far its course has been north-westward; at the mouth of Jonker's Hoek it turns to the west, and a run of two and a half miles through the flats brings it to the foot of Papegaaisberg, where it is joined by the joint Plankenberg-Kromme River system. The hills are then left behind and the river pursues its plain course across the Cape Flats, bending gradually southwards all the time, to escape at last into False Bay after a course of some twenty-six miles. The general relations of this river system are shown in Figure 1, while the detailed topography of that portion with which we are more immediately concerned is exhibited in the large scale map (Plate XXI). This map is only a portion of a new geological map of the neighbourhood of Stellenbosch which I hope to complete shortly. The following approximate measurements of the altitude of the water surface have been made with a good aneroid, checked by the known altitudes of the railway stations.
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Transactions of the Geological Society of South Africa, 16, 44-106
About the end of 1906, I wrote "Some notes on the geology of the Katanga district of the Congo State", which, along with the Geological map of Katanga, were published in the "Annales du Musee du Congo", Brussels, 1908. In the period which has elapsed since the above notes were written, so many new facts have been brought to light, and the field of research has been extended so much, that a considerable modification of the views expressed in them is necessary, and the object of the following pages is to put together, and render accessible, a generalised account of the geological information which has been gathered int eh course of my numerous journeys and investigations in various parts of the country during the last decade, supplemented by that conveyed in the maps, reports and specimens for prospectors employed by the Tanganyika Concessions, Limited, during that period, which has been kingly placed at my disposal. Previous to 1901, the only systematic geological information available concerning this part of Africa was contained in the papers of Monsieur Jules Cornet (see Bibliographical List), written as a result of his investigations in connection with the Bia-Franqui expedition into the Katanga district (1892-1893). M. Cornet's papers and geological sketch map afforded a good basis to work upon, and the results of my observations broadly confirm those of M. Cornet. But the more detailed study, which I have been able to devote to the work, has resulted in the accumulation of much fresh information and fuller details, so enabling me to further complete and extend the work which he began. In commencing work in what is practically a new country to the geologist, the notes taken on each individual line of march are at first bewildering in their complexity, but as more and more of the country is covered, the connection between the various facts recorded gradually comes to light, and enables the work to be carried on more systematically; but, as such observations are necessarily confined to a narrow width of country bordering the line of march over long distances, and although the network of routes in some parts of the country is comparatively close and the intervening untouched spaces small, in other parts of the country, these untouched areas are the predominant feature, so that w may only regard the resulting work as an approximation to the truth, and expect that as the work is carried on and new facts are brought to light, many corrections and modifications will be found necessary. I have retained the nomenclature of M. Cornet as far as possible, but where formations have been considerably modified, or where new ones have been discovered, I have named them after some important river or place, where they are well illustrated. For convenience, I have divided the matter in these pages under the following headings: -
PART I. - The geology of Katanga and Northern Rhodesia, with a geological map and sections.
PART II. - The relationships of the Central African rock systems to those of South Africa, and their probable age.
PART III. - The distribution and relative age of the Central African subsidences.
PART IV. - The structural regions of Equatorial and South Africa, with a geological sketch map.
In Part I., I will describe the sequence and general characteristics of the rock systems of Katanga and Northern Rhodesia, and give an outline of the Tectonic geology of this part of Africa. The geological map and sections which accompany this outline are based on a trigonometrical survey of part of Katanga, made by late Mr. J.H. Haydon, Surveyor to the Tanganyika Concessions, Limited, supplemented by careful compass route-surveys and sextant observations for latitude, etc., and barometric observations for heights. The portion of the map geologically coloured represents an area of over 250,000 sq. miles, or over twice the area of the British Isles, and about twenty-two times the area of Belgium. In Part II., I propose to show that the rock systems, as recognised in South Africa, cover the greater part of Equatorial and South Central Africa, having very similar lithological characteristics, and geological sequence, and also to show the reasons on which the general correlations are based, and how an estimate of their geological age has been arrived at. In Part III., I propose to show the general distribution and relative age of the large areas of subsidence which occur in Equatorial and South Central Africa. In Part IV., I have given a general summary of the conclusions arrived at, and on the accompanying sketch map I have shown the distribution of the rock systems described, and have also reduced the geological maps on the Transvaal and Cape Colony published by Messrs. Hatch and Corstorphine, and Messrs. Rogers and Du Toit on to the same map, so that the relationship of the various rock systems is well demonstrated. I have also, on this map, shown as near as possible the position and extent of the Central African subsidences. Such a map of these subsided areas bears a great resemblance to a map of the Martian canals, and when we consider that the length of the Zambesi-Luangwa graben, with its apparent prolongation into Gregory's "Rift valley" and onwards into Abyssinia is over 2,000 miles, or about one-twelfth of the Earth's circumference, then it may be that we have in these long subsidences an explanation of how the Martian canals were formed, if such in reality exist.
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Transactions of the Geological Society of South Africa, 16, xxii-xli, 5 pl
Exactly seventeen years have passed since I had the pleasure, as a Foundation Member of this Society, of listening to the inaugural address of our first honoured President, the late Dr. Exton. At the termination of that address he drew attention to some of the mineralogical and geological discoveries which had been made on the Rand, acting as a stimulus for further research and providing an excellent raison d'etre for the Geological Society of South Africa. Ten years ago another esteemed President, Dr. Molengraaff, commenting on the state of our geological knowledge of this country, enquired: "In which direction lies our field of investigation for the future, and what harvest may we possibly bring home?". The last question suggested the subject of my address this evening, for after all it is the practical and more selfish application of science to our needs which benefits mankind mostly, and the ultima Thule of such application is usually a harvest of some kind. In all parts of the universe important discoveries of mineral wealth have been brought to the notice of man directly through agencies of sub-aerial denudation. In each of the great Continents the denuding action of water, ice and wind have, in turn, placed great wealth literally at the feet of mankind, and by the methods of selection collection and eventual concentration, the products of sub-aerial denudation have gone far to enrich nations. Specific instances of such alluvial wealth are much too numerous to come within the scope of this address, but one can quickly bring to mind the great gold discoveries of North America, the beautiful alluvial diamonds of Brazil; the extensive tin deposits of the Malay Peninsula, and gem gravels of Ceylon; the gold, tin and gem deposits of Australia. In this respect South Africa has likewise much to be grateful for in the alluvial gold which attracted the pioneer digger to Barberton; the wealth of diamonds in the valley of the Vaal and elsewhere, which has made fortunes for a few ana a humble living for thousands of whites for forty years; the tin of Swaziland and the Cape Colony, all of which deposits have combined to indicate unmistakably the existence of enormous mineral wealth in South Africa, and stimulated the search for the sources of those much-desired commodities. For the mind to grasp the vast extent of denudation to which this sub-continent has been subjected it is necessary to formulate and accept for the time being a definite view regarding the form and configuration of South Africa at the close of the Karroo period. Its form is generally believed to have taken the shape of a huge table-land, varying in altitude above sea-level between 8,000 feet and 13,000 feet. We know from existing evidence in the Drakensberg Mountains that the Karroo sediments reached an altitude of fully 8,000 feet in Jurassic times, when the great volcanic outbursts and fissure eruptions of the Drakensberg altered the configuration of the country by piling up
between 4,000 and 5,000 feet of basic lavas over the southern portion of the Continent.
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Transactions of the Geological Society of South Africa, 17, 60-74
I. Introduction. II. Nature of the Formation Containing the Chromite - (1) Distribution and Field Relations. (2) Lithological Characters. (3) Petrography. (4) Original Nature. III. Manner of Occurrence and Distribution of the Chromite. IV. Characters of the Chromite. V. Associated Minerals. VI. Characters of the Chromite Bodies. VII. Composition of the Chromite. VIII. Origin of the Chromite
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Transactions of the Geological Society of South Africa, 17, xxii-xxxvii
In the discussion of Studt's important paper, " The Geology of Katanga and Northern Rhodesia". I may add a few notes concerning the geology of German South-West Africa. Stud believes that Passarge's Maseganite formation and Wagner's Inselberg Series represent the Swazi System in Damaraland. I should rather like to correlate them with the Ventersdorp System, while Wagner is of opinion that some of the conglomerates may represent the Banket of the Witwatersrand. From other parts of the country I have never seen conglomerates resembling those of the Witwatersrand, and I believe also that Kuntz would have observed them if they existed in the Kaokofeld, the north-western part of the German Colony, about which he and Krause lately gave valuable geological information. Voit in 1904 divided the crystalline coastal belt of Damaraland into three horizons, as follows: - (1) A granite-gneiss zone, (2) A gneiss-schist zone, (3) A schist zone.
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Transactions of the Geological Society of South Africa, 17, xxii-xxxvii
Some years ago, while reading the work of an eminent living geologist, I came across the following sentence:-
"In an uncertain science like geology one of the great difficulties is to keep an even balance between contempt and undue respect for authority".
There can, indeed, be little doubt that the conjectural element enters more largely into our science than into any of the other branches of scientific enquiry, yet if we contemplate the gradual evolution of geological knowledge and the splendid results achieved both in the domains of pure and applied geology, we realise the soundness of the fundamental principles on which our science rests, and are justified to look to the future for further and still greater achievements. The conspicuous manner in which conjectural aspects sometimes control the pursuit and results of geology is no doubt partly due to the inherent nature of geological investigation, but also arises from extraneous causes.
When we remember the ultimate aim of geology to unravel the history of the Earth, it is obvious how largely the element of uncertainty must figure in such a pursuit, for the various stages in the actual development are for ever buried in the long past, and only by much laborious observation of present conditions can we hope to succeed in fixing and understanding the principal landmarks in the Earth's natural history. It is a mere truism to say that without judicious speculation every science must remain barren, and this applies with exceptional force to geology. The natural and legitimate longing to get away from the ever increasing mass of minute facts towards bold and sweeping generalisations was felt even during the earliest stages in the historical development of geological science, and is reflected by the peculiar trend of speculative thought among the various schools of geology during the 15th, and during the early years of the 19th century. The publication in 1815 of the first geological map by William Smith, who with his marvelous "eye for the country" relied solely on the faithful evidence of nature, is thus rightly regarded as marking the birthday of scientific geology. Henceforth our science has advanced by leaps and bounds until, through the active and willing co-operation of an ever-increasing body of investigators throughout the world and with more refined methods of research, a vast storehouse has been gathered together of facts, which in some respects threaten to outrun their true significance and still await the advent of a genius who shall co-ordinate them under some fertile generalisation. In the youthful days of geology, speculation was not only rife but sufficient facts had not yet been accumulated to provide a wholesome check to unwarranted flights of the imagination. At the present day, when the need of bold generalisation is greater than ever, the difficulty of arriving at wider co-ordinating principles is also greater, for the tendency towards minute specialisation, which
dominates all scientific investigation of to-day, supplies an almost unlimited control.
Yet the scarcity of the scientific genius at the present time and the limitations set to the imagination through the more highly advanced state of our science, have their compensations, for whenever a grand conception is put forward and satisfies the numerous checks, which years of geological spade-work have furnished, we are justified in reposing increased confidence in its soundness and ability to survive the tests of time. In one respect other branches of natural science possess a distinct advantage over geology in their means of enquiry. I refer to the experimental method of investigation. At a time, when in the hands of Robert Boyle, a Michael Faraday, or a Berzelius, this line of research yielded numerous and important results, experimental geology was practically unknown, and has only quite lately begun to assume its rightful place. It may perhaps be possible to overestimate the value of an experiment in connection with a science that aims at elucidating the evolution of the earth as a habitable globe, owing to the peculiar difficulties in reproducing natural conditions, but one need not subscribe to Mr Bernard Shaw's dictum that "an experiment proves nothing because it is merely a put-up job".
Until recent years experiment in geology has been attended with indifferent results despite the labours of Sir James Hall, Daubrée, Favre, Cadell, and others, possibly because the problems were approached essentially from the geological side. It is not without significance, that the experimental method of investigation has arisen very late in the history of geology and has been attended with conspicuous success only along the avenues of physical chemistry, as strewn by the epoch making researches of Vogt, Doelter, Lagorio, Van't Hoff, the members of the Carnegie Institute and various others.
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Transactions of the Geological Society of South Africa, 18, 1-4, 1 pl
While visiting the Bembesi Diamond Field, at the invitation of Mr. A.E.V. Zealley, of the Geological Survey of Southern Rhodesia, I had the fortune to obtain several specimens of an intergrowth of diopside and ilmenite with a remarkably perfect graphic structure. The mixture is fairly common as fragments in the concentrates left by the prospectors who developed the two properties in the neighbourhood, the Colossus Pipe on the farm "Robins" and the kimberlite sill on "Wessels". The broken fragments of the mixture in the concentrates vary much in size; their surfaces are mostly freshly fractured, but sometimes they contain part of the original rounded surface of the nodule with some of the matrix attached. Two larger specimens were found; one which measures 85 mm. in length has only one freshly broken surface, it is clearly part of a flattened ellipsoidal boulder. The other specimen is from Wessels and is still imbedded in the kimberlite matrix.
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Transactions of the Geological Society of South Africa, 18, 102-117, 3 pl
Since the year 1896, when the investigations of the geologists of the Geological Commission of the Cape of Good Hope finally placed the glacial origin of the Dwyka conglomerate or tillite, as it has more recently been termed, beyond question, a wealth of information has been gathered in regard to the nature of this remarkable deposit, the source of the material of which it is composed, the character of the surface on which it reposes, and the extent and movements of the vast continental ice-cap which at one time covered a considerable portion of Central South Africa; and, although a great deal of detailed work remains to be done, the history of the Permo-Carboniferous ice-age in its broad outlines may be said to have been deciphered for the greater part of the area occupied by the Dwyka series. The present state of our knowledge concerning the subject may be briefly summarised as follows.
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Transactions of the Geological Society of South Africa, 18, 11-56, 2 pl
Upper Witwatersrand System defined (p. 12). A typical Central Rand section (p. 13). Classification and Nomenclature of the Upper Witwatersrand System (p. 14). Consideration of a general longitudinal section (p. 17). The Main-Bird Series (p. 17). The Main Reef and associated beds (p. 18). Evidence for the persistence of individual members (p. 21). Persistence of the main Reef Leader and its extension into the Eastern Rand (p. 22). The Main Reef and Black Bar (p. 23). The Bastard Reef (p. 25). Extension of the Black Bar and Bastard into the East Rand Proprietary Mines (p. 26). Conglomerates below the horizon of the Main Reef Leader in the far East Rand (p. 30). Modifications of Central Rand conditions in the Eastern Rand (p. 31). Importance of recognising the variability of the beds below the Main Reef Leader (p. 31). The "Slate" footwall of the Cason and Blue Sky Mines (p. 32). The Main Reef Leader the principal reef on the Eastern Rand (p. 32). The Blue Sky Section a starting point for erroneous correlations (p. 35). The Main Reef zone followed westwards from the Central Rand (p. 37). The Bird and Livingstone Reefs (p. 38). The Bird Reef Marker (p. 39). Quartzites associated with the conglomerate zones (p. 39). The Main Reef Footwall Quartzites (p. 39). The Kimberley-Elsburg Series - Kimberley Shales (p. 39). Kimberley Reefs (p. 40). Battery Reefs (p. 41). Joel Reef (p. 41). Thinning out of quartzites below Kimberley Reef on the East Rand (p. 42). Elsburg Reefs (p. 42). Distinction between Kimberley and Elsburg types (p. 43). No evidence of unconformity (p. 44). Nature of the relationship of the Elsburg Beds to the rest of the Witwatersrand System (p. 46). Conditions of deposition of the Witwatersrand System (p. 47). Distribution of the reef at the Nigel, Brakpan and other Mines - Existence of "shoots" (p. 47). Mode of deposition of the Main Reef Leader - Deltaic origin of certain beds (p. 50). Comparison of the Witwatersrand System with similar formations in other parts of the world.
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Transactions of the Geological Society of South Africa, 18, 118-128
Lead and zinc ores have for many years been known to occur in the Dolomite Series to the south of Zeerust. As was the case in America, lead was the first metal to be mined during the early working of the ores, the zinc being passed over as of no value, although in many cases the two ores occur together. The mines that are being worked at present lie about 17 miles to the south of Zeerust and about five miles east of Ottoshoop. There are two modes of occurrence of the zinc and lead ores in this district. The first is in the form of localised, more or less circular areas in the dolomite or chert, with no evidences of any continuous superficial ore connections between them. Typical examples are those on Witkop (288) and Buffelshoek (284), where the ores so far as prospected are confined to each individual circle. There are many other circles of a somewhat similar character, on various farms, on a few of which prospecting has not gone far enough to show whether or not they carry ores, while there ale others which have been noted but have not yet been touched by prospecting. The second is the local occurrence of isolated aggregations (disseminated deposits) of galena, sometimes attaining some size and often associated with similar aggregations of zinc-blende. These occur on the outcrops of the horizontal beds of dolomite, which is rarely tremolitic where they appear. The following farms contain scattered aggregates of zinc and galena ore sometimes of fair dimensions: Bokkraal (300) Stinkhoutboom (269), Rhenosterhoek (50), and Kaalplaats (97), on the Malmani river.
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Transactions of the Geological Society of South Africa, 18, 129-131, 1 pl
The late Mr. William Anderson was kind enough to donate to the Australian Museum a small collection of the carbonaceous mineral mentioned in his paper, and the following short account is based thereon:- The mineral is confined to a zone extending to a depth of 100 feet, and occurs as spherical, flask-shaped, or irregular rounded pellets up to three-quarters of an inch in diameter, embedded in calcite or, in one instance, in vein quartz. As the mineral is sometimes cracked and traversed by veinlets of calcite (Plate XVI., Fig. 3), we may conclude that the calcite was the later formed; moreover, there is no sign of conformability on the part of the carbon with the crystal outlines of the calcite, as we should expect if calcite were the earlier or if the two were formed simultaneously. The carbon occurs in two forms - one (a) black lustrous, highly polished, brittle, with a specific gravity of 1.845, and a hardness of 3 to 4; the other (b) duller in appearance, soft enough to mark paper like graphite, with a specific gravity of 1.122; (a) is the more abundant in the collection. By the courtesy of Mr. E. F. Pittman, Under-Secretary for Mines and Government Geologist, samples were analysed by Mr. J. C. H. Mingaye, Analyst to the Department of Mines, with the following results.
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Transactions of the Geological Society of South Africa, 18, 5-10
The discovery of radioactive substances has drawn attention to several minerals that have long been known to mineralogists and chemists as compounds of the rare elements, but which have been regarded as of scientific interest without importance in commerce or in the ordinary work of geologists. Though these minerals are of unusual occurrence, it is possible that they have often been overlooked both by geologists and prospectors, and it is the purpose of this note to describe tho occurrence of some such minerals in the hope that further discoveries may be made and that some of them may prove of economic importance. The demand for radioactive minerals is considerable and any ore containing only a few per cent of uranium or thorium has a commercial value and is directly saleable. For example, ore containing 2 % of uranium was being sold a year ago in the United States for £18 per ton of 2,000 lbs. It appears that radioactivity is associated, chiefly at any rate, with uranium and thorium, and it is with minerals containing those elements that we are concerned. The first group of such minerals described from South Africa seems to have been the rare minerals from Embabaan in Swaziland, found by Sydney Ryan and determined by G. T. Prior. The minerals are monazite and substances allied to euxenite and fergusonite; they occur in gravels along with cassiterite, corundum, scheelite, magnetite and garnet, and are supposed to be derived from the gneissic rocks of the district. The mineral described by Dr. Prior as allied to euxenite occurred as loose crystals with worn faces; it has sub-conchoidal fracture and a brilliant vitreous to greasy lustre; it is brownish black in colour and in thin splinters is translucent and isotropic. The sp. gr. is 4.99. The combined results of two analyses are given.
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Transactions of the Geological Society of South Africa, 18, 57-71, 2 pl
In previous papers some of the main features of the geology of the West and Central portions of the Witwatersrand have been dealt with. In the present essay the Eastern Rand will be treated on somewhat similar lines. The survey and mapping in detail of an area like the Witwatersrand by a single individual, while it ensures the application of a uniform standard in description, must necessarily require a considerable length of time, especially when the great economic importance of the goldfield and the vast accumulation of information derived from mining operations and innumerable boreholes is taken into consideration. Further, before a more or less intimate acquaintance had been made with the whole of the area it was scarcely possible to write a very full description of any particular portion, especially in such important respects as the comparison and correlation of various members of the Witwatersrand System, as developed in different portions of the Rand. On the other hand, in the course of the survey a good deal of information was obtained which it was possible to put into definite form and render available for use without waiting for the completion of the whole world. To do this has been the object of the various papers referred to, and the interest taken in the Eastern Rand at the present time seems to justify similar treatment of that area. It is anticipated that before long it will be possible to publish a connected account and a complete map of the whole Witwatersrand. It will therefore not be necessary in the present paper to do more than to indicate somewhat briefly some of the main points in East Rand geology which may be immediately useful to those interested in that particular area, more especially as some East Rand features have been touched upon in a recent paper. The extensive and comparatively shallow synclinal basin of the far East Rand, whose existence was demonstrated long ago by the work of Hatch and others, still remains largely undeveloped. To it, many look with a confidence which is largely justified by what we already definitely know of the area, for the maintenance for a very long time to come of the dominant position in the world's gold production held by the Witwatersrand. One sometimes hears references to the "decline of the Rand" as if that were an imminent event, but in view of the possibilities of such an area as the far East Rand, of the known resources of the Central and nearer East Rand, and of past experience as to the way in which, owing to the existence of bodies of ore of which no account had been taken in previous estimates, apparently moribund mines continue to flourish for years, thus to anticipate the decline of the Rand appears very much as if one should speak of the decline of a man in the thirties.
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Transactions of the Geological Society of South Africa, 18, 72-101, 7 pl
The country described in this paper is the north-western part of the Namaqualand division, and it extends from the Orange River, between Groot Derm and the neighbourhood of Henkries, in the north to the Bitter River in the south; it is bounded by the Atlantic on the west and a line passing near the western limit of Bushmanland on the east. It thus includes the coast belt, a considerable part of the Namaqualand highlands and the slope connecting those two regions; this slope is the northern continuation of the Western escarpment in Van Rhynsdorp, which can be followed as a fairly definite feature as far as Klipfontein or Anenous, but north of that place the high country is cut up rather irregularly by the streams leading to the Orange River, on the one hand, and directly to the sea on the other. The broad belt of quartzite and schist which starts near the Orange River and reaches the sea near the mouth of the Buffels River complicates the topography by offering greater resistance to denudation than the gneiss which forms most of the coast belt. The coast does not follow the strike of the foliation and bedding closely, but has a more north-westerly trend, and it is a low-lying shore as far north as a spot eight or ten miles north of Port Nolloth, where it becomes precipitous; north of this neighbourhood I have not yet visited it. As a rule the ground rises gradually from the shore, and evidence of fairly recent elevation in the form of boulders strewing the surface are found amongst the sand-dunes as far as two or three miles inland, but the presence of over-deepened valleys near the coast in the lower courses of the Bitter, Spoeg, Zwartleintjes and Buffels Rivers is proof of subsidence of more recent date than the raised beaches, which do not enter the valleys. The plateau country is confined to the region where the remains of a nearly horizontal covering of the Nama formation occur, and west of this region the surface is made of more or less distinct ridges trending in the direction of the strike of the sedimentary beds. This district where ranges are found lies in the north, and it is interrupted by the Kuboos mountain made of massive granite. The Tcoulyroup range east of the Kuboos granite trends south-east to the Orange River, and it is not strictly parallel to the strike of the rocks forming it; the highest points in the whole district are in the Tcoulyroup range. The Orange River always has water in it, but the mouth is open for a few months only, and the water comes from far up-country. The Buffels River, which drains Kamiesberg and a small area round Nababeep and Ookiep, has running water in it at intervals of several years, and the other rivers still less frequently. In this paper the structure of the rocks older than the Karroo formation will be described; the Karroo formation and younger rocks will only be mentioned in passing, and the large group of intrusions containing copper ore in the south-eastern part of the region will not be
dealt with.
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Transactions of the Geological Society of South Africa, 18, xxi-xxxi
At one of the earliest meetings of the Geological Society of South Africa some of its enthusiastic founders expressed the opinion that the scientific researches of the members ought to be in part at least directed towards geological problems which have a practical application. There was, in fact, a natural desire among those Transvaal pioneers into the realms of Geology, many of whom were interested in the exploitation of the mineral resources of the country, that Economic Geology especially as applied to mining should frequently provide material for description and discussion. That encouragement in the study of subjects which were not considered of immediate practical importance but of only scientific interest was, however, not lacking, is plainly disclosed in the early volumes of the Transactions. It is, indeed, often difficult to decide what is practical and what is not. That a discovery of purely scientific interest today is tomorrow a factor of economic importance is true in Geology as in any other science. The student who intends to seek for gold in the Archaean schists, regards as futile the laborious task of the palaeontologist who observes and records the minutest differences in the structures of long extinct animals; but, when the mining engineer engaged in the search for deeply buried coal seams is enabled to determine by means of the despised fossils the most favourable horizons for his operations, the value of such work at once rises in the estimation of its former critic. So with many of the problems in ore-deposition. To some the study of the genesis of an ore appears to be of theoretical interest only. It is not an uncommon experience to get a gentle hint from the man engaged on the mine that no doubt such a question is very interesting to people who have nothing better to do, but that he is too busy following the "values" to give much time or attention to such a matter. There is a certain expression of failure to grasp the idea that the following of the "pay-streak" and the finding of other "pay-streaks" may be facilitated by deductions from the genesis of the ore. Many of the results obtained in such a study may always remain of interest to the theorist alone, but there are, of course, already many instances of results becoming valuable practical assets.
It may at any rate be assumed from the nature of the Transactions that in the opinion of the early members of this Society the study of everything associated with ores and ore-deposits was considered of a practical nature so that, when I attempt to trace the progress in that subject which has been made by our members, I shall be determining in respect of one branch of our subject to what extent the desire of the founders of the Society has been fulfilled. South Africa with its varied deposits of gold, copper, tin and other metals has offered splendid opportunities for research work in this branch of Geology. The Transactions of the Geological Society and the memoirs of the
Geological Surveys give convincing evidence that they have not been neglected. As a result of twenty years close attention to the geological aspects of the different types of ore-deposits not only are the general characters of most well known but in many cases the minutest details have been examined and described. It appears to me, therefore, that there will be in the near future a marked change in the nature of contributions on ore-deposits. We must look forward to obtaining much more information of a detailed character. Intensive study of individual deposits must replace to a great extent the more attractive comparative accounts, and, since we have now reached the stage when this change will become more pronounced, I thought it might be of interest to review the work which has already been done. It is not my intention to compile a complete list of the papers dealing with South African ore-deposits but rather to comment on the results which have been achieved and to mention some which I would like to see attained and recorded in the Transactions in future years.
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Transactions of the Geological Society of South Africa, 19, xxi-xxxv
The copper-bearing rocks of Namaqualand fall into two sharply-defined groups - (1) those which occur in veins with a gangue of quartz, carbonates, felspar and chlorite, and (2) those associated with igneous intrusions in gneiss. The first group is found in the northern portion of the country, and has not given rise to any notable output of copper; the second group is the basis of the copper industry, and it occupies an area of some 2,000 square miles in the middle of the Division of Namaqualand, though the individual intrusions are small. It is a remarkable fact that these two forms of copper deposits are not found together; no rocks resembling those forming the southern intrusions have been found in the north, and in the region of the intrusions - large as it is, and though it has been more or less continuously prospected during the past seventy years - not one vein of the ordinary type has been opened up. When Andrew Wyley examined the district in 1856 he drew this distinction between the northern and southern occurrences, and he wrote as follows concerning the latter:- "The way in which the copper pyrites is frequently disseminated throughout the felspar rock, looking almost as if it were one of its constituent minerals, entirely precludes the supposition that it has been deposited in cracks or fissures after the rook had cooled and consolidated, as is the case with ordinary lodes or mineral veins. The veins must have been contemporary with the rock. We can account for the facts in no other way than by supposing that when this felspar rock came up, in a state of fusion, from beneath, it brought the copper along with it in the form, most probably, of copper pyrites distributed through its mass. This, on cooling, would naturally segregate itself into veins more or less definite, and when the circumstances were favourable into large lode-like masses, while a portion would still remain in a state of minute division throughout the rock". This is a plain statement of the view that the copper ore is, like the felspar, of magmatic origin, and that there was a certain amount of differentiation in place at the time of the intrusion of the felspar rock. I propose to lay before you tonight some of the evidence bearing on these points. The correct answering of these questions is of fundamental importance in the future development of the mining field, because the distribution of the ore is dependent on its mode of formation, and further search for it must be guided by the conclusions arrived at on that subject if the search is to be conducted on intelligent lines. It is worth remembering that the six mines being worked in 1914 were known and in process of being opened up in Wyley's time. There have been no important discoveries in new localities since then, though some places, especially Tweefontein and Nababeep New Mine, have exceeded his expectations, and others have fallen below them. The rocks containing the ore are of a varied nature, and may conveniently be called collectively the ore-bearer. The extreme members of the series are so different that one would not suspect them to be closely related without the clearest evidence. Thus there are rooks made up almost wholly of magnetite, quartz, plagioclase, hypersthene, hornblende and biotite respectively, but intermediate varieties are norite, mica-diorite, augite-diorite and diorite. The following table gives in a compact form the results of a microscopic examination of over 200 rocks, but it is incomplete, and there are doubtless a few other varieties amongst the 344 distinct groups of outcrops hitherto mapped, also there are probably more outcrops yet to be found.
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Transactions of the Geological Society of South Africa, 2, 150-157
The importance of the South African coal measures to the development of the mineral resources of the country in general, and of the mining industry of the Witwatersrand in particular, has cuased capitalists to turn their attention towards the opening up of the valuable stores of mineral fuel which nature has placed in such a favourable position with regard to the gold-bearing reefs of this portion of the Transvaal. Geological features, extent and description of the coal measures.
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Transactions of the Geological Society of South Africa, 2, 39-41
This paper is entitled "Faulting along the Main Reef Line" but it might just as well have been entitled "Subsidence or upheaveal" for a desire to investigate this question was the original incentive which led me to study the dip fualts in the various mines which I have had the privilege of visiting during the last six months. Upheaval, as you are all aware, is the sense to which the present elevated position of the Rand is ascribed by the majority of geologists who have studied the subject, and when I state broadly, to begin with, that I can see no evidences on the Rand of any great general upheavel, you will naturally ask at once how we in Johannesburg can be six thousand feet above the sea if there has been no upheaval.
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Transactions of the Geological Society of South Africa, 2, 47-51
In my paper, entitled "The extension of the Main Reef Westward of the farm Witpoortje", I traced the continuation of the series of sandstones, quartzites, and conglomerates to a position on the farms Elandsfontein and Oog van Wonderfontein, where they terminated against the granite dyke, which is apparently connected with a greater mass of granite outcropping on the farms Wildfontein and De Pan. I intend to place before the meeting this evening the result of my investigations on the area westward of this dyke, and over the greater portion of the country which I am describing this evening, and though neither time nor space will allow me to deal minutely with its geology, I will place before you the broad lines which show its connection with the area dealt with in my former paper, to which I must refer you for the general succession of the country dealt with.
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Transactions of the Geological Society of South Africa, 2, 5-32
I purpose to place before you a collection of facts gleaned during an extended period of examination and investigation, covering the tract of country from Johannesburg to Klerksdorp, a distance of over 100 miles. The extension of the Main Reef series, either to the east or to the west, is a matter of great importance to this community. Up to the present no one has been able to say with certainty where it is situated beyond the Witpoortje fault on the west or the farm Driefontein on the east. I do not intend this evening to deal with the extension of the Main Reef to the east.
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Transactions of the Geological Society of South Africa, 2, 53-55
The Black Reef has been laid down upon an igneous rock of an amygdaloidal character, which reaches down to the Elsburg series, and is several thousand feet in thickness. This amygdaloid can be found outcropping north of the Eckstein property all the way to the Elsburg series.
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Transactions of the Geological Society of South Africa, 2, 91-103, 109-120
The diamondiferous and auriferous deposits which were discovered and are in course of exploitation in South Africa, are so widely different to those I have met with in Australia and America, that I have devoted several years to their study so as to be able to explain the new facts which have come to my knowledge.
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Transactions of the Geological Society of South Africa, 20, 37-47
During the survey of the Barberton district a considerable number of dykes were located in the De Kaap and Komati River valleys, both in the granite and the adjoining margins of Moodies and the Jamestown Series, which show some features of more general interest.
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Transactions of the Geological Society of South Africa, 20, 48-50
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Transactions of the Geological Society of South Africa, 20, 51-52
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Transactions of the Geological Society of South Africa, 20, xix-xxxix
While engaged in deciding upon an appropriate subject for my anniversary address, it occurred to me that it might be interesting and useful to discuss in the light of newer investigations a few of the problems that. in the past, have greatly exercised the minds of South African geologists. From the numerous subjects that at once suggested themselves I accordingly chose the following, and propose this evening to deal with them in order of enumeration:- (1) The Problem of the Auriferous Conglomerates of the Witwatersrand. (2) The Genesis of the Diamond. (3) Is the Diamond susceptible of alteration under the influence of the agencies operative or specially active at or near the earth's surface. (4) The Salt Pan on the farm Zoutpan, No. 467, north-north-west of Pretoria.
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Transactions of the Geological Society of South Africa, 21, 1-26
Probably the earliest asbestos workings in the Transvaal are those of the farm Diepgezet No. 33, east of Carolina, where mining operations began about 1906 and have been carried on at intervals down to 1914. During the last two or three years prospecting operations in the Lydenburg district and east of Chuniespoort have proved the existence of extensive deposits of asbestos, which were known at least as far back as 1907, e.g., on Penge and Streatham. The difficulties of finding a market have now been largely overcome and the establishment of a flourishing industry, showing every indication of permanency, is thus in a fair way of being realised. For these reasons it seems worth while to place on record the geology of the principal occurrences of this mineral, with special reference to more recent discoveries, of which no information has so far been available, and which differ in several respects from the better known deposits of the Cape Province.
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Transactions of the Geological Society of South Africa, 21, 27-36
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Transactions of the Geological Society of South Africa, 21, 37-42
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Transactions of the Geological Society of South Africa, 21, 43-52
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Transactions of the Geological Society of South Africa, 21, 53-73
It is the intention in the first half of this paper to describe certain deposits of Corundum in the Tugela Valley that are of particular interest in adding to the long list of different ways in which this mineral can originate; at the same time the occurrence furnishes an interesting case, exemplifying the development of a "reaction-zone" between an ultra-basic rock and an acid-invading magma. The second half will deal with some Titaniferous-magnetite rocks carrying silicates and spinal that occur in the same neighbourhood as magmatic "segregations" within a plutonic body ranging in character from a gabbro to a pyroxenite, the accompanying features being analogous to those known in the central Tranvaal and in several other parts of the world.
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Transactions of the Geological Society of South Africa, 21, xvii-xxxvi, 1 pl
About one-half of the Union of South Africa is built up of strata belonging to the Karroo System, a formation possessed of characters of much more than uncommon interest even in this land of geological novelties, though perhaps this qualification is apt to be overlooked. Having as its basal member a Palaeozoic glacial deposit in extent and thickness exceeding that of any other continent, capped by volcanic flows of no small magnitude, and penetrated by igneous sills and dykes on a scale probably unsurpassed in any region of the globe, this enormously widespread formation was accumulated during the period ranging from the Upper Carboniferous to the close of the Triassic under physiographical conditions unusual and only with difficulty conceivable, while its remarkable vertebrate fauna, the product of evolutionary progress exercised over this extended time-interval, gives us glimpses of the terrestial life of an important section of Gondwanaland. In addition its great economic importance as our source of mineral fuel must not be overlooked. The Address that I have the honour to deliver to you tonight will outline merely the advances that have been made during the past fifteen years toward the detailed stratigraphy of the System, an important though admittedly a rather unattractive aspect of the many-sided Karroo "problem". With the history of Karroo investigation prior to 1902, when the division into the four series Dwyka, Ecca, Beaufort and Stormberg was definitely adopted by the Cape Geological Commission, it will be unnecessary to deal in view of the excellent account given by Dr. Corstorphine in an address before the South African Association for the Advancement of Science in 1904. Subsequent worn in the Cape Province has not only upheld the classification referred to, but has enabled further sub-divisions to be established. In the other three Provinces geologists made various attempts to apply the same grouping, but, unfortunately, for reasons that will become apparent in the sequel, such correlations were premature, and have proved to be of very little actual value. In the Transvaal, the Geological Survey, cogniscant of the inherent difficulties, avoided the use of any of the Cape terms, the Karroo system being mapped under the useful but non-committal terms "Glacial Conglomerate," "Coal Measure Series," and "Bushveld Sandstone Series," a course that under the circumstances has justified itself. While in the Cape the System was possessed of an immense thickness and apparently embraced a wholly conformable succession, in the Transvaal and in Natal not only was the formation much attenuated, but there was also a considerably different facies, while indirect evidence pointed to at least one important stratigraphical break in the northern Province. To the speaker it became obvious, therefore, that the only satisfactory way in which the divisional lines corresponding to those of the Cape could be established in the north and north-east with any pretense at accuracy would be by extending the boundary lines from the Cape border by way of Natal. During the past few years these have been carried partly by continuous mapping and partly by a network of detailed traverses right through Natal into the north-eastern corner of the Orange Free State and the south-eastern part of the Transvaal. This has enabled a three-fold sub-division (capable of being mapped) of each of the four series - though in certain areas one or more of these zones may be unrepresented; incidentally, the variations both in thickness and in lithology of each zone have been studied, the different scattered occurrences of coal have been relegated to their proper horizons, and a good deal of palaeobotanical material collected that will be of value in comparing tile beds with their equivalent strata outside South Africa. Although the advances that have been made are considerable, very much more is still to be learnt not only as to the general distribution and variation in the Union, but also as regards the detailed economic geology of the coalfields and their extension into more concealed areas. The greater part of this Address will naturally be devoted to the distribution of the Karroo System in the eastern and south-eastern part of the Union, and the only extenuation that can be put forward in defense of a rather bald recital of thicknesses and variations in lithological character is that only through such a quantitative though tedious exposition can a three-dimensional mental picture be formed of the composite mass of sediment that builds up so large a portion of the southern end of the African Continent.
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Transactions of the Geological Society of South Africa, 22, 1-25
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Transactions of the Geological Society of South Africa, 22, 112-117
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Transactions of the Geological Society of South Africa, 22, 26-45
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Transactions of the Geological Society of South Africa, 22, 46-67
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Transactions of the Geological Society of South Africa, 22, 68-89
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Transactions of the Geological Society of South Africa, 22, 90-111
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Transactions of the Geological Society of South Africa, 22, xxi-xxxxvii
In addressing you upon recent advances in Rhodesian geology, I have found myself compelled to limit the subject to certain aspects of the advances made in the last few years, and have chosen what I may call the stratigraphical aspect. I intend to touch upon igneous activity, earth-movements, or ore-deposits only so far as my main theme may be affected. And in doing so, it has seemed to me to be the natural course to follow, since the geological column of rock is the scale by which time relations are measured. If the scale be wrong, misleading deductions in regard to other matters of perhaps greater importance is the certain result.
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Transactions of the Geological Society of South Africa, 23, 1-42
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Transactions of the Geological Society of South Africa, 23, 114-117
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Transactions of the Geological Society of South Africa, 23, 118-132
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Transactions of the Geological Society of South Africa, 23, 43-51
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Transactions of the Geological Society of South Africa, 23, 52-58
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Transactions of the Geological Society of South Africa, 23, 59-63
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Transactions of the Geological Society of South Africa, 23, 64-97
The Pebbles of the Banket and their Distribution. - Distribution and Ratio (1) of dark coloured matrix, (2) of footwall materials. - Other Features of the Rock: (a) Values and their indicators, etc.; (b) Evidence of Metasomatism; Evidence of Contemporaneous Erosion; (d) The Reef Bands.
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Transactions of the Geological Society of South Africa, 23, 98-113
The following notes are the result of observations taken in 1918, during a wagon journey, occupying about a fortnight, through that part of Portuguese territory which lies between the two railway lines from Lourenço Marques, viz., to Goba, and to the Transvaal via Komati Poort. The precise course followed is shown on the accompanying sketch map. The western portion of the area is occupied by the heights of the Lebombos (rising to 800 metres above sea level at M'ponduhine) and the eastern slope of the range, which is intersected by deep gorges. Hereafter this slope will be referred to as the "foothills", for convenience sake. To the east of the foothills the country falls gently from about 100 metres to sea-level; but this plain is interrupted by the N. and S. escarpment, known as the Pequenos Lebombos or Little Lebombo Mountains, which rises to 275 metres. The greater part of the area drains into the Umbelusi river by means of the Movene Calichane and other streams. Owing to the irregularity of their beds the smaller streams in the dry season consist merely of a succession of pools. The low-lying parts of the country are deeply covered by a firm, dark brown soil or by loose sand. The nature of vegetation varies considerably, being either dense or thin bush, beautiful park country with scattered broad spreading trees and clumps of palms, or in the higher parts very sparsely wooded. No systematic geological work has ever been done in this area, and our previous knowledge of its rocks has been mostly derived from an account! by Dr. E. Cohen of a journey on foot made by him in 1873 from Lydenburg to Delagoa Bay, his course through Portuguese territory being a little to the south of the present railway line from Komati Poort to Lourenco Marques. Though, along the route he followed through this territory the rocks are largely obscured by surface deposits, he was able, in the published account of his journey, to describe the "felsitporphyr" of the Lebombos, the "felsitfels" of the Little Lebombos and the intervening "melaphyr." In 1909 Mr. J. McClelland Henderson gave a description of four types of rock, viz., silicified rhyolite tuff, pitchstone, rhyolite and diabase, met with in a journey from Lourenco Marques to Swaziland, along a route south of the Goba railway. The country immediately to the west of the Portuguese border, in the district dealt with in this paper, has been described geologically by Mr. H. Kynaston and Mr. J. Jervis Garrard. The rocks of this area consist of Karroo sediments (coal measures, marls, shales and fine-grained sandstones) resting unconformably on the older granite and associated rocks of the Swaziland System and dipping at a gentle angle (about 10°) to the east. These sedimentary rocks are overlain by amygdaloidal basalts, which in the neighbourhood of Komati Poort have probably a thickness of 6,000 feet. The basalts, which have been correlated with the volcanic rocks capping the Stormberg Series of the Drakensberg, are overlain by the rhyolitic rocks which form the Lebombo range. Besides dolerite dykes and sills, by which all the rocks above referred to are penetrated, there occur in the amygdaloidal basalts along the western edge of the Lebombos several extensive intrusions of granophyre, which may have a genetic connection with the acid lavas. The rhyolitic rocks extend for a considerable distance eastward into Portuguese territory (nearly nine miles, east of Namahacha) forming the Lebombo foothills. Northwards, towards the Komati River, the area occupied by the foothills is more restricted. At the bottom of the foothills and overlying the rhyolites are some rhyolitic breccias and tuffs, and these are succeeded by a series of amygdaloidal basalts, which form the low ground between the foothills and the Little Lebombo range. Near the base of these basalts is a thin intercalation of rocks of intermediate composition. The Lebombo range is made up of non-porphyritic fine-grained acid lavas, which are succeeded by a considerable thickness of rhyolitic breccias. Some acid lavas are associated with the latter rocks. Then follow further amygdaloidal basalts of which only the base is exposed, but about 900 feet of this rock have been penetrated by a borehole. All of the above-mentioned lavas and associated rocks dip at gentle angles (10 to 15°) to the east. Some of the apparently enormous thickness of the volcanic series may, of course be due to duplication by faulting, but I did not meet with any direct evidence of this. Close to Goba station was observed a small exposure of sandstones, grits and shales, composed of sorted rhyolitic debris, which appear to overlie the rhyolites of the Lebombo foothills, and dip under the succeeding basalts. East of the Little Lebombos isolated exposures of breccia are seen associated with ferruginous sandstones and also with shales. Near Bohane the railway line cuts through rocks of manifestly later date than the Karroo volcanics. These consist of soft chocolate-brown sandstones containing layers of well-rounded pebbles of rhyolite, agate, etc., dipping at a very gentle angle to the east. I was informed by Mr. S. J. Ryan that Cretaceous limestones are met with nearer the coast on the Tembe, Umbelusi and Maputo rivers About five miles S.-S.-W. of Pessene a dyke of nepheline syenite porphyry was met with, and another dyke of similar chemical composition, but very fine-grained and containing analcite (?) at the crossing of the Moulolo River by the Pessene-Namahacha road. Some four miles N. -W. of Bohane a hornblende lamprophyre, or vogesite, gives rise to an isolated hill, known as Mt. Violet. The general trend of all of these intrusions is north to south.
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Transactions of the Geological Society of South Africa, 23, xix-xxxiii
I will now discuss a physical feature known to all travellers between the coast and the Highveld - the great escarpment. I have had the opportunity of seeing it at various places between the Pietersburg district and where the Orange River traverses it, but the only part with which my personal acquaintance is fairly complete lies between the Orange River and Aberdeen; for much information about the eastern side I am indebted to the reports and conversation of past and present colleagues on the Geological Survey, and for discussions bearing on the escarpment, as well as on many other large features of the sub-continent, the papers written by Prof. Penck and Prof. W. M. Davis, after their visit to South Africa in 1905, are of the first importance. South Africa may be divided into an interior plateau and the country outside it; the plateau includes the Orange Free State, Basutoland, and the greater parts of the Transvaal and of the Cape Province. The plateau is bounded by an escarpment, which may be called the great escarpment to distinguish it from the many smaller features of the same kind; but in what follows it will be called simply the escarpment.
