Page:South African Geology - Schwarz - 1912.djvu/194

 to the outward edge lime, magnesia, and iron from the dolomites and ferruginous rocks, sufficient to convert the originally acid granite into a basic gabbro. Crossing over into Bechuanaland, the system is found prominently developed on the escarpment of the Kaap Plateau west of the Kimberley-Vryburg railway line. Thence it spreads out as a great flat plateau, gently undulated at first and then more intensely folded till it comes to the hills of Kheis quartzites in Prieska, where the system is lost. Possibly the Kheis Beds are the Transvaal Beds altered by still more violent crushing. We pick up the system again in German Namaqualand, where it forms several isolated outcrops near the coast, and is met with finally at Otawi. The system thus stretches, or stretched at one time, right across the Continent, so that it forms a belt of sediments forming off a northern shore, similarly to the subsequently deposited Cape Formation, which it closely resembles, similarity of conditions producing similarity in sediments.

The Black Reef Series lies at the base of the system. It is so called from a band of gold-bearing conglomerate (banket) which is found near the base, which, being full of pyrites, weathers with a black iron-stained surface. The gold is patchy, and though in places exceedingly rich, the banket is not exploited like the more steadily yielding Main Reef Leader. The quartzite of hardened sandstone, of which the most of the series is composed, is extraordinarily like the Table Mountain Sandstone in texture, tint, and mode of weathering, On the north of the Drakensberg escarpment the series is some thousand feet thick, but elsewhere it dwindles down to as little as a few feet only.

The Dolomite (Campbell Rand) Series lies above the