384 Transactions of the South African Philosoj^hical Society. 



sluggishly over the peneplains cut by itself and its tributaries ; and 

 their shape has been preserved during the period of rapid downward 

 erosion of the river valley since the uplift began which upset the 

 previous conditions. The Gouritz Eiver has not yet reduced the 

 gradient of its valley to such an extent that it can recommence the 

 work of lateral erosion. 



The general conclusions to which this enquiry into the history 

 of one of the Karroo Eiver Systems leads may be summarised : — 



1. The emergence of land to the south of the present Karroo, 

 due to the Zwartberg earth movements which took place some time 

 between the period of deposition of the upper part of the Beaufort 

 Series and the close of the Stormberg stage. A series of east and 

 west valleys was originated on this land, and these valleys were 

 extensively developed before the Uitenhage Series was formed. 



2. The formation of the main watershed of the Colony by the 

 uplift of the deposits of the latter part of the Karroo System ; the 

 uplift gave rise to the southerly drainage system of the Gouph and 

 Mordenaar's Karroo. 



3. The filling up of the east and west valleys by the deposits of 

 the Uitenhage period (Lower Cretaceous ?) which buried most of the 

 old surface features south of the Karroo. 



4. The emergence of the Uitenhage sediments owing to a con- 

 tinuation of the movement which brought about the formation of 

 the main watershed, and the prolongation of the river valleys south 

 of the watershed across the emerging Uitenhage rocks. 



5. The formation of the Gouritz Eiver system by the adjustment 

 of the streams that brought about the confluence of the Dwyka 

 Gamka and Buffel's Elvers, as well as other minor streams. 



6. The production of the peneplains, whose traces are found 

 widely spread between the Zwartebergen and the coast, during a 

 period of decreased erosion of the rivers. 



7. The renewal of the erosive powers of the rivers, which has 

 caused the cutting up of the old peneplains. 



The map of the Gouritz Eiver system, which is appended in 

 order to facilitate the reading of the paper, was kindly drawn up for 

 me by Mr. A. L. du Toit, of the Geological Survey, and is based 

 upon the Surveyor-General's map of 1895. The geological lines are 

 taken from the field maps of Mr. E. H. L. Schwarz and myself. 

 The black dots represent the positions of towns and villages, but 

 their names were omitted, so that the map should not be overcrowded. 

 The patches of high-level gravels and alluvium, capping the 

 remnants of the peneplains mentioned in the paper, are not repre- 

 sented in this map. 