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Transactions of the Geological Society of South Africa, 24, 1-10
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Transactions of the Geological Society of South Africa, 24, 11-16
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Transactions of the Geological Society of South Africa, 24, 111-149
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Transactions of the Geological Society of South Africa, 24, 150-167
In the hope that by mapping a small area in considerable detail information concerning the nature of the acid schists not likely to be brought out by mapping on a larger scale might be obtained, the writer several years ago commenced the study of a portion of the Bulawayo commonage, where the exposures appeared to be sufficiently good to promise satisfactory results. In this area, which lies in the angle between the railway on the north and the commonage fence on the, east, various breccias and cleaved rocks, including some of quite acid composition, form jagged outcrops on either side of a small spruit. Unfortunately the area proved to be too small to yield conclusive results, and mapping was extended southward to the Hillside intrusion and eastward for a distance of more than two miles over ground in which exposures were sometimes very scarce. The area thus extended is a little more than three miles wide by four miles long, and is drained by the Little Umguza river and its tributaries. The relief is generally low. The highest ground is formed by the syenite kopjes in the south-western corner of the map. There are other hills at the commonage eastern beacon and the granite porphyry mass on the eastern edge of the area. Scattered references to the rocks in this area occur in Mr. F. P. Mennell's writings (1, 2, 3, 4, 5). He described the petrology of the Hillside syenite in 1902 (1), and in 1906 he discussed the geological structure in some detail and gave a generalized geological map of the country round Bulawayo, including the neighbourhood here discussed (5). Grouping the whole series as "Bulawayo schists", he recognizes a stratigraphic succession of three groups, an epidiorite group at the bottom followed by banded ironstone and conglomerate groups in the order named, all dipping away from the great granite west of Bulawayo. He states (5, p. 258): "A little consideration will show that the great granite masses, which are so important a feature of these areas, must as a rule indicate anticlinal or dome-like structures, and we find in fact that where the dips depart from the vertical they are nearly always away from the granites. Where this is the case, the relative distances of the various rocks from the granites may be taken as one of the chief aids in the succession. For it stands to reason that the oldest beds will be nearest to the axis of elevation marked by the granites." Although the a priori method of reasoning is not likely to commend itself to geologists generally, there can be no question that as a statement of fact Mr. Mennell here enunciates an important principle in Rhodesian geology. It is a pity that the value of Mr. Mennell's account of these rocks is somewhat impaired by his failure to record the remarkable composition of the conglomerates, and his too evident anxiety to correlate the conglomerates with those of the Witwatersrand.
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Transactions of the Geological Society of South Africa, 24, 168-181
Although chrysotile-asbestos was found as far back as 1905 during the writer's examination of certain parts of the De Kaap valley below the Drakensberg escarpment, near the Kaapsche Hoop, it is only as the result of renewed attention directed to the base metals resources of the Union during the last few years, that the serpentine belt of the Jamestown Series has been systematically prospected. The existence of deposits of chrysotile in commercial quantity and quality in that formation having now been definitely established and their development reached the producing stage, it is the object of the following remarks to describe them with special reference to the farm Joubertsdal, where recent mining operations of the Amianthus Mines, Ltd., have disclosed some features unique in the geology of chrysotile occurrences.
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Transactions of the Geological Society of South Africa, 24, 17-52
No abstract.
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Transactions of the Geological Society of South Africa, 24, 182-187
Hitherto this beautiful mineral has only been known from a single locality at Dundas, near the Adelaide Mine, in Tasmania, and the object of this note is to describe a second occurrence in the asbestos workings near Kaapsche Hoop, in the Barberton District. The mineral was known in Tasmania since 1891, but until 1910 was referred to as Kümmererite, a chrome bearing chlorite with the same striking colour. The chemical composition of stichtite was first settled by A.J. Wesley, chief chemist to the Mount Lyell Company; the late W.F. Petterd fixed the individuality of the new species by naming it after Sticht, the general manager of the Mount Lyell Mining and Railway Company. In Tasmania, as well as at the Kaapsche Hoop occurrence, the mineral is intimately associated with serpentine, and appear to have risen in both localities as a secondary product. While in the third appendix to Dana's System of Mineralogy reference is made to the Tasmanian locality only, it appears that E.J. Dunn, in an article published in 1918, refers to his having found a violet-coloured mineral in the de Kaap Valley associated with serpentine, and, in a recent letter addressed to Dr. Du Toit, Dunn recalls his having located what is now known as Stichtite in September, 1883, in the old wagon road near the Kantoor (Kaapsche Hoop). According to the same information the new mineral was doubtfully referred to K„mmererite. The writer has been able to compare a piece of the material collected by Dunn, and it agrees with that seen in the asbestos workings on "Joubertsdal", where the track of the old wagon road still remains. The first discovery of Stichtite is, therefore, due to Dunn, and refers to the Barberton district.
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Transactions of the Geological Society of South Africa, 24, 188-227
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Transactions of the Geological Society of South Africa, 24, 228-231
The object of this note is to describe the formations building up Adriaanskop, with special reference to the quartz rocks, hitherto regarded as a modified form of the Bushveld granite. During a recent visit to this locality by Dr. A.W. Rogers and the writer fresh evidence was found which makes it almost certain that the quartzose formation is not of igneous origin, but represents masses of quartzite caught up and intensely altered by the granite.
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Transactions of the Geological Society of South Africa, 24, 232-249
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Transactions of the Geological Society of South Africa, 24, 53-70
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Transactions of the Geological Society of South Africa, 24, 71-97
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Transactions of the Geological Society of South Africa, 24, 98-110
Recent prospecting operations in the Bethlehem District have located an occurrence of crude oil in igneous rocks, which, while apparently falling into line with similar deposits in other parts of the Union, is in some respects unique and therefore deserves to be recorded.
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Transactions of the Geological Society of South Africa, 24, xix-xxxi, 1 pl
I had an opportunity of inspecting his (G.W. Stow) collection, now in Bloemfontein Museum. It consists not only of specimens of the various members of glossopteris flora, but those connected with the Northern flora rediscovered by myself in the same quarries long after he had died. I was given credit for new discoveries which Stow had sent to Bloemfontein twenty years before. This was a real misfortune. Had his collection been subjected to the same critical examination that Draper's had, the proper position of the coal measures would have been established. The circumstances of this has always been a puzzle to me; about the time Stow was actively engaged in his work in the coal deposits Dr. Exton, the first President of this Society and a very devoted and enthusiastic geologist, was settled in Bloemfontein. He had many varied interests: beside his professional work and social amenities was an energetic Town Councillor, twice, I think occupying the mayoral chair. His great work in Bloemfontein, by which he will be longest remembered, was the founding of the museum, of which he continued to be the active curator until he left for Johannesburg. Therefore I conclude it was not for want of interest that Stow's collection was overlooked, but more probably by reason of the opinion, then widely held, that the Plant fossils were of little value for discriminating the divisions in the order of the rocks in comparison with the huge animal remains which Bain had unearthed in Cape Colony, and which at this time had been found in the Free State. Dr. Exton had a lively interest in these reptilian remains; the last time I saw him before his death I remember the pride he took in showing me the small Mesosaurus which he called "Exton's Baby". It is now well known that there are two distinct floras connected with the period of maximum coal deposit of the world, and it is for the reason of the value and importance of coal to mankind that the fossil plants associated with these beds are of paramount interest to geologists. There are known as the Northern and Southern Flora. Of the one Lepidodendron is the principal type and of the other Glossopteris. In the struggle for supremacy between these two types one encroached on the province of the other, and in the sandstones near Vereeniging we get an intermingling of the two: impressions of lepidodendron and glossopteris in profusion on the same stone. It should be mentioned that very seldom either in the North or the South do we get recognisable fossils in the coal itself; usually they are found in the shales or sandstones interbedded with or overlying the coal seams, while the root impressions may be seen in the underlying hardened clays. Very occasionally we may distinguish the poorly preserved markings of the Cordaites or the seal-like marking of a Lepidodendron in the coal. At Vereeniging it is in the sandstones above the coal that the fossil leaves are so abundant that it sometimes appears as though the rock was composed of nothing but leaves matted together. Below the coal seams at Vereeniging and indeed associated with the Permo-carboniferous flora of the whole Southern Hemisphere, is the famed glacial conglomerate. In a local exposure on the banks of Zuikerbosch River, about three miles east of Vereeniging, in some stratified beds which appear to be of fluviatile origin, I have long known of the existence of the long strap-shaped leaf of cordaites, but only recently have I found undoubted evidence of plant fossils in the actual glacial conglomerate itself. At my dolomite quarry near Vereeniging Station intrusions of the glacial filled up and moulded themselves around the uneven masses of dolomite which formed the ancient land surface. Crevices and joints are filled with the concrete-like till; quite near the contact with the dolomite are usually a few thin bands of laminated clay shale, the lamina being a 1/4-inch thick or even less. These carry fairly well-preserved impressions of gangamopteris, some leaves being almost perfect and nearly 12 inches in length. Owing to the nature of the material they cannot be detached without breaking up. I have a few specimens here for inspection. They occur about 3 inches away from the actual dolomite. The fossils found at Vereeniging may be taken as representative of the same measures in South Africa generally. I have collected many of the same varieties at Witbank, where they occur in the shades above the coal, the sandstones there being altogether too coarse to carry impressions. Anderson's collection in Natal and those of the Geological Survey of the Cape Colony do not add any species of importance.
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Transactions of the Geological Society of South Africa, 25, 1-22
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Transactions of the Geological Society of South Africa, 25, 101-106
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Transactions of the Geological Society of South Africa, 25, 23-40
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Transactions of the Geological Society of South Africa, 25, 41-42
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Transactions of the Geological Society of South Africa, 25, 43-67
During the recent examination of the corundum field of the Eastern Transvaal some unusual varieties of corundum-bearing rocks were met with in many widely distributed outcrops. The distinctive and uncommon mineralogical composition of these rocks, repeated in a large number of occurrences, appeared to the writer to justify a special name, and in the memoir embodying the results of his examination the name marundite was applied, compounded from the names of the two essential minerals, viz., margarite and corundum. The object of the following remarks is to give a fuller account of the petrography of these rocks than was possible in the memoir referred to, and to bring further chemical evidence which has since become available.
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Transactions of the Geological Society of South Africa, 25, 68-71
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Transactions of the Geological Society of South Africa, 25, 72-78
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Transactions of the Geological Society of South Africa, 25, 79-80
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Transactions of the Geological Society of South Africa, 25, 81-100
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Transactions of the Geological Society of South Africa, 25, xix-xxxii
What is an alkaline rock? The term is as vague as unfortunately many other terms in our science are. In a general way it means any rock that is rich in silicates of soda and potash, whether in the form of felspars, felspathoids, micas, soda-pyroxenes, or soda-amphiboles; but the limits of the group are so ill defined that the name has never possessed any systematic value. If I am to discuss the problem of the alkaline rocks with you, I must first make it perfectly clear to you what the term alkaline rock means to me. In the commoner kinds of igneous rocks the alkali-metals are combined with alumina and silica in the molecular proportion of 1:1:6 (in felspars) or 1:3:6 (in micas). An alkaline rock, then, if names are to mean anything, should be one in which the alkalies are in excess of the 1:1:6 ratio, either alumina or silica or both being deficient. If silica is deficient, the alkalies and alumina form minerals that are unsaturated with regard to silica, such as the felspathoids, analcite and cancrinite, in which the molecular ratio is 1:1: (4 or less). If alumina is deficient, the deficiency may be made up by ferric oxide, zirconia or titania, giving such minerals as aegirine, riebeckite and eudialyte, in which the molecular ratio is again 1:1: (4 or less). The simplest way to define an alkaline rock, then, is to say that it contains minerals in which the molecular ratio of alkali to silica is not less than 1:4. A more technical definition would be as follows: An alkaline rock is one which contains normal metasilicates or orthosilicates of alkali-metals with aluminium, iron, zirconium or titanium, with or without other minerals. The difference between this definition and the current conception of an alkaline rock is that an excess of alkali-felspar (which is a poly-silicate) or of mica (which is an acid silicate) does not in my view entitle a rock to be called alkaline. The advantage of the definition is that it cuts out that doubtful borderland where it becomes a matter of individual opinion whether a rock is to be considered alkaline or not; and that it leaves us with a clean-cut natural group in which every rock contains either an excess of alkali over alumina or an excess of alkali and alumina over the available silica.
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Transactions of the Geological Society of South Africa, 26, 1-6
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Transactions of the Geological Society of South Africa, 26, 103-129
The portion of Portuguese East Africa dealt with in this paper is an area comprising 65,637 square miles, controlled by the Companhia de Moçambique. It lies between Southern Rhodesia and the Indian Ocean, and has the Zambesi for its northern boundary and part of the Limpopo for its southern. On the coast the southern limit is marked by 22nd parallel of latitude. During the years 1911 to 1914 the writer was in charge of a Mineral Survey of this region for the Comp. de Moçambique being assisted by Capt. R. C. Wilson. The war brought the work to a close, and later more urgent duties have delayed the publication of the results. Prior to the institution of the above survey, very little was known concerning the geology of this part of Africa. In 1901 Mr. A.R. Sawyer contributed a valuable paper dealing with the Manica Gold Fields, a, small mineral field near Massikessi (Macequece). In 1906, Brackenbury described the Edmundian copper deposit in the same area. Mr. Draper collected some U. Cretaceous and Tertiary fossils on the lower Buzi R., which were described by R. Bullen Newton in 1896. In 1894 Colonel Frere Andrada, a capable Portuguese mining engineer, contributed some information concerning the geology of the country between Lourenço Marques and the Zambesi. In 1906, M. J. Stephan, in this paper oil occurrences in South Africa, refers to the occurrence of Cretaceous and Lower Tertiary beds in Portuguese East Africa south of the Zambesi River. He mentions the teeth of Otodus obliquus in the Eocene and two divisions of the Cretaceous, an older and a younger series. The physiography of this area was discussed by Capt. Wilson and myself, in a paper in the Geographical Journal, with a supplementary one by the writer in the same journal in 1915. The nature of the work of the survey consisted largely of reconnaissance traverses in various directions. Much material was collected for petrological and chemical investigation, but unfortunately a great deal of it is still awaiting opportunity for its examination. As there does not appear to be any immediate prospect or completing this section of the work, I wish to place on record an account of the field observations, which will add something to the knowledge, of an extensive but little known area. The contributious by Mr. R. Bullen Newton and the late Mr. G. C. Crick, dealing with the Tertiary and Cretaceous fossils collected form a valuable addition to the paper.
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Transactions of the Geological Society of South Africa, 26, 13-30
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Transactions of the Geological Society of South Africa, 26, 31-49
In a previous communication to this Society read in October 1921, the writer gave an account of the geological conditions in which chrysotile asbestos occurs in a belt of serpentine belonging to the Jamestown Series on the farm Joubertsdal No. 99, some three miles from the village of Kaapsche Hoop. It was shown that the asbestos lies along more or less well-defined horizons in the serpentine, and satisfies economic requirements of quality and quantity, while the most interesting feature in the mode of occurrence is the extraordinary number of seams arranged almost strictly parallel to one another (so-called "Ribbon"-Rock). In another note, read on the same occasion, attention was called to the intimate association with the asbestos of stichtite, a mineral of striking lilac colour, which represents a hydrated carbonate of magnesium containing chromium. During the last eighteen months, the asbestos deposits have been further opened up both in the westerly portion of the serpentine belt - previously described - and in the easterly portion. The examination of the workings has brought out several new features, which it is the object of these notes to place on record, so as to bring the information up to date, specially as some of the evidence may be lost in the course of further development.
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Transactions of the Geological Society of South Africa, 26, 50-64
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Transactions of the Geological Society of South Africa, 26, 65-68
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Transactions of the Geological Society of South Africa, 26, 69-98
The construction of the Hartebeestpoort Dam with its canals, has necessitated making a number of extensive excavations and cuttings which afford many instructive outcrops along a practically continuous section across the highest beds of the Pretoria Series and the lowest portion of the overlying Bushveld Complex. The object of the following remarks is to record this fresh evidence, with special reference to the eastern canal section, since some of that evidence will no longer be available, when the dam is in full working order.
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Transactions of the Geological Society of South Africa, 26, 7-12
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Transactions of the Geological Society of South Africa, 26, 99-102
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Transactions of the Geological Society of South Africa, 26, xix-xxxiii
The first point which I would take up is the value of stratigraphy consistently carried out over large areas, with clue attention to both lithology and fossil remains, and I would illustrate it by reference to the coal deposits of Natal and Zululand. Dr. du Toit's presidential address in 1918, on "The Zones of the Karroo System and their Distribution", contained a most admirable demonstration of the point. By careful following up of the Karroo zones from the Cape, through Griqualand East, and the coal areas of Natal, he showed that the principal coal seams of Natal are associated with felspathic sandstones and grits in the Middle Ecca, sandwiched between the shales of the Lower and Upper Ecca; he showed that above the Upper Ecca there are again coal seams, though thin, near Willow Grange, Frere and Bergville, in the felspathic sandstones and grits of the Lower Beaufort, while still higher, above the Middle and Upper Beaufort, there are thin seams in the Drakensberg in the felspathic sandstones and grits of the Molteno beds. Prior to du Toit's work it was recognised that the Drakensberg coals were in the Molteno beds and clearly separate in age from the coals of the main Natal coal field, that having been shown from palaeobotanical evidence by the late W. Anderson, but it was not recognised that the Willow Grange and Bergville coals were not of Ecca age, and that the Ecca coals might possibly underlie them. If du Toit is right, and I cannot doubt it, I personally when in Natal was seriously in error, my sporadic observations having led me astray. Though I had some vague misgivings about the "coal measures" south of the Tugela, and therefore in my geological map stopped the line separating the Ecca and Beaufort before reaching that area, I certainly thought the known seams were the same as the seams worked at Elandslaagte to the north, and that it was useless to bore to any considerable depth below them. Whether it is worth while to bore there in view of such deep boreholes as those at Frere, Estcourt, Glendoone and Mooi River having been put down in the past, without finding coal seams of value, may be doubted, but, nevertheless, du Toit's stratigraphical work enables that economic question to be considered on a correct basis, which was not possible before. The value of the work, however, is not confined to the area in which it was done, for the information obtained may be applied tentatively elsewhere, as du Toit himself applied it in reference to coals outside the area which he had studied in Natal, but I wish, despite that, to draw attention to the need for similar stratigraphical work in Zululand. We pass on to consider another aspect of the subject. If there is any connection between the quality of the coal and its geological horizon, stratigraphical work for ascertaining horizons will obviously be of economic value. Du Toit, has suggested that perhaps it is a characteristic of the Beaufort seams to be anthracitic. I have a similar tentative theory that for South African coals the rule usually holds that where there is more than one series of closely associated seams, the geologically lower series, except when locally altered by igneous action, contain, the better coal for steaming purposes. The coal is generally cleaner and its fuel ratio, is nearer that most desirable. Taking the Umlalazi field, we find that those seams north of the Ibade stream are probably geologically above those to the south, though it is not quite certain. A series of analyses of those northern seams was made in 1898. Much reliance cannot, however, be placed on those analyses as indications of the character of the unweathered coal, as the samples were mostly from very shallow excavations on outcrops, in which the coal, which appears to weather exceptionally easily, contained much moisture. Indeed, I believe, though my information is indefinite, that somewhat later prospecting showed that much of the coal is anthracitic. Let us turn to another division of my subject, which will, I think, illustrate the fact that geological investigation with regard to such matters as the topography of ancient land surfaces, the uplift and subsiding of those lands, the changes of their climates and floras, and the mountain building movements of the past, should have practical value for guidance in mineral prospecting and development in the present. I say "should have," for my study has shown me how difficult it is to gather such a clear and consistent idea of the conditions under which our coal seams were formed as is necessary. On the map of South Africa we find coalfields distributed over the eastern portion of the Union, but none in the western portion. Unless theories with regard to, coal formation are far wrong, we owe the coal seams to the fortunate circumstance that, when, in changing climatic conditions, those periods suitable for the growth of coal vegetation were passed through, there was land, and much of it low lying and flat, gradually subsiding in and near that portion of Gondwanaland which is now Eastern South Africa. Even now our knowledge of the geological age of the coal seams may be incomplete, but it appears that in four different ages the conditions were suitable for coal formation, and that therefore we have seams or sets of seams in the Middle Ecca, the Lower Beaufort, the Molteno beds of the Stormberg, and in the Transvaal Bushveld sandstones and marls, which probably correspond with the Cave sandstone and Red beds of the Stormberg series.
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Transactions of the Geological Society of South Africa, 27, 1-38
I. Introduction. II. Outline of the geology of the area. III. The Wittpuetz Trough - The Folding within the Wittpuetz Trough. VI. The Folded Belt along the Coast. V. The Block-faulted Zones. VI. The Aus-Leuderitzbucht Gneiss Horst. VII. The Koichab Trough and other Tectonic Troughs of Great Namaqualand - The Koichab Trough - The Sulvia Hill Trough. VIII. General Summary and Conclusions - (a) The Wittpuetz Trough in Relation to the Geological Structure of South Africa, (b) The Folded Belt along the Coast in relation to other belts of folding in South Africa, (c) Alkaline Rocks in Relation to the Wittpuetz Trough. Bibliographical list
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Transactions of the Geological Society of South Africa, 27, 38-39
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Transactions of the Geological Society of South Africa, 27, 39-55
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Transactions of the Geological Society of South Africa, 27, 57-61
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Transactions of the Geological Society of South Africa, 27, 63-70
The main object of the present note is to correct some erroneous conclusions reached by the writer as the result of a preliminary survey in September, 1919, of part of the area under review. This is situated south of the Mutue-Fides-Stavoren tin-fields. It embraces the north-eastern corner of the Pretoria district and the portion of the Waterberg district adjacent to it. The conclusions alluded to are set forth in Chapter II of Geological Survey Memoir No. 16, "The Mutue Fides-Stavoren Tin-fields. "They have reference to the stratigraphical and structural relations of the rocks of the Rooiberg Series to a thick bed of hard white quartzite, in part conspicuously ripple-marked, that was assumed at the time to belong to the lower part of the Pretoria Series. On the farms Riffontein, No. 1831, Kwaggafontein, No. 1947, Salie Sloot, No. 1790 and Kwarriehoek, No. 1818, where it was studied, this quartzite and the Rooiberg beds in contact with it are much folded and faulted, and, from a section exposed in the southern part of the first-named farm, it was concluded that the Pretoria Series, represented by the White quartzite, as it may be termed, had been thrust from the south over the Rooiberg beds. For the plane of dislocation along which the thrusting was presumed to have taken place the name Riffontein Thrust was proposed. As a result of an examination during the past field season of a less disturbed area, lying to the west of that previously examined, it was found that this interpretation was entirely wrong. On the farm Vlakfontein, No. 1829, the White quartzite was found to overlie conformably brown and greenish-brown shaly sandstones and micaceous sandy shales belonging to the Rooiberg Series. It here caps a broad flat-topped hill, being disposed in the form of a shallow basin with dips ranging from 5° to 15°. The nature of the ripple-marking and current-bedding preclude the possibility of inversion. There can be no question therefore that the quartzite is a member of the Rooiberg Series. With regard to the dislocation, previously referred to as the Riffontein Thrust, this proved on re-examination to be a powerful fault along which the White quartzite has in places been overtilted towards the north-north-west.
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Transactions of the Geological Society of South Africa, 27, 71-75
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Transactions of the Geological Society of South Africa, 27, xix-xxx
In spite, however, of paucity in some directions, South Africa is known far and wide throughout the world for its diamond and gold deposits. It was in this country that the diamond was first found in its original home. It had been known and valued for thousands of years previously, but hitherto it had always been found in alluvial deposits. The first deposits found in South Africa were also of this character, but very quickly the outcrops of certain diamondiferous pipes were located and worked, but no one at first recognised that these were pipes going down to considerable depth. They were thought to be comparatively shallow deposits, more or less of the nature of those hitherto worked, and many diggers, when they had worked through the decomposed upper layer, abandoned their claims in the belief that they had come to the end of the diamond-bearing ground. Diamonds in igneous rock was an entirely new idea. The age of these pipes, and of the dykes usually associated with them, cannot be exactly determined, but they appear to be contemporaneous with each other, and to be younger than the Karroo System. It has been suggested that they are of Lower Cretaceous age. There must, however, have been diamond-bearing rocks of very much greater age than these pipes, because diamonds are found in the gold-bearing conglomerates of the Witwatersrand System, and these conglomerates represent the debris of a still older formation, which must have included diamond-bearing rocks. Further, diamond-bearing gravel is distributed over a very large area of country, mostly in the neighbourhood of the Vaal River and its tributary, the Harts, and whilst many of the stones have probably come from Kimberlite pipes and dykes, there are other stones of a white colour and brilliant lustre which have not hitherto been found in Kimberlite. Alluvial diamonds are so widely distributed over an immense area that it is difficult to believe that they all came to their present places through the more or less recent weathering of outcrops of Kimberlite. The areas where they occur were once entirely covered by Dwyka Conglomerate, and to a considerable extent Ventersdorp Lavas are found there. It is natural that the Dwyka should have been looked upon as a possible carrier and distributor of diamonds and as two small stones, which, however, were not typical river stones have been found in the ancient lava, it was suggested that it might be the original home of some of the diamonds. The evidence on the latter point is not yet looked upon as conclusive, but I suppose most geologists would agree as to the probability of the Dwyka being a carrier of diamonds. Now, the material forming the Dwyka came from the North, and so did that in the conglomerate beds of the Witwatersrand. Turning to our gold deposits, when they were first discovered they also were of a type unknown to the miner, and were at first looked upon with a good deal of suspicion. Gold had never been found before in an ancient conglomerate in sufficient quantities to justify mining. Had it not been for the fact that they contain much gold I do not suppose the conglomerates of the Main Reef Zone in the Witwatersrand System would have attracted the special attention of the geologist. As it is, they have been the subject of much study and investigation. From the very first discovery of the deposits theories as to the origin of the gold have been advanced, discussed and more or less accepted. Apart from their scientific interest these theories have had an important practical aspect. Quite naturally as being the most obvious e':planation the first theories suggested a placer origin for the gold, that is, it was thought that the gold and pebbles were brought down together and deposited contemporaneously in the position they now occupy, and it was also assumed that the conglomerates represented original shore deposits of narrow width, such as can often be seen on the seashore today. Thus it came about that the Rand was condemned as a permanent field for mining by certain mining engineers of great reputation, who believed that the gold would prove to be very irregularly distributed, and that the conglomerate would not go down to any great depth. Though this only acted as a temporary check, it did mean that for years few people believed in deep levels, and there were magnificent areas of mining ground which lay open for anyone to peg. There were certain objections to the simple form of placer theory which was at first promulgated, and a little later a precipitation theory was proposed. It supposed that the pebbles were first deposited, and that the water under which they lay became charged with gold which was precipitated amongst them. Though this theory had certain attractions it did not account for all the phenomena, and further assumed conditions so unlike anything which is known in the world that it never made a wide appeal and was accepted by comparatively few geologists or engineers.
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Transactions of the Geological Society of South Africa, 28, 1-17
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Transactions of the Geological Society of South Africa, 28, 135-176
1. Previous work. 2. Distribution of the Lower Witwatersrand System in the Vredefort Mountain Land. 3. Distribution and Horizons of the Metamorphosed Rocks. 4. Varieties of Altered Sediments. 5. Description of the Altered Rocks - (a) Mineralogical Composition. (b) Micro-structure and Order of Crystallisation. (c) Characterisation of the principal types of Altered Rocks. (d) Tabular Summary of Horizons and Constituent Minerals. (e) Note on Flinty Crush Rocks. 6. Progressive Intensity of Metamorphism. 7. General Nature of the Metamorphism. 8. The Vredefort Granite is not intrusive in the Lower Witwatersrand System. 9. The Causes of the Metamorphism. 10. Comparison with the Aureole of the Bushveld Complex
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Transactions of the Geological Society of South Africa, 28, 19-25
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Transactions of the Geological Society of South Africa, 28, 27-32
During the course of a geological survey of the Divisions of Humansdorp, Uitenhage, Port Elizabeth, Alexandria, Albany and Bathurst attention was paid to the various deposits after than the Uitenhage Beds; and the results obtained seem to be worthy of a brief description. Less has been published about the post-Cretaceous deposits of the south-eastern districts than about those further west: although Wybergh mentions the eastern limestones in his account of the "Coastal Limestones of the Cape Province", he confines his description to those of Riversdale and the country to the west of it. The post-Cretaceous deposits consist of surface quartzites, surface ironstones, sandstones, siliceous conglomerates, limestones, clays and sands; and a somewhat detailed account of their occurrence is necessary in order to decide as to the relations between these various types of deposit.
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Transactions of the Geological Society of South Africa, 28, 33-53
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Transactions of the Geological Society of South Africa, 28, 34-35
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Transactions of the Geological Society of South Africa, 28, 55-67
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Transactions of the Geological Society of South Africa, 28, 69-72
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Transactions of the Geological Society of South Africa, 28, 73-77
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Transactions of the Geological Society of South Africa, 28, 79-80
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Transactions of the Geological Society of South Africa, 28, 83-133
Classification of the Platinum Deposits of the Bushveld Igneous Complex
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Transactions of the Geological Society of South Africa, 28, xix-xxx
The subject of my address tonight is prompted by a study of the map of the Union prepared by the Government for the Wembley Exhibition. On it are shown the localities in which minerals have been found throughout the Union of South Africa, and although the subject is by no means a new one, I venture to deal with some of the more important developments. With a view to giving to each its proportional weight as a factor contributing to the prosperity of the Union, I have grouped them in the order of their economic importance and described their geographical and geological localities. Some of them are, however, at present more prospective than effective. These proportions are based on the figures appearing in the Government Mining Engineer's Report for 1923. Thus we find that the minerals in relation to the whole of the Union's production of raw material represents 40 per cent., and when these figures are analysed it is very interesting to note, as most of you are aware, that gold is responsible for 79 to 80 per cent. of the contribution amounting to £41,574,945 and constitutes, as well, practically 60 per cent. of the world's gold production. Of this percentage, all but approximately 2 per cent. is obtained from the conglomerate beds in the Witwatersrand horizon. The remaining 20 per cent. of the mineral production is accounted for by 11 per cent. in diamonds, 7 per cent. in coal, the latter including by-products, principally made up of coke; copper .77 per cent.; and silver .37 per cent.; it should be noted that in addition to this contribution of silver there is a larger amount contained in the gold bullion as well; tin .32 per cent.; lead .25 per cent.; asbestos .23 per cent., and then we experience a drop to a much lower percentage - osmiridium .084 per cent, and corundum .042 per cent. After which there is a group of much smaller contributors aggregating .034 per cent. consisting of iron pyrites, magnesite, vanadium, graphite, manganese, talc, mica, soda, mineral paints, arsenic, and iron ore. There are also a number of quarry products, aggregating 091 per cent., principally made up of building stone, fluorspar, and gypsum. Recently a prospective contributor has appeared in the shape of platinum which we are all sanguine enough to hope will eventually constitute a very important factor in the Union's contribution of mineral production. Before leaving this part of the subject, it may be interesting to note that the proportion of metallic compared with non-metallic minerals is as 80 per cent. to 20 per cent. As gold is our most important contributor it comes first and I hope it will continue to occupy that position for many years to come, as, in spite of the dire predictions of its character as an interlude, it is after all the most powerful economic factor in the development of any country.
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Transactions of the Geological Society of South Africa, 28, xliii-xlvi
In his interesting paper on "The Calcareous Tufa Deposits of the Campbell Rand", Dr. Young deplores (p. 65) the lack of a " Pleistocene glacial epoch, like that of the Northern Hemisphere, by which to define the upper limit of the Tertiary". It seems to me, however, that we have something in some ways better than a glacial epoch to define the upper limit of the Tertiary, or more accurately the beginning of the Quaternary. I refer to the bouchers of Chellean and Achuelean type, which the work of the last 16 or 20 years has definitely established as always Early Palaeolithic. Geologists are slow to realise that these bouchers may be used as a zone fossil to define the lower part of the Lower Pleistocene or the beginning of Quaternary times.
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Transactions of the Geological Society of South Africa, 29, 1-16, 2 pl
The object of the following remarks is to describe tho mode of occurrence of a very unusual rock with an extraordinary beautiful and striking appearance, due to many large lustrous plates of bright ruby coloured corundum. Such a rock has not been previously recorded as far as the writers are aware, and is remarkable (a) through the presence of abundant corundum and sillimanite in large crystals, and (b) from its situation well within the basic margin of the Bushveld: Complex, where the formation of a rock supersaturated with alumina appears to be foreign to the magma from which the norite consolidated. Though the existence of this corundum rock has been known for some twelve years, it is only quite recently, during their visits to the Lydenburg Platinum Fields, that the writers had an opportunity of making a detailed examination of its field relationship. In the course of this work Dr. I. B. Celliers rendered much valuable assistance.
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Transactions of the Geological Society of South Africa, 29, 109-135, 1 pl
Near Bandolier Kop in the Zoutpansberg district there are phosphate deposits of a nature unique in South Africa. Amongst known deposits, they are comparable with those of Canada and Southern Norway. Apatite occurs op three adjoining farms, Spelonkwater (927), Schaapkraal (451), and Mahilashoek (439). Spelonkwater is about seven miles from Bandolier Kop Station in an E.N.E. direction on the main road from Bandolier Kop to Elim, which passes the northern boundary of all three farms (Fig. 1).
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Transactions of the Geological Society of South Africa, 29, 137-140, 1 pl
The following plants were recorded: Schizoneura gondwanensis Feist.; Thinnfeldia ondontoptreoides Morris sp.; Thinnfeldia sp.; Ctenopteris sp.; cf. Pleuromeia; Dadoxylon, sp.; Rhexoxylon spp. It was concluded that although the evidence as to geological horizon yielded by this collection was somewhat conflicting, yet the balance of evidence was in favour of an Upper Triassic horizon. In 1923 the writer identified the Rhexoxylon referred to in the above list as R. africanum, Bancroft, and recorded the occurrence of the same species in the Red Beds of the Stormberg Series, at Lady Grey in the Cape. In 1924 a collection of impression material from Vernon's pit at Willoughby's was sent to the writer for investigation. These specimens are in most cases more complete than the specimens at the disposal of the previous investigators and throw some additional light on the nature of the flora. All the specimens described in the following account are from Vernon's pit, Willoughby's, near Gwelo, Southern Rhodesia, and are from the Somabula Beds, having been collected by Mr. A.M. Macgregor of the Geological Survey of Southern Rhodesia.
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Transactions of the Geological Society of South Africa, 29, 141-143
The writer has not visited Waaikraal since his original paper was written, and therefore has no first-hand knowledge of recent developments. The object of the present note is to place on record the occurrence in tile ore of a gold telluride, identified as krennerite. This was first noted in a specimen recently brought from Waaikraal by Mr. S. de Smidt, Deputy Inspector of Mines, Pretoria. The specimen, which shows the gold-bearer in a better state of preservation than any of the material collected by the writer, is made up of two bands of dark-coloured pyroxenitic gabbro separated by more normal quartz-gabbro. One of the pyroxenitic bands is rich in visible gold which occurs in grains up to 1.5 mm. across. Some of the grains consist entirely of gold. In others that metal is partially encased or intergrown with a lustrous greyish silvery-white mineral. This latter also occurs independently of the gold in small particles and irregular interstitial grains up to 1 mm. in length.
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Transactions of the Geological Society of South Africa, 29, 145-147
Professor Michael Lipovsky has recently published an interesting account of the geology of the Uralian platinum occurrences, together with his views on the origin of the Bushveld deposits. For the former, South African geologists will be deeply grateful, as it provides an admirable summary of the results of the very important investigations that have been carried out since the publication of the great classic of Duparc and Tikonowitch. The Professor's remarks on the genesis of the Bushveld deposits appear, on the other hand, to call for some comment, as I am afraid that, owing to the necessarily hurried nature of his investigations, he is taking away with him a rather incomplete picture of these occurrences. Some of his views are, moreover, likely to prove misleading to those who have not studied them at first hand. I would refer first to his statement that in my "Notes on the Platinum Deposits of the Bushveld Complex", I left without elucidation the question why iron, nickel and copper were concentrated in no other place than the horizon which at present forms the "Merensky Horizon". Surely Professor Lipovsky cannot have read the paper properly, or he would have seen that in the Lydenburg District, where the norite zone has been most thoroughly prospected, platinum occurs in association with nickel, iron and copper sulphides not on one but on eight distinct horizons. Further, that on each of these horizons the platinum-bearer stands in a complementary relationship to bands or lenses of anorthosite or anorthositic norite. It was this that led me to put forward the hypothesis - apparently not noted by him - that the magmatic concentration of platinum in these deposits was a necessary accompaniment, in those parts of the parent norite magma containing appreciable amounts of the metal, of a certain type of differentiation that gave rise on the one hand to norite or pyroxenite carrying primary sulphides and on the other to anorthosite or anorthositic norite.
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Transactions of the Geological Society of South Africa, 29, 17-46, 8 pl
The existence of manganese ores in the neighbourhood of Postmasburg appears to have been for the first time in 1922 by Captain T.L.H. Shone, while prospecting on the farm Doornfontein; subsequent work has demonstrated the deposits to persist over many miles of country as rich, ores available in quantities large enough to furnish an important manganese industry. The following details are based on an examination made by the writer in December last, supplemented by a second visit during February, in company with Dr. A.W. Rogers.
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Transactions of the Geological Society of South Africa, 29, 47-58, 3 pl
The object of the present note is to describe a remarkable pseudo-conglomerate. This has resulted from the metamorphism of a persistent bed of chert occurring at the top of the Dolomite Series west and south-west of the confluence of the Elands and Olifants Rivers in the Central Transvaal. Here the rocks of the Transvaal System, represented by the Dolomite and the lower part of the Pretoria Series, have been affected by powerful orogenic movements, and at the same time profoundly altered as a result of the contact action of the Bushveld Granite. The pseudo-conglomerate thus forms part of a succession highly metamorphosed rocks. The pseudo-conglomerate itself bears so striking a resemblance to a true conglomerate that it was at first taken for such. Its real nature was only established by prolonged field work and, had it not been for certain outcrops, would never have been recogniese. It is shown that it owes its origin partly to mechanical fragmentation and partly to the activity of heated circulating solutions. Recently pseudo-conglomerate of the same nature has been found in another part of the Transvaal where similar geological conditions prevail. It would appear, therefore, that this type of pseudo-conglomerate is the normal product of the metamorphism of chert of a certain kind through the combined influence of pressure and thermal metamorphism. It is considered possible that some of the ancient chert conglomerates described from other parts of the world may also be pseudo-conglomerates.
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Transactions of the Geological Society of South Africa, 29, 59-68
I. Introduction. II The Mount Waller Area. III. The Nkana Area. Iv. The Dwangwa River Area. V. Other areas. The first detailed account of the sediments of Karroo age in the area lying north-west of Lake Nyasa, known as the North Nyasa District of Nyasaland (Fig. 1), is due to A. R. Andrew and T. E. G. Bailey1 (see Fig. 1). These authors carried out a valuable preliminary survey of the country during the period 1906-09, and their observations have served as the basis for subsequent work upon the geology of Nyasaland. During 1924-25, however, there were found near the north-western shores of Lake Nyasa certain fossils that have proved to be of considerable importance in the geology of Nyasaland, and the object of this communication is to outline the effect of these discoveries upon our knowledge of the area, and to indicate how far it may be necessary to modify existing views. For example, the finding of Dinosaur bones has shown that certain beds that were regarded as being of Karroo age really belong to late Jurassic or early Cretaceous times, and the recognition of a Beaufort reptilian fauna in other beds has enabled the local sequence to be extended in an upward direction. The sketch-maps used in the illustration of these notes are based upon those originally given by Andrew and Bailey, which I have modified slightly in accordance with my own observations. Andrew and Bailey suggested that the Karroo of North Nyasa could be broadly sub-divided as follows:- (3) An upper sandstone and calcareous division. (2) A middle shale division. (1) A lower sandstone division. Of these, Division (2), like the corresponding beds of the Lower Shire area of the southern part of Nyasaland, is probably of Ecca age, while part at least of Division (3) is of Beaufort age; moreover, in the Lower Shire area the beds corresponding to Division (3) are succeeded by a great thickness of volcanic rocks that are probably of Stormberg age.
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Transactions of the Geological Society of South Africa, 29, 69-83
Dr. F. Dixey has been good enough to entrust to me for identification and report the very interesting collection of vertebrate remains which he made in Northern Nyasaland during the field-season of 1925; and he has been generous enough to agree to the retention of the majority of the specimens by the South African Museum. The vertebrates come from two distinct groups of beds - the Karroo rocks of Chiweta, which yield a typical Karroo fauna, and the later Mesozoic beds of Mwakasyunguti, which contain remains of large Dinosaurs. This paper deals only with the Karroo fossils. The geology of the Mount Waller Area and Chiweta Beds is dealt with by Dr. Dixey in a paper preceding this. The fossils occur at two horizons - the Lower Bone Bed (Bed No. 5 of the Chiweta sequence) and the Upper Bone Bed (Bed No. 7 of the same). The Lower Bone Bed yielded fossils marked "B1", which were "collected from a great thickness of the 1ower beds"; those from the Upper Bed (marked "B2") formed "an isolated group towards the top of the beds and lay on the ground within a radius of about 20 yards of one another". (Quotations are from a letter, F.D. to, S.H.H., 22/12/1925.) On development, it was found that many of the fossils were tantalisingly fragmentary, the cause being twofold - (a) the material was almost entirely in weathered nodules picked up at the surface; and (b) many of the bones were obviously broken before entombment. Nevertheless, it has been possible to write specific descriptions of several of the B2 forms, and to draw conclusions from a study of both groups.
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Transactions of the Geological Society of South Africa, 29, 85-90, 2 pl
Biotite-trachyte was discovered by the writer in July, 1925, in the Auas Mountains, about nine miles south of Windhoek, and the locality was recently visited by Dr. Rogers, Dr. Haughton and the writer. The trachyte occurs as a group of about eight necks with a few associated dykes. The occurrences are of special interest owing to the magnitude of the necks and the relation they bear to the discoveries of Dr. Rimann of trachyte and related alkali rocks, south of the Auas Mountains and in Bastardland.
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Transactions of the Geological Society of South Africa, 29, 91-94
The following is a description of an inexpensive piece of apparatus for determining the specific gravity of rocks. Its simplicity of structure lends itself readily to use in field work as well as in the laboratory.
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Transactions of the Geological Society of South Africa, 29, 95-108
The latest addition to the long list of the gold deposits of the Transvaal is an interesting and promising occurrence on the farm Waaikraal, No. 205, situated in the Rustenburg district, roughly 25 miles north-east of Rustenburg, und about 42 miles west-north-west of Pretoria. It takes the form of an irregular inclined concordant sill of a dark-coloured melanocratic igneous rock which, wherever opened up so far, has been found to carry gold in notable quantities. It will be shown in the sequel that the rock composing the sill is very variable in character and difficult to name, but that in its more typical development it is best described as pyroxenitic quartz-bearing soda-gabbro. It is a member of the Bushveld Igneous Complex. The sill and a number of lesser bodies of rock of allied nature are intrusive in a series of highly altered sedimentary rocks occurring some little distance above the contact between the norite and granite-granophyre zones of the Bushveld Complex. According to the Rustenburg Sheet (No. 4) of the Geological Survey map of the Transvaal, the norite-granophyre contact is in the neighbourhood of the deposit situated about 1,000 yards south of the southern boundary of the altered sedimentaries. The latter are thus here evidently both underlain and overlain by granitic rocks. They form a belt at least 600 yards in width, trending in a general west-north-west east-south-east direction along the boundary between Waaikraal, No. 205, and Beestekraal, No. 503. Toward the west-north-west, however, along the south-western boundary of Waaikraal, the continuation of this zone of metamorphosed sedimentary rocks follows the contact between norite and granophyre. This is also the case with a similar belt of sedimentaries on the adjoining farm Potgietershoogte, No. 721, to be presently referred to.
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Transactions of the Geological Society of South Africa, 29, xx-xxxiv
This is the first year in the history of our Society in which one, whose chief work has lain within the bounds of Palaeontology, has had the honour of occupying the Presidential Chair; and the moment, therefore, seems opportune to pass in general review the work which has been done in the study of South African fossil animals, to consider briefly the bearing of the results obtained from the geological point of view, and to state some of the problems which still await South African investigators in this subject. To one, at least, of our members Palaeontology is "as dry as the bones with which it deals". Fortunately, we are not all cast in the same mental mould; and to many there is absorbing interest in the study of the extinct forms which had their being in the past on this sub-Continent and in the seas which surrounded it and in following the evolutionary changes which the various groups underwent. Moreover (although not yet to any great extent in South Africa) Palaeontology has proved its worth when considered from a purely economic aspect.
