Page:South African Geology - Schwarz - 1912.djvu/176

 The Uitenhage Formation

While the Stormberg Formation was being laid down, and the volcanoes of the eastern part of Cape Colony were active, the western portion was being subjected to violent agitation from the thrusting in of the Karroo dolerite, and the Cape folded mountains were being formed. When the mountains were first thrust up the more superficial rocks were structurally weak from the bending, and readily gave to the action of weathering and erosion. The whole continent had risen 2000 ft. after the last beds in the central Karroo had been laid down and the first peneplain in these parts was already cut. On this peneplain, now elevated 4000 ft. above sea level, the debris from the mountains was deposited. As the torrents rushed from the mountains they carried enormous volumes of gravel with them; but the waters coming to the plain beneath lost their velocity and their carrying capacity, therefore the boulders were left lying at the foot of the hills. These boulder beds are the Enon Conglomerate, red below and white above, and 2000 ft. in thickness. The land was sinking again; part of the Enon Conglomerate, at Knysna for instance, fell beneath the sea and had marine organisms included in it. The whole continent was now once more nearly awash, and only the mountains towered above the plains. The lessened height of the mountains and the harder rocks exposed caused the succeeding deposits forming on their flanks to be only sands and muds. These were laid down on the plains, over which there were tracts of marsh land, freshwater pools and sand dunes, among which dinosaurs scrambled and left their bones. Cycads and ferns, much like the present-day forms, grew, and the remains are