THE GEOLOGICAL HISTORY OF THE COLONY 453 



scribed as cutting down their valleys through the Uiten- 

 hage beds to the underlying rocks, we must endeavour 

 to trace the events which have taken place since they 

 began to cut through the partially buried mountain 

 ranges. Throughout the southern districts of the Colony 

 there is abundant evidence bearing on this portion of its 

 history ; this evidence is given by the gravel and alluvial 

 terraces lying high above the beds of the modern rivers. 1 

 The absence of contoured maps and a close knowledge 

 of the height of the terraces greatly increase the diffi- 

 culties of the problem, and it would be useless to attempt 

 more than a sketch of the main conclusions to be de- 

 rived from the facts at present known. The oldest, or 

 highest, well-developed terraces lie over 1,000 feet above 

 the modern river beds, and there are still more elevated 

 terraces. When the rivers from the Karroo flowed at 

 levels about 1,000 feet higher than at present their 

 downward cutting powers were checked, and they, to- 

 gether with their tributaries, planed off the country to .a 

 more or less common level, producing a slightly undu- 

 lating plain, from which rose the long mountain ranges 

 and the smaller anticlines, such as the Caledon Moun- 

 tain and Warm Water Berg. The distinct terraces 

 forming conspicuous features on the slopes of the 

 Langebergen and Zwartebergen, where the hard folded 

 quartzites are cut to a nearly flat surface, were made 

 during this period of lateral erosion. The cause was 

 widespread, for we find its effects from the Transkei to 



l See also Schwarz, Q. J. G. S., Ixii., 1906, p. 70 ; Am. J. S., xxiv., 

 Sept., 1907; Geogr. Journ., March, 1907; T. S. A. P. S., xv., 1904, 

 p. 43. 