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Transactions of the Geological Society of South Africa, 3, 107-109
I should like to draw attention to an apparently unexploited but extensive body of sandstones in the Pretoria district, lat. S25°25'. These beds which might more correctly te termed quartzitic-sandstones, range in colour from red to chocolate and are first met with after leaving Rietfontein, No. 501 on the Middleburg Line of Railway and travelling due east.
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Transactions of the Geological Society of South Africa, 3, 12-16
The Klerksdorp, or Schoonspruit Goldfields, of which it is proposed here to give a short description, may be said to form the southwestern portion of the Southern Goldfields of the Transvaal, and lie at a distance of about 85 miles to the s.s.w. of Johannesburg. They include the greater portion of the basins of the Schoon, Koekemoer and Jagt Spruits, and smaller portions of those of the Vaal River and Yzer Spruit. To the north, the Potchefstroom and Ventersdorp fields are continuations of the strata, which on the south, are lost under the coal measures of the Kroonstad district of the Orange Free State. The geological conditions may be considered, generally speaking, as a replica of those obtaining on the Witwatersrand, with numerous local occurrences and modifications mainly due to the preponderance of igneous sheets and the general results of extensive volcanic action.
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Transactions of the Geological Society of South Africa, 3, 122-127
I wish to draw your attention once more for a few moments to the interesting discovery of a volcanic chimney, filled with a diamondiferous eruptive breccia, on the farm Rietfontein, in the neighbourhood of Pretoria. This diamondiferous breccia is of the same nature as the well-known "blue ground" of Kimberley mines, which is known in petrography as a peculiar kind of serpentinized peridotite breccia, for which the name "kimberlite" is now-a-days fairly generally adopted.
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Transactions of the Geological Society of South Africa, 3, 128-141
When engaged in investigating the geology of Vereeniging, I discovered some fossil plant remains which have since been identified by Mr. A. C, Seward, M.A., F.G.S., of Cambridge, as belonging to species of plants hitherto not known in strata of later date than the Permian, and he considers them to indicate the Permo-Carboniferous age of the beds in which they occur. The coal deposits of South Africa have generally been considered Triassic, and the question with regard to the fossils is - Do they represent survival of remnants of a carboniferous or permian flora into Triassic times; or is the coal strata which we have so long looked upon as Triassic in reality Permian?
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Transactions of the Geological Society of South Africa, 3, 147-148
Disagreeing with the theory of ascension, for the gold contents of the "banket" and also differing with M. de Launay and others in what is known as the "precipitation theory", he favours the "marine placer" deposit as the means whereby the gold was brought into its position in the conglomerate as well as the formation of the conglomerate beds themselves. Briefly, he maintains that the conglomerate beds were deposited by marine currents along a shore line; that the currents generally maintained an east-westerly course, influenced by the direction of the prevailing winds which again depend upon the direction of the rotation of the earth; that the gold was derived principally from the destruction of previously existing auriferous strata; that a portion of the gold may have been produced by recrystallisation, which would account for its crystalline nature, and finally he feels justified in concluding the other spots has rich as the Rand may be hoped for; that accepting the theory of marine "placer formation" a sudden failure of gold is not to be anticipated, and an examination of the conditions along the outcrop furnishes strong reason to believe that the yield will keep up to a great depth.
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Transactions of the Geological Society of South Africa, 3, 151-153
The occurrence of the peculiar lower Gondwana flora in South America, Africa, India and Western Australia, to say nothing of reptilian evidences, leaves little or no doubt that in early secondary times these widely separated areas were connected by a belt of land embracing the greater part of the earth's circumference in lower latitudes. And one of the pressing questions connected with the present distribution of the land faunas of the Southern Hemisphere is to determine the approximate geological date to which this land connection, or portion of it, persisted. If there is any hope of ever solving this question, it is only by the discovery of the remains of tertiary mammals in South Africa. At present the whole of the vast Ethiopian continent is an absolute blank so far as the history of tertiary mammals is concerned.
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Transactions of the Geological Society of South Africa, 3, 19-30
My intention this everning is to lay before this meeting some of the most interesting features in the geology of this country.
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Transactions of the Geological Society of South Africa, 3, 35-42
A brief description of the principal events in the geological history of the country, which have caused it to assume its present outlines, and have reduced it to the level at which we now find it.
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Transactions of the Geological Society of South Africa, 3, 42-44
No abstract.
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Transactions of the Geological Society of South Africa, 3, 49-52
Over the greater part of the Witwatersrand there is found a surface or sub-surface deposit, which appears to consist, at first glance, of ironstone nodules, either separate and distinct, or cemented together, like the clinkers from a highly pyritic coal. This rock, named oud klip (Dutch; old rock), from its decomposed nature, is a common surface feature over a large part of South Africa.
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Transactions of the Geological Society of South Africa, 3, 53-59
In the State Mining Engineer's Report for the past year there appears, in addition to the mass of valuable information - statistical and general - regarding the Mining Industry, several appendices - A D and E - which deal with the geological conditions of the Johannesburg, Lydenburg and Klerksdorp mining districts, respectively, and as the statements contained therein differ greatly from those of the leading South African geologists in general, and my own opinions in particular, I cannot allow them to go forth to the world unchallenged.
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Transactions of the Geological Society of South Africa, 3, 70-82
I wish to call your attention to the chief observations which have induced me to advance the following hypothesis, - that the valleys in the vicinity of Pretoria were formed by glacial action, and that the hills surrounding them preserve most distinct traces of a recent (probably diluvial) ice period.
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Transactions of the Geological Society of South Africa, 3, p146
I have much pleasure in announcing the discovery of a rich fossiliferous deposit of an exceedingly interesting nature. About ten miles from Johannesburg, on the farm Witkopje, and near to the Pretoria railway line, there is a pan or lake of considerable extent. Close to this pan can be seen the remains of the old stone wall built in the days when the farmer Du Preez owned the farms Riefontein and Witkopje. Mr. W.E. Allison, in picking out stones for building purposes, happened upon a fossil in one of the rocks taken from the old wall. This was shown to me, and, recognising the importance of the find, and being struck by the appearance of the deposit (apparently Locustrine) in which the fossil was encased, I suggested a careful search for more geological treasures.
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Transactions of the Geological Society of South Africa, 3, p149
Professor Prister presented the following note on Mr. Draper's paper, entitled "The Coal Deposits of South Africa". I have followed with great interest the paper by Mr. Draper, and, though we all know that large areas of coal exist in this country, I must confess its extent as revealed to us by Mr. Draper was a decided surprise to me. From a rough calculation I find that there is an area of, approximately 160,000 square miles where coal may be expected to occur. This immense deposit, taken in conjunction with the large deposits and occurrences of other minerals, especially excellent iron ores, magnetite, limonite, etc., will have a great influence on the industrial future of South Africa.
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Transactions of the Geological Society of South Africa, 3, p150
I agree with Dr. Molengraaff "that the discovery of diamonds at Rietfontein supports the theory that the element carbon can, under the conditions of heat and pressure ruling at great depths in the interior of the earth, only exist and crystallize in the modification called diamond", but it remains to be explained in what form the carbon was precipitated from the atmosphere when the earth and its atmosphere was in process of cooling. Will the hypothesis that the carbon was precipiated as a metallic carbide be considered as too imaginary?
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Transactions of the Geological Society of South Africa, 3, p48
Mr. Draper wished to call the attention of members to a recent discovery, derived from fossil evidence forwarded from the vicinity of Johannesburg, as well as from evidence discovered in India at about the same time.
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Transactions of the Geological Society of South Africa, 30, 1-4
No abstract. Dr. J. Malcolm Maclaren, in his book, "Gold", records the occurrence of tetradymite as an associate of gold only in two localities, namely, King's Mountain, North Carolina, and Clogau, North Wales. In view of the rarity of this association, and also as the discovery of tellurides of gold in the Rustenberg District has recently been announced by Dr. Wagner, it is considered that a deposit in Southern Rhodesia should be recorded. The occurrence is at the New Mystery Mine, which is situated on Ratanyana farm, in the West Gwanda District, one mile to the east of its westerly beacon. A road, 36 miles long, has been cut from Antenior Spur on the West Nicholson Railway. This road is passable for motors, with the exception of two sandy drifts at the Tuli and Mwewe rivers, where assistance must be obtained. The country-rock surrounding the mine is mainly serpentine, in which lie several narrow elongated outcrops of banded ironstone. It is comparatively near the edge of the schist-belt, as granite outcrops two miles to the north and about six miles to the west. The mine was pegged in June, 1925, by Mr. W.E. Hunt, the gold having been discovered by loaming. Trenching disclosed rich patches, which he attempted to develop on normal lines. A vertical shaft was sunk to 80 ft., and drives were put in at water-level, which is at 52 ft. As only low values were obtained beneath the surface indications, he decided to instal a small plant to treat the rich surface ore. A Tremain mill and cyanide plant were installed, and up to the end of September, 1926, 1,065 tons had been treated, giving an extraction of 975 ozs., valued at £4,110.
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Transactions of the Geological Society of South Africa, 30, 5-56
No abstract. Contents:
Location. Topography. History of mining activities: Gold, Lead and Zinc, Fluorspar. Geological structure. Stratigraphical geology: Surface deposits, Pretoria Series, Dolomite Series, Dolomite, Siliceous rocks (a) Cherts, (b) Quatzites, Shale, Intrusive rocks. Metamorphism of the dolomite. Economic geology: Fluorspar, Lead and Zinc Deposits, Resumé and Genetic Considerations. Comparison with deposits in other parts of the world.
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Transactions of the Geological Society of South Africa, 30, 57-68
No abstract. Contents: Early discoveries of diamonds in the Dolomite. Physical features. Geological conditions. Special geological features. Erosion of a dolomite area. Distribution of the diamonds. Quality of diamonds. Summary. Additional notes: Diamonds in coral reefs. Formation of chert ridges. Summary: From the foregoing brief description of the principal characteristics of the area dealt with, it will be seen that here, diamonds are being recovered under geological and physical conditions hitherto unrecorded in any part of South Africa. The writer has endeavoured to place before the meeting such evidence as he considered could be obtained by assuming that there had been no cataclysmic or catastrophic agencies in operation. No great floods or violent eruptions or disturbances of the strata. There is no evidence in favour of the existence of craters or volcanos in the entire area under description, even igneous dykes and sheets are by no means as common as in other parts of the country. Finally the cycle of geological events which culminated in bringing the diamonds within the reach of the miners' pick-axe, may be summarised as follows:- (1). The formation of Dolomite in the still waters of deep seated parts of an ocean, which covered a large portion of this continent. (2). The gradual shallowing of the oceanic waters with the consequent elevation of the Dolomite, until the action of waves and currents could exercise their force in breaking up the exposed layers of the Dolomite, and forming them into Breccias and Conglomerates. 3). The introduction of the diamonds, brought in by several streams from different portions of a more elevated land surface, and their distribution among the Dolomitic debris, by the action of the waves, currents, whirlpools, etc., in shallow water. (4). The deposition of the Pretoria series, which ultimately covered the entire Dolomite area wherever it existed in the Transvaal, and adjacent parts of South Africa. (5). The removal by ordinary atmospheric influences of portions of the covering bed, with the consequent exposure of the ancient sea bottom with its valuable diamond contents. Naturally, the surface as we see it today, has been considerably modified since its exposure, the southern portion of the plain has been lowered probably several hundred feet by natural agencies, but towards the northern limit of the Dolomite, the evidence in favour of the last condition (5) is conspicuous, especially on the Farm Nooitgedacht No. 241, where the workings have penetrated over six feet of sandstone and other rocks undoubtedly derived from the destruction of the Pretoria series, and beneath this layer, Chert was encountered, from which diamonds were recovered.
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Transactions of the Geological Society of South Africa, 30, 89-120
No abstract. Contents: Methods and scope of investigation: Data available, Area covered, Arrangement. Description of the Reefs: Stratigraphy, Mineralogy, Structure of the Reefs - Central Rand area, East Rand area. Distribution of the gold: Assay plans, Paystreaks - Variation in value, Shape and arrangement. Comparison of reef of high and low gold content: Secondary minerals and gold content - General, Microscopic study, Observations in Government areas. Relation of gold content to reef texture. Comparison of the reef zones in and outside of the paystreaks. Relation structure and paystreaks: The main synclinal fold, Faulting - Individual faultlines and gold values. Relation of dykes and paystreaks. Relation of paystreaks to the surface. Theoretical considerations: Origin of gold - Infiltration hypothesis, Redistribution of the gold in the reefs, Placer hypothesis, Metamorphism of the reefs and of gold. Origin of the reefs - Details of the current system of the Main Reef Leader. Practical considerations. Summary.
The paper is the result of an investigation covering a period of about two years on ten mines of the Witwatersrand. It is concerned chiefly with the presence of paystreaks in the reefs that are being mined for gold, and the means by which their determination can be used to assist development work on the mines. The first part of the paper is a description of the reefs, of the methods used to determine the paystreaks on assay plans, and of the peculiarities of the paystreaks. Then follows a discussion of the difference in the mineralogy texture and other characters of reef of high and of low gold content. The relations between paystreaks and structure are described, and also their relation to dykes and to the present surface. The origin of the gold is then discussed. It is concluded that the arrangement in plan of the paystreaks in relation to the folding, fracturing and the dyke intrusion that has taken place since the reef was formed, definitely disproves the hypothesis that gold entered the reef in solution and was precipitated there. It also disproves the idea that the gold has been redistributed to more than local extent in the reefs since the metal was first deposited. The origin of the gold as a stream laid placer deposit is proven chiefly by the close relation between sedimentation and gold values. Thus the more highly payable belt along the central axis of paystreaks occurs in reef of such character as to strongly suggest that it was laid down under the centre line of a current, while reef of lower value on either side was deposited in quieter waters adjacent to the central stream. The way the reef pebbles orient themselves in relation to the paystreak confirms this conclusion. This relation is borne out, furthermore, by the close connection between paystreak system on the East Rand as a whole, and the variation in sedimentary characters of the reef over that area. The reefs are flood-plain deposits. Because of their coarse texture
they are believed to have been deposited at some distance from the sea, and a glacial climate probably prevailed in the hinterland from which the pebbles came. Reasons are given for believing that the East Rand reef zone, and its paystreaks, are the result of a flood caused by the breaking away of a river of continental proportions from a main channel at a point near Benoni, and the spreading of its waters to the east and south-east. The Main Reef Leader from Crown Mines westward, on the other hand, was deposited by waters flowing over a plain in a westerly direction. From the knowledge gained by a study of paystreaks in the stoped sections of contoured assay plans, it is possible to sketch paystreaks between certain lines of development and to so locate development connections that they will pass through the centre of the pay area. Such information prevents the putting of connections through unpayable ground and the consequent abandonment of blocks that are partly payable. If information on the contoured assay plan is supplemented by the plotting of the direction of the long axis of pebbles in the reefs it is possible to form an idea of the position of payable ground ahead of development. These conclusions have been confirmed to a large extent by development work on certain mines during the last year. It is believed that the methods outlined will produce increasingly more effective results if the assay plans be kept to date over a period of years and predictions based on them be checked as development proceeds. The study of paystreak systems over broad areas is the only method, at present apparent, for arriving at reasonable conclusions as to the location of payable ore bodies in areas such as that east of Springs and south of the Central Rand. The high cost of exploration in some of these areas should make an investigation along these lines worth while.
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Transactions of the Geological Society of South Africa, 30, 121-132
During the period 1914-19 a unique combination of circumstances afforded me exceptional opportunities of studying weathering and sedimentation under desert conditions in the coastal belt of South-West Africa. These I used for making a detailed survey of the superficial deposits of that area, so detailed, indeed, that critics of my work have not hesitated to declare that I wasted too much time on them. Since then I have made a study of all available literature on the geological conditions in the arid regions of today. My present trip to South Africa was undertaken specially to collect further data on weathering and sedimentation in arid and semi-arid regions, not actually desert. Unfortunately I cannot expect to carry on this work in the same detail as in the desert of South-West Africa. I propose to take the opportunity this evening of explaining to you the aims of my investigations.
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Transactions of the Geological Society of South Africa, 30, 133-142
Although the presence of a large extent of Karroo Beds in the Warmbad District of South-West Africa has been known since the work of Dr. Range, and a very generalised idea of their distribution given on the published maps of Range, Wagner and du Toit, no detailed examination of their nature and distribution seems to have been made until the geological survey of the area was begun in 1926. During the course of that work the beds (including the Karroo dolerite sheets) were found to have an area considerably greater than that previously supposed and to possess features of somewhat unusual interest in their geographical relations to the older rocks; and it is felt, therefore, that a brief account of them and of their bearing on the history of Carboniferous glaciation would be of some value to other workers. The rocks preserved in the area are divisible into Dwyka Tillite, Upper Dwyka Shales, and Ecca Beds - the whole being cut by sheets of Karroo Dolerite. As will be seen in the sequel, the Dwyka Tillite is a two-phase one, some of the sediments comprised within it being the work of the Namaland ice, and the remainder deposited from the Griqualand West ice. The maximum thickness of the sequence is not less than 1,800 feet, made up of Tillite 200 feet, Upper Dwyka Shales 600 feet, and Ecca Beds 1,000 feet.
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Transactions of the Geological Society of South Africa, 30, 69-88
The occurrence in the Eastern Transvaal of extensive formations of igneous rocks rich in magnesia and carrying commercial deposit of magnesian minerals such as magnesite has long been known. Tin exploitation of magnesite (No. 1) began near Malelane in 1906, and was soon followed by the development of similar deposits south of Kaapmuiden (No. 2, page 305), while a few years later talc was produced (No. 2, page 310, and No. 3) close to Noordkap and near Sheba Siding (No. 4); then came the important discoveries of asbestos in the western end of the same formation north of Kaapsche Hoop (Nos. 5 and 6), which have added a valuable and permanent factor to the South African asbestos industry; more recently, a few miles south of Magnesite Siding, yet another asbestos occurrence has begun to be exploited. About three years ago a discovery of talc, in the same magnesian belt, was made a little east of Kaapmuiden Station; its developments indicate a deposit of promise as regards quality and quantity, likely to grow into a useful addition to the increasing list of economic base metal and mineral resources, and therefore worth recording.
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Transactions of the Geological Society of South Africa, 30, xx-xxviii
No abstract. Some six months ago the celebration of the fortieth birthday of Johannesburg afforded the community an opportunity of honouring the memory of those who did the pioneer work in the building up of the great gold mining industry of the Witwatersrand, and in founding what has become within so short a period the largest and most progressive town in South Africa. It has been suggested to me that it would be appropriate on this occasion to say something about the foundation of our Society, for, though it serves the whole of South Africa, it was in its inception a Johannesburg institution, and forms part of the work of the Johannesburg pioneers. It is well, too, I think to remind the younger generation from time to time how and by whom the privileges which they enjoy were secured. Accordingly, I shall take the history of the Geological Society of South Africa as a central topic, and group around it what else I may have to say. The earliest geological societies in South Africa were formed in Grahamstown and Graaff-Reinet, under the auspices of Dr. Atherstone and Dr. Rubidge respectively. They appear to have been of a purely local character, and I cannot find any record of their work. Doubtless, they were on the same plane as the literary societies of the period, and intended primarily for the purpose of mutual education in the principles of geology. These societies had been long defunct when the present Geological Society of South Arica was established, one of the original members of which claimed to be the last surviving member of the Grahamstown Society. Our Society was founded in Johannesburg in February, 1895, chiefly through the efforts of Dr. Hugh Exton and Mr. David Draper. An attempt to bring this about had been made by Dr. Exton some years previously, but without success. In 1894 a geological section through the Southern Transvaal, made by Dr. Draper under the auspices of the Witwatersrand Chamber of Mines, had been exhibited in Johannesburg, and as this aroused considerable interest among the community in the geology of the country, the opportunity was seized for the promotion of the new society. Dr. Exton was appointed President, and held this position till his death in 1903.
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Transactions of the Geological Society of South Africa, 31, 1-42
Difficult of approach, presenting a desolate and forbidding aspect from the sea, and mostly enshrouded in dense fog, what we propose to name the Diamond Coast of Southern Africa, attracted little notice until the year 1908, when diamonds were discovered near Lüderitzbucht. The discovery aroused great interest and in a very short space of time the remarkable detrital deposits, in which the gem here occurs, were proved to extend along the littoral from Conception Bay, in the north, to Chameis, near Angras Juntas, in the south, a distance of nearly 300 miles. The stretch of coast between Angras Juntas and the mouth of the Orange was also prospected in desultory fashion, but no diamonds were found in it. A German prospector, F. W. Martens, now living at Aus, resolved, however, to try his luck south of the mouth, and during 1909 he actually found seven small diamonds near Alexander Bay on the lower shingle terraces to be presently referred to. Martens pegged a number of claims, but gave up the idea of exploiting them when he found how small in comparison with the discovery areas granted in German territory were those granted on Crown Lands in the Cape Colony. It is of interest to record that four of his pegs were found in their original positions. Between 1909 and 1920 the Namaqualand littoral received very little attention from prospectors, though the late F. C. Cornell explored it during 1010 on one of his innumerable trips. In February, 1926, Mr. F. C. Carstens found a small diamond on the Port Nolloth Reserve, about 6½ miles south of Port Nolloth. and, on putting down a prospecting pit on the site of his find, located a deposit of lime-cemented diamond-bearing shingle in what appears to be an abandoned course of the Kamma River, lying some little distance north of the present course. Dr. W. A. Humphrey reported on the occurrence and published an interesting description of it. The discovery attracted numerous prospectors and a number of geologists to the area. It was quickly followed by further discoveries at The Cliffs, 11 miles north of Port Nolloth, at Buchuberg, 40 miles north of Port Nolloth, and at the Buffels River mouth, 32 miles south of Port Nolloth. One of the authors (H.M.) began work in the area in November, 1926, assisted by Drs. E. Reuning and I. B. Celliers. Having noticed that both at The Cliffs and at Buchuberg the diamond is associated with the shells of a remarkable extinct oyster, he decided to use this oyster as an indicator in the area immediately south of the Orange River mouth, where Messrs. Gordon and Kaplan were at that time prospecting, and had actually found several small diamonds on what are now the Victor Gordon claims. Some distance south of the ruins of the old stone house on the banks of the Orange, in which Sir James Alexander had stored copper ore during the thirties of last century, he found an outcrop of promising-looking shingle carrying oyster shells. He put Dr. Reuning to work on this, and it proved to be the
northern end of the extremely rich Oyster Line to be presently described. The first big diamonds were actually found by two Namaqualand Boers, the brothers Coetzee, working under Dr. Reuning's supervision. The discovery was followed by many others in the neighbourhood of Alexander Bay, and before long the whole of this area and all the gravel terraces along the south bank of the Orange River as far as Zendlings Drift were covered by prospecting areas. This was the position in February, 1927, when the Government prohibited all further prospecting for diamonds on Crown Lands in Namaqualand. By this time it had been established that, extending from the mouth of the Orange as far south at least as the south bank of the Groen River, there is a vast diamond field. Fortunately for the South African diamond industry in its present condition, the deposits are for the most part deeply buried by sand, surface limestone, and younger barren gravels. This, combined with their patchy and erratic distribution, of which there is already abundant evidence, and the general scarcity of water, renders it improbable that more than a small part of the field will ever be worked. Barring certain areas that are already pegged, or covered by prospecting areas, it is emphatically no field for the individual digger. As a preliminary to the description of the diamond-bearing deposits, it will be useful to give a brief account of the physiography and geology of this part of the South-West African littoral.
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Transactions of the Geological Society of South Africa, 31, 157-165
The structures about to be described, whose unusual and striking character is shown in the photographs illustrating this paper, were first observed by me in a section across the lower beds of the Campbell Rand or Dolomite Series exposed in the course of the Hol River, some two or three miles north of the village of Klein Boetsap in Griqualand West. Here the two branches of this stream descend abruptly from the Kaap Plateau into a short and precipitous gorge by which their united waters reach the broad valley of the Harts River. Except in heavy rainy seasons, their channels are occupied only by occasional pools with little surface flow. The dolomite, or more strictly dolomitic limestone, which in this neighbourhood is mostly obscured by calcareous tufa and other superficial deposits, is well exposed in the gorge and for a short distance above it, as also some three miles further down at what are locally known as the "lower falls". The rock is usually thin-bedded or flaggy, the beds ranging in thickness from less than an inch to about a foot. At intervals, however, as at the upper and lower falls, more massive strata occur, in some instances as much as six feet thick. The limestone is light to dark grey, the depth of colour varying with the amount of impurities which it contains. Interbedded with the limestones are occasional beds of shale from a few inches up to two feet thick. These rocks are readily eroded and are in consequence poorly exposed, being sometimes hidden by the fall of the overhanging limestones and at other times covered by calcareous tufa. The rocks forming the Campbell Rand or eastern escarpment of the Kaap Plateau generally appear to be evenly bedded with a very slight westerly dip. This holds true of the zones of more massive limestone exposed in the Hol River section, but not of the intervening thin-bedded flaggy limestone, which is bent into a series of close-fitting comical folds. That the massive strata, however, have not escaped the pressure which has thus bent the associated thinner beds is revealed by the peculiar structures which have been impressed upon them.
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Transactions of the Geological Society of South Africa, 31, 43-62
In the course of the geological survey of the western Stormberg, chiefly in the Molteno district, not only were a considerable number of volcanic necks encountered, but also numerous features of volcanological interest presented themselves, a discussion of which may perhaps add to our knowledge of the complex phenomena presented by Stormberg volcanicity. The volcanic plugs situated in this area show such an astounding variety, both as regards outer form and in the nature of their rock fillings, that a short description of the main points of their physical and petrographical features would seem to be justified. In order to facilitate such a description and render it as short as possible, a detailed survey of the main area of volcanic activity has been made, the results being embodied in the accompanying large-scale map. In addition a few diagrams have been added, which it is hoped will explain the particular features in question far better than any lengthy and detailed description possibly could. A treatment of such a subject, however, would be incomplete without reference to the questions of wider interest, that is to say, to the problems of Stormberg volcanicity in general. Further, the investigation of the local phenomena will be discussed in relation to deductions based on similar investigations elsewhere. In an undertaking of this kind, especially within the narrow limits of a short paper, there must be much that will remain problematical or is of a purely speculative nature. Considering, however, how much of volcanological theory in general is speculative, apologies on this account seem to be unnecessary. Nevertheless it must needs be a source of considerable satisfaction to an individual investigator to find his own observations link up with those of a similar kind made in other parts of the world and thus help to strengthen further the evidence for some outstanding fundamental theory. And such an outstanding and fundamental theory, no doubt, is that which conceives the earth's interior to be composed of successive shells of density increasing with depth, and which beneath the outer sedimentary and "granitic" shells postulates a continuous and universal substratum o£ basaltic matter, as expounded by Cotta, Green, Daly and others. Further, in this paper it is tacitly assumed that all volcanic action is due to abyssal and hypabyssal injection of an originally basaltic magma from the substratum, according to the hypothesis promulgated by Johnston-Lavis and Daly. Special facilities for the study of volcanic phenomena in the Molteno, district and their relation to the intrusive phase of igneous action were afforded by the extension of survey work beyond, that is to say below, the escarpment. In this way all horizons from the Drakensberg volcanics down to the Middle Beaufort Beds could be thoroughly investigated, and volcanic necks exposed at various levels could be examined. A short stratigraphical summary will perhaps serve to make this clear.
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Transactions of the Geological Society of South Africa, 31, 63-96
Several theories have been advanced to explain the origin of the African Rift Valleys. As will be seen later, the majority of these attribute them to the action of earth-movements. In the immediate vicinity of these valleys, the structures developed in the strata are frequently masked by the extensive outpourings of volcanic rocks. These " Rift Valleys " extend from Palestine in the north, along the Gulf of Sinai and the Red Sea, across Abyssinia, British East Africa and Tanganyika, at least as far south as the Zambesi Valley. Hence, it is clear that if they be due to the action of tectonic forces, these earth stresses must have operated through a large portion of the earth's crust. Consequently, the study of the geological structure and tectonic history of areas adjoining these Rift Valleys must afford valuable information as to the nature of the stresses, which have given rise to these exceptional earth-forms. Recently, the writer has been engaged in Uganda, Tanganyika and Kenya, and in the latter country geologically mapped a large area extending along the coast from the Tanganyika border in the south to the mouth of the Tana River in the north. This work disclosed geologically data which appear to have an important bearing on the question of the origin of the Rift Valleys. The details of this work are given in a comprehensive paper entitled " The Geology of Coastal Kenya and its bearing on the question of the origin of the Great Rift Valleys. "Owing to the cost of printing, your council were unable to publish the larger paper, so this abstract has been prepared. A brief reference to the geological history of the coastal region of Kenya will first be given, paying particular attention to the tectonic structure and history of the area. The previously advanced theories of origin of the Rift Valleys will then be briefly stated, and an examination of these made in the light of the further knowledge gained from the above study.
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Transactions of the Geological Society of South Africa, 31, 97-156
Pilansberg, or Pilaan's Berg, is the name of a remarkable group of hills covering an area of about two hundred square miles in the North-Western Transvaal. The name is derived from Pilaan, or Pilané, the family name of the chiefs of the Mokatla tribe; the spelling "Pilandsberg", which is sometimes used, is therefore incorrect. The name is used in the singular rather than the plural, because the hills form a geographical and geological unit; they are the deeply dissected relics of a single mountain block. From the physiographic aspect, the Berg attracts attention because it rises abruptly out of flat bushveld country, like a great island rising sheer out of the sea, and because it seems to be constructed of concentric rings of hills - a peculiarity which earned for it the name of Dubbelde Berg, or double mountain, from the early settlers in the district. From the geological aspect Pilansberg is remarkable as one of the largest bodies of highly alkaline rocks in the world, and also as an intrusion with well marked ring-structure. Pilansberg was mapped by Dr. W.A. Humphrey, of the Geological Survey of the Union of South Africa, in 1911. In the same year Dr. H.A. Brouwer published his well-known work on the Transvaal nepheline-syenites, a large part of which is devoted to the petrography of Pilansberg. To undertake a revision of the area after such a short interval must seem almost an impertinence, so I shall state briefly the reasons that led me to take this step. In following up the problem of the origin of alkaline rocks, I have already mapped and studied most of the South African occurrences of such rocks. It seemed likely that Pilansberg, as one of the largest alkaline intrusions in the world, would yield more information than the smaller intrusions have given, and it was primarily this expectation that led me, in 1923, to Pilansberg. It was evident to me, as it must be to anybody who reads Humphrey's and Brouwer's reports critically, that in spite of the admirable geological and petrographical work which these men accomplished respectively, there is a serious lack of correlation between the two contrasted aspects of the subject. Humphrey's work is incomplete in one respect, Brouwer's in the other; and as matters stood in 1923, one was left in doubt as to the petrological character of many of the rocks mapped by Humphrey, and in complete darkness as to the geological relations of those so minutely described by Brouwer. Here was a gap that needed to be spanned; and as it seemed that the bridging of the gap might very well lead to a solution of the special problem with which I was concerned, I resolved to re-map the whole complex on a large scale and to try to establish some relation between the geological and the petrographical characters of the rocks. In presenting the results of my study, I wish to express my high appreciation of the pioneer work of Dr. Humphrey and Dr, Brouwer. The former claims my admiration for the general correctness of the
mapping which he accomplished in part of a single field season - about a third of the time which I took to cover the same ground. To Dr. Brouwer I offer my compliments on his most careful and accurate mineralogical descriptions; I have attempted to supplement them, but I cannot hope to improve upon them.
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Transactions of the Geological Society of South Africa, 31, xix-xl
Significant is it of these times to review the subjects of the papers and addresses delivered before this Society since its foundation and to note their gradually changing aspect. From the purely provincial contribution, with its generally localised interests, we have arrived at papers dealing with areas still situate within this continent, yet well beyond the limit set to South Africa, though we fully admit their important bearing upon the problems of the Union. By degrees, however, is it being thrust upon our notice that the keys to many of our geological riddles - and they are by no means few - have to be sought for outside the confines of this country. More and more are geologists being compelled to seek out and utilise all available data from other lands; perhaps in no branch of the science is this more marked than in that of Economic Geology. At the same time such analogous and far-distant occurrences can scarcely be regarded as other than alien and not truly "South African"; they indeed constitute for us no more than practical, though illuminating, illustrations and guides in our sphere of research. It is my intention tonight to develop an important theme of a rather different kind, that being the case of a land, which, although situate on the further side of the South Atlantic, cannot strictly be regarded as "alien", a paradox which will receive its explanation in the sequel. This is the great continent of South America, a country not only possessing geological formations, but displaying a geological history marvelously similar to those of South Africa, despite the breadth of the intervening ocean. Evidence can, as it happens, be presented pointing strongly in the direction of the conception that in the past South America was united more closely to Africa than at present, but that these two masses became forcibly separated during the late Mesozoic through gigantic crustal movements, as portrayed under the now well-known " Continental Drift " or " Displacement Hypothesis", with which are particularly connected the names of Taylor and Wegener. Seven years ago I had the privilege, though many have called it rashness, of first championing in this country these undoubtedly revolutionary ideas, yet, since then, in spite of much active criticism, the arguments in favour thereof have definitely grown not only more numerous, but more cogent. My researches in South America in 1923 have indeed disclosed a wealth of unexpected data strongly favouring these heterodox opinions, and for the first time the Displacement Hypothesis can be regarded as having been placed upon a quantitative basis, so to speak.
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Transactions of the Geological Society of South Africa, 32, 1-25
Main objects of paper: (a) Some obeservations on the strike of the ancient schists of the subcontinent. (b) A brief discussion on what is believed to be a possible example of metallogenetic zoning in the Murchison Range. (c) A description of the first deposit of emeralds to be discovered in the Transvaal. (d) Some notes on colouring and colour zoning observed in some emeralds and beryls from the Murchison Range.
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Transactions of the Geological Society of South Africa, 32, 103-109
The rarity of the known nickel deposits in the Great Dyke of Southern Rhodesia is a matter for surprise when it be considered that the rock suite forming that curious geological feature is one in which nickel deposits might reasonably be expected to occur. The only published mention of the occurrence of nickel minerals in the Great Dyke known to the author was made by the late A.E.V. Zealley in the Southern Rhodesia, Geological Survey Short Report No. 3, in which, when describing "The Platinum Ore of the Dream Reef", near Lalapanzi, in the Gwelo District, that geologist mentions the discovery of "encrusting films and occasional veinlets of green and blue copper and nickel minerals, among which were recognized malachite, chrysocolla and an indefinite nickeliferous crust which is probably a mixture of genthite (nickel magnesium silicate) and zaratite (nickel carbonate). Pale green garnierite (slightly chromiferous) forms seams up to 1/4 inch wide in the gossan". All these minerals are stated to occur associated with haematite and chalcedony in the gossan of the platinum-bearing reef. Zealley further states that the source of the nickel minerals may be chalcopyrite and pyrrhotite, but that as unweathered rock was not available such a. suggestion was purely speculative. Three distinct occurrences of rocks rich in nickel occur in the area mapped in detail by the author in 1928, this area. consisting of some 45 square miles of the Great Dyke forming a portion of the Umvukwe Range and of about 100 square miles on the flanks of that intrusion.
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Transactions of the Geological Society of South Africa, 32, 111-149
In South-West Africa an extensive tract of country situated in the north-western portion of Damaraland and of which the Erongo mountains form the dominant morphological feature is generally referred to as the "Erongo Tinfields". Cassiterite was first discovered here in the north-western portion of the Omaruru division in the year 1909. In the following year considerable deposits, mainly of an eluvial nature, were found on the farm Ameib, about 18 miles north-west of Karibib, and situated immediately below the imposing southern escarpment of the Erongo mountains amid an unrivalled wealth of magnificent granite scenery. Owing to the promising nature of these fields, extensive prospecting operations were carried on, and to-day the tin-bearing area has been shown to extend from south-east of Karibib to beyond the Brandberg and Ugab as far as the southern portion of the Koakoveld, a distance of approximately 140 miles. The exact limits of the fields have, however, not yet been defined. Within the area so far investigated the tin-bearing pegmatites are found to occur along three well-defined main belts. The orientation of these belts is determined by the general and local strike of the ancient sediments and the contacts of the intruded old granites. Beginning in the north-west what may be referred to as the Northern Belt begins with profuse development of pegmatites around Uis, and from here continues westwards over a distance of about 25 miles to Ploeger's claims south of the Brandberg. The exact distance of its further extension westwards towards the sea is unknown. The Great Central Belt along the Omaruru River commences on the lower course of this river west of Neineis and then continues over Nobgams, Humdegams, Tsomtsaub, Paukwab, the Thelma Mine and Kohero as far east as the western slopes of the Kompaneno mountains, north-west of Omaruru township, a total distance of about 60 miles. This belt comprises some of the most important tin-occurrences of the whole fields. The Great Southern Belt commences in the west a short distance north of Ebony, and then continues past Sandamab, between Usakos and the Great Spitzkopje, to the south-western corner of the Erongo, fringes the foot of its southern escarpment, crosses the Khan River a few miles north of Karibib, and then continues along the banks of this river as a continuous belt as far as Otjimboyo and Otjakatjongo, 30 miles east of Karibib. The total length of this belt is approximately 80 miles. Near the south-western corner of the Erongo this great belt sends off a subsidiary branch along the slopes of the western escarpment of these mountains, while another subsidiary belt leaves the main belt near the confluence of the Khan and Etiro rivers and undergoes its main development on Erongo-Kanona below the T.P. Erongo. It was the investigation of these tin-deposits, from which during, the past ten years there have been produced 2,100 tons of concentrates of an average content of over 70 per cent. SnO2, which formed the main objective of the geological survey of this area. The following paper is mainly intended as a brief summary of the results obtained and the conclusions arrived at. Before entering on the discussion of the tin-bearing pegmatites n short table of the general geology of the area will be given in order to show the relationship of the pegmatites to the great variety of intruded granites. For further details concerning the general geology reference should be made to the previous paper on this area.
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Transactions of the Geological Society of South Africa, 32, 151-164
The area under consideration is about 68 square miles in extent and is situated some 18 miles north-east of Pretoria. It is bordered by the Pretoria Series and the Norite on the south, the Red Granite on the west, the Felsites on the north, and the Waterberg System on the east, while it is itself mainly constituted of felsite. The chief interest lies in its centroclinal structure, the ring-shaped arrangement of its intrusions of dolerite, undersaturated alkaline rocks and a sometimes well-developed agglomerate of a similar distribution. These features are recorded on a geological map accompanying this paper In an appendix a detailed description is offered of an occurrence in this area of a rather unusual rock consisting mainly of fluorite and apatite.
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Transactions of the Geological Society of South Africa, 32, 165-170
The somewhat remarkable occurrence of cassiterite to be described in the following paper is situated approximately 40 miles from the sea and some 23 miles north of Arandis station in the Namib forming the hinterland of Swakopmund. Contents: Locality. Historical. Geology. Mode of occurrence of the cassiterite and minerals associated with it. Hydrothermal nature of the deposit.
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Transactions of the Geological Society of South Africa, 32, 171-176
Amongst several samples sent to me by Dr. Gevers, from a tin mine near Arandis, was a rock consisting of quartz, oxides of iron, cassiterite and a green mineral. This, from its tin content and properties, could not be identified as any known mineral of tin. An examination of this material was, therefore, undertaken, and, from the following results, it seems that a new tin mineral has been discovered. For the purpose of identification we will call this mineral "Arandisite".
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Transactions of the Geological Society of South Africa, 32, 177-186
Although the geology of this area, and Northern Swaziland generally, has been described by Dr. A. L. Hall in the "Geological Survey - Memoir No. 9", no detailed work has hitherto been carried out on the extremely interesting area of Forbes Reef. In view of the renewed interest displayed during the present year in the mineral potentialities of Northern Swaziland, the following notes on the Forbes Reef Concession may prove of interest. Since the author of this paper was fully occupied with various mining duties during a three months' stay at Forbes Reef, little time was available for any detailed geological work, though there is ample scope for it in this area. At Forbes Reef we have many fine examples of ore deposits lying in the crystalline schists of the Jamestown Series, near the intrusive "Old Grey Granite".
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Transactions of the Geological Society of South Africa, 32, p. 187
During the past year (1928) Miss Wilman has acquired for the McGregor Museum, Kimberley, some unusually large crystals of Smithsonite (ZnCO3) from the Rhodesia Broken Hill mines. They are slightly yellowish in colour and at the surface consist of a thin film of dull grey material which obscures their transparency. All the crystals are simple rhombohedra, the largest perfect specimen being 1.1 in. along its axis, while a larger crystal which is distorted and cleaved measures as much as 1.3 in. across. Crystals previously discovered have all been extremely small, the largest recorded, also, from the same locality, being about 0.5 in. across (E. D. Mountain, Min. Mag., 1926, Vol. 31, p. 51). Attempts to measure the cleavage angle showed most cf the crystals to be slightly composite, but some good measurements gave an average of 72°24', for the rhombohedral angle. The crystal faces did not give good reflexions. These specimens were exhibited at the South African Association for the Advancement of Science meeting at Kimberley in July, together with a fine cleavage-rhomb of Iceland spar weighing 10 lbs., which had come from the Kenhardt district, and also been acquired by the McGregor Museum.
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Transactions of the Geological Society of South Africa, 32, 27-30
The question of oreshoot extension is a most important one, not only to the geologist, but also to the mining engineer. The problem is apparent when ore reserves are estimated, and when the future development policy of the mine is being considered. Accurate sampling and the mapping of all geological features, such as dykes, faults and widths of sediments, are essential to the prediction of extension of shoots. "Impartial, detailed mapping often automatically solves many problems through the completeness of the picture presented". - Mr. Harrison Schmitt, Chief Geologist, New Jersey Zinc Company. It is too often found that winzes are started where the only apparent reason is that it is 500 feet, or a certain distance from its neighbour, whereas, by a close study of the geological features, the most economic position and direction can be determined. Dr. Reinecke read a paper before this Society on his Colour Contour Assay Plans. Since then his method has been extended to other fields. The geology of the Lydenburg District has been fully described by Dr. Wagner in several pamphlets and papers. I am indebted to Dr. Wagner for the section of one of the dunite pipes. This pipe is essentially a core of hortonolite dunite, surrounded by olivine dunite, pyroxenite and anorthositic spotted norite. The dip - 80° - is at right angles to the dip of the pseudostratification of the Merensky Reef. Contour plans of several levels have been completed. The method is as follows:- On a scale of 1:100, the exact location and the assay values in pennyweights of every sample taken is plotted on the plan. Equal ore value lines are then drawn, the intervening spaces being coloured. The platinum contents rise successively through the series from yellow to violet, the green indicating unpay. Turning now to the Witwatersrand, a rapid method of determining the direction of a pay shoot will be described.
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Transactions of the Geological Society of South Africa, 32, 31-55
Extent of area. Physiography. Stratigraphy. Tectonics
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Transactions of the Geological Society of South Africa, 32, 57-60
While dolerite intrusions in unbedded rocks almost invariably assume the form of vertical or steeply inclined dykes, sheets of Karroo dolerite in the Old Granite are known from the work of Humphrey and du Toit in Northern Natal and Piet Retief. The occurrence is so rare, however, that a few notes on similar sheets further north seem appropriate. In the north-east corner of the Ermelo District there are two dolerite sills intrusive into the Old Granite. The higher has to-day only a small extent. The lower sill, on the other hand, extends from west to east over a distance of at least 30 miles, while the width from north to south is not less than 10 miles and may be considerably more. The full extent is not known, as mapping was not continued north of Latitude 26°15', nor across the Swaziland border. In the present paper this sheet will be called the main sheet. In spite of its wide extent, the main sheet has a thickness of only 90 or 30 feet, and this thickness varies but slightly. It is sometimes duplicated, as on Glenmore 222 and Dundonald 219. On the whole the sheet is approximately horizontal, the altitude of the outcrops being round about 5,000 feet, but locally it sometimes dips at considerable angles, up to 30° or so. On steep slopes it gives rise to terraces which are often prominent features, recognisable over distances of many miles. The granite is massive, gneissose patches being very rare, and there is no conspicuous horizontal jointing or rifting. The occurrence of a thin horizontal sheet for great distances therefore seems all the more remarkable. The outcrops of the main sheet form a number of closed curves, surrounding areas in which the sheet is present below the surface.
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Transactions of the Geological Society of South Africa, 32, 61-63
On the farm Middledrift No. 191, about nine miles N.E. of Lothair Station, in the Ermelo District, a sandstone dyke occurs in the Old Granite. The outcrops were traced, with interruptions, for over a mile, but the length of the dyke is probably much greater. It is vertical and from seven to twelve feet wide. It strikes N.W.-S.E., which is the prevailing direction of the dolerite dykes that traverse the granite in large numbers. One of these occurs about 200 yards N.E. of the sandstone dyke. It is 40 yards wide and consists of hornblende-dolerite. Like the overwhelming majority of dykes in the granite, it is of pre-Karroo age. Tile sandstone dyke is cut by a sheet of Karroo dolerite, and is therefore older than the latter. The best outcrops occur in the bed of a small stream which runs along the dyke for a short distance. It is from seven to eight feet wide and stands approximately vertical where a waterfall exposes it through a height of about 10 feet. The walls are flat and smooth, and the contacts are sharp. The dyke is sometimes displaced laterally through a distance of two or three feet, and then continues again in a straight line. On its N.E. side there are several veins of the same material. The majority occur at a distance of about 14 yards from the dyke, but a few are nearer and some can be seen branching off from the dyke. Their width varies from less than a mm. to 10 cm. or so, and they behave exactly like igneous veins. They follow straight or crooked lines and are usually roughly parallel to the dyke. As a rule they seem to be nearly vertical or steeply inclined. The sandstone of the dyke is a fine-grained, compact, massive rock. It is fairly well-cemented and tough when fresh, but exposed blocks are friable and crumbling, with a harder dark brown or black ferruginous surface, resembling desert varnish. Sometimes the dyke-rock projects a few feet above the surrounding granite, and then the dark colour renders it liable to be mistaken for dolerite, even from a short distance. The weathered sandstone is generally brown or reddish-brown. When fresh, parts are cream-coloured, light grey or light brown, sometimes with a slight tinge of purple, and other parts are dark brown, the dark colour being due to the greater abundance of ferruginous (limonitic) cement. Under the microscope in thin section it is seen that quartz grains make up over 80 per cent. of the rock. They range from 0.015 to 0.8 mm. in diameter. Those from 0.07 to 0.8 mm. across are well rounded while the others, with diameters less than 0.07 mm., are sub-angular. This shows that the sand must have been of wind-blown origin.
