50 



KNOWLEDGE 



[March 2, 1896. 



Kivers, to the south and north reapoctivcly. The Wit- 

 ■watersrandfc is, indood, the water-parting between the two 

 great river-basins, the northern portion of the Transvaal 

 being formed by the slopes, with low hill ranges, from the 

 High Yeldt to the Limpopo llivor. 



Eastwards, the High Veldt rises to greater surface 

 altitudes, until it attains the crest of a section of the 

 Drakensborg range of mountains, running north and south, 

 and culminating in the Mauach Herg, seven thousand one 

 hundred and scvonty-sevrn feet above tlie level of the sea. 

 This range descends ou its eastern side witli a steep 

 escarpment — prominent along which is seen the peak of 

 Spitz Kop — to the great De Kaap Valley, about throe 

 thousand feet above sea-level, that extends to the Loborabo 

 Mountains, forming the eastern boundary of the State. 



stratified rocks have a general southerly dip and east and 

 west strike. The dip is usually at a very high angle, 

 sometimas even nearly ninety degrees, but commonly 

 from forty-five to sixty degrees, though a few miles to the 

 south of Johannesburg and beyond Eagle's Nest the bed3 

 iire neiirly horizontal. It is in these rocks that the 

 auriferous beds of the Witwatcrsrandt occur. The word 

 "beds" is used here advisedly, for, although the term 

 " reefs " is the name locally and generally given to these 

 rocks, they are unmistakably sedimentary beds, and 

 contcmporaacous portions of the geological formation 

 in which they are contained. Tlicy are, therefore, of an 

 altogether different character from the well-known auri- 

 ferous " reefs " of other gold regions, which are quarts 

 veins traversing the massive rocks across their pianos of 



Seetiuu S. to X. Trum tlii' \'uiil Valk'y iicross tho Witwatcivniudt. Lcugtli of Scclion, lio uiilcs. 



WiTWATERSRANDT 



TitaL River 



Klip Miver 





I itfci 



N 



2 ?, 2 i_ 



W. Water Parting between tlic Vaal and Limpopo River Basins. 5. Basalt. 4. Hif,'li Veldt Beds, Coal-bearing (Karoo Beds). 



3. Ivlip Kiver Series. 2. Qnartzite Shale Scries, with G, "Banket" (Gold-bearing Conglomerates). 1. Granite. 



With the exception of the De Kaap Valley, the Transvaal 

 consists of a portion of the elevated interior land of the 

 continent of Africa that constitutes what is called the 

 Central African I'lateau, of which the Witwatersrandt is 

 therefore a part, and the Vaal Valley and the Limpopo 

 northern valley are but depressions in the plateau. 



The region generally is occupied by rolling grass-covered 

 uplands, with ridges of bare rocks standing above the 

 general surface — in some districts at frequent intervals. 

 This rocky-surface character is given by a large amount 

 of igneous rock in granitic bosses and dioritic and basaltic 

 masses and dykes, together with the outcrops of the 

 older stratified and metamorphic rocks of the country. 

 Some of the dykes, from their position, have been sub- 

 jected to less denudation than adjacent masses, and so 

 form in places narrow ridges called "necks," which have 

 sometimes a deep ravine on each side. The whole area is 

 intersected by river valleys formed by the streams (torrents 

 at times) feeding the two bounding rivers, both of which 

 rise in the Transvaal, but How, however, in opposite 

 directions : the Vaal Eiver running westwards to the great 

 Orange River, which it joins beyond the south-west 

 extremity of the Republic, and the Limpopo flowing east- 

 wards towards the Indian Ocean. An important tributary 

 of the Limpopo, called Olifant's Eiver, traverses the interior 

 of the area, dividing the eastern half very equally into 

 northern and southern portions. 



The Transvaal as a whole is formed by Plutonic granites 

 and diorites, volcanic basalts and dolerites, crystalline 

 metamorphic schists and gneisses, with unconformable 

 but undoubtedly Pabeozoic stratified rocks ; and these are 

 succeeded by a later series of rocks, again unconform- 

 able. Over large areas the outcrops of these rocks are 

 concealed by superficial deposits of varying thickness, 

 giving a red soil immediately below the turf. The older 



original deposition. The so-called " reefs " of the Rand, on 

 the contrary, are merely certain beds of a quite conform- 

 able series of stratified rocks, which consequently have a 

 common dip and strike, and may, therefore, be considered 

 to be one geological formation. It is this fact that gives 

 to the occurrence of gold in the Transvaal an unique 

 character, and renders it, from a geological as well as from 

 an economic point of view, especially interesting. 



The massive rocks in which the gold-bearing beds 

 occur — the " country rock " — are for the most part hard 

 quartzites, sandstones, and bluish shales, and the whole 

 formation has been called the " qnartzite shale series." It 

 is altogether of enormous thickness, estimated at three 

 miles, or sixteen thousand or seventeen thousand feet. 

 From the absence of fossils — or at least from none having 

 as yet been found — there is great difEculty in assigning to 

 this great series of stratified rocks (which have been 

 correlated with the Table Mountain Sandstone) any other 

 than an approximate geological age ; but from its general 

 stratigraphical position with reference to the other South 

 African rocks, and from its unconformability with over- 

 lying coal-bearing formations, it is certainly of PaliBozoic 

 and most probably of Silurian age. The whole of the rocks 

 of South Africa may be classified as follows in descending 

 order ; — 



Upper 

 Karoo. 



16. Superficial deposits. 



(15. Voleanic rocks, 

 l-l. Cave sandstone. 

 I 13. Red beds. 

 'o U2. Moltcno beds. 



o /ll. Karoo beds (Seantort 



^ 1 10. Kiniberlev shales. 



^ Lower J Unconi'ormability. 



9. Ecca beds. 

 8. Dwyka conglomerate. 

 Unuouformabilitv. 



beds). 



Karoo. 



\ 



