74 HE. p. H. HATCH GEOLOGY OF THE [Feb. 1 898, 



circumstances, and certain sections, where strati graphical com- 

 plexities made it desirable, have been mapped in greater detail. 



The physical featnres of the South African plateau or ' High Yeldt ' 

 have been so often described that I will only briefly refer to them 

 here. To the traveller by train from the south, with the eye wearied 

 by the interminable stretches of uniformly flat and uninteresting 

 country in the Orange Free State, the Southern Transvaal presents 

 by contrast a pleasing aspect, on account of its more broken and 

 diversified scenery. Ranges of low hills alternate with stretches 

 of rolling and grassy uplands, which, in the summer or rainy 

 season, have a delightfully fresh and green appearance. 



The highest elevation is reached at the Witwatersrand (highest 

 point 6000 feet above sea-level), which forms the water-parting 

 between the tributaries of the Yaal River, flowing into the Atlantic 

 Ocean, and the Limpopo or Crocodile River and its tributaries, 

 flowing into the Indian Ocean.^ 



The lines of elevation have mainly an east-and-west trend, con- 

 forming almost invariably with the strike of the bedding. Usually 

 there is an abrupt escarpment on one side, while the opposite flank 

 corresponds to the angle of dip of the beds. The hill-ranges are of 

 unimportant height relative to the surrounding plains, being rarely 

 above 300-400 feet.' 



The Magaliesberg forms the natural northern boundary of the 

 district under description. The sedimentary strata of which it is 

 composed are on its northern side faulted up against massive igneous 

 rocks of basic character, belonging to a portion of the ancient crys- 

 talline floor of South Africa; while to the south there is a varied series 

 of sedimentary and volcanic rocks of Palaeozoic age, through which 

 the ancient crystalline rocks here and there protrude. This series 

 of beds, which is generally known as the Cape Formation, extends 

 to the Vaal River, where it disappears under the flat-lying strata of 

 the Karoo Formation, the latter constituting almost the sole rocky 

 covering of the Free State and the Eastern Province of the Cape 

 Colony. 



We have therefore, in describing the rocks of the Southern 

 Transvaal, to deal with three principal subdivisions, namely : — 



(1) The Karoo System. 



(2) The Cape System. 



(3) The Archsean System. 



The following description of these formations will be greatly 

 facilitated by reference to the map and sections that accompany this 

 paper. (See PI. VI.) 



^ The most important streams in the district under consideration are the 

 Blesbok Spruit, Klip E,.. Mooi 11., Kockemoor Spruit, and Schoon Spruit, 

 tributary to the Vaal river ; and the Pienaars R., Aapies R., Hennops E,., 

 Yokeskey R., Crocodile R., Magahesberg R., and Hex R., tributary to the 

 Limpopo. 



^ The principal hill-ranges are the Magaliesberg, Witwatersberg or Daspoort 

 range, Kalkhevivel, "Witwatersrand, Klipriversberg, Gatsrand, Zuickerboschrand, 

 and the Venterskroon Hills. Isolated hills are the Losberg, Tafelkop, Spitskop, 

 and Platberg — names indicating the configuration of the hills designated. 