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Transactions of the Geological Society of South Africa, 32, 65-88
Former Work and Acknowledgements. Conclusions. History. Topography. Geology. Ore Bodies. Practical Considerations
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Transactions of the Geological Society of South Africa, 32, 89-102
The notes are based upon observations made by the writers during a geological survey of part of the Warmbad District, South-West Africa, in the course of which special attention was paid to the occurrences of lead ores in the neighbourhood of Aiais. It is not proposed to discuss the general geology at length, as this will be done in the forthcoming "Explanation to the Geological Map;" attention will rather be drawn to the mode of occurrence of the mineral veins.
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Transactions of the Geological Society of South Africa, 32, xxi-xl
In last year's address the geology of South Africa was compared with that of South America, and weighty arguments were brought forward in support of the theory that the two continents were formerly close together and have since drifted apart. These arguments were based upon a great mass of geological evidence, largely the result of Dr. du Toit's personal observations both in South Africa and South America. Strong support for the displacement hypothesis of Taylor and Wegener has lately also been supplied from the northern hemisphere, where Bailey has shown that the Hercynian and Caledonian mountain systems begin to cross each other in the British Isles, and that the crossing is completed in eastern North America, which, as he remarks, "involves a recognition of some type of continental drift". (5, p. 814). "It is as if the Atlantic did not exist or, in other words, as if Wegener, after all, were a true prophet". (4, p. 674). The theory of continental drift has been widely discussed and severely criticised during the last few years. In reviewing the recently published symposium on the subject, Holmes says, "The impression that remains with me after considering all the adverse criticism is that .... when all has been said, there remains a far stronger case for continental drift than either Taylor or Wegener has yet put forward". (91, p. 433). With this opinion many will agree. I wish to discuss the theoretical aspect of the subject and shall attempt to, show that the magmatic cycles of Joly and Holmes provide the key to the solution of the mysteries of continental drift and ice ages. The existence of isostasy proves that the continents consist of lighter rocks overlying a heavier substratum which completely surrounds the globe. As the continents are continuously worn down by the agents of denudation, isostasy causes the denuded surfaces to rise up again. The rise is, however, less than the thickness removed by erosion, so that the height of the continents gradually dec
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Transactions of the Geological Society of South Africa, 33, 1-3
During the examination of a large number of asbestos prospects and properties in Southern Rhodesia, I have been greatly impressed by the amount of misdirected energy and wasted money expended in various ways upon such properties, the major portion of which would have been saved if a little thought and scientific knowledge had been brought to bear upon the various problems encountered. Having obtained all the available field evidence during the examination of almost any mineral deposit, it is necessary, in order to deduce its possibilities as an economic proposition intelligently, to obtain a working hypothesis, based upon such evidence, of its mode of origin. Without such a hypothesis it is impossible, in ninety-nine cases out of a hundred, to form any opinion as to what is likely to be encountered below the surface, or, in the case of a mine, at greater depth. I propose accordingly, first, to say a few words upon the origin of the chrysotile asbestos deposits of Southern Rhodesia. These may be divided into two main types, depending primarily upon the age of the serpentine-rock in which they are encountered. 1. Deposits in rocks of the Basement Schists. (These rocks are probably identical with those of the Swaziland System of the Union of South Africa). 2. Deposits in the rocks of the Great Dyke. (These rocks are identical with those of the Bushveld Complex). Deposits of the first type are of overwhelming importance, including as they do those of Shabani and Mashaba, whereas the only producer of the second type is the Ethel Mine, Lomagandi District, where an extremely limited, laterally, deposit occurs.
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Transactions of the Geological Society of South Africa, 33, 103-109
Some months before his untimely death, tho late Dr. Percy Wagner suggested to me that any further information I might obtain regarding the interesting new platinum group minerals which have recently been discovered in the Transvaal should be submitted to the Geological Society of South Africa. Perhaps these notes can be regarded as a small tribute to the great work Dr. Wagner did for geology in South Africa. With the exception of a short but important communication from R. A. Cooper (Journal Chem. Met. and Min. Soc. of S.A., April, 1929), the whole of the published information on this subject, including the very notable work of Professor H. Schneiderhöhn, is collected in Wagner's book (Platinum Deposits and Mines of South Africa). Since this appeared I have from time to, time obtained material from the Potgietersrust and Rustenburg mines of the Potgietersrust Platinum Company, on which further examination has been possible. For much of this material I am indebted to Mr. F. Wartenweiler consulting metallurgist to that company. As far as I have been able to determine, platinum and its allied elements occur in both districts in the following forms:- (a) Platinum sulphide (cooperite); (b) impure or crude metallic platinum; (c) sperrylite; (d) palladium antimonide (stibio-palladinite); (e) alloyed with or in solid solution in iron nickel sulphides.
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Transactions of the Geological Society of South Africa, 33, 111-133
Description: The Shale Zones; The Conglomerate Zones - The Main Reef Group, The Main Reef Leader. Origin of the System: Wave Action - Stationary Sea-level, Falling Sea-level, Rising Sea-level; Current or Stream Action - Direction of Pebble Axes; Marine Origin; Continental Origin - The Siwalik System, The Witwatersrand System - The Main Reef Leader and Similar Conglomerates, Iron Ore Conent of the Shale Zones.
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Transactions of the Geological Society of South Africa, 33, 13-18
On introducing the following notes for your consideration I wish to state that I am a mining engineer, having only a fair working knowledge of geology. I therefore ask you to treat kindly anything that may appear unusual. I have during the past two years been occupied principally in reporting on, and opening up, various asbestos propositions, and have had the privilege of visiting over thirty crocidolite and amosite occurrences in both the Prieska-Vryburg and the Pietersburg-Lydenburg areas. It is convenient for the purposes of these notes to deal with the areas separately at first.
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Transactions of the Geological Society of South Africa, 33, 19-30, 1 pl
Obituary and Bibliography.
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Transactions of the Geological Society of South Africa, 33, 31-47
A dolerite sheet on Revolt Farm, seven miles north-east of Marandellas, has long been known to show marked marginal assimilation. Mr. H. B. Maufe, Director of the Southern Rhodesia Geological Survey, drew the attention of the author to this sheet, and suggested that a description of it would be of interest; consequently, two week-end visits were made in March and June, 1928, respectively, during which a rough sketch-map of the area was made with the assistance of Mr. R. McI. Tyndale-Biscoe. The dolerite is intrusive into granite, and has the undulatory form common to many such intrusions into unbedded rock; for this reason it has been deemed advisable to term it a "sheet" rather than a "sill". The sheet is in two portions, of which the northern portion lies at a higher level than the southern and evidently represents a local transgression of the magma to a higher horizon. It is shown on the Geological Survey map of Southern Rhodesia as a hooked outcrop reaching northwards from the railway between Marandellas and Theydon, with a sharp western hook at the northern end, this hook represents the northern and higher portion from which hybridization of the dolerite was first recorded along the Marandellas-Mrewa Road.
The granite is of Archaean age; it is of the massive, non-gneissose type usually found in those portions of the bathyliths removed from the schist contact. No accurate dating of the dolerite is possible, but it forms one of numerous intrusions reaching from Wedza in the south through Marandellas to Mount Darwin in the north. These intrusions are somewhat indefinitely referred to as the "late Karroo" dolerites, and may perhaps be considered as being roughly equivalent to the basaltic lavas in the faulted areas to the north and south, viz., the Zambezi and the Limpopo Valleys. Whatever exact age may be assigned to them in time, there is no genetic connection between them and the granite into which they are intrusive.
The Northern Portion of the Sheet.
- This portion of the sheet forms the top of a flat ridge carrying the Marandellas-Mrewa Road. The red soil derived from the dolerite has been extensively cultivated, and continuous outcrops are rare except round the margin of the intrusion, which corresponds roughly with the crest of the ridge. This portion of the sheet has been eroded very nearly into two separate pieces, a sharp downward pitch westwards having saved it from complete disseverment. At its narrowest part, and along the presumed axis of the pitch, there is a line of granite and hybrid boulders standing above the surroundings by a few feet. This line of boulders apparently represents a relic of the original roof, which is otherwise absent. The sheet here cannot, therefore, have been very thick - estimated at about 30 feet - and it is of interest in view of the extent to which hybridization has taken place. Hybridization is seen to its fullest extent on the northern extension or lobe, where the ground is covered by large
boulders of dolerite carrying up to 50 per cent. of granite xenoliths. All stages of digestion are seen down to otherwise apparently "clean" dolerite carrying glassy blebs of quartz. The largest xenolith measured was some 18 inches across. Hybrid rocks can, however, be picked up at intervals round the whole margin of the intrusion where the absence of soil favours it, these outcrops are chiefly boulders, solid "living" rock being comparatively scarce. Associated with the hybrid is cup-weathering, in which the hollows indicate the former position of xenoliths.
The Southern (Main) Portion of the Sheet.
- Dolerite is exposed on the southern flank of an eastward-flowing stream and on the western flank of a small northern tributary. The latter stream has evidently cut downy arcs and sideways (westwards) along the lower contact, exposing a smooth, sparsely vegetated and easy slope of granite to the east, and having a more abrupt slope of dolerite and associated rocks to the west, well-covered with soil and grass and crowned by a miniature scarp of hybrid and granite. Observations were restricted to this western flank of the northern tributary where the stream has eroded through the whole thickness of the sheet. In ascending from the stream to the crest, the following rocks were observed in order: altered granite, olivine-dolerite, perioditite, dolerite, hybrid rocks, altered granite, granite. Unfortunately, nothing remotely approaching a continuous section is provided in the area examined; any conclusions which may be based on the petrography of specimens from scattered outcrops must therefore be necessarily tentative and open to modification or rejection in the future.
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Transactions of the Geological Society of South Africa, 33, 49-59, 1 pl
Obituary and list of publications.
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Transactions of the Geological Society of South Africa, 33, 5-12
Dr. Reinecke, has asked me to make a few notes on amosite asbestos to be presented at this meeting. I will endeavour to interest you with a few of the salient points pertaining to this remarkable mineral.
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Transactions of the Geological Society of South Africa, 33, 61-63
In a paper recently presented before the Royal Society of South Africa, the writer has described a new species of the Ammonite genus Placenticeras which he had the good fortune to find near Bogenfels whilst on a short visit there with Dr. A. L. du Toit and Dr. Knetsch, geologist to the Consolidated Diamond Mines of South-West Africa. The occurrence in that locality of this Upper Cretaceous ammonite associated with numerous specimens of an Upper Cretaceous species of Exogyra definitely confirms the presence of Upper Cretaceous marine beds in the Namib littoral. In a paper read before this Society in 1909, Dr. Merensky recorded from near Elizabethbucht the presence of three species of fossil shells common in the Campanian deposits of Pondoland, and postulated thereon an extension of the Upper Cretaceous sea along the coastal belt of that area. Possibly owing to the fact that the fossils in question were not made available for examination, and that their exact locality was never re-discovered, doubt was cast upon Merensky's hypothesis; and opposition to it became strengthened when examination of fossils from Bogenfels (including Turritella, Mactra, Ostrea, etc.) by Böhm led their investigator to place the age of the beds as Tertiary - first Miocene and then, with more material at his disposal, as Middle to Upper Eocene. This new discovery, therefore, places Merensky's statement that Upper Cretaceous marine beds occur within the area within the bounds of certainty. The outcrop which yielded the Placenticeras and Exogyra is a small one of buff-coloured sandy limestone crowded with shells of the latter genus and lying a few hundred yards south of the exposures which have yielded the fauna described by Böhm as Eocene, and at a height of about 10 metres below these exposures. These latter it is proposed to call for convenience the Turritella-beds, while the lower will be called the Exogyra-beds.
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Transactions of the Geological Society of South Africa, 33, 65-87
Dr. Reinecke, Past President of the Geological Society, of which I have the honour to be a recent member, in his anniversary address, 'The Relations of Geology to Industry" referred in general to the applied geophysics of today. In connection with his address permit me to give you some further illustrations and make a few remarks on one of the most important of the four geophysical methods. The preponderance of rather old formations and extensive granite masses in the geology of South Africa is the reason why these modern methods of economic geology have so far found very little application here. While in U.S.A. more than 300,000 square miles are investigated by torsion balances and 150,000 square miles have been examined by seismometers, these two methods in South Africa, as far as my knowledge goes, have been applied but once, i.e., in the area of Inyaminga. The great possibilities for these methods, in Mesozoic oil-bearing sedimentary areas as, for instance, the Gulf-coast of Texas or the sedimentary plain of Northern Germany, are absent here almost completely. Although both these methods may be used in geologically older areas for the successful solution of certain mainly tectonic problems, so far in South Africa only the electric and magnetic methods of applied geophysics have been used. The radioactive and geothermic measurement methods are not yet sufficiently developed and the possibilities for their application are too small. As for the geological and mining problems in South Africa, the electric and magnetic methods of investigation are the most suitable. and as the magnetic method has many advantages over the electric method and probably will here find much more application than heretofore, I have selected these magnetic methods for the subject of my paper today. Considering the vastness of the field presented by magnetism today it is only possible to give a general introduction into the present state of this auxiliary method of modern economic geology.
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Transactions of the Geological Society of South Africa, 33, 89-102
The Makarikari region, in the north-eastern part of the Bechuanaland Protectorate, is one about which very little geological information has been published. This fact is the justification for these notes, which are based on a hurried reconnaissance left by the Imperial Secretary, Capt. the Hon B. E. H. Clifford, C.M.G., M.V.O., during parts of June and July, 1929. Captain Clifford, under very trying circumstances, performed some valuable astronomical work upon which the accompanying map is based (Fig. 1). He has recently dealt with the geographical aspects of the region in a paper to the Royal Geographical Society. Other records are the work of early travellers, and were mainly published in the last century. Dr. Livingstone crossed the western part of the salt pan country about 1851, and Schultz traversed the eastern border of the Makarikari along the Serowe-Nkate Road in 1884. These, and other records, are summarized by Passarge, who, though he traversed the Botletle River and the little Makarikari, did not visit the great Makarikari salt pan itself. The Botletle River has more recently been described by the late Professor E.H.L. Schwarz.
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Transactions of the Geological Society of South Africa, 33, xxiii-xlii
The purpose of this paper is to review the main lines along which the science of geology has been applied to economic problems. The most obvious line of application is that bearing on the discovery and development of mineral deposits and of petroleum and water. Others that are not as well known but have yielded equally important results are geological studies bearing on civil engineering and the investigation of deposits of stone, sand and clay for use in structural work. The uses to which a science can be applied depend in a great measure on its development. There is a qualitative stage during which new facts are discovered. A quantitative stage during which masses of facts bearing on any problem are available for the verification or modification of hypotheses, and there is a prophetic stage in which the consequence of certain conditions or combinations of conditions can be predicted with certainty. In all stages of a science there must be qualitative work, in some sciences much quantitative work has been done, in others the science has advanced far into the prophetic stage. In chemistry, for instance, if certain quantities of two salts are added to each other under given conditions of temperature and pressure, the results can, in many cases, be predicted with certainty. The science has passed in certain of its phases from a qualitative through a quantitative to the prophetic stage. In geology an increasing amount of data is being applied in a quantitative way to the verification of hypotheses, and the soundness of the conclusions arrived at increases with the degree to which the quantitative method is employed. Much remains to be done, however, before geology can attain to a scientific status, that is, equal to that of chemistry. The following is a very brief outline of the various phases of economic geology, of the problems encountered, and of some of the methods employed in their solution. More space is devoted to the discussion of recent lines of development, such as geology applied to reservoir construction, and geophysical prospecting, than to other, and in some cases more important, phases of the subject.
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Transactions of the Geological Society of South Africa, 34, 1-18
One of the most notable developments of geology during the last decades has been the slow and gradual recognition that ice-ages have at intervals chilled the surface of our planet long before the advent of the last Pleistocene period of glaciation, from the effects of which our earth appears to be just emerging. The remarkable exposures and excellent descriptions of the South African Dwyka Tillite have played an important role in furthering and finally establishing the general acceptance of world-wide pre-Pleistocene periods of glaciation. An outstanding and somewhat unexpected result of the invigorated search for fossil glacial deposits down the geologic time-scale has been the accumulating evidence to show that they appear to be most abundant, even crowded, in the ancient sediments forming the surface of our earth. Thus in Canada, where the largest area of pre-Cambrian rocks in the world is exposed, according to Coleman ice-action has been proved or shown to be probable in all the main sub-divisions of pre-Cambrian rocks. The amount of evidence of glacial work in these ancient periods is all the more surprising "when one considers the age of these rocks and all the possibilities of the destruction or permanent burial or submergence of the tillite, or else of its complete metamorphism into schists". (Ibid., p. 240.) While not very long ago it was generally held, that the climate of our globe had experienced a gradual decrease in temperature, culminating in the (then only known) Pleistocene ice-age", it now appears probable, that the pre-Cambrian was the coldest part of the earth's history, with glaciers at work within every one of its main sub-divisions. Part of this effect may, however, be due to perspective, the more distant glaciations being apparently crowded together, because we do not appreciate the intervals between them". (Ibid., p. 240.) Glacial action being mainly chronicled by land-deposits and the bulk of preserved and investigated sediments being deposited in the sea, it is obvious that we must look to the ancient, long-established, rigid land-masses, such as the Canadian shield and the South African sub-continent, for the most complete record of ice-ages. Having passed through the stormy stage of its development at a very early date of the earth's history, South Africa presents to the investigator a very long succession of continental and shallow-water deposits dating right back to pre- and early Proterozoic times and only rarely interrupted by marine invasions. It is not surprising, therefore, that South Africa already presents a formidable array of proved and well-established ancient tillites. With the extension of geological research into the more remote and less known areas, this record, judging by past experience, will in all probability be still further augmented and make South Africa into what it is fast becoming - the classical country for investigations in ancient glaciology. The following short paper is intended to serve as a
brief description of a peculiar group of rocks belonging to the Fundamental Complex of South-West Africa and possessing all the characteristics of a true glacial deposit, and, it is hoped, will add another well-established tillite to South Africa's already formidable list. It will be shown that the tillite to be described presents reliable evidence of an ice-age older than any yet recorded from South Africa, and is in all probability more ancient than the oldest, well-established glacial deposit hitherto known, i.e., the Huronian Cobalt Tillite of Canada.
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Transactions of the Geological Society of South Africa, 34, 107-127
The prime object of this paper, is to expound the idea of a metamorphic origin for the pyroxenitic assemblage, a view that differs vitally from those advocated by both Drs. A. L. Hall and S.J. Shand. While much of the arguments may seem of a rather academic nature, it is only fair to point out that this problem, or some variant thereof, is one that has obtruded itself from time to time in the science of geology, particularly in the case of the extensive apatite deposits of Eastern Canada, and that it furthermore deals with a branch of metamorphism, which has not received the attention that it undoubtedly deserves.
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Transactions of the Geological Society of South Africa, 34, 129-150
Although small in size compared with similar areas in Australia and North America, the Artesian Area of South-West Africa is of economic importance to that country, as by reason of its situation on the western edge of the Kalahari desert it has rendered habitable and potentially productive a strip of that scrub covered sand, which before the discovery of the water was considered as only fit to be left to the game and the Bushman. Further, the discovery of the water at this spot has encouraged the search for more, and so the surrounding areas have been drilled and opened up for the settler. The first boreholes which gave flowing water were drilled by the German Water Boring Department while endeavouring to find out whether the Upper Karroo sediments were coal bearing. After the Great War the area was further developed, and many more holes were drilled by the Irrigation Department of the South-West Administration.
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Transactions of the Geological Society of South Africa, 34, 151-162
The Zoutpansberg range of the Northern Transvaal has not yet been mapped by either the Geodetic or the Geological Survey, and much of it is comparatively unknown country, falling within native territory, and not readily accessible. The range, which consists of rocks of the Waterberg System, extends for more than 100 miles in an E.N.E. direction from Louis Trichardt. In width it does not exceed 20 miles, but rises several thousand feet above the surrounding country and presents bold escarpments on both north and south. It is generally recognised as being composed of several parallel ranges. Dr. E.T. Mellor, in 1908, investigated the north-western portion and found clear evidence of faulting on the northern margin. He noted the repetition of beds from south to north and concluded that strike faults had produced the three parallel ranges. Mr. T.G. Trevor, in 1917, paid a brief visit to Lake Funduzi in the central part of the range. He suggested that the deep erosion of an old plateau had produced the longitudinal valleys of great depth and with precipitous sides. Dr. A.W. Rogers whilst on a journey around the eastern end of the range in 1923, remarked the discrepancy between the trend of the range which is E.N.E. and the strike of the beds which is E.-W. or even S. of E. He found, also, evidences of post-Karroo faulting on the N., E. and S.E. of the range, and, further north, strips of Karroo rocks in older gneiss, the former bounded by fault planes parallel to the Zoutpansberg. He therefore supported Dr. Mellor's view that the multiple range was produced by faulting. The present notes are the result of observations made by the writer during an excursion for science students of the University of the Witwatersrand in July of this year. Unfortunately very adverse weather conditions, which greatly hampered photography and scientific work generally, were encountered. The writer ventures to present them, imperfect as they are, since they bear on the questions of the repetition of volcanic rocks in the Waterberg System and on faulting in the central part of the range, particularly around Lake Funduzi. The party proceeded eastward from Louis Trichardt for about 27 miles along the main road at the southern foot of the range, and then branched off to visit the forest station at Entabene. The route lay across ancient granite and gneiss. The plantations lie at altitudes between 4,000 and 5,000 ft. The branch road leading to them is very steep and is cut, from the base of mountain, through a bluish-green fine-grained volcanic rock, exhibiting vesicular and porphyrite structures and resembling, in hand specimens, an andesite of the Ventersdorp System. The contact between Waterberg sandstones and lava lies at an altitude of 4,500 ft. on the crest of the hill behind the chief forest officer's house. Coarse reddish grits and fine pebble conglomerate were noticed among the basal sedimentary rocks. A thick dyke of very dark and apparently fresh dolerite traversed the
sedimentary beds near the contact.
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Transactions of the Geological Society of South Africa, 34, 163-164
The water issues from a narrow fissure in a dyke, which is situated about 2,680 feet below the surface. The pressure at the point at which the fissure was intersected is negligible, and the volume small. The temperature of the air in the shaft varies from 62° to 68°, according to whether the ventilating fan is in operation or not, while the water in the fissure was found to be 77°. An attempt was made to gauge the rock temperature in the vicinity, but conditions militated against proper investigations being carried out, and the best that could be done under the circumstances was to drill 2-ft. holes in the solid rock in a dead end of a station, about 250 feet above, the fissure, where the cooling effect of the atmosphere and ventilating fan were at a minimum. The holes so drilled were filled with water and plugged, and after 48 hours the temperature of this water was found to have a mean value of 68°. However, similar tests carried out some 2,000 feet further west on the same elevation showed the mean temperature in the main workings of the mine to be 77°, thus coinciding with the temperature of the water in the fissure. It has been stated that both the volume and temperature of the water have fallen since the fissure was first encountered, but there is no means of proving the truth of this statement.
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Transactions of the Geological Society of South Africa, 34, 19-58
Chapter 1: Description of the deposits (South West Africa, Cape Province). Chapter II: Palaeontology of the deposits. Chapter III: Correlation of the deposits.
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Transactions of the Geological Society of South Africa, 34, 59-60
Seasonally banded or varved shales are known to occur with the Dwyka Tillite in Natal, the Cape Province, and South-West Africa, but, as far as I am aware, their presence in the Transvaal has not been recorded. An occurrence in this province, near Middelburg, is, therefore, perhaps worthy of notice. On the farm Klipplaatdrift No. 52, about 17 miles N.N.E of Middelburg, and a few miles north of the northern extremity of the main body of Karroo beds, there is a small outlier of Dwyka tillite and shales, between the Selons River and the western boundary of the farm. Some of these shales, exposed in a shaft recently sunk, show well-marked varves. The outcrop of the tillite is marked by a roughly circular ring of boulders of red bushveld granite, old grey granite, quartzite, weathered schist and other rocks. Within this ring, which is only about 200 metres in diameter, the ground is flat and bare, without boulders or outcrops. Two shafts, each about seven metres deep, have been sunk within the circular area, one near the centre and the other beside the ring of boulders. In the outer shaft there is tillite from top to bottom, but in the other the tillite is overlain by 4½ metres of shales and mudstones, followed by one metre of subsoil and soil. The tillite is of the usual type, consisting of rounded pebbles and angular fragments of various rocks in a blue-grey argillaceous-sandy matrix. The transition from tillite to shale is gradual, through gravelly mudstone, gritty mudstone or shale, and sandy shale, the inclusions becoming fewer and smaller, while the grain of the matrix grows finer and banding appears. The banding is caused by thin fine-grained layers alternating with thicker coarser-grained layers, a coarse and a fine layer together representing one year's deposit. The lowest varves are thick, sometimes as much as 50 mm., or even more, but the thickness decreases upwards. About 30 cms. above the tillite the thickness of the varves ranges from 5 to 25 mm., while the sandy components of the rock have all but disappeared. The varves now rapidly become thinner, and 60 cms. above the tillite their thickness averages 2 mm. or less. From here upwards the thickness varies between 0.4 mm. and 20 mm.
In the lower part of the deposit the coarser layers are somewhat sandy and the banded rock is tougher than higher up, where it is a fragile, brittle mudstone, breaking in all directions equally easily with a curving fracture which can be described as "pseudo-conchoidal". When exposed to the air in the wet state in which it occurs in the shaft it crumbles and falls to pieces almost immediately, but if it is allowed to dry very slowly, wrapped up in paper, for example, comparatively large specimens remain intact. The banded mudstone consists of narrow dark greenish-grey bands alternating with wider bands of a dull dirty-yellow colour. The dark bands are from 0.1 to 0.4 mm. wide, while the width of the light bands varies from 0.2 mm. to 20 mm. Under the microscope
the dark bands are seen to consist of very fine-grained material of the clay grade (0.003-0.01 mm. in diameter), while in the light bands coarser material predominates. The latter were, therefore, laid down in summer, the former in winter. The average thickness of the varves is about 5 mm. The total thickness of the deposit, which is 15 metres, therefore, contains about 300 varves, showing that for 300 years after the ice-sheet began to retreat from this point there was a marked difference between the summer and winter sediments. The sediments were apparently deposited in a glacial lake fed from the melting ice, and the decrease in the size of the grain from the tillite upwards corresponds to a decrease in the turbidity of the water due to the retreat of the edge of the ice-sheet. The conspicuously banded mudstones are overlain by very fine-grained, extremely fragile, dull-yellow mudstones or shales, showing a faint banding - almost too faint to be seen. These shales must have been deposited some considerable distance from the melting ice, after all but the finest particles had been dropped from, suspension. The particles were so small that the difference between the summer and winter deposits became inconspicuous. The thickness of these upper faint varves is generally between 1 and 2 mm. The whole bed, which is nearly 3 metres thick, is, therefore, the accumulation of about 1,500 years. When varved shales weather, the banding which is so conspicuous in the fresh rock generally becomes indistinguishable, and the crumbling fragments exposed at the surface resemble ordinary shales or mudstones. It is, therefore, highly probable that in the course of future work varved deposits will be found in many new localities in South Africa.
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Transactions of the Geological Society of South Africa, 34, 61-80
The following notes are intended to serve as a brief description not only of the actual deposits of rock-salt and occurrences of high-grade brine in the Swakopmund area from an economic point of view, but also of the younger and recent history of that portion of the coast of South-West Africa. In a country where ranching and the production of skins will always play an important role in its development, a supply of cheap salt of good quality, both as a lick and for curing skins, is essential and it is to be hoped that in the future the vast supplies of rock-salt provided by South-West Africa itself will be drawn upon to a greater extent than has hitherto been the case. Apart from their commercial possibilities, the study of the most youthful deposits along the present shore also throws interesting light on the physico-chemical process of salt-precipitation.
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Transactions of the Geological Society of South Africa, 34, 81-106
Palabora is the name of a district lying just north of the junction of the Selati and the Olifants Rivers in the North-Eastern Transvaal, some fifty miles east of the Great Escarpment or Drakensberg. The general elevation of the district is 1,100 to 1,200 feet, as against 4,000 to 5,000 feet above the Escarpment. The surface features are those typical of the Low Veld: a gently undulating to nearly flat country relieved only by an occasional granite kopje, the whole thickly covered with bush and low trees. Geologically the region is one of ancient schists and granites in which there are many reefs of mica and corundum-pegmatite. Crystalline limestone appears in various places among the schists, and at Lulu Kop, the centre of the Palabora district, a mass of highly metamorphic limestone forms a hill about 300 feet high, covering an area of almost a square mile. The nearest unaltered sedimentary rocks appear fifty miles south-west of Palabora, in the Great Escarpment, and again forty miles east, in the Lebombo monocline. It is clear that the whole region has been deeply eroded since Karroo time. Palabora made its first appearance in geological literature in 1895, when E. Cohen described a melilite-augite rock from the "Umgebung der Palabora Erzablagerungen". This rock was given to Cohen by F. Jeppe, of Pretoria, and nothing is recorded about the manner of its occurrence in the field. Twelve years later, S.M. Tweddill described some rocks from the Leydsdorp district in the annual report of the Geological Survey for 1906. One of these rocks vas a dark-green pyroxenite like those to be discussed presently. E.T. Mellor described the geology of the district about Haenertsburg and Leydsdorp in 1907. The limestone of Lulu Kop and the ancient copper workings there were well described, and brief reference was made to the igneous rocks surrounding the Kop. Mellor recognized the presence of pyroxenite and syenite, and wrote: "it appears that there is a transition from the granites
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Transactions of the Geological Society of South Africa, 34, xxv-xxx
The Anniversary Addresses of Presidents of this Society have, in the past, been of such importance to the science of geology as to make it extremely difficult for one who is not a geologist to maintain the standard set. I must, therefore, seek your indulgence for choosing a subject which is not of direct importance to geologists and for clearing with this subject more from the point of view of the mining engineer than of the geologist. It is, however, accepted that the spheres of work of the geologist and of the mining engineer are closely related and interdependent and, in these notes on the development of ore deposits in South Africa, I hope to indicate how closer co-operation might be obtained to their mutual advantage and for the benefit of South Africa.
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Transactions of the Geological Society of South Africa, 35, 1-28
Historical. Mode of Occurrence. I. The Hot Springs of Gross Windhoek. - Table of Temperature, Nature of Water with tables of Analyses, Radioactivity of Water, Nature of the Spring-Fissure, Nature of the Fissure-filling. II. The Hot Springs of Klein Windhoek - Mode of Occurrence, Table of Temperatures, Nature of Water. III. Origin of the Hot Springs
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Transactions of the Geological Society of South Africa, 35, 115-118
The Chuos Tillite was described by the latter author from Western Damaraland, and its discovery in the Rehoboth and Windhoek districts of great importance, not only in showing its wide distribution in a constant horizon, but also since it here includes a facies for which no other explanation than glacial activity is reasonably possible
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Transactions of the Geological Society of South Africa, 35, 119-124
The presence of rock-phosphate in an area near Langebaan Road has been known for some years. The writer has had two opportunities of examining the deposits, one in 1997 and one a few months ago, and it is thought that the following notes may prove to be of interest. The area examined comprises part of the farm Langeberg, near Langebaan Road Station, on the railway from Capetown to Saldanha Bay, and is approximately 110 miles from Capetown by rail. The terrain consists of flat country about 105 feet above mean sea-level, bounded on the south-east by a low ridge and on the north-west by a lower ridge lying between Langebaan Road and Langeenheid Siding. The flat ground thus forms a belt striking approximately north-east to south-west.
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Transactions of the Geological Society of South Africa, 35, 125-188
Chapter I - Felsites of the Premier Mine Type - (1) The basic rocks. (2) The "intermediate" belt. (3) The felsites. Discussion of the Observations - (1) The fine grain of the felsites. (2) The transition and the accompanying alteration. (3) The problem of magmatic differentiation in sity. (4) The origin of the rocks in the sill and the felsites in general. (5) The origin of the quartz-plates. (6) The genetic relationships of the Premier Mine type of felsites. Chapter II - Normal Felsites of the Bushveld Complex and Related Acid Rocks - (1) On a traverse across granite, granophyre and felsite. (2) Other analyses of felsites and granite. (3) Classification of the Bushveld felsites. (4) The affinities of the acid Bushveld rocks. (5) The relationships of the acid member of the Bushveld. Chapter III - Notes on the Norite-body - (1) Analyses of rocks from the norite-body. (2) The mode of intrusion and the differentiation. Chapter IV - Comparison of the Bushveld with other Localities - (1) The Duluth Lopolith. (2) Pigeon Point, Minnesota. (3) The complexes of Mull and Ardnamurchan. (4) Other occurrences. (5) The Breven Dyke, Sweden. (6) The norite-micropegmatite of Sudbury
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Transactions of the Geological Society of South Africa, 35, 191-192. 1 pl
The writer was recently given the opportunity of examining a small vein in the southern part of Government Gold Mining Areas, which contained minerals not of common occurrence in the mines of the Witwatersrand. The vein was found in the south-east section at a depth of about 3,700 feet. There the beds of the Main Reef Series dip to the south at about 12°. They are intruded by a basic dyke, referred to as the Van Ryn Deep dyke, which strikes roughly east-west and dips 45° to the south. At the contact of the southern face of the dyke and the Witwatersrand beds, the Main Reef Leader, the hanging wall quartzite and the footwall shale, are all dragged over and dip for a few feet at a high angle to the north. The small vein referred to occurs along this contact. The vein, in the form of a narrow elongated body, was approximately 15 feet long, extending down the upper surface of the dyke, about 12 inches wide and about 6 inches thick. It consists predominantly of minute aggregates of chlorite, giving the rock a greenish-black colour with a compact and dense appearance. The following properties of the chlorite were determined. Biaxial positive; α 1.609, β 1.609, γ 1.614 (all values ± .003) 2V very small, slightly pleochroic, with X and Y greenish-yellow, and Z very pale-brown. Z approximately normal to 001. d < v slight. These properties correspond closely to the variety of chlorite listed as prochlorite by Larsen. In addition to the chlorite, cobaltite is present in fairly large amounts. It is typically silver-white in colour, and occurs in large irregular masses showing no crystal outlines. One or two small isolated crystals, however, have been observed. Oxidation has produced a small amount of erythrite in some of the specimens examined. Well-defined crystals of apatite occur distributed in the chlorite. These range from microscopic size up to individuals 95 mm. x 20 mm. in cross section. Running through the apatite are numerous minute veinlets of quartz and chlorite. The only other occurrence of apatite in veins associated with the Main Reef Series that has been recorded was found in the Jumpers Deep Gold Mine, under somewhat similar conditions.
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Transactions of the Geological Society of South Africa, 35, 193-196
The pre-Cape sediments are divided into three groups, the Malmesbury Beds, the French Hoek Beds, and the Klipheuvel Beds, of which the first is the oldest and the last the youngest. In the area under discussion, the Malmesbury sediments consist essentially of argillaceous beds (clay-slates), which have undergone conversion into spotted slates and hornstones by the thermal metamorphism consequent upon the intrusion, of granite. Quartzites play a subsidiary part in the series. At one locality - Blaauwberg Strand - there has been discovered an intercalated band of volcanic rocks, consisting of highly-sheared greenish slaty amygdaloidal lavas which lack quartz phenocrysts, and can be most probably classed as trachytes showing flow-structure, and of fine-grained devitrified obsidian, with irregular veins of reddish ash containing small angular fragments of quartz, and impersistent and irregular bands of agglomerate. The exposure is an isolated one, and no similar occurrence has been recorded in beds that undoubtedly can be classed as Malmesbury.
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Transactions of the Geological Society of South Africa, 35, 29-36, 3 pl
In a previous paper read before this Society I have given a brief description of the peculiar domed limestones of the Campbell Rand Series (Dolomite Series) exposed in the bed of the Hol River, near Boetsap, in Griqualand West. A recent visit to the same neighbourhood revealed that the rocks are more varied and interesting than I had supposed. It is particularly to the frequent occurrence amongst them of stromatolitic or algal limestones that I desire in this paper to call attention.
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Transactions of the Geological Society of South Africa, 35, 37-67
I. Introduction. II. Physical Features. III. Geological Formations. IV. The Granite. V. Table Mountain Series. VI. Karroo System - 1. Dwyka Series, 2. Ecca Series. VII. Karroo Dolerite. VIII. Cretaceous System. IX. Pleistocene System - 1. Bluff Beds, 2. Boulder Beds. X. Recent Sediments - 1. Red and Brown Sand, 2. Alluvium, 3. Dunes and Beach Sand. XI. Geological Structure. XII. Post-Cretaceous History - 1. Pleistocene Movements, 2. Recent Events - (a) Raised Marine Terraces, (b) Geological History of Durban Bay.
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Transactions of the Geological Society of South Africa, 35, 69-84, 2 pl
The belt of hilly country lying beneath the southern slopes of the Zwartberg Mountains in the Oudtshoorn District of the Cape Province, is formed by a series of quartzites, slates, limestones and other rock-types of pre-Cape age. The discovery of the now famous Cango Caves in one of the larger of the many limestone formations has focused much attention upon the district, which each year is visited by hundred of tourists. Named the "Cango Beds" by Corstorphine in 1898, these pre-Cape rocks were taken to represent a facies of the Malmesbury Beds, but though they exhibit many characteristics in common with those formations, the Cango Beds also present many unique features. In the present work an attempt has been made to obtain a more detailed knowledge of their nature and field-relationships, with a view to establishing their stratigraphical succession and instituting a closer correlation with other formations in South Africa than has hitherto been possible.
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Transactions of the Geological Society of South Africa, 35, 85-96
While investigating the, salt-deposits of the Cape Cross Pan, the writer, in 1930, mapped its surroundings and encountered two interesting groups of igneous rocks. The first comprises rocks belonging to the Kaoko eruptive cycle of uppermost Karroo (Stormberg) age, the other consists of alkali-rocks intruded into the former in post-Karroo times. Brief reference to the first group of rocks has already been made by Reuning in several publications dealing with the Kaoko-Sediments and Lavas of the southern Kaokoveld. In a more recent paper he has communicated analyses of the three main rock-types. Mention of the Red Granophyre is further made by Du Toit in his "Geology of S.A.", p . 261. To Reuning we also owe fossil evidence of the Karroo-age of these rocks.
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Transactions of the Geological Society of South Africa, 35, 97-113, 2 pl
This paper is the outcome of an examination in November and December, 1930, of the South-West Africa lepidolite deposits. The continued interest in these deposits, and the fantastic newspaper reports, with their consequent numerous enquiries, make its publication a matter of public interest.
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Transactions of the Geological Society of South Africa, 35, xxv-xxxiv
Two years ago the retiring President, Dr. L. J. Krige, gave us an address on "Magmatic Cycles, Continental Drift and Ice Ages", and dwelt upon the hypotheses upon which the assumptions were made to account for these phenomena. The geologist concerns himself with the constituents of the crust of the earth and the processes by which its form is altered. His brother, the geodesist, by measurement endeavours to arrive at the true figure of the earth, and by this means is in a position to render the geologist considerable assistance. The geologist has incontrovertible evidence that the outer surface of the earth is continuously moving from place to place. The geodesist has shown by measurement that the earth is in the form of an ellipsoid of revolution. Arcs of meridian have been measured at various times in different places on the earth's surface. These measurements have indicated that the length of a degree diminishes from the equator to the pole, and hence that the polar is shorter than the equatorial diameter. The same proof is forthcoming by observing the time of swing of the pendulum. It may be shown that as the pendulum alters its position from the equator to the pole, the time of swing is accelerated, indicating that the polar is shorter than the equatorial diameter of the earth. The procedure in measuring an arc of meridian consists in first measuring a base line with the greatest precision possible, and by a series of suitable triangles connecting the ends of the arc, and thus determining accurately the distance between them. At the end of the chain a check base is measured with similar precision to the original to test the accumulated effect of the small errors of observation in the angles and to serve as a means of adjusting the values thereof. At each end of the arc very careful observations are made astronomically to determine the latitudes and longitudes of the end points, as well as the azimuths of lines proceeding from these points. Thus, the tendency of these errors of observation to cause a slew in the general direction of the triangulation net is obviated. When a triangulation net has been adjusted, the latitudes and longitudes of the apices of the individual triangles may be determined from the lengths and directions of the lines joining them. Differences are usually found to exist between the calculated and observed latitudes and azimuths. This indicates a difference between the calculated and observed directions of the plumb-line. We may digress here to show why this is so. In determining latitude astronomically, we endeavour to obtain the distance of the pole from the horizon, or more commonly the complement of this angle which is the angular distance between the pole and the zenith. If there be a deflection of the plumb-line, the spirit-level of the instrument will be deflected to the same extent, and hence our observations will be vitiated so that the observed latitude will not correspond to the true latitude. The difference
will be equal to the angle between the observed and true zenith. From observations for azimuth of lines to east and west points, we may find the deflection in that direction. Hence, with these two components we may find the resultant direction between the observed and true zenith. The irregularities in the surface of the earth and the unequal distribution of mass of the material composing it cause the deflection of the plumb-bob and the resultant intensity of gravity.
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Transactions of the Geological Society of South Africa, 36, 1-28
A more or less circular outcrop of the so-called "Old Granite of the Transvaal" occupies an area about 28 miles in an east-westerly and 20 miles in a north-southerly direction, just north of Johannesburg. Except on the south-west and the east, where pre-granite schists form the margins, this rock-mass is surrounded on all sides by younger formations: the Witwatersrand System in the south, a small portion of the Ventersdorp Beds in the east, and the Black Reef series towards the north. All these dip away from the central granite-core. To the fieldwork of A. L. Hall and the late H. Kynaston in the beginning of this century, we owe the existence of a map of this area on a scale of 2.347 miles to the inch, appearing on two different sheets, issued by the Geological Survey of the Union of South Africa. This map was taken as a basis for the map accompanying this paper. A grid on the map serves for orientation.
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Transactions of the Geological Society of South Africa, 36, 101-112
Severe earthquakes are rarely felt in this country and the importance of the recent shocks in Zululand has, therefore, been somewhat overestimated in the area principally affected. Although its destructive power was comparatively slight, the energy of the Zululand earthquake far surpassed that of the great majority of South African occurrences, and an account of the effects observed, therefore, seems desirable.
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Transactions of the Geological Society of South Africa, 36, 113-116
Some years ago one of the writers was shown a very interesting area in the Sub Nigel Mine, where extensive changes had taken place in the character of the Main Reef Leader. The specimens obtained at the time have recently been carefully examined, and show the presence of the mineral monazite, which has not previously been found in the Witwatersrand mines. In the actual locality where the mineral was found, Stope No. 26 3A Under, the exposed contact, between the reef and the footwall, was extremely irregular, due both to minor folding and to undulations in the surface of the footwall shales. This resulted in considerable variation in the thickness of the reef over short distances. The average thickness of the conglomerate reef was about thirty inches, but over a length of about twenty-one feet, where the reef had been entirely replaced, its original thickness must have varied between one and six inches. The Main Reef Leader in this area shows, under the microscope, a certain amount of replacement by chlorite and sericite, but still maintains the essential appearance and characters of a conglomerate. Over the length of twenty-one feet previously mentioned, however, where the thickness is considerably reduced, the replacement has been so complete that the character of the original rock is entirely absent, and it is changed to an aggregate consisting almost entirely of chlorite and sericite. The colour of the rock is a dark greenish black, and its texture is fine grained, dense and compact. Only rarely may a small fragment of an original pebble be seen. This complete replacement, in this case, is probably due to the much narrower channel through which the solutions were suddenly forced to pass, while they were depositing the chlorite and sericite, at the same time as they were removing the conglomerate in solution.
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Transactions of the Geological Society of South Africa, 36, 117-119
The object of this note is to place on record the occurrence of cinnabar on the farm Bynestpoort No. 520, Pretoria District, about 20 miles N.E. of Pretoria, to which attention was drawn by samples sent to the Geological Survey for identification by Mr. P. A. J. Bodenstein. As far as can be judged at present, the occurrence is not of any economic importance, but it is regarded as worthy of note on account of the fact that it is only the second authentic occurrence of the mineral cinnabar that has been recorded in the Union of South Africa. The other is that near Hectorspruit, in the Barberton District, described by A. L. Hall (Geological Survey, Memoir No. 9, p. 312). As will be shown later, this occurrence is probably genetically related to the intrusive felsites of the Premier Mine area, and, from this point of view, is also of importance as it is the first time that cinnabar has been found in association with any member of the Bushveld Igneous Complex, thereby adding another mineral to the already long list of minerals formed during its accompanying period of mineralisation. The cinnabar occurs in and adjoining a brecciated zone in the Magaliesberg quartzites, which occupy the high ground immediately north of the course of the Pienaar's River, which runs through Bynestpoort from east to west.
