380 Transactions of tlic South African Philosophical Society. 



The striking regularity of the southern rivers in maintaining their 

 channels across the diversified surface south of the Karroo is strong 

 evidence in favour of the view that the general slope of the new land 

 formed by the rising surface of Uitenhage rocks was, generally 

 speaking, in direct continuity with the southern slope of the pre- 

 existing watershed to the north. It is, in fact, probable that the 

 rising of the southern part of the slope was but the accompaniment 

 of the later history of the formation of that watershed and its southern 

 drainage slope. 



The published descriptions of the Uitenhage Series'" plainly 

 show that the earth movements which have affected the southern 

 part of the Colony since their deposition were insignificant 

 when compared with the Zwartberg movements, and at the same 

 time that they produced a certain amount of difference in level 

 in different parts of the area affected. The Oudtshoorn area has 

 been less affected than the area south of the Langebergen. In Eivers- 

 dale, for instance, the observed dips in the Uitenhage River beds 

 rise to 20° or even more, and the direction of dip is generally toward 

 the north or north-north-east, showing that there was a sinking of 

 the Langebergen, or of the country on the southern flank of that 

 range relatively to the country still further south, but this alteration 

 of level has had no effect on the course of the Gouritz River, which 

 traverses that part of the country. 



After the Uitenhage sediments emerged from the w^ater, the 

 Karroo rivers ran southward from the watershed, across the partially 

 buried mountain chains, and their beds in the lower half of their 

 courses were formed by the Uitenhage rocks. These rocks are of a 

 rather loose incoherent nature as compared with the Karroo rocks 

 and those forming the buried mountain chains, and the rivers must 

 have lowered their valleys comparatively quickly as long as the hard 

 rocks of the unconformably buried ranges were not reached ; but 

 after these rocks had been laid bare in the valleys, the rate of the 

 cutting down of the river channels must have decreased. The main 

 river channels, at the time of the first exposure of the hard rocks 

 below^ the Uitenhage Series, must have been well developed, so that 

 the rivers could not find easier paths to the ocean than the courses 

 given them on the emergence of the Uitenhage sediments. It thus 

 came about that the rivers had to cut their valleys in the extremely 

 hard quartzites of the Zwartebergen, Gamka Hills, Langebergen, and 

 other previously buried ranges that lay in their way. We must 

 thus look upon the river system south of the Karroo as a super- 



* Ann. Rep. of Govt. Comm. for 1898, App. III., IV. and V. ; 1899, App. II. ; 1900, 

 App. I.; and 1901, App. I. 



