THE GEOLOGICAL HISTORY OF THK COLONY 447 



the immense thickness of lava, described in a previous 

 chapter, put a stop to the deposition of ordinary sedi- 

 ments, and the conditions under which sandstones, 

 shales and other sediments are formed seem never to 

 have prevailed again in the interior of the Colony. 

 The present state of our knowledge of the volcanic 

 series is too imperfect to allow a satisfactory statement 

 of the effects due to the volcanic episode to be made ; 

 but it is certain that one result was to add a great 

 volcanic pile to the north-eastern end of the newly 

 emerged land. 



The present main watershed of the Colony was pro- 

 bably produced during the Stormberg period by the rising 

 of a low tract of country from the Karroo area, trending 

 in a north-easterly direction. In trying to explain the 

 fact that the southern rivers rise along the axis of a 

 wide syncline and flow across its edge, one must re- 

 member that the deposition of the later part of the 

 Karroo formation involved the levelling up of the basin 

 and the disappearance of the synclinal structure in the 

 uppermost beds. When, however, the land emerged, by 

 up-warping, along what is now the watershed, the slope 

 given to it caused the rivers to flow south-east and north- 

 west, although the synclinal arrangement now exposed 

 in rocks that were then deeply buried was not destroyed. 



There seems no escape from the conclusion that denu- 

 dation has proceeded uninterruptedly from the close of 

 the Stormberg period (Jurassic) to the present day in 

 the interior of the Colony. No deposits of later age, 

 other than river gravels, alluvium and sand, have been 

 found north of the folded belt. 