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Transactions of the Geological Society of South Africa, 36, 121-136
The main purpose of this paper is to demonstrate by means of a detailed description of two widely separated sections that the rocks of the Dolomite Series, and its equivalent in Griqualand West, can be arranged into groups indicative of varying conditions of deposition within a general shallow water environment. The sections studied are one near Boetsap, in Griqualand West, and the other about 200 miles distant on the western Witwatersrand.
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Transactions of the Geological Society of South Africa, 36, 137-176
From June to the beginning of September, 1932, I had the opportunity of carrying out geological investigations in this territory on behalf of the Companhia de Diamantes de Angola (Diamang). As I had the assistance of all persons locally employed and could use the Company's motor service, and had, in addition, the full benefit of the local knowledge of the Company's employees and of all previous research and prospecting work, it was possible to cover a wider area and to get much more information about the geology of this part of Angola than would have been possible if I had had to travel on my own. About 4,000 miles by motor and 250 miles on foot were made in various trips across the country between the Cunene mouth and Benguella in the west and the " Planalto " of the Chella in the east. More detailed investigations were carried out in the coastal belt between the Cunene and Porto Alexandre. Extensive walking in numerous trips where motor transport failed, more especially towards the Cunene River and further inland, served for the more detailed exploration of the geologically interesting problems of that area. I also visited the Planalto of Mossamedes, i.e., the country around Lubango, Humpata and Huila, and the coastal belt near Chapeu Armado, 100 km. north of Mossamedes. It is with a great deal of pleasure that the author acknowledges the valuable assistance rendered to him by the representatives of the Companhia de Diamantes de Angola, especially by the Board of Directors for giving permission to publish the results of these investigations, and to the consulting engineer, Mr. H. T. Dickinson; furthermore, to Mr. J. Hermans, who was in charge of the Company's prospecting work north of the Cunene mouth; from him most valuable information was received, while he always facilitated the very difficult problems of transport with never-tiring personal efforts.
Contents: Previous exploration work. Main physical and geological features. i) The Serra de Chella, ii) The Lunda Axis or Rise (Schwelle), iii) The Namib Peneplain, iv) The Coastal Belt. Stratigraphical scheme: Classification and description of rocks. i) Table of formations, ii) The Pre-Damara Gneiss, iii) Damara System, iv) The Muva-Ankole System of South-Western Angola, v) Rocks intrusive into the Damara and Muva-Ankole Systems, a) The Chella Granite, b) The Anorthosite-Gabbro Suite. vi) The Konkip Formation, vii) The Chella Formation, viii) Karroo Intrusions and Cretaceous volcanics, ix) Cretaceous and Tertiary Formations.
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Transactions of the Geological Society of South Africa, 36, 29-40
The following paper is concerned with the probable causes of variation in the quality of amosite fibres as encountered in the asbestos mines at Penge.
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Transactions of the Geological Society of South Africa, 36, 41-64
The object of this paper is to endeavour to give a somewhat more detailed description of the breccias occurring on the farms Roodeplaat No. 314 and Derdepoort No. 469, eighteen and five miles respectively north-east of Pretoria. Although frequently referred to, the breccias in both localities have never been adequately described, and I hope that this attempt will throw more light on their field relationship as well as their petrographical characters.
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Transactions of the Geological Society of South Africa, 36, 65-68
In the "Explanation" of the Geological Map of Heidelberg, the absence of markedly calcareous sediments in the Witwatersrand formation was commented on. Since then I have seen a paper by W. H. Penning, in which he mentions calcareous deposits in connection with the Kimberley conglomerates, but no details are given, and, so far as I know, limestones or rocks with more than a very small percentage of carbonates in them have not been noted in that position by other writers. The rocks in which original constituents have been replaced by carbonates, such as Professor R. B. Young described, are not considered here, for there is no reason to think, that the carbonates in them were originally part of the Witwatersrand sediments. The dolomite of the Transvaal System probably overlay the whole of the Rand in former times, and was a possible source of carbonates, as it is now over wide areas east, west and south of the Rand.
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Transactions of the Geological Society of South Africa, 36, 69-72
The following geological formations were encountered: Table Mountain Sandstone, Bokkeveld, Enon Conglomerate (Uitenhage Series) and Recent Deposits.
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Transactions of the Geological Society of South Africa, 36, 73-76
Weltevreden, 17 miles west of Prince Albert, affords, like the Gamka Poort, a fine section across the Cape System. The Weltevreden River, flowing northwards, has cut right through the upper part of the Table Mountain Sandstone and the succeeding Bokkeveld Beds, to join tile Gamka River about 3 miles to the west, on the lower portion of the Witteberg Beds. The hard white Table Mountain Sandstone passes up without any sign of unconformity, into what has been taken as the base of the Bokkeveld, a brownish sandstone, 208 feet thick, carrying casts of shells at its junction with the first Bokkeveld shales. This passage bed yielded "Scaphiocoelia africana," S. africana cf. var. elizabethae and "Bellerophon." Above this sandstone lie in order:- First shales (684 feet thick). - They consist of greenish or bluish mudstones, becoming darker upwards. Fossils are: Pleurodictyum bokkeveldense, Nuculana viator, Nuculites pacatus, Palaeoneilo antiqua, Conularia gamkaensis, Orthoceras bokkeveldense, Spirifer antarcticus, Leptocoelia flabellites, Chonetes (Eodeovonaria) aff. arcuata, Homalonotus herscheli, Typhloniscus baini, Proetus malacus, Bainella bokkeveldensis, Ophiuroidea, crinoid stems. Below is a description of what is apparently an undescribed ophiuroid from the first shale bed. Ophiurites Sp.
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Transactions of the Geological Society of South Africa, 36, 77-88
A brief discussion of the hitherto unknown types of alkali-rocks from the Regenstein vent, is the main purpose of this paper.
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Transactions of the Geological Society of South Africa, 36, 89-96
During a regional survey of the Pietermaritzburg district, undertaken during 1932 in connection with a thesis for the degree of M.A. in geography at the Natal University College, Mr. Hodson, in company with Mr. R. M. Jehu, head of the Geography Department at that College, discovered evidence of Dwyka glaciation on the top of Table Mountain, Natal, and specimens of the rocks collected there were sent to Professor Mountain for examination. Subsequently, in the early part of 1933, both of the present authors were able to examine the locality together, and a careful examination was made of both the glacial pavements and also of the overlying glacial deposits. Photographs were taken of the occurrence, and further photographs were subsequently taken of the specimens collected both as hand-specimens and in thin-section. The locality described in this paper (see Fig. 1) is situated in the district of Pietermaritzburg in the province of Natal. Fifteen miles almost due east of the city of Pietermaritzburg, there is a flat-topped mountain which forms a prominent topographical feature, visible from a number of points in the vicinity of the city, and which is known as Table Mountain. It is easily accessible from the city under most weather conditions, although the fold has been made up only a part of the way. The mountain stretches from east to west about two miles, and from north to south approximately three-quarters of a mile. The trigonometrical beacon at the highest point of the plateau is situated in lat. 20°36'02" S. and long. 30°35'51" E. at an altitude of 3,143 feet above sea-level. The structure of the mountain appears to be in part relict, and in part tectonic, being bounded on the north-western side by a series of step-faults, which have together let down the beds to the north through a height of some six hundred feet. It appears that at one time the plateau extended several miles further in the other directions, but the Umgeni and Umsindusi Rivers have isolated Table Mountain by cutting deep gorges around it. All the sides of the mountain present perpendicular and overhanging krantzes of Table Mountain Sandstone some six hundred feet high, with the exception of one portion to the north-west, where the ascent of the mountain may be made with comparative ease.
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Transactions of the Geological Society of South Africa, 36, 97-100
During the course of the work in connection with the geological survey of the area lying between Springs and Bethal, included in the unpublished Geological Survey Sheet No. 51 (Bethal), a visit was paid to the old abandoned Abor Colliery, situated about two miles north-east of Abor Station on the farm Vandyksput No. 88. As preliminary work was then in progress towards reopening the colliery, my attention was drawn to the presence of a presumed fire-clay deposit, above the entrance of the edit to the mine, by one of the officials. At the time a small hand-specimen was taken from the lower unfossiliferous part of the layer, as I did not believe that the rock possessed fire-clay properties to any remarkable degree. About two years afterwards, I had the opportunity of visiting a small quarry near Maggies Colliery on the farm Vaalkrans in the Middelburg district, where a similar clayey deposit was worked for the manufacture of sewerage pipes, etc., during the last decade of last century. This latter deposit also occurred in lens-like fashion in medium-grained sandstone, but is much harder than the Abor occurrence. The inferior hardness and similar appearance to the Vaalkrans deposit, coupled with proximity to the Witbank-Germiston Railway, induced me to pay another visit to the Abor Colliery, for a closer examination of the deposit, and it was on this occasion that numerous impressions of leaves in the deposit were discovered.
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Transactions of the Geological Society of South Africa, 36, xxiii-xlviii, 1 pl
In the address which I have the honour to deliver here this evening, it is intended to summarise in a general way the information now available about a subject in which I am specially interested, and to which my field work has been for the most part confined. In view of the pronounced recent revival of gold mining activity on the Rand, and the consequent closer attention that is being directed towards the thick succession of ancient sediments, in which is located the most remarkable of modern gold fields, the present occasion would seem a suitable one in which to present a short account of the characteristics and behaviour of the rocks belonging to Witwatersrand System in areas that lie beyond the Witwatersrand itself. Nearly fifty years ago, after the first gold had been discovered by Fred Struben in a conglomerate on the West Rand and a great rush had set in towards the Witwatersrand, men began to look further afield for the extension of the extraordinary and apparently persistent gold-bearing conglomerates. Rocks like those on the Rand were soon recognised in the Heidelberg, Klerksdorp and Vredefort-Parys areas. The presence of Witwatersrand beds in areas other than that of the Witwatersrand was proved. For many years, however, mainly on account of the rather complicated structural features, the proper sequence of the beds that build up the Witwatersrand System and the relation of this formation to other strata of later date and to the Old Granite were not fully recognised. Correlation of the various beds with those found in districts remote from the Rand was thus greatly handicapped. Probably the first step towards unravelling the problem was that taken by the late Dr. David Draper when, in 1894, the Chamber of Mines engaged his services "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". Since then geologists and mining engineers have been gathering facts concerning the geology of this area, and of these W. H. Penning seems to have been, the first to use the name Witwatersrand Series for the large development of slates, banded siliceous ironstones, quartzites and conglomerates. In many instances, however, their writings which are considerable. reveal a conspicuous want of agreement in the conclusions arrived at, and it was not until Dr. E. T. Mellor undertook and completed his now well-known large-scale geological map of the Witwatersrand Gold Fields that a complete section of the Witwatersrand System was presented. To him we are indebted for a proper classification which has "eliminated much confusion, vagueness and unfortunate detail". The establishment of a classification and the thoroughness with which Dr. Mellor has described the sedimentary beds have provided a basis for the investigation of the Witwatersrand strata in the outlying districts.
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Transactions of the Geological Society of South Africa, 37, 1-4, 1 pl
The geological map, by Carl Mauch (Plate 1), is of special interest to this Society because it appears to represent the first serious effort to map geologically a considerable area in the Transvaal. His travels into the interior took him from Port Natal (Durban) to the Zambesi, and his wanderings continued from 1865 to 1872. He was accompanied on his first trip to the North by Hartley, the well-known hunter. The geological map by Mauch is not dated, but was probably completed in the early seventies after the termination of his travels. The map is drawn to a small scale (about 70 miles to the inch) and has no accompanying key in explanation of its colouring and the rock formations depicted. Under a magnifying glass, however, one is able to decipher the rock names and some topographical features.
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Transactions of the Geological Society of South Africa, 37, 103-144, 1 fig
Since the closing years of the last century the presence of Witwatersrand beds in the Klerksdorp district, and therefore the possible extension of the great auriferous conglomerates of the Rand into that part of the Western Transvaal, have, from time to time, aroused much interest, discussion and speculation. The complete sequence of beds constituting the Witwatersrand System is not exposed there. Moreover, the members of the system which are present reveal a complicated structure, the unravelling of which is rendered more difficult and arduous by the unconformable relationship to the Ventersdorp beds, by the flat nature of the country, and by large stretches of ground showing no outcrops. It is not surprising, therefore, to find in a rather voluminous literature on the geology of that area, considerable differences of opinion regarding the identity, correlation and structure of the Witwatersrand beds. In a bulletin issued recently by the Geological Survey Division of the Department of Mines, a brief account of the Witwatersrand System in the Klerksdorp-Ventersdorp area and its main structural features is given. An attempt has also been made to correlate the various beds with those in the Rand. The work embodies some of the results obtained in the course of a detailed survey of that area during the last few years. As there are members who in the pursuit of their professional duties have become acquainted with, and others who may be interested in some of the geological features of the area, it was felt that by recounting here what has already been said some valuable discussion and criticism as well as additional information may be drawn forth, all of which would lead to a better understanding and solution of the geological problems involved.
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Transactions of the Geological Society of South Africa, 37, 145-152
During the past decade, attempts have been made in certain quarters to throw doubt upon the accuracy of the Geological Survey's mapping of the areas in which rocks of the Witwatersrand System occur and of the interpretation given by tile Survey to the succession within that System. These attempts have found their fullest expression in the publications of W. E. Bleloch, who produced in 1933 a pamphlet entitled "The Future of the Far Fast Rand Goldfields", illustrated by a map, and who has recently issued another map (May, 1934) showing his interpretation of the succession in all the areas in which Witwatersrand rocks occur. It must be said at once that these are not geological maps in the strict sense of the term. They do not faithfully represent the positions of outcrops as seen in the field, but are in the nature of impressionistic sketches showing the general relationships and general strike of belts of rock in the areas considered. Writing for himself and for those who think as he does, the author of these works differs from the Survey in the following points:-
1. The Survey has mapped the amygdaloid at Boksburg Lake as continuous with the Bird Reef Marker, whereas its opponents consider that this is a fundamental error and that the Boksburg amygdaloid lies within the Jeppestown Beds.
2. On its reading as given in (l), the Survey has mapped the Blue Sky-Nigel Reef as Main Reef Leader. The protagonists of the opposite view maintain that the Blue Sky-Nigel Reef, lying as it does below the amygdaloid, cannot belong to the Main Reef group of conglomerates which overlies the Jeppestown Beds.
3. The failure on the part of the Survey to recognise the supposed difference in horizon of the Bird Reef Marker and the Boksburg amygdaloidal lava is said to have resulted in its failure to recognise what is called, in the publication referred to, the "Boksburg Fault".
In connection with these controversial points the writers desire to place on record certain facts, some of them recently observed, which seem to clarify the position.
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Transactions of the Geological Society of South Africa, 37, 153-162, 4 pl
There is abundant evidence that several of the great limestone formations of Palaeozoic and earlier age, including the Dolomite Series of South Africa, originated largely as calcareous muds and sands deposited in wide-spread shallow seas. Their rocks are characterised by a comparative paucity of organic remains and the occurrence within them of the peculiar structures known as "stromatolites", now commonly ascribed to the activities of algae. The circumstances that produced these vast accumulations of calcareous sediment are little understood, but some light has recently been shed on the subject by the work of the "International Expedition to the West Indies" in the Bahamas which is the only region where, at the present day, continuous deposition of calcareous muds is known to be proceeding over a very considerable area of shallow-sea bed. To quote Dr. R. M. Field, who was in charge of the Expedition, "the Great and Little Bahama Banks represent some 20,000 to 30,000 square miles of shallow-water marine carbonate sediments, mantling a block or horst which is bounded by deep water on all sides. The Great Bahama Bank or lagoon averages from three to five fathoms over an area of some 7.000 square miles". The absence of arenaceous and argillaceous sediments is due to the separation of the Banks from the mainland by deep water, and the circumstance that the islands, which are raised only a few feet above sea-level, are composed of calcareous material. The largest of these islands is Andros, which has an area of about 2,000 square miles, and here, as well as in the wide stretch of shallows to the west of the island, much of the work of the Expedition has been carried out. These investigations show that most of the mud ("Drewite") of the shoals is derived from the erosion and reworking of the unconsolidated calcareous deposits which form the greater part of Andros; that the shoals of the Bahamas constitute great evaporating pans, in which calcium carbonate is being precipitated directly from the seawater; that the mud-bottomed shoal-water is in general very poor in marine life, both plankton and benthos, the contributions to the sediment made by marine invertebrates and calcareous algae being in consequence very small; that in the mangrove swamps along the west coast of Andros calcareous mud is being actively precipitated through the action of bacteria; and that in Andros alga-controlled sediments are accumulating over considerable areas.
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Transactions of the Geological Society of South Africa, 37, 163-170, 3 pl
It is the purpose of this paper to describe briefly the principal changes, effected under the influence of circulating solutions, which the rocks of the Dolomite Series have undergone since their consolidation. With one exception, they are all more or less familiar, but the opportunity now afforded of examining great thicknesses of the dolomitic limestones of the Southern Transvaal in borehole cores makes some generalisation possible. The local replacement of the limestones by ores will not be dealt with.
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Transactions of the Geological Society of South Africa, 37, 171-204
If on a map of the Union of suitable scale one marks each kind of mineral deposit by some distinctive symbol, two striking aspects at once hit the eye:- (a) the remarkable variety of mineral deposits with which Nature has endowed our country, and (b) the large concentration of these occurrences in the northern and north-eastern parts of the Union, well away in the Hinterland of our earliest white settlements. It is, therefore, almost certain that in the mind of the Man in the Street, this great mineral wealth will be associated with the Transvaal and in particular with the gold mining industry within that Province as a thing of vital economic importance to himself, for he has most probably come to realize, though perhaps only in a vague sort of way, that in the end he has to rely directly or indirectly on the sustained success of that industry for his bread and butter. That there is much justification for this attitude becomes at once apparent, when one considers the actual value of the gold mining industry for the whole period over which there are records, round about 45 years, and compares it with the two mineral deposits (diamonds, coal) next in order of economic importance; the results are given in Table 1 as follows. The paramount position of gold is readily understood by recalling, that it is the only non-competitive mineral commodity, at once disposed of in the markets of the world as soon as it is recovered in negotiable form. On the other hand, in the successful exploitation of mineral deposits other than gold, international marketing conditions, especially in the disposal of base metals, play a very important role, an aspect that does not appear to be invariably realized in the proper manner.
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Transactions of the Geological Society of South Africa, 37, 205-212
When I joined the staff of the Geological Survey, I found great difficulty, especially with badly weathered samples, in identifying with any certainty kimberlites and gravels derived from them. Certain volcanic breccias and ultrabasic rocks resemble them so closely in the weathered condition that it is very difficult to distinguish between them from hand specimens in the laboratory. I, therefore investigated several samples of kimberlite, all from different localities, by the methods used in sedimentary petrography in order to find out whether they could be readily identified by their heavy mineral concentrates. This giving little satisfaction, I tried mineralogical and spectroscopic tests (using a wave-length spectroscope and the visual spectrum only) on various mineral fragments, picked from hand specimens and concentrates, in order to test out more fully the idea suggested by J. S. van der Lingen in his paper on garnets. The results obtained from this investigation have been used over a period of years now, and so further checks have been added to them. These results included the investigation of rocks thought to be closely related to kimberlite. The Spiegel River Melilite-Basalt and another olivine-bearing rock very closely resembling kimberlite from S.E. of Aus are the only two of this type investigated. The first is said to contain much melilite, and this I did not check; the second contains a little, but is mainly composed of olivine, etc. The results certainly confirmed those obtained by J. S. van der Lingen, and agree in most cases with those given by S. J. Shand. As I have examined kimberlites from about 50 different occurrences - micaceous, brecciated and basaltic varieties included - the results obtained may be of interest. The fact that the rock was kimberlite was supported by rock-sections up to about the fortieth examination; since then section-cutting has been discontinued and the kimberlite identified from concentrates and minerals picked from the sample, except when no typical kimberlite minerals are found. The results are not a generalisation from a few determinations. Over 300 separate mineralogical and spectroscopic determinations have been made in most of the cases mentioned below, except with perofskite and the other minerals obtained by separation methods and not by hand picking.
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Transactions of the Geological Society of South Africa, 37, 213-220
The object of the following note is to place on record the mode of occurrence and characters of the gold deposits found at the Eagle's Nest Mine near Barberton. They are of particular geological interest quite apart from their encouraging values, because the reefs belong to a type of gold deposit that one would on general grounds not expect to meet with at their actual horizon, since the only reefs comparable to the Eagle's Nest ore bodies lie at Noordkaap, within the mineralogical contact belt of the intrusive Crocodile Poort granite, i.e., some seven miles to the N.N.W.
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Transactions of the Geological Society of South Africa, 37, 221-252, 5 pl
In 1931 alla 1932 the writer mapped the eastern portion of the Windhoek district, as well as portions of the adjoining districts of Okahandja and Rehoboth. Since the results of these investigations differ considerably from the early pioneer reports of Rimann, who in 1910 and 1911 mapped the Rehoboth district (Bastardland) and the adjoining portion of the Windhoek district as far north as the southern slopes of the Auas Mountains, they are here presented in their essential features, accompanied by maps on the scale of 1:150,000. By far the most interesting part of the Windhoek district is its southern portion: the mountainous tract to the south of Windhoek, extending from Lichtenstein and Oamites to beyond the Elephant's River. The rest of the district is almost entirely composed of monotonous biotite-schists, which towards the east disappear beneath the wind-blown sands of the Kalahari basin. Only the maps covering the southern, south-eastern and central parts of the district have therefore been chosen to accompany this paper. On the whole, the area just referred to presents considerably greater difficulties in the unravelling of the structure of the Fundamental Complex than Western Damaraland, where a detailed stratigraphy has been established. This is partly due to the greater degree of tectonic disturbance in the central portion of South-West Africa (Windhoek and Rehoboth districts) and the constantly high, mostly vertical dips of all sediments south of the Auas Mountains. In addition, variation in petrological facies of several horizons of the Fundamental Complex further helps to complicate matters. The contemporaneous survey of the adjoining (western) portion of the Rehoboth district by W. P. de Kock, therefore, was a most fortunate and valuable circumstance.
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Transactions of the Geological Society of South Africa, 37, 253-278, 1 pl
Extending from the Winter Hoek Mountains north-west of Tulbagh Station to Zuurbraak, 15 miles east of Swellendam, the Worcester Fault roughly marks the southern boundary of the high-lying Karroo country. As a result of the enormous downthrow a strip of Malmesbury rocks, one to six miles wide, is found directly adjoining sediments belonging to the Cretaceous, Karroo and Cape Systems over a distance of nearly 115 miles. In mapping the fault-zone from Nuy to Zuurbraak, the main object was to investigate the nature and age of the fault. The stretch from Gouda to Nuy was also traversed, but not mapped because the larger part of it is covered by recent gravels which obscure the line of faulting. The mapping was done by plane-table traverses, using the scale of 6 in. to a mile.
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Transactions of the Geological Society of South Africa, 37, 279-287
The Barberton Goldfield, as one of the oldest in Southern Africa, needs no introduction. The area has been fully dealt with in its general aspects by Dr. A.L. Hall, to whom due acknowledgement is here made, in his Geological Survey Memoir. Further acknowledgement is due to Mr. G.G. Hewitt, late manager of the New Consort Gold Mines, whose ideas on ore genesis in the Barberton District have been of great assistance to the writer. This paper deals more especially with the economic aspect, and represents a study of the structures and conditions controlling ore deposition which have been helpful in locating extensions of existing deposits or new deposits.
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Transactions of the Geological Society of South Africa, 37, 5-52, 1 pl
With the aid of a grant from the Research Grant Board, the geological mapping of the area in the north-eastern part of the Bushveld Complex, shown in Plate II., was undertaken in 1927. When the mapping was nearly completed it had to be abandoned until 1932, when research was continued with the aid of a Porter Scholarship. After returning to the Geological Survey, the mapping was completed in 1932. Additional material was collected in 1933, and investigated at intervals between field work. Chemical analysis was carried out in the Department of Geology, University of Pretoria. The present contribution may be considered as a companion paper to the one on the Bushveld Felsites, the information on which was incorporated in a subsequent paper written by Prof. P. Niggli. Between the times of publication of these two papers Bushveld geology advanced a notable step by the appearance of Dr. A.L. Hall's Memoir on the Complex. The present study was actuated by a desire to obtain more petrographical data, and to see in how far such information could be used in the understanding of the major petrological problems of the Bushveld.
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Transactions of the Geological Society of South Africa, 37, 53-56
It might be of interest, after Dr. Lombaard's paper on the Norite of the Bushveld, to record the results of mechanical separations and of searches made for accessory minerals associated with the norite. The norite examined comes from a quarry on the south side of Bon Accord hills and is on a lower horizon than the material from Bon Accord examined by Dr. Lombaard. Many attempts were made to get a good separation of the felspar and pyroxene fractions and these results are instructive. A few pounds of norite were crushed and sieved and the fractions examined. It was found that material coarser than 100 mesh did not give separate mineral fragments, but contained a fair percentage of composite fragments. Between 100 and 200 mesh there were very few composite fragments, and below 200 mesh exceedingly few were detected. Bromoform-Separation of the + 200 - 100 fraction gave: Felspar: 33 per cent, pyroxenes: 67 per cent of the -200 fraction, after washing out dust, even less felspar. The appearance of the rock showed this to be obviously incorrect, so that it seemed as if the felspar crushed more readily than the pyroxenes. In the crushing, a larger proportion of felspar thus went into the -200 fraction and here was so fine that it washed off as dust more readily than the pyroxene. It was therefore apparent that if accurate results were to be obtained complete samples must be crushed and the whole separated.
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Transactions of the Geological Society of South Africa, 37, 57-68
The association of kimberlite with eclogite has given rise to many interesting speculations regarding tile genesis of the diamond, the composition of the deeper zones of the lithosphere, and even the origin of leucite rocks. In view of the amount that has been written about kimberlite in the last sixty years, it is surprising to find that there is still a good deal of obscurity about matters of simple fact. For instance, I find no satisfactory statement of the relative abundance of the various mineral species; no sufficient mineralogical diagnosis of some of them; and many contradictory statements about their composition. This uncertainty relates particularly to the minerals of the pyroxene group, to which no less than nine different names have been applied, some of them being used in different senses by different writers. It seems to me to be essential, before one enters upon any discussion of the problems presented by kimberlite, to try to clear up these obscurities and contradictions. In attempting to do so, I shall first discuss the available information about the pyroxenes and then submit such supplementary data as I have been able to gather from a study of the heavy concentrates from the pulsator.
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Transactions of the Geological Society of South Africa, 37, 69-86
The area described is a narrow strip of the coastal belt extending from Classen Point westward towards the Gamtoos River. The series of grits, limestones, phyllites and quartzites occurring in this roughly triangular area is sharply contrasted with the rocks forming the mountain ranges and dissected peneplains of Table Mountain Sandstone forming the Northern boundary. Although nowhere is the Table Mountain sandstone found to lie unconformably on the earlier series, this has been taken to represent the most easterly occurrence of several inliers of pre-Cape rocks occurring in the Cape Folded Belt. On lithological resemblances these have been correlated as the Malmesbury Series. In the absence of any fossil evidence, the attempt at correlation has been based purely on the similarity of the rock types. For the survey, field maps were prepared from the Uitenhage Divisional map, scale ½-inch to the mile. In these the scale of the latter was increased four times, by the method of squares, making two inches to the mile. In the past interest has centred in the area on account of the lead, silver and copper mines on the Maitland River. Here repeated attempts have failed to set the occurrence, as a mining proposition, on a sound financial basis.
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Transactions of the Geological Society of South Africa, 37, 73-74
The specimens described come from the Aletta iron-ore mine. They are named Discitoceras bowdeni sp. nov. The discovery demonstrates that some of the Karoo beds of Natal if not actually marine are certainly estuarine or deltaic.
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Transactions of the Geological Society of South Africa, 37, 87-96
The object of this paper is to give a short description of the geology of certain fluorspar deposits in the neighbourhood of Hlabisa, Zululand. The area was visited for a few days when the writer had the opportunity of accompanying Mr. V. H. M. Barrett, Deputy Commissioner for Mines, Natal, and Mr C. Orpen, Claims Inspector, on un inspection tour through portions of Northern Natal and Zululand in September, 1933. The area in which the deposits arc situated extends from about ten miles north to about three miles south of Hlabisa, and is not more than three miles wide. In the limited time at my disposal the exact location of the deposits and the delineation of the boundaries of the geological formations was not attempted, owing to the fact that the prospecting claims are not surveyed and the degree sheets are not sufficiently accurate and detailed for that purpose, but the approximate position of the various deposits that have been opened up are indicated in the accompanying sketch plan.
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Transactions of the Geological Society of South Africa, 37, 97-102
In view of the controversy which is at all times liable to be renewed regarding the origin of the gold in several of the conglomerate beds forming a portion of the Witwatersrand System, it appears advisable to place on permanent record the manner of occurrence of certain spectacular finds of native gold in the underground workings of the City Deep Mine. Within a comparatively recent period two distinct occurrences have been discovered, and the similarity between them, enables one to speculate upon the causes which led to the deposition of the gold as found, with more likelihood of being correct than in the case of an isolated unique instance. The more recently located native gold occurred in a working immediately above the twenty-sixth level of the mine at a depth of approximately 5,700 feet below the surface, or 300 feet below sea-level. It consisted of a limited amount of beautiful gold crystals interwoven in the form of a series of small mats occurring between the walls of a fissure in the Main Reef Leader. In the vicinity of this occurrence there is a dolerite sill varying in thickness from two to four feet, and dipping to the south-south-west at a slightly smaller angle than the dip of the Main Reef Leader, which dips to the south at about 34 degrees. The sill is, in this spot, above the leader, being separated from it by a few feet of quartzite. Thirty-five feet to the south of the occurrence of native gold a thrust fault dipping to the south at about 70 degrees, with a throw of about eight feet, has displaced both the Main Reef Leader and the dolerite sill. On both sides of the fault, from twenty feet to one hundred and twenty feet south from the fissure containing the gold, the quartzites of the hanging and footwalls of the Main Reef Leader, and the quartz grains interstical to the pebbles of that conglomerate, have been intensely desilicated and sericitised with the production of a coarse-grained sandy mud, from which the pebbles may be easily extracted. About four feet northwards from the fissure a large vugh containing a quantity of beautifully shaped rhombohedral calcite crystals six to eight inches in size was encountered, cutting across the plane of the Main Reef Leader at an angle of about 60 degrees. Both the strike of the fissure itself and the longest axis of the vugh were approximately parallel with the strike of the fault. The occurrence of native gold discovered in the City Deep Mine about three years ago, was found on the horizon of the twenty-seventh level, about 3,600 feet eastwards and about 400 feet lower in the plane of the Main Reef Leader from that just described.
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Transactions of the Geological Society of South Africa, 37, lxi-lxxxi
It was always a puzzle to me why the questions of correlation of different horizons of the Witwatersrand sediments in the localities away from the Central Rand with those of the standard Rand Section (which, after all, are pure scientific questions) were very often debated in a rather emotional atmosphere. That is why I consider it a most fortunate idea to bring the discussion of the questions raised by the authors of the joint paper, " Observations on the Correlation of Certain Rock Units in the Upper Witwatersrand Beds", into this Society. Here, I think, is the best place to stifle our emotions and to follow quietly the arguments whithersoever they may lead. I think everybody will admit, that in the absence of fossil evidence and in the face of highly changeable nature of the Witwatersrand sediments, often on a short distance, the correlation of such sediments in the remote localities with the well-known Rand section is an extremely difficult task. The lithological characteristics of the rocks, and sometimes even the succession of beds, especially if it is taken in isolated sections, are not a sure guide. In the majority of cases the only method to arrive at a correlation which is as close to the truth as possible is to balance the evidence for and against different possibilities, taking into account all known facts, and to see which alternative is more probable. I am therefore in complete agreement with the concluding remark of the authors of the joint paper, drawing attention to the unreliability of basing the correlation on a comparison of hand specimens of rocks from different localities, in the face of vast material recorded as a result of geological mapping in the areas where this work was done.
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Transactions of the Geological Society of South Africa, 37, xxiii-xxxix
In order to do full justice to this subject it would be necessary to enter into so much detail that the resulting paper would be too unwieldy for any purpose other than its publication in book form. I shall endeavour, therefore, to sketch rapidly the highlights of the subject only, and shall hope that anyone who is interested sufficiently in the subject to wish for further information, will refer to the publications mentioned in the bibliography to be found at the end of this paper, when published.
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Transactions of the Geological Society of South Africa, 38, 1-28, 3 pl
The rocks to be described occur within an area of roughly a thousand square miles in extent lying SSE from Kidete (old) Station on the Tanganyika Central Railway, being a belt of country some twenty miles wide, extending from the railway line on the north practically to the Kilosa-Iringa road on the south. (See Map 1.) The northern portion of the area comprises more or less dry flat bush country with occasional isolated prominent hills rising above the plain. Further south is high, much dissected mountain land on the fringe of the Usagara Mountains, rising to the forest belt and including the Mafwemero, Tagwana Mountains, the Mangalissa and prominent peaks such as Lunensi, Manamgali, NkalaO, Gurui (6,920 feet above sea-level) and others. Rivers include the Romuma, flowing north, but drying up in the dry season before reaching Kidete, the Tschogwe flowing north-east and the Mtschasima and the Mwega flowing south. Throughout this area the rocks are crystalline gneisses of the Archaean Complex, representing a series of sediments with some associated basic intrusions all highly metamorphosed, penetrated and injected with igneous rocks mainly of granitic or pegmatitic character. The sediments consisting originally of quartzites, grits, impure arenaceous sediments, shales and calcareous shales are now converted to gneisses representative of a high grade of regional metamorphism. This area was included in a reconnaissance by D. Orr in 1929, and a brief description is contained in the Tanganyika Territory Geological Survey Annual Report. 1929, pp. 35-41.
Intruded into this complex is a suite of younger igneous rocks which have not been involved in the general metamorphism. Although entirely free from the high grade metamorphic effects which influenced the area, some of the members are at times difficult to differentiate in the field from older metamorphic rocks, owing to assumption of a primary or an injection banding. Types represented include ultrabasic rocks, gabbroid rocks, plagioclase pegmatites and aplites, soda granites, etc. A table enumerating the various types and the localities at which they occur is given below. A weak development of sulphides of copper is associated with the pegmatitic phase. The ultrabasic rocks occur as intrusions with strikes varying between NW-SE and E-W (magnetic bearings), and, following the general trend of banding in the gneisses.
The Massokini-Lufusi occurrence takes the form of a laccolitic sill traced for a distance of some 7,000 feet. It is strongest at the eastern or lower end, being some 70 feet in thickness. Towards the west and at an elevation several hundred feet higher, it is not more than 30 feet in thickness. Just west of its thicker development the ultrabasic material pinches rapidly, and banded gabbroidal and dioritic rocks are encountered. Olivine bearing types are confined to the lower portion of the intrusion.
The Werners Kopje occurrence has a more or less circular outcrop with a diameter of
about 600 feet, but truncated on its western side by a northerly trending oligoclase pegmatite dyke, which sends out small tongues into the ultrabasic rock. Towards the SE the intrusion passes beneath alluvium, but by following this direction similar intrusions of fine-grained rather felspathic varieties are encountered, so that one appears to be dealing with intermittent bodies along a characteristic directional line. In the Werners Kopje rock olivine bearing varieties are associated in an irregular manner with olivine free more felspathic auto-granulites.
The Kisi Path intrusion, composed entirely of very fine-grained auto-granulites, has a NW-SE strike, and preserves a uniform width of outcrop of about 300 feet for a distance of 1,500 feet. At its extremities it apparently passes out into banded types. The gabbro at Kitati River is a broad body likewise following the trend of gneissic banding. It is cut by pegmatites, and these rocks occur in the gneisses in the vicinity. The pegmatites are all of markedly lenticular character, rapidly pinching from widths which may be up to 100 feet but are generally not more than 5 or 10 feet, and fingering out into the gneisses. They are found cutting the basic and ultrabasic rocks generally with roughly northerly trends transverse to the strike of the rocks they intersect, also traversing the gneisses themselves. A fairly large group of these rocks is found cutting the country rock at Mtschasima River, where soda granite is also found as bands in the gneiss. The aplites occur as narrow veins sometimes as the offshoots of pegmatites. They were generally encountered cutting the ultrabasic rocks, a fact no doubt in part due to the obvious contrast to these dark coloured surroundings. Viewed as a whole, the intrusions appear to occur in a zone with a dominant trend a little to the east of true north and conforming to that of the two main river valleys - the Romuma and the Mtchsasima.
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Transactions of the Geological Society of South Africa, 38, 30-39
Obituary - Bibliography.
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Transactions of the Geological Society of South Africa, 38, 41-55, 3 pl
Following on an introduction on the geology of the environment of Leydsdorp (N.E. Transvaal), the Cam and Motor Mine (Gatooma) of the Globe and Phoenix Mine (Que Que) and on the nature of the ore bearing rocks some twenty different opaque minerals from the areas in question are described, amongst which a few rare types are included. As far as the limited distribution of the antimonite in the Murchison Range is concerned, in contrast to that of the other minerals, the author sees in the correspondence of a zone of calcareous rocks with this so-called antimony belt another explanation to account for this phenomenon besides that of metallogenetic zoning which has to contend with many difficulties. Finally, an attempt has been made to represent the age relations of the ore-minerals schematically.
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Transactions of the Geological Society of South Africa, 38, 57-71
The following paper is an attempt to give the results of a particular aerial survey which has been put to geological use. The difficulties encountered and special features of aerial photography used in this instance are not necessarily to be accepted as general in the geological application of the aerial survey, since the size of the area climate, altitude, topography and general geology are all important modifying factors. These factors must, of necessity, determine not only the practice of the aerial photography, but also the degree of direct interpretation possible, as well as the ground work required. Area.- The area under discussion is situated north of Selukwe in south-central Southern Rhodesia. A strip running 20°E. of North, 18 miles long and 7 to 4.5 miles wide, was photographed and then geologically mapped. The area lies between Lat. 19°26' S. and 19°45' S. and between Long. 29°55' W. and 30°06' W. The block covers 99 sq. miles.
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Transactions of the Geological Society of South Africa, 38, 73-90
In the Central and Northern Transvaal and in Southern Rhodesia the Upper Karroo is known to transgress across older horizons and locally even to rest upon pre-Karroo formations, and it is of some interest to enquire to what extent this transgression can be followed northwards into central and eastern Africa, and into other parts of ancient Gondwanaland. On the information then available an attempt was made by the writer in 1929 (III (3)) to pursue this question, in so far as it relates to Africa, and while later work has shown the need for modification, in some details, of the views then expressed, the suggestion as to the existence of a widespread Upper Karroo transgression in central and eastern Africa would appear to be reinforced by later observations in certain areas. I should like to acknowledge here, as I have elsewhere in the course of the paper, Dr. A. L. du Toit's brief but stimulating references to this question in his "Geology of South Africa". Where fully developed, as in the Cape Province, the Karroo sequence is an unbroken one that embraces strata ranging from the late Palaeozoic to the early Mesozoic, as shown in the following Table. The base of the Molteno Beds is everywhere conformable with the underlying Upper Beaufort Beds. Where the Molteno Beds are present the Red Beds overlie them conformably; where the former are absent, as in the northern part of the main Karroo basin, the Red Beds lie upon the Upper Beaufort Beds, but without angular discordance. In the Central Transvaal, the Red Beds rest unconformably upon the Middle Ecca and upon pre-Karroo formations. In the northern Transvaal corresponding beds rest unconformably upon older rocks. In some places the Cave Sandstone is absent, the Drakensberg lavas resting directly and unconformably upon the Red Beds and even upon the Molteno Beds. Moreover, along the Lebombo belt, when followed from south to north, the Karroo sediments progressively diminish in thickness, apparently through the dwindling or disappearance of the middle or lower portions (IV (3), p. 195). In the upper Zambezi area of the north-western part of Southern Rhodesia (IV (1), p. 255) the Karroo forms a broad and roughly synclinal belt, in which the upper divisions overstep the limits of the lower and ultimately come to lest upon the pro-Karroo complex, just as in the stretch from Natal to the Transvaal. For example, in the Kafue Valley, north of the Zambezi, the Escarpment Grits and the Forest Sandstone, representing the Stormberg, rest upon the schists and gneisses, while on the southern side of the belt in the Mafungabusi district, and at Somabula, beds corresponding to the Stormberg again overlap on to the Archaean. Moreover "not many miles south-west of Wankie the whole of the sediments have vanished and the basalts are apparently dying against a ridge of crystalline rocks" (IV (1), p. 253). Comparable basins of deposition, with overlap of the upper beds, exist to the east and north (III (3)).
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Transactions of the Geological Society of South Africa, 38, 91-92
A tract to the east of Genadendal, Caledon district, indicated on Sheet 1 of the geological map of the Cape as an unbroken anticline of Table Mountain Sandstone, was found to include a "window" of some 15 square miles in extent, revealing the underlying Malmesbury Beds and intrusive granite. Shown reduced in Fig. 1; this was mapped on the scale of 4 inches to 1 mile. This window, 10 miles long by 1 1/4 wide, has been eroded along the axis of the anticline. The Table Mountain Sandstone forming its south-western side makes quite a low ridge plunging in that direction beneath flattish ground built of Bokkeveld Beds, while that of the opposite side rises precipitously into the main range, which exceeds 5,000 feet in places. The mountain mass, with patches of forest along its face, gives off a number of sub-parallel streams, which escape through gaps on its further and lower side. The carving out of the window has been due to stream erosion following a presumed line of weakness. The soils on the T.M.S. are grey, sandy, acid and poor; those on the Malmesbury are brownish-black and better, while those on the Bokkeveld are the best, being sweet and fitted for agriculture. The Malmesbury Beds consist of soft shales with quartz veins, the ridges being sometimes blanketed with shed quartz. The granite, a simple biotite variety, is porphyritic, but finer-grained at the contacts with the Malmesbury Beds into which it is intrusive. The T.M.S. rests unconformably upon the Malmesbury. In the south-western body it consists of a series of sandstones, often felspathic in nature and much jointed, and develops a zone of white quartzites about 400 feet thick at the top, where it passes conformably up into yellow Bokkeveld shales. Tests at old prospecting pits in the Malmesbury and pannings in the neighbouring streams failed to produce a colour of gold. Fine terraces consisting of quartzite boulders occur on Lindeshof, 3 miles south of Oudebosch. Many high-lying gravels, deposited by the River Zonder Einde, show that this river has flowed at a level of at least 200 feet above its present one.
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Transactions of the Geological Society of South Africa, 38, 93-112, 2 pl
During the 1932 session of the South African Association for the Advancement of Science at Durban, a visit was made to the Coedmore Quarries, situated some seven or eight miles south-west of Durban, under the leadership of Dr L. J. Krige, to see among other things the dolerite intrusion in Table Mountain Sandstone which is exposed in the quarry. Since Dr. Krige's previous visit to the quarry, considerable excavation had taken place, and there were now to be seen a number of pale patches of various shapes and sizes within the dolerite. The resemblance between certain horizons in the invaded T.M.S. and some of these pale patches in the dolerite was so marked that it was immediately suggested that the latter were xenoliths of T.MS. The Manager, Mr. P. E. Bawden, moreover, informed us that this pale material kind been supplied to customers together with the dolerite under the trade-name of whinstone, and that the latter had objected that it was quartzite and could not be used for the same purpose as dolerite on account of its hardness. The quarry is situated on the farm Bellair, and in Dr. Krige's map the dolerite outcrop is shown as a semi-circular thick line just to the right of Mt. Vernon Station. The T.M.S., which is invaded by the dolerite, appears to have been brought up by faulting against the Dwyka Tillite which is exposed in various cuttings opposite the quarry. The latter is excavated in the side of a hill, and at present is roughly oval in shape with its long axis running north-south. Actually it is almost completely surrounded by worked faces with narrow entrances at the north-east and south-east corners. The T.M.S., of which some forty feet are exposed in the upper part of the western face, is almost horizontally bedded, but possesses a slight dip towards the east and is also to a small extent arched up about an east-west axis, producing a slight pitch towards the east. That this structure is not due to a laccolithic form of the dolerite is seen from the fact that the T.M.S. forming the floor is folded in the same manner. The nature of the T.M.S. varies considerably for different horizons, but it is most commonly a feldspathic sandstone, though in some parts it is quartzitic and in others appreciably argillaceous. In the coarser layers the quartz and orthoclase grains attain a dimension of 7 or 8 mms., while certain horizons are fairly coarse and dark coloured, and might be termed greywacke.
