436 THE DWYKA GLACIATION 



Dwyka period. The southern mountain ranges were 

 not yet in existence, the rocks which afterwards built 

 them up were lying horizontally below the surface of 

 the lake. The nearest land lay to the north ; the 

 southern portion of it consisted of the then recently 

 exposed Witteberg deposits ; north of this area there 

 were belts composed of the Bokkeveld and Table 

 Mountain series, while still farther north lay a hilly 

 country composed of the Pre-Cape rocks. This country 

 gradually became snow-clad, and glaciers and eventually 

 a sheet of ice, of too great size to be called a glacier, 

 slowly moved towards the lake, carrying with it mud, 

 sand, pebbles and large blocks, derived from the sur- 

 rounding land. Most of these materials reached the 

 bottom of the great lake, but it is more than likely that 

 parts of the unbedded tillite in Prieska and elsewhere 

 in the northern districts are the remnants of moraines 

 that lay between the ice and the floor in the lower parts 

 of the land, or that were piled up in front of the ice. 

 Meanwhile the floor of the lake sank, so that at least 

 1,000 feet of conglomerate accumulated over the south- 

 ern part of the Colony ; the water stretched farther and 

 farther north as time went on, so that at the close of 

 the glacial period shales were being deposited at least as 

 far north as the Molopo. 



The thousand feet of mud and stones which must 

 extend over thousands of square miles under the 

 southern part of the Karroo, and formerly spread as 

 far south as Worcester, and very probably farther 

 than the present southern limit of the continent, re- 

 present the products of denudation of a large tract of 