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Transactions of the Geological Society of South Africa, 38, xxiii-lxvi
I have chosen this wide topic for the subject of my Address, because, tonight, we are observing the Fortieth Anniversary of the foundation of the Geological Society of South Africa and of the Cape Geological Commission, which was later absorbed by the Union Geological Survey. These two institutions have long worked together in effective co-operation, and have, in intimate association, played a predominant part in the history of South African geology. I have been tempted to cover the field universally because of opportunities I have enjoyed in past years for observing the scope and functions of geological surveys and societies in many parts of the world. The great bulk of the original scientific and technical work accomplished by geologists finds public expression through the publications and exhibits of national surveys and self-supporting societies. Their annals, during a century and a quarter of gradual expansion and co-ordination, reveal the growth of the geological profession and the history of geology as an independent science. Geological organisations are now firmly established amongst all races and under all forms of society and of political regime. National geological societies, representative of twenty countries, have a combined membership of 8,000, and there are many other associations dealing with local districts or with particular branches of geology whose membership totals a further 10,000. Independent geological surveys have grown to be an essential factor in the functions of progressive government in nearly every country; indeed, it has been broadly claimed that the degree to which a State supports its geological and other scientific departments may be taken as a fair measure of its enlightenment. The history of the premier geological surveys (notably in England, Canada and U.S.A.), the association between surveys and industrial development in new countries, and the technical functions of geological departments in general are subjects which have been discussed widely and frequently in recent years - too often, unfortunately, in the form of special pleading for adequate governmental or public recognition of the essential needs of an effective survey and of the practical benefits to be obtained. These aspects will be covered incidentally, but my principal aim is to present an impartial review of conditions throughout the world as they stand today. In recent years, the attitude of Governments towards the work of geological surveys has steadily improved, and in spite of severe retrenchments, necessitated by the industrial depression, the present position is sound and impressive. For 106 countries, states and provinces supporting independent survey, which have been investigated, the following summary is given as a general measure of activity, rather than for purposes of comparative inference.
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Transactions of the Geological Society of South Africa, 39, 1-44
This paper deals with the geophysical magnetometric prospecting carried out on the south-westerly extension of the Witwatersrand goldfields. This was the first serious attempt in recent years to prove the extension of these goldfields to the south-west, and also the first time that a geophysical method of prospecting had been applied on a large scale to investigation on the Witwatersrand.
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Transactions of the Geological Society of South Africa, 39, 211-214
This brief note has been written, not with the idea of contributing anything new to our present knowledge of the Witwatersrand System, but rather to offer a few suggestions to the younger generation of geologists on points which have recently arisen, or are likely to arise, in that connection, and it might perhaps be better described as a note on Rand reef nomenclature. Since the publication of my various papers on Rand geology between 1910 and 1917, and the issue of my map of the Witwatersrand in the latter year, several valuable contributions to the subject have been made by various observers. Considering, however, the amount of exploratory and development work accomplished during the period in question, there would appear to be much still to be added to our accumulated data with regard to the geology of the Witwatersrand. Recently, in his presidential address to this Society, Mr. Carleton Jones has made a very welcome contribution to our knowledge, and has brought together a mass of information which will be of the greatest use to all who are interested in the Rand, especially from a practical mining or a financial point of view, and the value of his up-to-date presentation of the available information with regard to the various reefs of economic importance which are being exploited to-day is greatly enhanced by the excellent series of plans and diagrams by which his address is illustrated. These, especially, should be of the greatest service in making clear both to the technical man, whose opportunities of observation are limited to a particular locality, and to the non-technical man, who wishes to gain a clearer idea of the relationships of what has now become quite a formidable list of reefs of economic importance. The additions to this list in recent years have, of course, been due partly to the necessity in some of the oldest mines of exploiting all available sources of ore supply, and partly to the increased price of gold having brought previously unpayable rock into the category of economic ore. I may say that it was this presidential address that prompted me to write this note, and I trust I may be pardoned if, from a purely geological point of view, I draw attention at this stage to some aspects of a suggestion made in that address, so that these may receive proper consideration at some later date, when Mr. Carleton Jones has embodied his views in a paper which he has signified his intention of submitting to the Society, and which I might not then have an opportunity of discussing.
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Transactions of the Geological Society of South Africa, 39, 215-222
The importance of chromite as a South African mineral product has been enhanced during recent years, and since 1932 its annual production has risen by nearly 300 per cent. The Geological Survey has undertaken field investigations into the chrome ore resources of the Bushveld Igneous Complex, and to the writer fell the task of examining some occurrences in the western portion of the Complex. In the course of this investigation in the Western Transvaal, an interesting sector of the Critical Zone in the Bushveld gabbro could, because of the amount of prospecting, for the first time be adequately, even if not completely, examined. Many exposures were poor, while prospecting pits had fallen in and were of limited usefulness. Prospecting began 10 years ago during the platinum boom, when interest centred around the location of the Merensky Reef; recently renewed activity was occasioned by the search for payable chromitite seams, which lie in lower horizons than the Merensky Reef.
The country occupied by the Bushveld gabbro is very flat in the Western Transvaal; thus outcrops are scarce and detailed geological interpretation becomes difficult - this accounts for the fact that the more dissected country of the Eastern Transvaal, with its better exposures, has furnished the greater part of our knowledge of the Complex. It becomes, therefore, desirable to compare new data from the west with that which has been established in the east, and for the Complex as a whole. It is thought that the more or less complete section across the economically most interesting zone of the Bushveld gabbro from a remote locality in the Western Transvaal, which has only recently been linked by the railway warranted a short paper, the bulk of which will appeal in subsequent publications of the Geological Survey. This paper is not intended to be a petrographical study; it is merely a summary of observations in the field with an attempt at their interpretation. The area under consideration lies mainly on the farms Swartkop No. 355 and Schildpadnest No. 233 in the Rustenburg district near the siding Tussenin on the Thabazimbi-Pretoria railway line. This recently constructed railway line, along which iron ore is railed to the Steelworks at Pretoria, has made it possible for a chrome mine (the Swartkop Chrome Mine) to start operations recently on the farms Swartkop and Schildpadnest, through which, incidentally, the Merensky Reef runs. The platinum reef continues to the farm Elandsfontein, on which the now abandoned mine plant and dumps present a dreary picture. The chrome mine is being exploited by the African Mining and Trust Co., Ltd. Their mine exhibits several distinctive features:-
(1) Although the chromitite horizons run from the Pretoria district into the Rustenburg district more or less continuously, as far as is known, with a strike of about 150 miles, the Swartkop Mine is the only working mine in the Western Transvaal.
(2) The Swartkop Mine is 485 miles by rail from
the coast - further than any other chrome mine in the Union. Steelpoort, the clearing station for the bulk of our chrome ore production, and situated in the Lydenburg district, Eastern Transvaal, is about 350 miles from the coast.
(3) This mine produces the highest grade of chrome ore in the Transvaal; the highest grade in the Union is produced in small tonnages in Natal.
(4) The chromitite seam mined is the thinnest seam mined in the Union.
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Transactions of the Geological Society of South Africa, 39, 223-261, 1 pl
No abstract. Contents: History of the exploration work of Western Reefs from 1933-1936. Methods of exploration - (a) Surface prospecting, (b) The topographical survey, (c) The geological survey, (d) The geophysical survey: 1. Magnetic shales in the Witwatersrand beds, 2. Magnetic lavas in the Ventersdorp System, 3. Magnetic shale bands in dolomite, 4. Ultrabasic dykes and fissures, 5. Faults, 6. Usefulness of magnetometric methods in the Klerksdorp district, e) Aerial survey, (f) Drilling. The Witwatersrand beds in Western Reefs boreholes - A. - The Government Series, Drilling for the Buffelsdoorn Reef east of the Buffelsdoorn Fault, Rietfontein and Hessie Boreholes, Drilling for Reefs in Government Quartzites south of the Reitkuil Syncline. B.- The Jeppestown Series, C. - The Upper Witwatersrand Beds: Main-Bird and Kimberley Series. D. - The Gold Estate or Elsburg Quartzites. The Ventersdorp System. Faulting revealed by Western Reefs boreholes.
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Transactions of the Geological Society of South Africa, 39, 263-280
The dissected belt of country lying immediately to the south of the Elandsbergen in the Uitenhage and Humansdorp districts of the Gape Province, is composed of a series of pre-Cape rocks, of which limestones, phyllites, grits and sandstones are the predominant rock types. The area described in the present work, as shown by the accompanying sketch map, slightly overlaps the north-western corner of that mapped by Amm, and stretches in a north-westerly direction to the railhead at Patentie, with the Elandsbergen as the northern boundary. A detailed geological map of the area is given on Plate XLI. Lithologically, the rock types, which are a continuation of the exposures in the valleys of the Maitland and Van Staden's Rivers, show similarities with these. They also exhibit in a general way characteristics which suggest their being a facies of the Malmesbury Beds exposed to the west in the Oudtshoorn district. The survey was carried out, for the greater part, on the Divisional maps of Uitenhage, scale ½ inch to the mile, and of Humansdorp, scale 1 inch to the mile. The former was enlarged to 1 inch to the mile by the method of squares. In the more complicated areas a scale of 4 inches to the mile was used. The area is of economic importance as it has very large supplies of practically magnesia-free limestone, which is used for the manufacture of cement. A large quarry is in operation at Loerie, and previously one was in working at Patentie.
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Transactions of the Geological Society of South Africa, 39, 281-316
Contents:
Part I - Summary of occurrences of melilite basalt and related rocks of South Africa.
Part II - Description of the various occurrences.
Part III - Genesis of melilite basalt.
Part IV - (a) Relation between melilite basalt and kimberlite. (b) Acknowledgments. References.
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Transactions of the Geological Society of South Africa, 39, 317-330
While the stratigraphy of the Karroo beds of southern South-West Africa has been worked out with a considerable amount of detail, mainly by Range and Wagner, the succession within the Karroo System in the northern portion of the territory has until comparatively recently remained more or less obscure. In southern South-West Africa mainly the lower two members of the Karroo System (Dwyka and Ecca Series) are represented. The Beaufort beds are not recognisable, and the Upper Karroo beds (Stormberg Series), with the exception of the basalts, form only a very minor and subordinate part of the whole succession.
North of the Khomas Highlands conditions appear to be reversed. The lower Karroo beds are apparently entirely absent, except: in the immediate coastal area [Kaokoveld], and it is the Upper Karroo beds, the Stormberg Series, that dominate the landscape in certain areas. In addition, while the Stormberg lavas in the southern area (Hoachanas plateau) comprise only normal basalts and andesites, in the northern region they exhibit intense differentiation, grading from basalts (melaphyres) to acid quartz-porphyries in the Kaokoveld and Erongo regions. The relevant beds of the latter region were first briefly alluded to by Gürich in 1891 and described in detail by Cloos in 1913 and 1919. In 1928 they were re-examined by Frommurze and Gevers and their Karroo age suggested.
The geology of the Kaokoveld was first described in outline by Kuntz in 1913. More detailed investigations were later carried out by Reuning, whose discovery of Karroo fossils (Mesosaurus) at the Dorosberg in 1925 for the first time definitely proved the Karroo age of these beds. Identical sediments and lavas can be seen intruded by a youthful granite, forming the final differentiation product of the Stormberg eruptive cycle, at the Brandberg, thereby rendering the correlation of the very similar Erongo sediments and lavas, which are intruded by an identical granite, with the Kaoko beds very likely. Stahl mainly investigated the tectonic features of the Kaokoveld; and showed that in its north-western portion the Karroo beds have been downfaulted into narrow "graben". While the Karroo beds of the coastal area, therefore, have received a considerable amount of attention in recent years, the corresponding beds in the interior plateau of Hereroland have been less fully described, although a number of references to individual localities have been published by Hermann, Range, Wagner and Reuning. To the latter we owe the very important discovery of the great Waterberg fault. (See Map, Plate XLII.) These beds, referred to as the Waterberg Sandstone, were until comparatively recently assigned to the Nama System and correlated with portions of the Fish River beds in southern South-West Africa. The discovery by Elmenhorst, however, of reptilian tracks, described by Gürich in 1926, on the farm Otjihaenamaparero, situated on the south-western slopes of the Etjo Mountain, proved their very much later age, and suggested correlation with the Stormberg Series. In 1926 Gröpel found a portion of a reptilian skull in these beds on the farm Breitenbach, north-east of the Waterberg. Stromer v. Reichenbach determined the fossil as the cast of part of the facial portion of the skull of a Karroo, reptile, but owing to the poor degree of preservation, a closer determination was impossible. In 1928 Range and Kräusel gave a brief description of the development of the Karroo beds throughout the entire territory including brief references to the beds under discussion. In 1929 the writer briefly described these beds as developed at the Etjo Mountain and the Omatako. Since then the writer had further opportunity of studying the Etjo beds in different localities, and although the investigations are not complete, particularly in the region of the Omboroko Mountains, the following notes are herewith presented as a further contribution to the knowledge of the Karroo beds of northern South-West Africa. The main purpose of this paper is to show up the close similarity of these sediments to the Stormberg beds of the Union.
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Transactions of the Geological Society of South Africa, 39, 331-378
Pegmatites, while seldom of outstanding economic importance, are often characterised by a great variety of different minerals, among them many of rare and precious species. Not only do they often form veritable storehouses of a great number of unusual minerals not found in any other type of deposit, but these minerals often also attain prodigious dimensions. From an early date, therefore, pegmatites have evoked a considerable amount of interest from mineralogists and petrologists and different theories have from time to time been put forward to explain their origin. These theories have been ably reviewed by K.K. Landes in his recent paper on the origin and classification of pegmatites, to which the reader is referred. Among the older theories is that assuming an aqueous origin for pegmatites, there being two conceptions: Lateral secretion, now mostly discarded, and Selective solution. According to the former theory the constituents of pegmatites were supposed to have been leached from the surrounding rocks by groundwater and re-precipitated in fissures. The latter theory still has a number of adherents when applied to the lit-par-lit pegmatites or venitic "adergneisses" of ancient magmatic regions. Eskola has recently revived this theory with a considerable measure of success. He distinguishes between juvenile (primary) and palingenetic magmas, the latter being due to partial fusion of rocks in deeply submerged root-zones of ancient mountain chains. The process of differential anatexis or refusion advocated by him for the pegmatitic veins of certain migmatites, apparently not associated with bodies of intrusive granite, involves the heating under certain conditions of rock masses, mixed with water or other fluxes, above the melting temperatures of those constituents possessing the lowest melting point, the squeezing out of this refused liquid by tectonic stresses and its injection into neighbouring rocks as granitic or pegmatitic veins to form migmatites. These are the secondary pegmatites of Fersmann. The general concept as applied to ordinary pegmatites for some time past has been that pegmatites represent the residual melt of the final stages of magmatic consolidation, in which various volatile components, known as "mineralisers," and their compounds have gradually become enriched. The original conception of this mode of origin postulates the crystallisation or precipitation of the various minerals found in pegmatites from the pegmatitic melt as such. The latter, while essentially a silicate melt, is thought to be in an attenuated state, containing a large proportion of water and other volatiles in solution. To designate this admixed condition tile term "aquaeo-igneous" fusion is employed. In character this fusion is thought to be nearer a true igneous melt than to a normal aqueous solution. Field evidence and microscopic examination, however, have made it increasingly clear during the last decade that by far the greater bulk of the numerous and varied minerals found in pegmatites cannot have originated by a simple process of crystallisation or precipitation from an "aquaeo-igneous fusion," containing all their ingredients in solution, but owe their existence to complex processes of replacement. These take place during subsequent periods of alteration of the original pegmatitic material after its partial or more or less complete solidification. Pegmatite mineralisation now appears to be a very complex and long drawn out process, involving a considerable number of successive stages. Apparently Brögger was the first to recognise pegmatite mineralisation to take place in successive stages. His account of the alkaline pegmatites of Southern Norway, published in 1890, some 35 years before the views promulgated by him became generally accepted, will always remain a classic of pegmatite investigation. The conception of complex replacement processes in pegmatites has been developed particularly in America during the last decade by Hess, Schaller and Landes. Their observations, coupled with those of Müllbauer in Europe, placed this view on a firm basis, and to-day it appears to be generally accepted, although with certain reservations in some quarters. In 1928-1930 the writer had the opportunity of investigating and mapping a very extensive and prolific pegmatite region, the Erongo Tinfields of South-West Africa. These investigations led to views on the part of the author very similar to those promulgated in America by Hess, Schaller and Landes. A number of clearly discernible phases of mineralisation were recognised and described by the present writer and his colleague, Dr. H. F. Frommurze. Since then the writer has further extended his knowledge of pegmatites by investigating and mapping in 1934 another very varied and profuse pegmatite field, that of Northern Namaqualand in north-western Cape Province. A full account of this interesting region has appeared in the publications of the Geological Survey of the Union of South Africa in Pretoria, to which the reader is referred for greater descriptive detail of the general geology and individual pegmatite occurrences. This publication contains a full descriptive account of the mineralogy of the pegmatites by Mr. F. C. Partridge, mineralogist to the Geological Survey of the Union of South Africa. The writer wishes to express his indebtedness to Mr. Partridge for his active collaboration. The purpose of the present paper is to set out the most salient features of this pegmatite field as affecting the general problem of mineralisation in pegmatites and to outline the successive phases of mineralisation as observed in the pegmatites of Namaqualand.
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Transactions of the Geological Society of South Africa, 39, 379-428
Contents:
I.- Progress of investigation.
II - Kimberlite:
Kimberlite, Dutoitspan. Chemical composition.
Relation between kimberlite and olivine-melilitite.
Comments on the origin of kimberlite.
III. - Olivine-melilitite.
Olivine-melilitite (melilite-basalt), Spiegel River.
Chemical composition.
IV. - Inclusions of the peridotite suite.
Enstatite-peridotite or saxonite, Bultfontein.
Chemical composition.
Harzburgite, Wesselton.
Chemical composition.
Lherzolite, Wesselton.
Chemical composition.
Phlogopite-glimmerite or phlogopite-rock, Wesselton.
Chemical composition and its bearing on the process of phlogopitisation.
Chrome-diopside. Jagersfontein.
Chemical composition.
Garnet, Secretaris.
V. - Eclogite nodules.
Eclogite, Roberts Victor.
Chemical Composition.
Eclogite, Jagersfontein.
Chemical Composition.
Eclogite, Wesselton.
Diamond-bearing eclogite, Crown Mine.
Period of phlogopitisation.
VI. - Xenolith of basic granulite.
Basic granulite, Cordaat's Kuil.
Chemical composition.
VII. - Xenoliths of the "amphibolite" group.
Hornblende-gneiss, Wesselton.
Hornblendite-appinite Series, Wesselton.
Chemical composition.
VIII. - Outstanding problems.
Kimberlite xenoliths and the constitution of the South African crust.
Comments on the nature and origin of magmas.
IX. - Acknowledgments.
X. - Bibliography.
XI. - Explanation of plate.
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Transactions of the Geological Society of South Africa, 39, 429-440, 1 pl
Earthquakes of the fifth or higher degrees of intensity occur in South Africa at the rate of about one per year, but weaker shocks are much more frequent (4, p. 119). The intensity of both the Swaziland and Fauresmith occurrences reached the 6th degree, on the modified Mercalli scale (5, pp. 977-283) . After these earthquakes a list of questions concerning them was sent by the Geological Survey to several hundred magistrates and post offices in the areas thought to have been affected. Most of the lists were returned, with more or less satisfactory replies. Information was also received from the Meteorological Office, Pretoria, and supplementary data were obtained from the newspapers. Seismograph records were supplied by the Union Observatory, which also kindly forwarded the original seismograms on loan. To Prof. A. Brown, Head of the Department of Applied Mathematics of the Capetown University, I am indebted for the Capetown records and special reports on the two occurrences by Dr. P. G. Gane. All this assistance is very much appreciated and gratefully acknowledged. These earthquakes occurred in the two most important areas of seismic instability in South Africa, namely, the south-eastern part of the Orange Free State, with the adjoining portion of the Cape Province, and the Swaziland-Zululand region (4, p. 118). The maximum intensity of the shocks was much smaller than in some previous occurrences. The positions of the isoseismal lines on the accompanying sketch-map are only approximate, the data available being insufficient for greater accuracy.
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Transactions of the Geological Society of South Africa, 39, 441-456
In reading through the geological literature dealing with Potchefstroom and environs, one is impressed with its scantiness. This fact forces one to the conclusion that this part of the country, despite its central position amongst the actual or potential goldfields of the Transvaal, has in the past received very slight attention from geologists. This apparent disinterestedness must probably be ascribed to the fact that the solid geology is comprised of rocks which are generally considered to be of no economic importance. The question of structure in relation to practical economic problems was evidently overlooked for the same reason. In the course of an official investigation of the underground water resources of the Potchefstroom District in April this year, the writer was afforded the opportunity of making an exhaustive study of the geological structure in an attempt to account for the emergence of several springs along the Mooi river. This led to the discovery in the Potchefstroom Townlands of certain rock-types which had no counter part in the Transvaal system. A comparative petrographic examination proved that these rocks were agglomerates and tuffs referable to the Ventersdorp system. The hitherto unsuspected presence of rocks of Ventersdorp age served as a valuable clue to the stratigraphical setting and aided directly in the differentiation and identification of the contiguous quartzites. The latter were previously correlated with the quartzites of the Timeball Hill horizon, but were now found to belong partly to the Black Reef series and partly to the Hospital Hill series of the Witwatersrand system. The occurrence of pre-Transvaal rocks in close proximity to the Timeball Hill horizon of the Pretoria series focused attention to the complexity of the structure and stressed the need for the modification of its interpretation. To unravel the complicated tectonics it; was decided to re-map portions of the area. The detailed mapping, which was commenced in May and completed in July, furnished the key to the geological structure and resulted in the discovery of the Potchefstroom thrust fault. This paper serves to record briefly the outstanding geological and structural features observed in the field.
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Transactions of the Geological Society of South Africa, 39, 45-76
The area was investigated geologically with the following objects in view: - (1) To determine the relationship of the limestone layer to that of the Magaliesberg quartzites. (2) To study the origin of the massive garnets associated with the limestone. (3) To determine the cause, nature and intensity of metamorphism which this limestone, together with the other neighbouring rocks, have suffered.
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Transactions of the Geological Society of South Africa, 39, 457-460
Although the so-called fuchsite at Mashishimala has been known for a long time and much of it has been collected and distributed throughout the world on account of its showy appearance, the writer knows of no detailed mineralogical investigation of it. It has been established that the mica is a chrome-bearing potash type, but few of the properties of the material are known. The writer's examination of many green micas from the northern and north-eastern Transvaal indicated that their composition, although approaching the mineral-type fuchsite, was nearer muscovite. As no analysis or optical data were available for the coarsest material known (the Mashishimala occurrence), an investigation was undertaken to establish its composition and to see what influence Cr2O3 has on the muscovite-molecule These investigations led to the conclusion that a better name for this mineral and the green micas in the Transvaal is chrome-muscovite. The chrome-muscovite at Mashishimala occurs with cyanite, corundum, rutile and felspar. An excellent description (with photomicrographs and a diagram) of the rock has been given by A. L. Hall in Memoir 15 and Memoir 6 of the Geological Survey of the Union. For convenience, a summary of his work is given. "Near the contact between granite and hornblendite and within the latter lies the corundum-bearing rock in rudely lenticular bodies recurring at intervals and encased in flaky bronze-coloured micaceous material. The composition is given by cyanite, ruby corundum, vivid emerald-green mica, biotite and plagioclase. The distribution of the constituent minerals shows much variation - ranging from rudely banded rocks, in which one or other may occur alone or predominate, up to massive types consisting of several constituents in relatively equal proportions." A brief description of the associated minerals will suffice.
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Transactions of the Geological Society of South Africa, 39, 461-464
While examining some new specimens of ore from the Potgietersrust Tinfields the writer came across a few minerals that, to his knowledge, have not been recorded from South Africa or from this area, and ascertained new facts about minerals already known to occur there. It was thought that this information would be of interest. In addition to the more usual minerals associated with the cassiterite, i.e., quartz, felspar, sericite, tourmaline, fluorite, chlorite, calcite and iron-magnesium-calcium carbonates, many minor constituents have been described from these fields. In all the deposits arsenopyrite and some pyrite also occur. Molybdenite and molybdite have been recorded from Groenvlei, Appingendam and Zaaiplaats; wolframite and scheelite from Groenvlei, Appingendam, Welgevonden; bastnaesite from Groenvlei, Appingendam, Welgevonden and Sterkwater. Galena and chalcopyrite have been obtained from Zaaiplaats Groenvlei and Appingendam, and sphalerite from Zaaiplaats. Native copper was found on Appingendam. Topaz was reported from several localities, but its presence has been denied by Merensky. Orthite also said to be present cannot be found. When reading the Geological Survey's Memoir on the Waterberg Tinfields, the writer came to the conclusion that, from the published description, the mineral referred to as orthite could not possibly be that mineral. As numbers of specimens of bastnaesite, first described by McDonald, had been identified from many localities in this area, it seemed likely that the mineral referred to was really bastnaesite. A re-examination of the specimens and thin sections detailed in that memoir proved that in no instance was orthite present, but that bastnaesite always occurred - in one specimen A 543, showing much tourmaline, it was a major constituent. It appears that orthite does not occur in this field.
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Transactions of the Geological Society of South Africa, 39, 465-478
The raw materials available for use in the manufacture of silica refractories include the following: - 1. Quartzites. 2. Sandstones and ganisters. 3. Cherts and flints. Each rock type varies considerably, depending on its origin and geological history. For instance, sandstones may contain minerals high in alkalies, and cherts and flints may be contaminated by calcite or dolomite.
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Transactions of the Geological Society of South Africa, 39, 77-80
During the past few years the author has carried out a large number of determinations to ascertain whether any relation exists between proportions of heavy minerals in Witwatersrand Bankets and their corresponding gold content. The pyrite, which is the most abundant of these heavy minerals, was studied in greater detail than the other heavy constituents. The pyrite occurs as two main types, one being round to ellipsoidal in outline, and the other well defined cubic crystals to irregular grains. In many parts of the Witwatersrand where the conglomerates are mined the predominant shape of the pyrite is ellipsoidal. In the quartzites and shales associated with the reef and in quartz veins, only the cubic type, however, is found. The ellipsoidal pyrite (nodular or buckshot pyrite) is definitely of a secondary origin, resulting from the replacement of original minerals of this general shape in the banket, and specimens can be observed enclosing quartz grains incompletely replaced by the pyrite. This form of pyrite is particularly well developed in the Buckshot Leader Reef (Rietfontein Consol. Mines) and in the Battery Reef (Randfontein Estates Gold Mining. Co.), and is also present in large quantity in certain conglomerates of the Black Reef Series. Pyritic "nodules" up to a foot long occur in the quartzite above the Main Reef at the Nourse Mines. Several general features were observed when carrying out the work on the gold content of the conglomerates, which are of interest. High gold values in the reefs usually occur in moderately wide or thick reefs with large pebbles, where such reefs contain appreciable pyrite. The presence of a large amount of pyrite does not in itself, however, indicate a high gold value, but where, that factor is taken into consideration, in relation to the average pyrite content of that particular reef the rule is for the gold content to increase in value as the pyrite increases. This is also true of the Banded Pyritic Quartzites, such as those found on the Central Rand. Such investigations were carried out for all the well-defined conglomerates of the Witwatersrand System, both in the Lower and Upper Divisions. In addition, a large number of assays were made on various rocks met with in boreholes and cross-outs and similar relations were found, namely, that the absence of pyrite was accompanied by the absence of gold.
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Transactions of the Geological Society of South Africa, 39, 81-210
Contents:
Introduction: A. Preamble. B. Previous literature. The Karroo Dolerites. Physical features. Geology. Petrography: A. Eruptive rocks of the Basal Zone. B. The hornfels or hornstone floor of the intrusion. C. Vein and dyke systems in the Basal Zone and silicates associated with the ore. Minegraphy of the ores. Distribution and economic aspects of the ores. The genesis of the ore. Literature.
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Transactions of the Geological Society of South Africa, 39, Annex, iii, 139 pp.
For the purpose of the following account, the close of the pioneering period of geological investigation in what is now known as the Union of South Africa is taken to be Monday, February 4th, 1895, when a meeting was held in the Council Room of the Witwatersrand Chamber of Mines, with Dr. Hugh Exton in the chair, to consider the founding of the Geological Society of South Africa.
A few geologists had been employed for short periods by the Governments of the Cape Colony, the Orange Free State, Griqualand West and Natal before 1895, but in that year the Cape Government appointed the Geological Commission of the Cape of Good Hope to organise a geological survey of the Colony; Mr. J. X. Merriman was Chairman, and the other members were Dr. Thomas Muir, Dr. David Gill, Mr. Thomas Stewart and Mr. Charles Currey. Mr. Stewart M.Inst.C.E., is the only survivor of these men, and he still takes a lively interest in the geological work being done in South Africa. The Commission appointed Dr. G. S. Corstorphine to direct the survey, and mapping was begun in February, 1896. The appointment of Dr. G. A. F. Molengraaff as State Geologist in the South African Republic followed in September, 1897, and Mr. William Anderson began the geological survey of Natal and Zululand in 1899.
The arbitrarily chosen date falls a few years after the publication of the first two volumes of Eduard Suess's synthesis of the then known geology of the world, "Das Antlitz der Erde", of which Marcel Bertrand wrote that future historians of geology would say that it marked "the end of the first day, when there was light". The accounts of the geology of South Africa in his volumes are a summary of the work done by our Pioneers. In general, the chosen date will be observed, but it has to be overstepped on occasion, especially when work in the Transvaal is concerned, though no attempt will be made to cover the great advance in our knowledge of South African geology since 1895, for that would involve doubling the size of this account while much of the work is beyond the pioneering stage and has been done by men who are still active.
There is a contrast between the histories of discovery in the north and south; in the south Bain and Stow each had a very large share in laying the foundation of our present knowledge, their work was done before and during the early days of diamond mining. After the discovery of gold, the north became the more attractive region, and many men with some knowledge of rocks went to the Transvaal. Though Mauch was eagerly noting geological facts in the Transvaal before 1870, and in a way played the part of Bain there, he had not read Lyell's "Principles" or any other work which inspired him geologically as that book had inspired Bain. We must remember, however, that it was Bain's collection of fossil reptiles that created the great interest in his work amongst geologists in England; without those bones we may suspect that much less notice would
have been taken of his structural and stratigraphical work, some of which was at variance with the views of men like Krauss and von Hochstetter, who had the advantage of scientific training, and who published their observations before and after the appearance of his work. Bain did not fall into their great stratigraphical mistake, which was of little concern to geologists in Europe, but the Karroo fossils aroused an interest in the geology of the Cape Colony which was denied to the less easily accessible Transvaal until gold was discovered there, and, of course, for some years afterwards the great thing was to get the gold without worrying overmuch about structure and stratigraphy. So figures in the north are less outstanding, and there was a welter of conflicting and unsubstantiated views before the founding of this Society, and Dr. Molengraaff's work as Government Geologist, provided the means of co-ordinating observations.
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Transactions of the Geological Society of South Africa, 39, xxiii-lvii
The auriferous deposits of the Witwatersrand are so regular as compared with ore-bodies generally encountered in metalliferous mining, and are so relatively easy for the mining man to follow that, although the recorded production of this gold field from 1887, the year after it was discovered, to the end of 1935, is 292,954,367 ounces of fine gold from 873,570,055 tons of ore, much less attention has been paid to detailed geological study of these conglomerates than to gold fields of lesser economic importance in other parts of the world. Most of the geological study of the Witwatersrand has been of the system as a whole, and much has been written regarding the origin of the deposits. While such study has been of extreme interest and importance, I have felt for some time that collation of the vast amount of information respecting the productive and non-productive reefs of the Upper Witwatersrand System below the Elsburg Series, available in the survey offices of the mines of the Witwatersrand, would be a useful contribution to the economic geology of this field. Permission to obtain this information was courteously granted by all the mining companies - a striking illustration of the spirit of co-operation that pervades the entire Industry - and the purpose of this address is to summarise the details regarding the reefs occurring in individual mines and to correlate these reefs from the viewpoint of the Witwatersrand as a whole. The confusion which exists to-day with regard to nomenclature of the reefs in various Witwatersrand mines is further justification for investigation of the subject.
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Transactions of the Geological Society of South Africa, 4, 103-115, 2 figs
It is well known that at least the greater part of the base of the Karoo system in South Africa is formed of a peculiar conglomerate, generally known as the Dwyka conglomerate. Wherever within the vast area it is known to occur its examination has proved it to be characterized by some constant and special features.
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Transactions of the Geological Society of South Africa, 4, 11-15
According to public opinion it is only necessary to bore a hole deep enough into the crust of the earth, and a stream of water will immediately rush forth; facts are, however, completely in opposition to this theory. Though numerous boreholes have been put down on the Rand in particular and in the country in general, but a very small proportion of them has struck underground sources of water supply of sufficient strength to flow from the orifice of the hole. On the Rand there is not a single instance of this being the case; so far as I am aware. Yet within a certain depth from the surface water is fairly plentiful, and a great portion of the supply required for the use of Johannesburg is derived from the bore-holes and pits which have been put down in the more porous surface layers.
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Transactions of the Geological Society of South Africa, 4, 119-147, 2 sections
Owing to the total want of assistance, no regular survey or mapping has been possible during 1897. I have, however, been enabled by means of several journeys in the southern and eastern portions of the Republic, to collect certain data, which will be of importance to the future Geological Survey. These concern the general geological structure, and the succession of the formations, about which notwithstanding - or perhaps actually on account of - the large number of specialists, of greater or less repute, who have identified themselves with the study of geology of this country, the greatest differences of opinion exist. The only point upon which these opinions are fairly unanimous, is the recognition of three principal divisions in accordance with Schenck: - 1. - The South African Primary formation (Schenck) or Primary System (Hatch). 2. - The Cape formation. 3. - The Karroo formation, represented in the South African Republic almost exclusively by its upper sub-division, the Stormberg Beds. How the different divisions of these formations succeed, or are connected with each other, or which sub-divisions belong actually to each formation, are questions which up to the present, however, have received the most divergent answers. Yet the correct interpretation of these is of the greatest importance, not only to the Geological Survey, but also to the agricultural and mining industries of this country. Wat is the correct position of the dolomite formation, from which almost all the perennial streams have their origin? What is the correct relation between the gold-bearing formation of Barberton and that of the Witwatersrand? Is the dolomite formation, which in the district of Lydenburg contains so many gold bearing quartz beds, the same as the dolomite formation at Malmani, where the gold appears to occur in a totally different manner? What position does the sandstone formation with banket beds, in the district of Waterberg, occupy with regard to the other gold-bearing formations in this State? These are a few out of the many problems whose correct solutions will naturally result from a thorough knowledge regarding the sequence of the formations in this country. In order to approach the solution of some of these problems during this year, I have surveyed several lines of section in directions specially selected for the object in view, and I have now shown on plate 1 the geological features of one of these, while the general results of my jouneying are presented in the following chapters.
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Transactions of the Geological Society of South Africa, 4, 151-152
Dr. Molengraaff's paper on "The Glacial Origin of the Dwyka Conglomerate" is undoubtedly one of the best studies on South African geology we have had the pleasure of hearing in our Society. The more the paper is studied, the greater its classical value for science and mining industry will be appreciated. Dr. Molengraaff took, I think, sufficient precautions that the glacial era of which he speaks should not be confounded with that which I dealt with in August, 1897. I fully agree with Dr. Molengraaff, and recognize that I have been mistaken in supposing that the glacial phenomena observed in Pretoria and on the Rand, were of the Quaternary epoch, when they are in reality most probably Permian.
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Transactions of the Geological Society of South Africa, 4, 153-156
The paper read before this Society by Dr. Molengraaff at the October meeting is certainly the most important contribution to South African geological literature that has been published during the last 25 years. It has finally, set at rest the much debated question regarding the origin of that greatly misunderstood formation, the Dwyka conglomerate.
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Transactions of the Geological Society of South Africa, 4, 157-158
I cannot see any evidence in favour of an older coal period than that which we call the Molteno beds, and Dr. Molengraaff's recent researches on the eastern scarp of the Drakensberg, to my mind, are decidedly antagonistic to any such theory as that advanced by Mr. Dunn. I believe eventually the Beaufort beds will be grouped with the Molteno as a sub-division, the former distinguished by the yellow colour of the rocks and their spheroidal weathering, the latter by the characteristic false bedding, coarseness of the sandstones, and their coal contents. The apparent unconformity between the Molteno and the Beaufort beds being due to false-bedding on a gigantic scale. Accepting Dr. Molengraaff's determination of the Ecca beds as glacial deposits, we have distinct evidence contra to the theory of coal beds being contained therein and consequently I am unable to support Mr. Dunn in his opinion that coal will be found in the Karoo by boring.
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Transactions of the Geological Society of South Africa, 4, 159-161
There is no doubt that the springs which occur in the plains not being strong enough to form a stream (owing to the levelness of the country) they would form vallies or produce a small marsh, which in reality was the nucleus of the pan. The animals would collect to these spots, and the process of pan formation would commence; by their treading in and around these springs mud would soon be formed, this in turn (or a small portion of it) would be literally carted away on their hoofs and legs. Mr. Braecke, Prof. Prister, Dr. Molengraaff and Mr. Draper also give their opinions with regard to the formation of pans.
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Transactions of the Geological Society of South Africa, 4, 167-168
Mr. Alison's interesting paper on the Origin and Formation of Pans opens up a field for investigation, though I do not think that his explanation of their origin is applicable in all cases. We must rather classify the pans in accordance with the rocks in which they have been excavated and search for points they have in common. We were informed at the last meeting of pans formed in granite rocks, in dolomite, in sandstone and in shales, and we see from this that these hollows are not limited to any one particular series. This indicates that the forces in operation were more or less general, and were modified by special causes acting in particular cases. If we study these pans in detail we will better comprehend their forces.
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Transactions of the Geological Society of South Africa, 4, 169-170
The author of the brief but interesting paper "On the Origin and Formation of Pans", has certainly struck upon an original idea, which hitherto has escaped the notice of all writers who have studied those most puzzling occurrences upon the plains of South Africa, which we call pans. Anyone acquainted with this country during the time when countless herds of Wildebeest, Quagga, Blesbok, Springbok, etc., roamed over the plains, will recognise the great effect they would have upon the area of those small pools to which they resorted to quench their thirst. Thousands of animals drinking daily and each one removing only a small mass of mud, would in the course of a season transport many tons. Mr. Alison is also quite correct in stating that the antelopes would prefer the security afforded by the open ground surrounding the pans, to the danger from attack by the larger carnivore, which would lurk in the reed grown banks of the rivers which intersect the country. But all pans are not influenced by this cause. Many are situated in such positions that but few animals could reach them, for instance the large pan on the summit of Platberg, the table mountain near Harrismith, O. F. State, the pan on the Inquela mountain near Newcastle, and many others in like spots. Also the large granite pan on Panfontein, west of Krugersdorp. There are also many pans which have evidently been produced by the chemical decomposition of the mineral matter by the acids produced from the vegetation growing in them, as well as isolated instances where shrinkage of the strata has been the main cause, but these last are rare.
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Transactions of the Geological Society of South Africa, 4, 171-172
During my visit to Knysna in 1897 I saw what I considered evidences of glacial striations and worked out a theory of the "Phantom Pass" being a moraine. Glacier-ice records can and are met with not only in Eastern Africa but also in South-Western close to the sea-board. The area over which I noticed the ice scratchings was south of the Outiniqua Mountains, a few miles west of the edge of Knysna forest and south of the post road between Knysna and Georgetown, there I found, near a large vlei, the clearest evidences of any, but not decided ones. I examined the boulder beds of Phantom Kloof (on the sides of which the post road is cut - it makes an ascent of at least 800 feet), the boulders consist of sandstone and quartzites, which appear to have been waterworn but not like cliff-debris, these boulders were smoothed and rounded and varied in size from a ton weight down to lbs., they were invariable flattened on the underneath side but showed, as far as I saw, none of the striae I looked for, this may be accounted for the their want of hardness.
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Transactions of the Geological Society of South Africa, 4, 173-174
I wish to call your attention to a couple of pieces of sandstone lying on the table. Their peculiar form will certainly not fail to attract your attention, as it did mine. Those two pieces are samples of thousands of similar fragments lying strewn upon the flank and top of the hill, at whose foot lies the hotel of "Orange Grove", which runs parallel to the reef of the Geldenhuis Gold Mine, ending where this mine has its pumping station. Their peculiar polish, expecially on one side, calls again for an explanation, of its origin, will reopen tonight the discussion upon the glacial phenomena on the Rand.
The Dwyka conglomerate, as explained by Prof. Molengraaff, passed over a contemporaneous formation to the Rand in other parts of the country.
The question that presents itself in our minds, is how te explain the presence of such relatively small traces of such huge glaciers which were able to form the Dwyka conglomerate?
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Transactions of the Geological Society of South Africa, 4, 175-181
I venture tonight to lay before you a few considerations regarding the formation of the Rand conglomerates. I will begin by briefly sketching one of the most important theories of the deposition of these beds and point out objections which, to my mind, render it untenable, and later will adduce some ideas on the explanation which seems to me the most feasible and which has been adopted in a measure by geologists, such as Mr. Kunst, Mr. G.F. Becker, Dr. Carrick, Mr. Ballot and others.
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Transactions of the Geological Society of South Africa, 4, 19-36
To enumerate and discuss the different hypotheses which have been advanced and abandoned regarding the origin and mode of formation of the auriferous beds of the Witwatersrand, would occupy more time than is at my disposal this evening, so I will confine my remarks principally to the theories advanced by Professor de Launay and Professor G.F. Becker and a paper by Mr. Julius Kuntz.
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Transactions of the Geological Society of South Africa, 4, 37-40
Tin is usually found in the form of oxide, containing tin 78.6 per cent, and oxygen 21.4, in pure specimens of the mineral, which is known as cassiterite, and in rocks or deposits, of Paleozoic, Plutonic, and Tertiary origin. In rocks of the two former it is found in lode form, while the alluvial deposits may be relegated to the Tertiary epoch, although they rest on rocks of different kinds. The tin lodes of Cornwall illustrate their existence in rocks of Paleozoic and Plutonic form, as they are in both granite and slate, and also in the junction of the two. Tin is usually found in connection with granite, although in the best mines of the world, the lodes are not in granite as the surface; I allude to the Dolcoth Tin mine in Cornwall which is in slate, and the Mount Boshoff Tin mine in Tasmania, where the tin bearing rock is between porphyry and slate.
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Transactions of the Geological Society of South Africa, 4, 43-45
On reading Professor Prister's paper it strikes me as partaking more of the nature of a chemical and metallurgical one than what one would expect to hear read before a Geological Society, but allowing this to pass, I would like to point out that the Professor assumes a pre-excitant, or co-excitant state of things favourable to this theory, and on this assumption, pure and simple, his theory is based. Vide par. 4, p. 22 of his paper. But for the sake of argument let us test this theory by observed facts and see if it will hold water, and here let me say that the question of the precipitation of the gold after it had been brought to the presumed sea shore, as sought to be explained by the Professor, admits of a great deal of controversy which would be of a purely chemical nature, and hence I shall not touch on it here. According to the theory under discussion, 1st, the most gold should be found in the reef, or vein, containing large pebbles. 2nd. If the Main Reef series be rich in gold, the upper, or overlying as well as the underlying reefs, in that particular zone would be comparatively poor in gold, and vice versa. Neither of these, I beg to submit, can be proved by actual facts.
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Transactions of the Geological Society of South Africa, 4, 47-51
To the many theories already existing on the origin and formation of the Witwatersrand auriferous conglomerates, one more has lately been added - that of Professor Prister. The whole question can be divided into two main points; firstly, the formation of the Witwatersrand beds, and secondly, the origin of the gold in the conglomerates. On the first point geologists generally agree in putting his formation among the littoral deposits, the constituent parts of which were brought down by the rivers as the debris emanating from the rocks already existing. It is, however, impossible to believe that all these enormous masses of quartz stored in the quartzitic sandstone and conglomerates, or even in the latter only, emanate only from gold-bearing quartz veins, as some geologists assume, but it is most probable that all the then existing quartz containing rocks, especially the quartzites and quartzitic schists of the Namaqualand formation, and the granite containing large quantities of individual quartz as well as quartz veins, have also contributed detritus for the formation of our conglomerates you will find among them vein quartz as well as individuals, quartzite, and quartzitic schist.
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Transactions of the Geological Society of South Africa, 4, 53-57
The Author of the paper rightly remarks that the discussion of geological problems is very difficult when chemical and physical processes are so interlaced. The agencies which contributed to the formation of the sandstones and conglomerates are apparently very distinct from those which furnished the precious metals which give to the Witwatersrand beds a special economical importance, but the one depends on the other so closely that in studying our local formation we must touch on several branches of the science. Many able authorities favour the idea that the sandstone beds are of marine origin, being a redistribution along the coast line of the rounded debris brought by rivers, which must have been of considerable magnitude, from an area very much above the level of the locality in which they (the beds) were laid down. But before this theory can be accepted I think that certain points require some explanation. For instance, did the original shore gradually sink along a well-defined line and so permit the accumulation of layer after layer of sandstones, or did the coast line gradually advance landwards as the depression went on. In the latter case it would be natural to suppose that the upper series would extend, when laid down, far beyond the edges of the lower series; but the opposite is apparently the case, and we are left to imagine an epoch of very energetic denudation when the missing portion of the upper beds was carried away.
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Transactions of the Geological Society of South Africa, 4, 77-86
Bibliography
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Transactions of the Geological Society of South Africa, 4, p 5
The discovery of true diamond bearing volcanic pipes, which was announced at the September meeting of the Society, has since been verified by the State Geological and many others who were able to speak with authority on the subject. Many diamonds have since been found, and in addition to the original discovery to which Mr. M.E. Frames and myself so largely contributed, other pipes have been found in the vicinity, notably one on the adjoining farm Elandshoek. The diamonds from this last discovery are of better quality than those from the Rietfontein pipes.
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Transactions of the Geological Society of South Africa, 40, 1-42
Scattered throughout the reports of the Geological Commission of the Cape of Good Hope and the geological literature of Southern Africa in general are references to, and descriptions of, the silicified rocks formerly known as "Surface Quartzites" but now known as silcretes in conformity with the nomenclature proposed by Lamplugh. These silcretes are well developed in the Kalahari (23) and the coastal belt of Southern Africa from beyond the Cunene river on the west coast, to Kentani near East London, in the east; the most northerly occurrence reported in the coastal area is at Mount Frere (5). Isolated patches are found in the Transvaal and somewhat larger occurrences are to be seen in Rhodesia (12) and the Congo (16). The silcretes occurring in the Namib, which are of the Kalahari type, have recently been the subject of a very extensive investigation by Storz (30). As the coastal occurrences of silcrete differ from those of the Kalahari, we believe that the results of a detailed investigation of these rocks developed so typically in the vicinity of Grahamstown, are worthy of record. Most of the material for this paper was collected while the authors were students in the Deparment of Geology, Rhodes Univercity College, Grahamstown. Without the interest, criticism and contributions of Professor E. D. Mountain, and the facilities to complete the laboratory investigations, afforded by the Directors of the Minerals Research Laboratory and the Geological Survey, these observations would have remained incomplete.
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Transactions of the Geological Society of South Africa, 40, 121-126
This paper is intended as a preliminary to a projected paper on the relation of gold to certain structures at Randfontein Estates. Some of the matter described here has already been dealt with by Prof. R. B. Young in his most excellent book, "the Banket", the recapitulation being justified by some additional information obtained and by the emphasis it is intended to place on certain aspects. The danger of drawing conclusions from unusual specimens is fully realized, but it must be pointed out that in spite of the fact that Randfontein Estates is a low grade mine, visible gold in the Leader (South) Reef is a common occurrence. In fact, owing to the exceptionally narrow width of this reef, rich values over the channel width have to be present, to make it at all payable. It is believed that owing to this comparative abundance of visible gold, its relations may be taken as typifying the behaviour of gold throughout the mine. The specimens exhibited at the presentation of this paper have been collected over a period of many years, largely by Mr. E. R. Roberts, the Chief Surveyor of Randfontein Estates.
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Transactions of the Geological Society of South Africa, 40, 127-162
About five years have now elapsed since drilling operations were commenced by West Witwatersrand Areas, Ltd. During that time, and especially in the last two or three years, a large amount of information has accrued as a result of the extensive drilling programme carried out; the broad features of the geology in so far as they affect economic issues, are now known, and the potentially economic horizons of the Main Reef group have been shown to extend throughout these areas, over the greater portion of which their position has been accurately delimited by drilling. Further drilling, in providing additional reef intersections, and more closely defining reef positions in certain localities, will serve to complete, rather than to modify, our present knowledge, and it has appeared opportune at this stage to present an account of the results already obtained and their bearing on our understanding of the geology of the Far West Rand.
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Transactions of the Geological Society of South Africa, 40, 43-119
1. A petrographical study supplemented by chemical analyses, enables one to recognise para- and ortho-rocks amongst the pre-granite rocks of the Vredefort region. Many minerals in these rocks show signs of alteration, pointing to a change in the physical conditions subsequent to their formation. This feature is most marked in certain garnet-bearing rocks, the garnets possessing well-developed kelyphitic rims.
2. For purposes of comparison a petrographical account is given of some six examples of typical para-rocks which originated through contact metamorphism from the aureole of the Bushveld Igneous Complex, and from the Witwatersrand System in the Vredefort Mountainland. Certain sillimanite-bearing nodules in a rock from Lydenburg have drawn special attention.
3. The pre-granite rocks are regarded as having suffered an older metamorphism, regional in character, and a younger one, due to the contact with the intrusive granite.
4. The alteration of garnet to cordierite and hypersthene raises the question of the stability relations between these minerals. A statistical survey of the rocks bearing them indicates that under the same physical conditions - in the katazone with contact metamorphism-cordierite forms when mg is high, while garnet is the favoured phase in an iron-rich environment. The physical conditions, however, also play an important part in these relations.
5. Amongst the para-rocks a magnetite-bearing rock is shown to possess many features in common with the enlysites. A survey of these latter rocks, as far as their chemical and mineralogical composition, their classification and their mode of origin are concerned, is added. In the magnetite-bearing rock from Vredefort the ore may have been introduced during the intrusion of the granite.
6. As far as our present knowledge reaches, the ortho-rocks represent largely original ultrabasic rock-types (hornblende peridotitic- and pyroxenitic magma-types). The low al values is an outstanding feature.
7. By comparing the products of metamorphism from other localities in South Africa with those of the pre-granite rocks in the Vredefort region, the characteristics of these latter rocks, especially their mineral paragenesis, is clearly demonstrated.
8. The mineralogical and textural features of the Old Granite of the Vredefort region are described. Several analyses give information about its chemical composition. An acid rock occurring in dyke-like habit in the granite is regarded as related to certain quartz-keratophyres intrusive into the Witwatersrand System.
9. Variation diagrams of the Old Granites from the Union of South Africa serve to illustrate the nature of this rock group. Its homogeneity on the whole is very noteworthy. Certain variations are considered, such as the De Kaap Granite and those from Natal. Although those from Vredefort possess many distinctive characters, they nevertheless certainly belong to the Old Granites of South Africa.
10. The granitic rocks from Southern Rhodesia are represented in separate variation diagrams from those of South Africa, and differ from them in possessing somewhat higher c and mg values. It is probable that the latter characteristic is expressed in the mineralogical composition by a difference in the pleochroism of the biotite.
11. The granodioritic and the quartz-dioritic nature of the Old Granites is emphasised, and contrasts markedly with other granitic rocks from South Africa.
12. The petrography of the pseudotachylytes is discussed in so far as it has a bearing on the problem of the origin of these rocks. The results of röntgen-ray analyses of the pseudotachylytes do not bear out the supposition that the rock has originated through fusion.
13. The chemical affinities of the pseudotachylytes with the enclosing rocks are considered, and although the vein material possesses several noteworthy features, we are not in a position to ascribe these to any other cause than mere accident.
14. The basic granophyres are described in considerable detail. A fibrous variety and a granular variety are distinguished. With the aid of chemical analyses and other features the abnormal composition of the groundmass of these rocks is pointed out.
15. It is suggested that the pseudotachylyte did not arise through solidification from a melt, but where coarsely crystallised, through recrystallisation in the solid state. Otherwise in the ultra-microscopic varieties it may only represent very finely pulverised rock material.
16. The basic granophyre cannot be regarded as a normal differentiation product of the magma with which it may possibly be connected. An explanation is outlined by which this rock-type is referred to an original alkali-lamprophyric magma which has assimilated mainly quartzite and granite. The special conditions favouring the formation of this abnormal and yet comparatively homogeneous rock are fully in accordance with the complicated tectonic history of the region. wIts close relation to the pseudotachylytes is also taken into consideration.
17. The primary structures in the Old Granite from Vredefort, in so far as they could be analysed, indicate that the circular structure of the region might have been largely determined by the nature of the Basement Complex.
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Transactions 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 magnificance, 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. Contents: Dependence of civilisation on the mineral industry. Growth of the mineral industry. Copper. Iron. Coal. Petroleum.Gold. Localisation in geographical distribution of mineral deposits. The mineral industry in South Africa. Applied geology in the mineral industry. The future of mining geology. Mining geology in South Africa. As a result, coupled with the increase in the price of gold and the possibility of working ore of lower grade, the life of the Rand now appears assured for a period undreamt of during the times before 1932. The search for precious metals and minerals has been responsible, in no small measure, for the discovery and colonisation of entire continents. "Gold rushes" into lands previously unoccupied or only supporting a scant pastoral population have culminated in the political and economic expansion of the two Americas, Australia and Southern Africa. The gold production of some of these countries today may be completely subordinate to the proceeds from pastoral and agricultural activities, but yet it was the lure of the precious metals that first drew men thither in large numbers. The prospector's pick has often blazed the trail for territorial expansion, and in numerous instances the miner has been the pioneer of industry and the herald of empire (T. A. Rickard, "Man and Metals," p. 1049.) Mining is the basic industry of Southern Africa. It gave an incentive to geographic exploration and to the subsequent building of railroads. It attracted an ever-growing population to the country, vastly in excess of that which, owing to adverse climatic and market conditions, could have been sustained by pastoral and agricultural pursuits alone. Mining created markets for the products of the latter, which otherwise could not have been produced profitably. Johannesburg today is not only the centre of the largest gold field ever known and the largest city in Africa outside two ancient cities of Egypt, it also is the industrial centre of Southern Africa and a market for farmers beyond the boundaries of the Union. Such a rapidly progressing industrial revolution, pushed with all the vigour characteristic of pioneers developing a new country, could not fail to disturb the political and social conditions in South Africa. While the latter still present many grave problems of increasing difficulty, happily the former, more than ever before, have been directed towards a common goal of progress and prosperity. Much has been said during the past six months on the importance of the gold mining and mineral industry in general for the past and future development of South Africa. Being a geologist, I may perhaps be forgiven for marring use of this aspect in reviewing the gradual growth and development of economic and mining geology, which undoubtedly, have received a very substantial and beneficial stimulus through the unprecedented mining activities throughout the world during the last three decades. The determined efforts, following on the political unrest and economic difficulties since the Great War, on the part of some countries towards reaching a state of autarchy or, as far as possible, independence of imports from other countries, have given a further impetus towards the application of geology and allied sciences to the search for and development of deposits of economically useful and strategically important minerals. In a country such as ours, where, owing to a number of climatic factors adverse to agriculture and a particularly liberal endowment with a large variety of minerals, mining represents the key industry, it is only natural that the possibilities in this direction should be investigated and exploited to the fullest possible extent. Obviously such investigations are most successfully carried out at times of national prosperity and definitely should be undertaken long before the spectre of exhaustion of one dominant mining area raises its head or even becomes an imminent possibility. The mining companies are fully alive to the situation and also the Union Government is to be congratulated on its foresight in initiating already at this stage an extensive campaign for thoroughly investigating the future possibilities of the Union's mineral resources. For one significant fact emerges from a study of the history of the mineral industry throughout the ages: in general the life of a nation is incomparably longer than that of an individual ore-deposit or mining area, no matter how stupendous its magnitude. In addition, ore-deposits of exceptional size, such as the Witwatersrand, in the case of most metallic minerals at least are decidedly unusual. Only rarely have mineral deposits, with an at all appreciable output, been mined for very lengthy periods comparable with the lives of nations. A few, however, have outlived a whole sequence of nations, though this would not have been the case under the stupendous rate of modern production. Such an instance is afforded by the great cupriferous pyrite deposits at Rio Tinto near Huelva in Spain. As early as 1240 B.C. the enterprising Phoenicians had begun to mine these deposits, at first apparently for gold and silver in the uppermost portion of the oxidation zone. By 1100 B.C. copper from rich oxidised ores at Rio Tinto had become one of the important resources of the Phoenician empire. The merchants and navigators of this enterprising people brought tin from Cornwall, another very ancient mining area, melted it with copper from Rio Tinto to make bronze, and traded the latter to all the peoples around the Mediterranean. The Carthaginian Hamilcar at a later date, when the daughter colony of Carthage had usurped the empire and power of the Phoenicians, introduced systematic mining by great armies of slaves. In 210 B.C., Publius Scipio Africanus finally drove the Carthaginians from southern Spain, and soon the growing Roman empire sent hundreds of thousands of slaves to work in the mines of Rio Tinto which in spite of the primitive mining methods were finally worked down to a depth of more than a thousand feet, with drives and cross-cuts running all over an area one by two miles in extent. Judging from the slag dumps, the Romans must have produced many million tons of ore, some estimates suggesting 20-30 million tons. Mining at Rio Tinto ceased in the 5th century A.D., when the country was overrun by Vandals and Visigoths. During the Middle Ages the Moors reopened the mines, recovering copper from enriched copper sulphides. The Moors were expelled from southern Spain by Ferdinand III in 1248 A.D. and mining once more ceased. From the 17th century onwards Rio Tinto was worked on lease by foreigners, and in 1873 it passed into the hands of an English company, the Rio Tinto Mines, Ltd. At the beginning of this century, in addition to producing copper, pyrite became valuable for the manufacture of sulphuric acid. 40,000 tons of copper and approximately four million tons of pyrite were produced in 1926. It has been estimated that the Phoenicians and Carthaginians mined several hundred thousand tons of ore at Rio Tinto in roughly a thousand years, the Romans 20-30 million tons (probably an exaggerated estimate) in approximately half that period, while the moderns have taken 150 million tons from the same ore bodies in less than 50 years. And yet the Rio Tinto mines are said to have 200 million tons of ore in reserve - considerably more than their entire production up to the present. (Joralemon, "Romantic Copper," p. 36.) While these ore-bodies. therefore, have been mined at intervals for more than 3,000 years, the rate of modern production, if continued at the same pace, would have exhausted them in less than 130 years. This example forcibly illustrates the furious pace of production in modern times, a pace so stupendous, that, if continued, few even of the largest ore deposits will last for much more than a hundred years. In outlining the growth of mining geology I propose, first, to sketch in a brief and summary way the growth of the mineral industry as such, the sheer bulk of which on closer inspection assumes positively overwhelming proportions.
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Transactions of the Geological Society of South Africa, 5, 19-23
Mr. Bleloch is correct in saying that the formation of the Rand conglomerates is of such economical importance, that the interest in it must be perennial. As my studies of the Rand progress I become more and more convinced of the correctness of the hypothesis, that we have here to deal with a shore deposit. It remains an open and most important question, where the shores are to be looked for? Were they along a coast line indicated by the Hospital Hill slate series, by the granite, or must we look further north or south? As far as I have understood Mr. Bleloch, he fixes the shores at the Hospital Hill slate series, and interprets the doubt (?) of Dr. Molengraaff about the conformability of these series with the Main Reef series into an unconformity. He goes further than this in saying, that probably a part of the Hospital Hill slates were employed for the formation of the Main Reef series. For those two most important points Mr. Bleloch does not bring any other observation, that the existence of zircon, tourmaline, rutile, etc., in the matrix of the conglomerates. Mr. Bleloch will excuse me, if I find his support too weak, as those minerals could very well come into the matrix from the same source as the gold and the pyrites. This I have already explained in a paper published by this Society. If the position of the shores on which the Rand was deposited is not yet fixed, we have all evidence that the Rand conglomerates were deposited by currents. These currents could be: (a) River currents, (b) great oceanic currents, (c) or tidal currents.
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Transactions of the Geological Society of South Africa, 5, 24-25
Having read Mr. Bleloch's paper, which was read before the members of the Geological Society at a late meeting, and having been asked to reply to some of his assertions, I do so with pleasure; though I regret my paper must be brief, for to reply seriatim would occupy too much of your valuable time. In order to make my remarks clear to you I have loaned to the Secretary for this evening, a Tracing of a Geological Map compiled by me for Mr. John Hayes Hammond, some five years ago; also a section taken across the Magaliesberg Mountains north of Pretoria, through Pretoria, Johannesburg, to a small town in the Free State called Parijs. The map will show that there are many granite bosses on the north, south, east, west, etc., which have tilted the formations; from the section I have drawn showing the suppositional deposition of the beds of this vast series, that the force exerted in some localities has not been so great as in the immediate vicinity of Johannesburg is evident, but that these granite intrusions raised, tilted, and folded the conglomerates, with the underlying quartzites and shales of the Hospital Hill series there can be no doubt, for I have found vast masses of these rocks lying in blocks and disintegrated debris over several of these bosses.
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Transactions of the Geological Society of South Africa, 5, 26-29
In general I agree with Mr. Draper in the position of the conglomerate beds, and their relation to the underlying Hospital Hill series of slates, etc. I have found no sign of such unconformity as would naturally occur if we had to deal with a series of beds laid down on sloping shores, as Mr. Bleloch has assumed to have been the case. Before proceeding any further to deal with Mr. Bleloch's views, it would perhaps be as well to quote from other writers bearing directly on the subject under discussion.
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Transactions of the Geological Society of South Africa, 5, 3-15
The author of the paper read at our last meeting has revived a subject which I had hoped would be allowed to rest until a geological survey of the Rand had been completed. It is a subject the discussion of which unfortunately leads to no definite results, firstly because the evidences within our reach are fragmentary and indefinite, and secondly because none of us are in a position to undertake the necessary investigations which would enable us to deal with the subject as exhaustively as its importance demands. Personally, I had determined never publicly to revert to the matter of the Main Reef extensions; as I have discovered the utter futility of trying to convince those who had already formed their opinions on the subject, and because the area which I still hold contains the extension of the Main Reef westward has not yielded satisfactory results though the insignificant prospecting operations along the line indicated, have not settled the question definitely. Mr. Bleloch has, however, thought fit to single me out from a host of authorities who have written extensively upon the origin and formation of the Rand conglomerates, and tho have honoured me by objecting generally and specially to my views thereon, and I have in consequence been left to alternative but to reply to his attack, though I now do so much against my will. I must confess that after very carefully reading Mr. Bleloch's paper, I am unable to grasp his ideas on the "Rand Conglomerates". It appears to me, however, that he has formed an opinion which he does not support by the slightest local evidence, that these famous auriferous fields consist of "a series of sub-shore deposits, banked up by the ocean currents and waves against a sloping shore", and that "very considerable tilting and denudation have taken place but nothing of the kind required by the upheaval of continuous horizontal beds". He also favours the idea that "there is unconformity between the upper beds of the conglomerates (the Elsburg series) and the lower or Main Reef. He states that the "great break at Witpoortjie only exists as a comparatively small local fault", and that "the Botha series will be found extending on through North Roodepoort and underlying the main Reef series throughout the Rand". Further, that the diabase amygdaloid of the Klipriversberg lies unconformably upon the upper portion of the Buffelsdoorn series. He supports these opinions principally by elementary quotations from the standard works on geology, referring only to Mr. Julius Kuntz, Dr. G.F. Becker; Mr. John Ballot, and Dr. Carrick upon local matters, but utterly ignoring the great number of writers such as Schenck, Penning, Alford, Walcott Gibson, Schmiesser, de Launay, Hatch and Chalmers, Logan Lobley, Sawyer, Truscott, and many others who hold totally different opinions. But he has even included in those authorities, whom he considers favour his views, two - Dr. Becker and Mr. Ballot - who, though of opinion that the auriferous deposits are
"placers", both admit that there has been great tilting generally and not only locally. The former in granting the conformity of the conglomerate beds to the great thickness of strata underlying them, and the latter by advancing the theory of general step faulting. Mr. Bleloch has then only two authorities left - or three, if he includes Mr Gardner Williams, who originally advanced the theory that "these conglomerates were merely surface deposits along ancient beach lines". I will now proceed to deal with Mr. Bleloch's objections.
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Transactions of the Geological Society of South Africa, 5, 30-42
In replying to the criticisms on my paper on the "Rand Conglomerates", these notes are divided into two parts, in reply first to those papers which were on the whole in support of my views - viz., Mr. Bawden's and Professor Prister's and, next, to those which have condemned me personally, as well as my modest opinions, in language which cannot be said to be always calm or even courteous, save in a purely Pickwickian sense.
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Transactions of the Geological Society of South Africa, 5, 45-52
The following remarks and other matters are, to some extent, necessitated from the fact that some of my previous writings have recently been referred to. On my return to England, in 1889, after a short visit to this country, I wrote my views, and read them as a paper before the North Staffordshire Institute of Mining and Mechanical Engineers. The following is an extract from this paper: - "There is no doubt that at the time of their formation the "Banket Beds lay flat, or nearly so, and that they have been tilted along their present Northern Extension, in some places nearly on end, just as the seams of coal in some parts of the North Staffordshire coal-field. As shown in figure 1, the Banket formation must at one time have extended northward and lain at a very high elevation. This northern extension has been denuded away during countless ages. The gold in denuded Bankets may have been collected in neighbouring alluvial deposits". These views, which distinctly propound the Anticlinal theory lately combated, I see no reason to alter. A different theory to account for the tilting of the Rand beds has lately been advanced. Such a theory, however, could hardly, I suppose, be advanced to account for the inclined position of coal beds, especially of those in the North Staffordshire and other coal-fields where the- seams are not only turned up to an angle of 90 degrees, but even surpass the vertical so that the roof is underneath, and the floor above the seam. If coal seams can be tilted and cast off by denudation, so can other beds.
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Transactions of the Geological Society of South Africa, 5, 61-63
Messrs. Seward and Leiller concur in considering the Vereeniging coal, etc., as older than the Stormberg coal, and think it possibly of Beaufort beds age. If older than the Stormberg, the Vereeniging coal seams and associated beds are probably still older than the Karroo beds, including the Beaufort sub-division, for these are remarkably well exposed in the Camdeboo, Beaufort and other ranges of mountains, and although I have carefully observed the beds from top to bottom no sign of coal measures or seams was noticed in them; there is a general absence of fossil wood in these beds also, while in the underlying Ecca beds silicified wood is remarkably abundant. In the shales accompanying the abnormal coal at Camdeboo, Glossopteris, Calamites, etc., are present, also much iron pyrites, associated with white sandstones. I have not yet visited the Vereeniging coal seam, but intend doing so on my return, and should any evidence of a definite nature be obtained it will be communicated to this society. If glaciated material could be obtained above the coal seam this would be quite conclusive as to the zone to which the Vereeniging coal belongs. The mere fact that the seam rests upon Dwyka conglomerate proves nothing, unless a distinct conformity is present.
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Transactions of the Geological Society of South Africa, 5, 63-65
The question of coal seams in the Sub-Karroo measures has engaged a great deal of attention for many years, but to date no workable coal has been found. It is stated that Glossopteris - a typical fossil of the Transvaal and Natal coal measures - has been found in the Ecca shales, which, according to Dr. Molengraaff, have been deposited from material derived from the trituration of rocks in the glacial Dwyka conglomerate. The discovery of this fossil involves questions which cannot be gone into to-night, but a cursory glance at the conditions prevailing during the period of continental glaciation reveal facts which are opposed to the theory of coal occurring in these glacial shales. The climatic conditions must have been too severe to have supported an abundant flora, and the occurrence of Glossopteris leads to the hypothesis that either this plant existed in pre-glacial times, and was preserved in the glaciers, and on the retreat of them was deposited in the Ecca shales, or it was a plant living in an extremely cold climate. The occurrence of Glossopteris on the other hand, associated with abundant reptilian remains in a higher horizon, is against the latter view, and points rather to the fact that it preferred a warm clime.
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Transactions of the Geological Society of South Africa, 5, 69-75
I wish now briefly to review how matters stand concerning the big problems of South African geology, and perhaps I may in passing just touch upon a few of the minor ones. To begin with the chief problem, the key to all the others - I mean the knowledge of the formations taking part in the structure of this country and the relative position of one to the other - that is still very imperfectly solved. It is, certainly, almost generally accepted that three main divisions must be distinguished in the series of formations of the Transvaal, each of them being separated from the other by a very marked unconformity. These three main divisions are, reckoning from below upwards:- 1. The South African Primary System. 2. The Cape System. 3. The Karroo System.
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Transactions of the Geological Society of South Africa, 5, 75-77, 2 figs
The writer begs to submit to you a few theories on the above subject. To illustrate same a rough plan and cross section is appended. An accurate survey has not been made, and the lines of outcrop are approximate only. That in his opinion a huge earth movement has occurred in the neighbourhood of Witpoortjie causing a fault extending from Vlakfontein or even still further south up to Honingklip on the north. The ground on the west side of the fault has been moved forward by an undulatory movement. On the east side of the fault the ground is practically undisturbed excepting close to the fault. The movement which pushed the earth northwards caused crumblings and undulations, synclines and anticlines
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Transactions of the Geological Society of South Africa, 6, 101-103
The Kromdraai quartz reef is a bedded vein in the quartzites of the Black Reef Formation. It does not change its horizon all along the strike, and is alwys found intercalated between the two beds of quartzites overlying the Black Reef. These two beds of quartzite were separated by a very thin band of slate, from one to six inches in thickness. The fissure opened along this line of weakness, and was filled in the first instance by a blue laminated quartz with stringers of iron and arsenical pyrites along the interstices between the laminae. The quartz is rarely compact, and wherever this is the case the pyrites is irregularly interspersed. The fissure, however, opened a second time and allowed the deposition of a milky white compact quartz with irregular bunches of iron and arsenical pyrites. In the latter, arsenical pyrites predominates, whilst the blue quartz carries more iron pyrites. The white vein is the more irregular one and disappears sometimes altogether, especially towards the western extension. In many cases both veins have an equal development. The white vein forms just as often the footwall portion as the hanging-wall portion, and is also sometimes found in the centre of the blue vein. In only very few instances the white vein predominates and fills the fissure nearly entirely, but the blue vein never fails to put in an appearance.
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Transactions of the Geological Society of South Africa, 6, 104-105
The granite, invariably met with at the base of the Lower Witwatersrand Beds, is generally considered an intrusive rock. It is certainly a fact that in Capetown the old granite is intrusive in the Malmesbury Beds, but I am not aware that a similar occurrence can be found in the Transvaal, though no doubt the existence of amphibolites, chloritic schists, quartzitic schists, with contact minerals such as garnets, andalusite and tourmaline, appear to speak for contact metamorphism caused by the intrusion of the granite.
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Transactions of the Geological Society of South Africa, 6, 106-110
There has been some sensation lately on the discovery by Mr. Bleloch of the Main Reef in the Klerksdorp district on the farms Palmietfontein and Buffelsdoorn. It would be rather a wonderful thing to have the Main Reef discovered in a district which has been already searched for many years; but though the discovery may be proved to be an error, some valuable geological work has been done by Mr. Bleloch, which enriches our knowledge of that district. The theory, according to which the Main Reef runs through Buffelsdoorn and Palmietfontein, is chiefly based on the occurrence of similar rocks in the same general succession at the Henry Nourse and on the farms Buffelsdoorn and Palmietfontein. Although it seems peculiar to select the strata at the Henry Nourse for comparison with the Klerksdorp Formation, whilst there are so many more and better profiles, especially on the West Rand the latter being nearer and probably more similar to the Klerksdorp district, let us now keep to the profiles given.
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Transactions of the Geological Society of South Africa, 6, 114-115
Mr. Dorffel's paper has raised a question of great geological interest, and the opinion therein expressed is the more valuable because the writer is intimately acquainted with the well-known contact zone of Eibenstock in Saxony. Considering, say, the granite immediately to the north of Johannesburg; firstly, if the Witwatersrand Beds had simply been denuded from its surface, one would expect the granitic mass to stand out boldly above the surrounding country; secondly, if the granite were intrusive, reasoning from analogy with other districts where it is intrusive (e.g., Cornwall and Devon), the same would be expected as in the previous case; thirdly, if the Witwatersrand Beds had been laid down more or less horizontally on the granite, and the latter had subsequently been elevated in certain places, owing to the crumpling and folding of the earth's surface due to contraction as a consequence of secular cooling, fracturing the overlying beds, which, owing to the alternations of conglomerates, quartzites and shales, would be brittle and non-elastic, then what actually does occur is just that which would be expected, viz., that a portion of the upturned edges of the lower Witwatersrand Beds should stand up above the level of the adjacent granitic mass, forming an abrupt escarpment In the particular district under consideration, contact minerals such as tourmaline, garnets, axinite, etc., are not present or, at all events, not in noticeable quantity; and this is only natural if pressure-metamorphism only has occurred. However, the absence of these minerals is no proof that there teas been no contact-metamorphism, for, as Dr. Hatch has recently pointed out, the slates of the Witwatersrand district are closely related to the quartzites in composition, and that, although it is possible that there is some admixture of clayey matter, they are of a quartzitic nature. This being so, it may be the constituents necessary to produce the usual contact minerals may not exist or not in sufficient abundance.
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Transactions of the Geological Society of South Africa, 6, 116-122
Before proceeding with the following criticism dealing with Mr. Kuntz's paper on the Main Reef Horizon in the Klerksdorp district, I wish to say that, although in direct disagreement with my views, I have found Mr. Kuntz a most courteous antagonist; and I wish to thank him for his kindly reference to the work I have been doing at Klerksdorp. I may say that the basis of the work of correlation which I have undertaken was the definite statement made in a report by Mr. David Draper on the western area generally and on Rheebokfontein in particular, that the well-known quartzite ridge, running N.E., S.W. from Rheebokfontein to Eleazar, and situated about one-and-a-half miles west of the Buffelsdoorn Mine, belongs to the same horizon and is identical in character and in geological position to the similar ridge running along the Rand to the north of the Main Reef Series, and known how for years past as the Green Quartzites. This statement, and the report generally, was confirmed and countersigned by Professor Molengraaff. Having called in two such able and experienced geologists, I thought it would be a foolish thing not to take steps to profit by their advice. Accordingly, I set to work and made an exhaustive comparison of the rooks overlying the Green Quartzites in the Buffelsdoorn area with the rocks underlying the Main Reef Series on the Rand, working chiefly across the Henry Nourse section. The results of this examination are, to my mind, extraordinary in the closeness of the correlation established. Not only has it proved to a demonstration that Mr. Draper and Dr. Molengraaff were right as to the identity of the Green Quartzites, but the positions of such important divisions of the Witwatersrand beds as the Carrick Shales, the Government Reef Series, the Main Reef Series, and the Bird Reef Series have been definitely located, and that for the first time in the Klerksdorp area. I have shown the results to Mr. Kuntz, among many others, and he alone has expressed a definite opinion that the correlation is erroneous.
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Transactions of the Geological Society of South Africa, 6, 123-125
I do not intend to discuss Mr. Kuntz's paper in detail, but wish to remove all doubt from his mind regarding the green quartzite on Palmietfontein and Buffelsdoorn. As he states, "there are several beds of green quartzite in the Witwatersrand Beds, and it is necessary to find the Hospital Hill State beneath the true bed in order to be certain as to its geological position". This is exactly what I did before I came to the conclusion that the green quartzite at the Buffelsdoorn poort was the continuation of the bed found under the Main Reef Series. I followed the Hospital Hill Slate from Lapdoorn, where it outcrops very boldly through the farms Leeuwfontein No. 656, Kromdraai No. 391, Rooipoort No. 380, Syferfontein No. 390, Buffelsdoorn No. 660, on to Rheebokfontein No. 550. Along the whole of this distance the slates can be traced, though the striped variety rarely comes to the surface. The green quartzite bed can also be followed distinctly. I place specimens on the table for the members to examine. These were taken from different spots on the farms Buffelsdoorn and Rheebokfontein. To my mind they are conclusive, and consequently I hope Mr. Kuntz will be convinced.
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Transactions of the Geological Society of South Africa, 6, 128-129
The arrangement of the rock specimens collected by Mr. W. Bleloch from the Henry Nourse section, and from Buffelsdoorn and Palmietfontein into parallel series of similar colour, mineral composition and texture, and also succeeding each other in a precisely similar manner, leads us to infer that the succession of beds from the green quartzites to the whetstone above the Bird Reef Series is approximately the same in the three districts. Although Mr. Bleloch does not expressly state this identical succession, it appears to me that this is the basis of his correlation. It is evident that such a correlation is based upon a supposed similarity in the conditions prevailing at approximately the same time in the three districts, that is to say the conditions were such as to produce strata consisting of rocks of the same texture and composition, and also having the same order of sequence in the three places. This result is somewhat remarkable if we consider the distance between the Henry Nourse and Buffelsdoorn, and as Mr. Draper has stated in his paper, "it would be wonderful indeed if the resemblance between the different sections did not vary". It is, however, in the strata immediately above the Main Reef Series that differences are readily discoverable. So many boreholes have been sunk in the central and western Rand that we know precisely the nature of the rocks immediately overlying the Main Reef Series.
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Transactions of the Geological Society of South Africa, 6, 130-132
No abstract. Mr. Kuntz reply to each discussion on 'The Main Reef Horizon in the Klerksdorp district' by W. Bleloch (pp. 116-122, D. Draper (pp. 123-125), J. Zimmerman (p126), M.S. Higgs (p127), and D. Wilkinson (pp. 128-129).
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Transactions of the Geological Society of South Africa, 6, 16-19
Apart from its own existence, the most interesting feature about the Transvaal coal is its intimate association with that much discussed rock, now definitely recognised as of glacial origin, the Ecca or Dwyka conglomerate. Taking Vereeniging as a locality typical of the coalfield, one finds that the coal there rests on the glacial conglomerate, while here and there on the roof of the seam are lenticular patches of the same deposit. The sandstone forming the main covering to the coal not infrequently contains scattered boulders of quartzite and other rocks common in the conglomerate, and there can be no doubt that the ice-action responsible for the conglomerate of the foot-wall, was also the source of the erratic boulders in the sandstone above the seam. In correlating the coal formation in the north with the beds of the Cape Colony, one must bear in mind first the position it occupies in relation to the Dwyka conglomerate, and second the evidence of the fossil flora. I agree therefore with Mr. E.J. Dunn's later view as expressed in a paper entitled "The Dwyka Coal Measures at Vereeniging", and consider not only the coal of Vereeniging and that of the Orange River Colony, but also that of the eastern Transvaal and the neighbouring portion of Natal as of Ecca age.
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Transactions of the Geological Society of South Africa, 6, 20-26
The main outlines of this interesting and extremely well-defined Mountain-land have been known for years, and the object of this paper is to bring before the members of the Society some details, which may help to explain the uncommon tectonics of this area. The South African Primary System, Cape (Transvaal) System, and the Karroo System are discussed in the paper.
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Transactions of the Geological Society of South Africa, 6, 3-8
The main object of the paper, therefore, is rather raise discussion on what, in my opinion, are important geological economic features, possibly of great future industrial importance, to mining operations in this district (De Kaap).
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Transactions of the Geological Society of South Africa, 6, 30-34
Dr. F. H. Hatch said:- Dr. Molengraaff has described the main features of the Vredefort district with great clearness, and I think that he has brought together a considerable amount of evidence to favor his view that the beds have been overtilted. When I first studied this district in 1896, it appeared to me that the apparent inversion of the beds might be explained by overthrust faulting, i.e., that the Lower Witwatersrand Beds had been thrust up from below, and brought to lie over the Upper Witwatersrand Beds, and that a similar fault existed between the Upper Witwatersrand Beds and the Dolomite, the position of this latter fault being masked by an intrusion of basic igneous rock. The relation of the Dolomite, Black Reef, and Klipriversberg Amygdaloid I then considered to be normal, i.e., that the Rlipriversberg Amygdaloid occurred to the north of the Black Reef, and the Black Reef to the north of the Dolomite. Subsequent examination has strewn me that Dr. Molengraaff is right in holding that the Quartzites referred to are the lowermost beds of the Gatsrand formation, and that the Rlipriversberg Amygdaloid lies to the south of the Dolomite; the Diabase, which lies to the north, belonging to the Gatsrand formation. With regard to this part of Dr. Molengraaff's theory, I am now quite in agreement with him, and I think it extremely probable that he is also correct with regard to the overtilting of the Witwatersrand Beds. The Honorary Secretary read the following contribution to the discussion by Mr. Stanger Higgs:- Dr. Molengraaff has described the general geological features of this district in his recent paper (S. A. Geo. Soc., June 8th, 1903) most fully, so in order to avoid prolixity I shall follow the sequence of beds as described by him, south to north. A. Granite, B. South African Primary System, 1. Lower Witwatersrand Beds, 2. Upper Witwatersrand Beds. C. Amygdaloidal Diabase. D. Cape (Transvaal) System, 1. Black Reef Series, 2. Dolomite Series, 3. Gatsrand Series.
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Transactions of the Geological Society of South Africa, 6, 34-46
Mr. A.R. Sawyer said: - Following on the question relating to the occurrence of carbonaceous shale on the Dwyka Conglomerate at Prince Albert which I asked Dr. Corstorphine at the last meeting, I would refer to Section III, pages 9-11 of the report I made to the Cape Government in 1893 on the geology and mineral resources of the division of Prince Albert and surrounding districts, and to the plans and sections which accompany this report, relating to this particular question. Dr. Corstorphine has been the geologist of the Cape Government for some years subsequently and has in that capacity had more time to give to the subject than I had during the few months whilst I was engaged on my report. I think therefore that his comments on this particular part of my report must be very valuable. I append portions of Tables III. and IV., and would refer to Section No. 4 and Plan No. 2 of that Report. Since then I have sum; a shaft between the Upper and Lower Rooikopjes, south of Heidelberg, in what I have called the South Rand Coal Field (see paper read September 14th, 1897, before the Institution of Mining Engineers). Besides the thick coal seam exposed thereby, I found blackband ironstone as a lenticular mass amongst the sandstones and further Lepidodendroid fossils. I also found interbedded white limestone similar to that occurring in the carbonaceous shales of Prince Albert. It is now generally admitted that the flint breccias which I found in the borehole at Viljoens Drift, and the breccia which I found subsequently in abundance in the South Rand Coal Field form part of the Dwyka Conglomerate formation, and that the overlying Coal measures do not form part of the Ecca Beds, but of the Beaufort Beds. I have described the Dwyka Conglomerate occurring in the South Rand Coal Field in my paper bearing that title. I have described it there as breccia, as with few exceptions the pebbles and blocks are angular. It varies in thickness from a few feet to 251 feet, but its average thickness is about 60 feet. The blocks and pebbles consist of quartzite and quartz, gneiss, shale, etc. The occurrence of brick-red grains is characteristic. This is also characteristic in the Viljoens Drift breccia. The breccia is in some places interstratified with thin beds of shale and sandstone. It rests immediately on the granite and on the "banket formation" at the edges. As a rule the deeper it is the thicker it is. The matrix consists in part of quartzite grains and fire clay. The thick coal seam is only from 60 to 120 feet above the breccia. At Viljoens Drift the lower coal seam is only 60 feet above the breccia, which is 46 feet thick. In this connection the following parts of sections of boreholes which I have put down between the Upper and Lower Rooi Kopjes south of Heidelberg are of importance.
Dr. G. A. F. Molengraaff said:- Dr. Corstorphine basing his conclusions on finds made in the Viljoensdrift Mines, where coal seams occur interbedded with layers of the Dwyka
Conglomerate, takes the coal beds of the Transvaal to belong to the Ecca Beds in which beds he embodies the glacial conglomerate, known as Dwyka Conglomerate. Thus he considers the Transvaal coal to belong to an older period than the coal found in the Stormberg Beds in the Cape Colony. Thus I think Dr. Corstorphine goes much too far in saying "Now in the Transvaal the coal sandstones follow directly above the Dwyka Conglomerate, and stratigraphically they are therefore in the same position as the Ecca Beds of the Cape". I think that the development of the Karroo at Vereeniging District, because of its local character, does not justify this generalisation. Dr. Corstorphine replied. As regards the probable existence of Coal in the Ecca Beds of the Cape Colony raised by Mr. E.J. Dunn in 1886, and referred to by mr. Sawyer, I know no facts whatsoever in support of that theory. As presented for publication Dr. Molengraaff's portion of the discussion reverts to his former view. There is not, however, so much divergence as might appear between that view and mine The most essential is the difference of opinion as to the development of the Karroo Beds at Vereeniging, and the view one takes of the conformable succession of sandstones above the Dwyka in Ermelo, Vryheid and Middelburg To my mind the mere fact that a coal seam occurs several hundred feet above the Dwyka in these districts, does not necessarily prove that coal seam to belong to a different period geologically from the seam found directly on the Dwyka at Vereeniging. The material deposited immediately upon the glacial conglomerate from the streams which emerged from the ice, is not likely everywhere to have been fine silt, and the thick sandstones found above the conglomerate in one locality may well be the exact correlative of thin beds of shale in another.
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Transactions of the Geological Society of South Africa, 6, 47-49
In connection with Dr. Molengraaff's paper, in which he refers to the relative ages of the Vredefort and Half-Way House granite masses, it may not be out of place to remark on other granite masses in the Transvaal.
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Transactions of the Geological Society of South Africa, 6, 50-51
The first section is taken through Venterskroon and Potchefstroom, and continued to the north-west and south-east. It represents a stretch of country about 40 miles in extent, viz., from the granite in the Orange River colony to the Lower Witwatersrand Beds some distance north of Buffelsdoorn. The second section is taken in the same direction, but further to the north, through Koloniesplaats and Lapdoorn. It is partically identical with the north-west portion of Section No. 1. This section, which embraces a distance of 11 miles, is interesting as showing a rather sharp anticline in the Gatsrand and Dolomite formation.
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Transactions of the Geological Society of South Africa, 6, 56-57
Following the observations of Mr. E. J. Dunn at Vereeniging, Dr. Corstorphine appears to base his opinion on the age of the Central South African coal measures, mainly on the result of his observations of the association of Coal and Dwyka at Vereeniging. I have not had the privilege of inspecting these associated measures at Vereeniging, but from observation elsewhere - in the Transvaal and Natal - it appears to me that at Vereeniging there is a hiatus in the geological sequence that is misleading.
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Transactions of the Geological Society of South Africa, 6, 58-59
The sections out of the Potchefstroom district shown at the last meeting by Dr. Hatch, contain some interesting facts which induce me to say a few words on them. The first longer section shows a syncline of the Witwatersrand formation covered by amygdoloidal diabase, Black Reef. dolomite and Gatsrand formation. Though the Venterskroon beds tip to the south we must say "syncline", because we know that the normal dip is away from the granite boss and that therefore at a shallower or greater depth the dip must turn to the north. This fact as well as the position of the other younger formations were known already, but the term "Lower Witwatersrand formation" for the northern part of the syncline is new. The geological maps of that district give the Witwatersrand beds there as upper and lower ones, and it was some time ago and after my first trip to Klerksdorp, that I suggested to Dr. Hatch a corresponding alteration of his map giving all the Witwatersrand beds outcropping between Randfontein and Klerksdorp as "Under Main Reef formation". If we divide the Witwatersrand beds into three parts, the lower from the sericitic schists and quartzites overlying the granite to the quartzites overlying the Hospital Hill shales, the middle one from there to the neighbourhood of the Main reef and the upper part including Main reef and Elsburg series, then the upper beds are entirely covered by the overlying younger formation. The lower ones are uncovered south-west of the line Thys-syn-doorns-Du Toits Spruit, and the middle beds begin to re-appear from below the diabase in Eleazar and Buffelsdoorn towards Klerksdorp, consisting of coarse sandstones with interstratified conglomerates and red shales.
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Transactions of the Geological Society of South Africa, 6, 60-67
Data requisite for the determination of the relative age of old river deposits. The types of implements of use in investigating the relative age of old river deposits. On the discovery of a drift on the farm Roodekop containing implements of eolithic and later types. On the discovery of implements of palaeolithic types in the drift of the Bezuidenhout Valley. On the discovery of implements of neolithic type on the farm Elandsfontein no. 2.
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Transactions of the Geological Society of South Africa, 6, 70-73
The slates occurring in the Hospital Hill and Witwatersrand series are of sedimentary origin.
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Transactions of the Geological Society of South Africa, 6, 75-76
Professor Molengraaff has dealt with the Vredefort granite mass in a paper which he read before this Society recently. The object of this paper is to supplement his remarks so far as they affect the eastern and south-eastern extension of this granite mass. The accompanying plan shows the course which I believe the belt of Hospital Hill and Witwatersrand rocks assume in that direction from evidence which I have obtained.
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Transactions of the Geological Society of South Africa, 6, 79-81
The members of the Geological Society of South Africa are much indebted to Mr. Corstorphine for bringing forward such an interesting subject as the geological age of the Central South African Coalfields. There has always been a difference of opinion between what we may call the Cape geologists on the one hand, and Transvaal geologists on the other on this question, and the views of those acquainted with the geological deposits of both colonies cannot fail to be interesting, but the writer imagines that when Dr. Corstorphine has had more experience of the coal deposits of the Transvaal he will modify his views as to the productive coal measures being of Dwyka or Ecca age, and therefore contemporaneous with the glacial deposit. There is nothing remarkable in the kind of association existing between the Transvaal coal formation and the Dwyka conglomerate, as similar deposits occur in other parts of the world where a similar pronounced unconformity exists, but it does not necessarily follow that wherever the Dwyka exists Ecca beds or even coal seams will accompany it; in fact, in the Transvaal it is only in limited areas that the Ecca beds are found, and any skilled prospector would immediately cease prospecting for coal when be struck the Dwyka conglomerate. Dr. Corstorphine has failed to show that the boulders overlying the coal seam at Vereeniging are of Dwyka age, as it is not unusual to find boulders amongst the sandstones of the coal formation, and at such horizons as to make their association with the Dwyka an impossibility. It is also a mistake to regard the Vereeniging coal deposits as typical of the Transvaal coal deposits, as a matter of fact they are fortunately far from being so, and can only be said to be a type of the irregular occurrence of isolated coal deposits existing in this portion of the Transvaal, evidently laid down at different horizons, as scarcely any two deposits - and especially coal seams - occur at a similar distance above the Dwyka conglomerate.
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Transactions of the Geological Society of South Africa, 6, 82-88
Since errors have crept into the list of the fossil flora of the Transvaal, which are quoted and transmitted by most writers on the subject, I beg diffidently to suggest that a catalogue be prepared including only those known to have been found here, and determined by some specialist in fossil botany. The great importance of fossils, is, that a list of them taken in combination with a general law affords a means of determining the geological age of the strata in which they occur.
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Transactions of the Geological Society of South Africa, 6, 89-90
Nepheline-syenite was discovered in the Transvaal by Prof. E. Cohen in 1873 close to the Zwartkoppies, not far from Rustenburg. The specimens he collected were described later by Mr. Wülfing, and determined as "foyaite". In this porphyritic rock the nepheline was found only in the groundmass, filling, together with sodalite, the gaps between the large, lath-shaped phenocrysts of feldspar. Twenty-five years later, in 1898, I found nepheline-syenite in several localities in the Bushveld, especially on the farms Zeekoegat No. 287, and Leeuwfontein No. 320, both situated north of the portion of the Magaliesberg between Derde Poort and Franspoort, and also in the vicinity of the Bothasberg, north of Middelburg.
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Transactions of the Geological Society of South Africa, 6, 9-11
The curious ridges of quartzite that project up upon the beach are noteworthy (in looking at the drawing it must be remembered that, owing to the difference between the horizontal and vertical scale, they are much exaggerated), but are paralleled on the modern shoreline in the immediate neighbourhood. The beach, which is at a considerably higher level than the modern one, consists of pebbles of quartzite. In places these are cemented together into a hard conglomerate. It contains numerous, but much-rolled shells, of which the following is a list of those I obtained. As will be seen later on, they have an important bearing on the evidence afforded by this section. The commonest was Cominella porcata.
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Transactions of the Geological Society of South Africa, 6, 93-94
The cobalt lodes on the farm Eenzaamheid - better known as Balmoral - occur in a grey dense quartzite belonging to the upper Magaliesberg formation. The geological horizon is well determined by the outcrop of typical Magaliesberg quartzites on the farm Dwaalfontein, six to seven miles south of Balmoral. The northern portion of Dwaalfontein, the farm Hartebeestefontein and the extreme southern portion of Balmoral are covered hy Coal Measures. An outcrop of Dwyka Conglomerate strikes across the southern portion of Balmoral, dipping gently south. The Dwyka overlies, unconformably, of course, beds of blue and red shales, partly highly ferruginous, belonging to the Waterberg formation. Here and there typical Waterberg conglomerates are very conspicuous. The greater portion of the farm is covered by these shales, with the exception of the centre of the southern portion, where the Waterberg shales have been removed by denudation, and the Magaliesberg quartzites with the cobalt lodes exposed. It is also here that we meet with intrusive rocks. Red granite forms an enormous boss along the western boundary, and is probably the exposed part of a laccolite. Numerous veins of the same rock can be seen crossing the road to Spitzkop. This rock is a holocrystalline aggregate of orthoclase, quartz and mica with fluorite as au accessory. In the dykes, quartz and mica predominate, and felspar is subordinate. The rock is similar to the one described by Dr. Molengraaff in his report of 1898.
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Transactions of the Geological Society of South Africa, 6, 95-97
The object of my mission was to verify the existence of certain banket beds, of which samples had been sent to Johannesburg and on assay had given good gold values. Unfortunately for those interested, this banket was found to occur simply as boulders, mixed with a great number of other boulders of non-auriferous banket, quartzite, slate, and quartz in a coarse gritty matrix, consisting chiefly of quartz, and cemented by oxide of iron.
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Transactions of the Geological Society of South Africa, 6, 99-100
The conclusion to which the exposures in the Suikerbosch Rand River lead one is that the "new formation" is essentially a volcanic one, lying unconformably upon the older Witwatersrand Beds, and itself covered unconformably by the Black Reef Series. It holds therefore the stratigraphical position to which the Klipriversberg Amygdaloid has been assigned, and the association of the amygdaloid with the slaty diabase and volcanic breccia in the Suikerbosch River Valley is good evidence that when the whole of the "new formation" is known we shall have the complete history of that phase in the geological history of the region of which till recently the Klipriversberg rock alone was the recognised representative. The recognition of the position of this great volcanic series has an especial interest, as it is more than probable that it will be found to have representatives in the amygdaloids, quartz-porphyries, and quartzites of the Vaal River and the Kimberley mines, and in the volcanic rocks of Beer Vley, Hopetown, and so afford us a new and much needed element of correlation for the rocks of the Transvaal and the Cape Colony.
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Transactions of the Geological Society of South Africa, 6, p126
I beg to pass also a few remarks on Mr. Kuntz's interesting paper. The most western point in the West Rand district, where up to now the Witwatersrand Formation has been tapped, is on the farm Twyfelvlakte No. 286, where a borehole has been sunk in order to ascertain the Main Reef Horizon below the Dolomite. This borehole has intersected Witwatersrand Formation from 1,250 to 2,116 feet, at which depth the hole has been abandoned. A great number of leading engineers and geologists have inspected the core of this hole, and, as far as I can gather from their reports, they unanimously come to the conclusion that the borehole was located too far north to explore the Main Reef Horizon. They all based their opinions on the fact that the position of the Witwatersrand Formation intersected in the hole consists of banded and slightly magnetic shale interbedded in quartzite. These gentlemen consequently have indirectly declared that all shales of that specific character belong to the Sub-Main Reef Horizon.
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Transactions of the Geological Society of South Africa, 6, p127
At the last meeting of the Society Mr. Julius Kuntz has referred to the beds at Venterskroon as representing Elsburg Series, and I think that it is only my duty as one who has had years of experience in that district to express my opinion to the effect that the Amazon Series is undoubtedly Elsburg, and further to point out that in this formation the only shale beds that occur are absolutely different to the shales which occur at Buffelsdoorn, or the shale which overlies the Buffelsdoorn Series on Palmietfontein. At Buffelsdoorn and on Palmietfontein the shales in their undecomposed state are dense, green, tough, hard, highly ferruginous beds, which on weathering acquire the colour of red ochre, or rather hasmatite, while the shales in the Elsburg Formation are really more truly fine-grained sandstones with a shaley structure, more or less friable and micaceous. In this matter I must agree with Mr. Kuntz, therefore, that in spite of the similarity in the shape of the pebbles in the Buffelsdoorn and Elsburg Series, it is highly improbable that they are identical.
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Transactions of the Geological Society of South Africa, 6, p15
The President pointed out that there was a contradiction on page 4 of Mr. Rathbone's paper, where he first stated that "the most ancient rock formation which underlies all the other rocks, and may consequently be termed the basal rock in this district, is granite", and a little further on said that "the granite has at some remote geological period tilted up the adjoining strata". He would like to know what Mr. Rathbone's opinion on this question was, because, of course, as soon as one admits, as he was personally inclined to do, that the granite has been intruded into the stratified rocks of the district, it is necessary to look on the granite as younger than the surrounding rocks. The President could not agree with Mr. Rathbone where he identified the Duivel's Kantoor conglomerates with those found near the "Three Sisters" and "French Bob". The Kantoor conglomerates belong to the Black Reef Series, and lie with a most distinct unconformity on the much older rocks of the Barberton Series, to which rocks the conglomerates of the "Three Sisters" and the " French Bob" belong. Neither could he see how the argillites of the Pretoria beds overlying the Kantoor conglomerates, a big body of dolomite and chert, however, intervening, could be correlated with the Pietermaritzburg shales, which are considered to belong to the Ecca shales. In enumerating the gold-bearing deposits, the President thought that Mr. Rathbone had omitted one important - and in the Barberton district, largely represented - class of lodes, viz., those found in fault or thrust planes. They generally show beautiful slickensides on their walls, as for instance at the United Ivy mine, and were probably formed at the time that the strata were folded by the mountain building forces.
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Transactions of the Geological Society of South Africa, 6, p68
In the south-western and southern portion of the Transvaal occur some more or less scattered rocks, the correlation of which with the known formations has been always doubtful. Amongst these I will quote the banded cherts and conglomerates with big boulders of Hartebeestfontein to the west of Klerksdorp, the boulder beds of Zendelingsfontein in the Klerksdorp district, which contain so many boulders of auriferous conglomerate that prospecting work has been carried out on them for gold, and the shaly conglomerates which occur under the Black Reef series on the farm Kromdraai to the north of Krugersdorp. My investigations have led me to the conclusion that all these different rocks belong to a hitherto unrecognised formation, which is younger than the Witwatersrand Beds, but older than the Black Reef Series. This formation is chiefly composed of shales, schists and shaly congomerates, banded cherts, amygdaloidal diabase, tufas, grits and very coarse conglomerates.
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Transactions of the Geological Society of South Africa, 6, p69
On the farm Stinkhoutboom, near Reitsburg, in the Orange River Colony, there is developed between the Black Reef proper and the Klipriversberg Amygdaloid a considerable thickness of coarse conglomerate, in which lie flattish pebbles or boulders of fine quartzite, the matrix being very gritty.
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Transactions of the Geological Society of South Africa, 6, p74
I may mention that this pseudomorphosis was, in the paper referred to, described as an occurrence of calcite pebbles, and it was attempted to explain how waterworn pebbles of such soft a material as calcite is could be associated with hard quartz pebbles.
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Transactions of the Geological Society of South Africa, 7, 1-6
No abstract.
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Transactions of the Geological Society of South Africa, 7, 110-114
The object of this paper is, firstly, to describe certain variations of the granite mass of the Balmoral district of the Transvaal, which is situated some fifty miles to the east of Pretoria, and is traversed by the Delagoa Bay Railway; and, secondly, to indicate the probable relation of the red granite to the cobalt lodes of that district. The granite mass covers an area of, approximately, ten square miles, and occurs on the south-western portion of the farm Eenzaamheid, on the south-eastern portion of Spitkop, and extends a short distance on to Hartebeestfontein.
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Transactions of the Geological Society of South Africa, 7, 115-116
I now wish to lay stress on the fact that there exists in many places in the Vredefort area a rather sudden alteration in dip of the strata between the upper and the lower portions of the Upper Witwatersrand Beds - a fact of which, although I observed it in many places, I have not given the significance it most probably deserves.
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Transactions of the Geological Society of South Africa, 7, 117-122
The line of section indicated in the title passes through the Heriot, Jumpers Deep, and Jupiter properties, and is continued at right angles to the strike to the granite on the north and the diabase on the south. The main features of this section are shown in the second and third portions of the accompanying diagram.
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Transactions of the Geological Society of South Africa, 7, 123-129
The country to be dealt with in these notes lies in the Eastern Transvaal, roughly between the Usutu River on the north, Bangkop on the west, Swaziland on the east, and Piet Retief on the south. Naturally, the geological features of such an extensive piece of country must be dealt with in a very general manner, and only the most prominent points can be mentioned. The field work on which this paper is based extended over thirty days, and during that time a large area was covered. Nerston: Gleneland section. The granite. The gneisses, schists, etc. The quartzite-conglomerate group. The conglomerates. The diabases. The Dwyka Conglomerate and Ecca Shales.
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Transactions of the Geological Society of South Africa, 7, 130-132
On a recent trip through a portion of Bechuanaland, I was struck by the fact that some of the typical Transvaal formations cover a wide tract of country in that region. The Dolomite, for example, with its associated Black Reef, and the overlying Pretoria Series, have an extensive development outside the Transvaal.
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Transactions of the Geological Society of South Africa, 7, 133-135
On a recent journey through the districts traversed by the Elands and Olifants Rivers, further occurrences of the conglomerate and associated grits and sandstones were met with, some forty-five miles further north than those above referred to. Some interest attaches to these outlying portions of the conglomerate as bearing on the general question of the original extent of the Glacial Conglomerate in South Africa.
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Transactions of the Geological Society of South Africa, 7, 136-139
No abstract.
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Transactions of the Geological Society of South Africa, 7, 140-145
Macroscopically, the conglomerates occurring in the Witwatersrand Series consist chiefly of rolled fragments of quartz; but fragments of quartzite, banded chert, and slate also occasionally occur. The quartz and quartzite fragments, from their well-rounded character, have obviousloy been water-borne; the banded chert and slate pebbles are usually of a more angular and elongated shape. The pebbles are of all sizes, but in the Main Reef Series the average dimensions are those of a small walnut. They lie in a matrix of quartz grains, which, by the deposition of secondary quartz, has been cemented to a hard and compact mass.
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Transactions of the Geological Society of South Africa, 7, 147-150
On a recent visit to the hill range known as Mont Maré, eight miles south of Pietersburg, I collected a series of schistose rocks, which especially roused my interest on occount of the prevalence in them of types which are generally held to be characteristic of a zone of contact metamorphism around granite intrusions. Mont Maré is an east and west range, situated immediately south of the old Kaffir station of Marabastad, and known before the discovery of the Witwatersrand as the Marabastad Goldfield, quartz veins being there worked for gold. The beds composing this range dip at a high angle (about 70°) to the south, and a section across their upturned edges discloses a great variety of rocks of sedimentary origin, but bearing evidence, in their foliation and richness in secondarily developed minerals, of strong metamorphism. Among the most highly metamorphosed members of the series are "knotted" schists containing both andalusite and ottrelite, ottrelite schist, phyllite and hornblende schist, while less altered types are micaceous quartzite, a banded quartz-magnetic rock (the "calico rock" of the old miners), and conglomerate, the latter sparingly developed.
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Transactions of the Geological Society of South Africa, 7, 15-17
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Transactions of the Geological Society of South Africa, 7, 151-160
The question whether the "Old Granite" is intrusive or not in the Witwatersrand Series has been discussed at length by several members of this Society, who have come to the conclusion that it does not intrude into these beds. Having had occasion to study several occurrences of intrusion of old granite into schists and quartzites at localities which are situated a hundred miles and more apart, it is my intention to lay these observations before the members of this Society. I will further try to establish the geological position of these schists, and by so doing, strengthen the argument in favour of the non-intrusion of the old granite into the Witwatersrand Series. The localities visited are so situated that I consider that the observations there made may be safely generalised, and applied therefore to the whole of the Transvaal, as well as to the adjoining States.
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Transactions of the Geological Society of South Africa, 7, 18-26
No abstract.
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Transactions of the Geological Society of South Africa, 7, 27-29
No abstract.
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Transactions of the Geological Society of South Africa, 7, 30-38
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Transactions of the Geological Society of South Africa, 7, 39-50
No abstract. General description of the Waterberg Formation. Extent of the Formation in the Transvaal. Previous references to the Formation. Relation of the Waterberg Formation to the Pretoria Series. The Wilge River section. The Balmoral section. Relation of the Waterberg Formation to the Red Granite. The base of the Waterberg Formation traced westward from Balmoral. Relation to later formations. Comparative age of the Waterberg Series. General summary.
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Transactions of the Geological Society of South Africa, 7, 51-56
No abstract. The Red Granite. Old granite and gneiss. The Dolomite Series. The Waterberg Series.
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Transactions of the Geological Society of South Africa, 7, 57-69
No abstract. The Karroo beds. Dolerite dykes and sheets of the post-Ecca age. Contact phenomena of the dolerite dykes and sheets. The Dolomite and Black Reef Series. Contact phenomena of the syenite sheets. The Upper Witwatersrand beds. Lower Witwatersrand beds.
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Transactions of the Geological Society of South Africa, 7, 7-8
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Transactions of the Geological Society of South Africa, 7, 70-76
Whilst the eastern part of the South African Continent has become famous for its gold and diamond mines, the western part seems to have been neglected by nature, its wealth in useful minerals, so far as at present known, consisting only of some rich copper deposits. Originally, certain eruptive vein rocks and crystalline schists seem to have been the mother rocks of the copper ore, from where it later on was transmitted also to other strata by lateral secretion, percolation, precipitation, etc. Today copper ore can be found in almost every formation - in veins, in layers, in fillings of caves, etc. Little Namaqualand. Great Namaqualand and Damaraland.
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Transactions of the Geological Society of South Africa, 7, 77-94
The following notes refer to a stretch of country situated in Damaraland, German South-West Africa; special investigations were made in that part of the country, which on the north and south is bordered by the Swakop and Kuiseb rivers respectively, on the west by the eastern boundary of the British Walfish Bay Territory, and on the east by about the 16th degree of longitude. I need hardly say that the accompanying stratigraphical map, covering an area of about 8,000 square miles, and made in a few months, does not pretend to be more than a sketch; it is merely attached to the paper for guidance and to show the principal tectonic features of the country, especially the relations of the granite to the Malmesbury Beds. The gneiss-schist area. Table Mountain Formation (Nama Formation of Schenk). Ore deposits.
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Transactions of the Geological Society of South Africa, 7, 9-12
To the east of Heidelberg a mass of granite is exposed over a portion of country which comprises the upper drainage area of the Suikerboschrand River. It is a typical grey granite, similar in all essentials to that lying north of the Witwatersrand. Along the western edge of the Suikerboschrand mass, through the farms Rietfontein 72, Kuilfontein 289, Vrischgewaagd 337, and Uitkyk 97, there stretches for a distance of about ten miles a conspicuous escarpment of the lowest Witwatersrand Quartzites, whose fallen debris generally covers the actual line of contact.
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Transactions of the Geological Society of South Africa, 7, 95-96
The Taaibosch Spruit referred to is the one that flows into the Vaal south-west of Vereeniging. The occurrence of stone implements in the deposits of this stream was originally pointed out to me by Mrs. L.I. Hutt, who, shortly after the publication of my paper on the discovery of implement-bearing deposits in the neighbourhood of Johannesburg, drew my attention to the fact that there were two specimens of Palaeolithic type from the farm Vaalbank in the Society's collection, and that she possessed a third, which she afterwards very kindly gave me. Having been down in that direction on one or two occasions since, I have been enabled to investigate for myself the relation of these implements to the deposits from which they were supposed to have come, and have obtained some data, which I venture to think are sufficiently interesting to bring before my fellow-members. The more important finds comprise a group of implements of Palaeolithic type form beneath and a group of implements of Neolithic type from above the alluvium. Implements of Palaeolithic type from beneath the alluvium. Other implements from the Taaibosch Spruit.
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Transactions of the Geological Society of South Africa, 7, 97-109
Although the geological features of the Bezuidenhout Valley and the adjoining area have been long known to local geologists, and have been referred to by several writers, no serious effort has been made to discuss them definitely or at length. The present paper is essentially an attempt to clear up some of the difficulties presented by the rocks of the valley; but in the course of our investigation we have found many points of geological interest outside the valley area, and we have therefore shown these on the accompanying map, which has consequently become a geological map of the invirons of Johannesburg. We scarcely expect to have our views of the structure of what is geologically an intricate piece of country accepted without discussion; but we believe that our explanation of its difficulties is the simplest, and therefore the most likely to be correct. Topography. The Witwatersrand beds. The Valley Fault. The beds forming Langerman's Kopje. The amygdaloidal diabase and associated rocks. Deductions as to the position of the Elsburg beds in the geological succession.
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Transactions of the Geological Society of South Africa, 7, p146
My object in bringing this very brief note before the Society is mainly to publish the accompanying figures of typical implements from this locality.
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Transactions of the Geological Society of South Africa, 8, 1-6
The country described in this paper, and shown on the accompanying map, is situated mainly in the Rustenburg district. It is crossed in a north-east and south-west direction by the range of hills known as the Witfonteinberg. This range is well defined for a distance of about fifty miles, and connects the Dwarsberg on the west, with the Waterberg Hills on the north-east. It forms a division between the plain, dotted with groups of small hills extending southwards to the Pilandsberg and the Bushveld, which on the northern side extends from this range to the Transvaal boundary.
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Transactions of the Geological Society of South Africa, 8, 104-105
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Transactions of the Geological Society of South Africa, 8, 106-107
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Transactions of the Geological Society of South Africa, 8, 108-109
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Transactions of the Geological Society of South Africa, 8, 110-134
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Transactions of the Geological Society of South Africa, 8, 135-137
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Transactions of the Geological Society of South Africa, 8, 138
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Transactions of the Geological Society of South Africa, 8, 139-140
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Transactions of the Geological Society of South Africa, 8, 141-146
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Transactions of the Geological Society of South Africa, 8, 147-150
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Transactions of the Geological Society of South Africa, 8, 151-157
Among the various problems which the Rand has presented to the geologist and the engineer, there has perhaps been none of greater interest than that involved in tracing the course of the Main Reef in the Far East Rand. Nowhere else in the world, probably, has deep boring been relied on to such an extent as in this region where the difficult work of following a sub-outcrop, overlain by many hundreds of feet of Karroo and the older Dolomite Beds, has been undertaken. In establishing the limits of the syncline formed by the Main Reef in the Far East Rand, the northern rim was first mapped out on Modderfontein No. 112 and Klipfontein No. 206, into Holfontein No. 227, the southern rim being surmised in the so-called Nigel Reef on Varkensfontein No. 217. This theory of the connection which might be found to exist between the Main and Nigel Reefs was suggested by Dr. Hatch as early as 1895; and his paper on the "Extension of the Witwatersrand Beds Eastwards," read before this Society in June, 1904, set forth the evidence for correlation. At that time a series of boreholes on the farms Grootvlei and Palmietkuil had partially delineated the eastern rim of the Main Reef Syncline, thus supporting the theory as to the continuity of the Witwatersrand Beds east and south towards the Nigel area. In the discussion that followed, the course of the Main Reef sub-outcrop beyond Daggafontein Borehole No. 1 was a point on which considerable diversity of opinion was expressed. It appears, however, that the results of subsequent boring operations on Daggafontein, taken in conjunction with the published results of Droogefontein borings, plainly corroborate the correlation theory, and refute the suggestion that the Main Reef outcrop would be found about 1,500 feet above the Nigel Reef. Before proceeding to a detailed account of the Daggafontein borings and the evidence to be deduced therefrom, bearing on the extension of the Main Reef in the Far East Rand, may I be permitted to refer briefly to the results of drilling on Droogefontein? The plan of the Far East Rand accompanying this paper shows the position of the Droogefontein Boreholes 1, 2 and 3, which, according to the published results, penetrated the Black Reef Series, the Amygdaloidal Diabase, the Bird, and the Modderfontein Series, cutting the Main Reef at depths of 1,514 feet, 1,351 feet, and 1,171 feet respectively. The data whereby the dip can be calculated accurately are not at my disposal, but a rough estimate based on the results of the Grootvlei-Palmietkuil joint Borehole and Droogefontein Boreholes 2 and 3, would probably make the dip of the Main Reef here between 7 and 8 degrees in a south-westerly direction, and give the contour line as indicated on the accompanying plan. Thus the drilling operations on Droogefontein have yielded important results in delineating a further portion of the eastern rim of the syncline and confirming the theory as to its course. Southwards from Droogefontein, the Palmietkuil
Boreholes and the Daggafontein No. 1 Borehole had previously indicated the course of the Main Reef for a further distance of 3½ miles, but beyond that point there existed an unknown territory in which theorists had free play. This area, comprising, roughly, the farms Daggafontein, Rietfontein and Vlakfontein, was left to be explored before a correlation between the Main Reef and the Nigel Reef could be definitely established; and in this way the later borings on the farm Daggafontein constitute an important link in the chain of evidence, establishing the continuity and regularity of the Witwatersrand Beds to within 51 miles of the Grootfontein Central Nigel Deep joint Borehole, and showing the existence of a reef at the base of the Kimberley Series, carrying good gold values and separated from the Main Reef by the complete series of rocks ordinarily encountered. With regard to Daggafontein drilling results, the impression appears to exist in the minds of some that much diversity has been found in the various boreholes, but the detailed sections given on Plate XVI. showing the rocks penetrated will dissipate any such idea; on the contrary, all the Daggafontein Boreholes to date have passed through a perfectly regular sequence of strata, and the section of Borehole No. 1 may be taken as typical of any or all of the boreholes on this property. The following is a summary of the results.
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Transactions of the Geological Society of South Africa, 8, 158-166
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Transactions of the Geological Society of South Africa, 8, 16-25
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Transactions of the Geological Society of South Africa, 8, 167-174
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Transactions of the Geological Society of South Africa, 8, 26-27
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Transactions of the Geological Society of South Africa, 8, 28-32
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Transactions of the Geological Society of South Africa, 8, 33-37
Under the name of Springbok Flats is usually included an extensive tract of generally flat country, extending from the neighbourhood of the Pietersburg Railway south of Warmbaths, north-eastwards as far as the location of Zebedela, a distance of some seventy miles. The Flats average about twenty miles in breadth, and thus include an area of some 1,400 square miles. A very large proportion of the total area, including nearly the whole of the more low-lying portions, consists of a huge sheet of amygdaloidal diabase known as the "Bushveld Amygdaloid". In the south-western portion of the Flats this broad expanse of diabase is bordered, both on the north and south, by low ridges rising from 50 to 200 feet above the general level. As a rule, these ridges are deeply covered with loose yellow sand, from which sandstone occasionally crops out, usually as small hummocky masses a few yards in diameter, but sometimes of larger dimensions. These more extensive outcrops give rise to numerous kopjes of a uniform and peculiar type, which form one of the most characteristic features of the Springbok Flats. A few of the larger of these kopjes, such as the Moloek's, Pankop, Zandfontein Kopje and Moroelaskop, are distinguished by special names, but the majority are nameless.
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Transactions of the Geological Society of South Africa, 8, 38-41
In the course of recent work in the neighbourhood of Rhenoster Kop, which lies about twenty miles north from Balmoral, a number of interesting rocks were met which throw considerable light upon the conditions prevailing during the deposition of the lower portion of the Waterberg Series.
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Transactions of the Geological Society of South Africa, 8, 43-46
The Murchison Range trends from the Drakensberg in a north-easterly direction for a distance of sixty to seventy miles. It consists along its entire extent of parallel chains of mountains, frequently intersected by cross valleys, and standing out conspicuously from the Low Country plains. The highest summit is the Spitzkop, with an elevation of just one thousand feet above the level of the plains. Gold-bearing deposits occur in the range over the greater part of its extension, and in its immediate neighbourhood.
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Transactions of the Geological Society of South Africa, 8, 47-55
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Transactions of the Geological Society of South Africa, 8, 56-62
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Transactions of the Geological Society of South Africa, 8, 63-65
Mr. C. D. Lealie, who has traveled for some months in the Lydenburg district, brought a very interesting collection of rocks from there, and by his courtesy I am now in a position to give a short note on some of his specimens which were exhibited to this Society on 20th February, 1905: crocidolite, andalusite-mica-schist, andalusite-hornfels, andalusite rock from the farm De Paarl no. 628.
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Transactions of the Geological Society of South Africa, 8, 66-81
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Transactions of the Geological Society of South Africa, 8, 7-15
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Transactions of the Geological Society of South Africa, 8, 82-87
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Transactions of the Geological Society of South Africa, 8, 88-103
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Transactions of the Geological Society of South Africa, 9, 1-9, 2 pl
During the later months of 1905 I made a geological survey of a large part of the Hay Division, and a rapid journey from Campbell to Barkly West and Kimberley. Much information was obtained as to the relations to older and newer rocks. The following account is a summary of the results, and it includes a few observations made on the journey to Barkly West. Contents: Topography of the area. Succession of strata. The Campbell Rand Series. The Griquatown Series. The glacial beds in the Griquatown Series.
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Transactions of the Geological Society of South Africa, 9, 10-15, 4 pl
In the following pages we propose to give an account of some of the results obtained during a recent survey of the rocks associated with or overlying the Pretoria-Johannesburg granite boss. Through the work of Molengraaff, Hatch and Corstorphine, the existence of a series of rocks, mainly igneous and younger than the Witwatersrand Beds, but occupying an unconformable position below the Black Reef Series, has now been recognised as the Ventersdorp System. The occurrence of beds belonging to this system in the neighbourhood of Kromdraai, north of Krugersdorp, was noted by the late Mr. Dörffel, and while our own work largely bears out Dörffel's conclusions, we find associated with true Ventersdorp conglomerates, a series of sedimentary rocks, which are best placed in the Swaziland Series. The area from which our observations are drawn forms a belt of country about seven miles from the base of the dolomite southwards, and follows the northern edge of the granite boss from Kromdraai across the Crocodile River to Knoppieslaagte, a distance of about 25 miles. Within these limits occur the following formations:- . Black Reef Series, which overlies all other rocks with a striking unconformity. 2. Swaziland Beds. 3. Ventersdorp Beds.
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Transactions of the Geological Society of South Africa, 9, 111-116
A bore of some considerable geological importance and local interest has lately been sunk on the seaward aspect of the Bluff, Durban, about a mile to the south of its extreme northern end. The object of the bore was to ascertain the presence or absence of payable coal, in a small outlier of Ecca Shales, in the vicinity of the Port of Natal. The result from this point of view was unsuccessful. The general geology of the neighbourhood of Durban has been described by me in the Second Report of the Geological Survey of Natal and Zululand, pp. 107-117; there is therefore no necessity to go into details here. Beneath the business part of Durban and under the bay, a small outlier of Ecca Shales occurs, and it was in this basin only that there was the most remote possibility of the occurrence of coal. The lower Ecca Shales, which outcrop at Jonsson's Bore on the west side of the bay, near Congella, dip slightly towards the sea, and they are present under the Bluff and out to sea. This Ecca outlier is bounded, on the landward side, from the mouth of the Umgeni River, by the Ecca Glacial Conglomerate (Dwyka) of the Berea Ridge, from the southern end of which the boundary of the basin is formed by the outcrops of the Table Mountain Sandstones of the Clairmont Estate. Evidences of the presence of these sandstones as bed rock also occur in the alluvial deposits of the flats around Jacob's Railway Station, on the western side of the Bluff Peninsula, a few miles from the sea coast. The extent of this outlier of Ecca Shales is therefore very limited to landward. That portion of shales exposed near Congella, on the western side of the bay, belongs to the Lower Eccas, which rest on the Glacial Conglomerate of the Berea Ridge. In all the coalfields of Natal and Zululand payable coal-seams are only present in the Upper Ecca Series or in the Lower Beaufort Beds. The line of division between these two series is quite, as yet, an arbitrary one. It therefore follows that, if coal occurred under the Bluff, the Upper Ecca Series must, at least, come into the section. If it had done so, it would have been struck immediately after passing through the Cretaceous rocks, which were met with in the bore. This was not the case, and the result has been that the boring through the Ecca Series has been entirely in the Lower Eccas. I have no doubt that had the bore been proceeded with the Ecca Glacial Conglomerate would have been struck at no great depth below the point at which the bore was stopped, namely, 1,786 feet.
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Transactions of the Geological Society of South Africa, 9, 117-124
The Roberts Victor mine is situated on the farm Damplaats, in the Boshof Division. The adjoining country consists of bare undulating veld, dotted with innumerable pans. Contens: Karroo System. Pre-Karroo rocks. Petrological notes by R.B. Young. Post-Karroo deposits. Pans.
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Transactions of the Geological Society of South Africa, 9, 125-128, 3 pl
Since no other formation in the Transvaal has yielded any undoubted fossils, a special interest attaches to those of the coal-measures and associated strata. But although the Karroo System is rich in vegetable remains, which are sufficiently abundant to give rise to those thick seams of coal which form so valuable a portion of the mineral wealth of the country, our collections of fossils from these rocks are still very small, and our knowledge of the flora of the coal-measures correspondingly incomplete. Fortunately for the miner and for the consumer of coal, but unfortunately for the geologist and palaeontologist, Transvaal coals are in most instances so readily accessible and so easily got that little mining work is done outside the seams themselves, and consequently opportunities of investigating the contents of the sandstones and shales associated with the coal-seams, and which are the most likely source of good specimens, are comparatively rare. Welcome assistance in the work of unravelling the geological history of the country comes, however, occasionally from quite unexpected sources, as when in the instance presently described a river like the Vaal dissects out from its enclosing matrix of shales and lays bare for examination a wide stretch of fossil forest, such as enables one to form a very clear picture of the conditions under which some of our coal-seams originated. The coals worked at Vereeniging lie at a comparatively small depth below the surface, and occasionally the seams crop out on the banks of the river, and when the river is low are exposed in its bed. About one and a half miles below the railway bridge, and a quarter of a mile below Viljoen's Drift, a broad anticlinal fold brings a coal-seam to the surface in the bed of the Vaal. Usually the river completely covers the coal, but in October last owing to the exceptionally small quantity of water passing down the stream, the upper surface of the coal was uncovered over an area of upwards of two acres extending along the Transvaal side of the river. (See Plate XXIV.) The surface of the seam thus exposed is thickly covered with the casts of roots and stumps still occupying their original positions, as well as the prostrate stems of the trees which, with their predecessors, produced the material out of which the underlying coal-seam was formed.
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Transactions of the Geological Society of South Africa, 9, 16-18, 1 pl
The following remarks are intended chiefly as an explanation of the accompanying map. This map shows in accurate detail the remarkable faulting that takes place along the Main Reef horizon as it approaches the first of the many dislocations that make up the great Witpoortje break. It was surveyed by the stadia method during my spare time, when surveyor and assayer to the Saxon Gold Mines. It is a curious feature of the area covered by this map that, on account of the very remarkable nature of the faulting, the Main Reef as it goes westwards approaches nearer and nearer to the Livingstone conglomerates (which are themselves practically undisturbed), until, with a very low dip, it is only a thousand feet away. The Main Reef horizon in this area is represented by the Main and South Reefs, the Main Reef Leader of the Central Witwatersrand, with its characteristic footwall bed, being absent. The Main Reef is much reduced in thickness, and the South has thinned out from six inches to one. I have some thin sections of these conglomerates. They are very similar to those that have been described from other parts of the Witwatersrand. The interstices between the quartz pebbles and grains are filled with sericitic matter, quartz mosaic and pyrites-the last usually in well-defined crystals. Interesting features are the frequent corrosion of and the occasional presence of pyrite crystals in the original quartz grains. Colourless prisms of a mineral possessing high relief and occasional cross-jointing occur in all the sections, and are particularly abundant in one. It is evidently the mineral chloritoid referred to by De Launay. This mineral is also very abundant in the footwall bed of the Main Reef Leader of the Central Witwatersrand. Sections from the 800, 1,100 and 1,400 feet levels of the Jumpers Deep are crowded with it.
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Transactions of the Geological Society of South Africa, 9, 19-31, 2 pl
In the following contribution I propose to give a short account of the geological features of the Komati Poort Coal-field, an area of particular interest at the present time, not only from an economical point of view, but also in its purely geological aspect. The public is interested ii. the coal, while the character and succession of the principal rocks developed in this district afford an equally attractive subject to the geologist.
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Transactions of the Geological Society of South Africa, 9, 32-33
In view of the great interest which the members of this Society invariably show in the work of the Geological Survey, I would like to make a few remarks in connection with that work, and especially with reference to certain points raised by Dr. Hatch in the course of his Presidential Address at our last Annual General Meeting. I am quite aware that Dr. Hatch's object was to assist the Survey, yet I think that some of his remarks appeared to give an unfavourable and wrong impression with regard to the work that the Survey has been and is carrying on. Now, with regard to the first of these differences, namely, the geological position of the Transvaal coal-bearing beds, I will not say anything just now, except that the Geological Survey is at present investigating the facts bearing upon this question, and not shelving it, as Dr. hatch seemed to think. Then, with regard to the existence or non-existence of an older system of sedimentary rocks than the Witwatersrand Beds, and the relationships of the Old Granite, surely the paper by Messrs. Hall and Humphrey, dealing with the rocks underlying the Black Reef north of Krugersdorp, and embodying the result of work done last October, is sufficient evidence that these important questions are not being neglected either.
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Transactions of the Geological Society of South Africa, 9, 34-39, 3 pl
During the earlier part of a recent journey through Griqualand West, we had many opportunities of observing glacial phenomena of Dwyka age. Our previous knowledge of the glacial geology of this area was mainly derived from the writings of Mr. G. W. Stow1 and Mr. E. J. Dunn. In the unpublished writings of the former there still lies hid a wealth of information on the subject, and in our paper we shall endeavour to encroach as little as possible on the material dealt with in these MSS., which we trust will shortly be given in a suitable form to the public. The glacial phenomena south of the Griqualand West border have been described by Mr. E. J. Dunn and by Messrs. A. W. Rogers and E. H. L. Schwarz. From Riverton, on the north, our route followed more or less the course of the Vaal River, and of the Orange River after its confluence with the former, as far south as Prieska. We therefore travelled along the western fringe of the Karroo System, and naturally met with numerous exposures of the Dwyka moraine and the glaciated floor on which it rests. From Riverton to the southern extremity of Kareyn Poort we passed over volcanic rocks with several outliers of the Lowest Karroo Beds resting upon them. These igneous rocks outcrop to considerable distances on both sides of the Vaal River, and stretch as a broad belt in a north-easterly direction into the Transvaal. There is an extensive outcrop of apparently the same rooks at Douglas, and to the north-west and south-east of that town. They are largely basic in composition, and are probably all of Ventersdorp age. Generally, they form gently undulating or hilly country, which, notwithstanding the results of weathering, still presents the characteristic contours of a glaciated region, and in which, as might be expected, the present drainage system can be seen accommodating itself more or less to the glacially modified pre-Dwyka river valleys. The rocks to the west of the Vaal and Orange Rivers, from the Hart River to the Sand River, are mostly the quartzites, shales and limestones that underlie conformably the thick limestone of the Campbell Rand. These rocks have a gentle dip to the south-west. West of the Orange River, from the Sand River to Prieska, the banded jaspideous and magnetic rocks of the Griquatown Series underlie much of the extensive deposit of Dwyka moraine which is found in this area. As one approaches Prieska, glaciated hills of the Griquatown rocks project above the surrounding moraine. The pre-Dwyka land surface in the area dealt with in this paper consisted, as far as can be seen, of a somewhat hilly region of volcanic rocks to the north-east; to the west, of an area rising gently in terraces in that direction, and consisting of quartzites, shales and limestones; and to the south, of a rugged hilly country of thin-bedded jaspideous and magnetic rocks. The general downward slope of the whole area was to the south-west.
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Transactions of the Geological Society of South Africa, 9, 40-52, 3 pl
For many years the Klerksdorp district has attracted the attention of the geologist, as well as of the mining engineer, and much diversity of opinion has been expressed as to the proper reading of the phenomena there. The following paper deals with some of the problems which present themselves, and of which I have tried to give a solution. The general geology of the district has been treated by Mr. G. A. Denny in his book on the Klerksdorp Goldfields, and many papers have been written on individual geological questions by members of this Society and others. To these I refer in the separate sections of this paper. The first impression one receives on paying even casual attention to the district is that there has been much disturbance, and that there is considerable divergence from the persistent stratigraphy of the Central Witwatersrand area. As Mr. Denny has said, differences of bedding, of strike and dip, and of horizons, calculated to confuse the observer, are met on every hand. As far as my study of the district has gone, all these differences are referable to two causes:- Firstly.- The unconformity of the Elsburg Series to the beds of the Witwatersrand System; and, Secondly.- Manifold and repeated folding of the strata caused by a pressure directed from west to east, and subsequent faulting, oblique, as well as longitudinal.
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Transactions of the Geological Society of South Africa, 9, 53-56
During our recent journey through Griqualand West we met with many evidences that the Palaeolithic Period of South Africa is of considerable antiquity. In this paper we present only a selection of the large amount of data which we collected supporting this view.
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Transactions of the Geological Society of South Africa, 9, 57-66, 1 pl
Calcareous rocks of at least four different ages occur in Griqualand West. They belong respectively to the Campbell Rand Series, the Griquatown Series, the Ecca Series, and recent surface deposits. The extent and general character of all of these, excepting the Ecca limestones, which are of little importance, have been described by G. W. Stow and A. W. Rogers. I intend to deal, in this paper, more especially with the mineralogical composition and structure of the rocks. For the satisfactory study of limestones, especially when they are more or less dolomitic, it is almost essential that analyses of the rocks should be available. Lemberg's solution, which stains calcite but does not affect dolomite, is extremely useful. Other less satisfactory means of distinguishing between rock-forming calcite and dolomite are afforded by the greater solubility in dilute acids, the more frequent twinning and the rarity of rhombohedral crystals in the case of the former mineral. The following fifteen analyses of Griqualand West calcareous rocks have been made by Professor G. H. Stanley from specimens with which I supplied him.
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Transactions of the Geological Society of South Africa, 9, 67-73
The country referred to in these notes, and shown on the accompanying plan (Plate XVII.), is the triangular area lying between the Elands and Oliphants Rivers, the junction of these rivers forming the apex, the base being a line running in a north-westerly direction from the farm Wagendrift on the Oliphants River to the farm Valschfontein on the Elands River. The Moos River, which divides this area in two portions, forms a rough topographical boundary, south of which the country is broken up by several parallel ranges, becoming very rugged indeed further south; to the north, however, the country lying between the Elands River and the range along the foot of which the Moos River winds on its way to join the Oliphants, is flat and covered with thick bush and sand, outcropping rocks being very scarce. The formations met with in this area are as follows, in ascending order:- (1) - Dolomite Series. (2). - Pretoria Series. (3). - Plutonic Series of the Bushveld. (4). - Waterberg Series. (5). - Karroo System. (6). - Diabases.
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Transactions of the Geological Society of South Africa, 9, 74-81, 1 pl
Among the commonest phenomena met with in coal mining in the Transvaal is the occurrence, in practically all those collieries whose workings are sufficiently extensive to have opened up any considerable area, of what are variously known in different localities as "wash-outs", "washes", and "mud-dykes". This last term is also applied, and much more aptly, to true dykes of intrusive igneous rock which have been more or less completely reduced by weathering to clayey decomposition products. General characters of "wash-outs". Views generally held as to the nature of "wash-outs". Special features of weathering in the Karroo Formation. The nature of "wash-outs". Changes in the coal due to weathering. The origin of pans.
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Transactions of the Geological Society of South Africa, 9, 82-89, 1 pl
The Tygerberg Range is situated about ten miles to the north of the Zwartebergen in the Southern Karroo; its highest point, the Groot Tygerberg, being about twelve miles north-east of Prince Albert Village. Roughly speaking, it consists of a main white quartzite range flanked north and south by ranges of lower hills. The strike of these ranges is parallel to that of the Zwartebergen - that is, east and west; they emerge suddenly from the large surrounding plain lying to the north and south, whilst they gradually die out to the east as well as to the west. The main central range consists entirely of Witteberg Quartzites; the hills to the north and south consist of individual monticules formed by the different members of the Dwyka - and even of the Ecca - Series; they are roughly arranged in lines parallel to tile strike of the central range. Two consecutive hills on the line of strife of these parallel ranges need not necessarily be constituted of the same beds of the above series.
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Transactions of the Geological Society of South Africa, 9, 90-96, 2 pl
No abstract. Contents: Topography. Geological formations. Karroo System. Ventersdorp System. Quartzite beds underlying the diabase. Primary rocks. General structure.
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Transactions of the Geological Society of South Africa, 9, 97-110
The question of the age of the Transvaal Coal-Measures and the exact position which they occupy in the sequence of strata included under the Karroo System, is a point concerning which there exists considerable diversity of opinion among South African geologists, and is still an unsettled question in Transvaal geology, upon which there will probably only be final agreement when our knowledge of the Karroo System, which is at present more or less limited to certain special districts, is made at least equally complete with regard to the extensive intervening areas. As a result of observations made in different localities during the past two or three years, and more particularly in the course of recent survey work in the Witbank district, additional data have been gathered which I should like to place before the members of the Geological Society. While these data are not of a character to settle the question of the position of the Transvaal Coal-Measures, yet it is hoped that they may throw some additional light on certain doubtful points, and so aid in the ultimate solution of the problem. Before, however, considering such new facts as may have become recently available, it will be useful to review as briefly as possible the various opinions held with regard to the correlation of the Transvaal Coal-Measures, and the arguments which have been advanced in their favour. In Cape Colony, where the Karroo System attains its typical and most complete development, and where the nature and succession of the Karroo rocks has long been a subject of study, the following sequence has been more or less definitely established.
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Proceedings of the Geological Society of South Africa, 9, xxi-xxxiv
The subject of this address is a brief account of the succession, thickness and geological history of the South African, and more especially of the Transvaal, formations. The information necessary for such an account as I propose to give is, of course, very incomplete, but in broad outline the succession is now known, and some speculation as to the physical conditions that prevailed during the building up of the region may, perhaps, be permitted. I propose to deal with the period of the geological history of this country that came to an end with the close of Karroo times. The Karroo Period ends with the Stormberg rocks (Rhaetic): since that time South Africa has, with the exception of a small coastal area, been a land surface, and the rocks have, consequently, been exposed uninterruptedly to the forces of denudation. Contents: 1) Order of superposition of the stratified rocks. 2. Thickness of the strata. 3. Geological history of the rocks.
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Proceedings of the Geological Society of South Africa, 9, xxxix-xl
I have been very much interested in this paper, and I would like to say that I consider the evidence brought forward by the authors is strongly in favour of the Zwartkop Series being distinct from the Lower Witwatersrand (quite apart from the relation of either to the granite), and belonging to Dr. Hatch's Swaziland System. Mr. Hall gives a thickness of about 1,200 feet for the Swartkop Beds, whereas the thickness of the Lower Witwatersrand Series is given by Drs. Hatch and Corstorphine as from 10,000 to 12,000 feet, and if the two series were the same it would be difficult to account for such a rapid diminution in such a comparatively short distance.
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