62 Transactions of the South African Philosophical Society. 



Mountain series there. The Witteberg series is also apparently 

 absent. This would explain the absence of quartzite pebbles in the 

 Molteno beds in that part of Griqualand East. 



We see now that at the commencement of the Molteno stage the 

 supply of comminuted ferruginous material was cut off and replaced 

 by the detritus of a land surface built up of granite, metamorphic 

 rocks, and quartzites. 



The action of the Zwartberg movements caused an elevation of 

 the strata in the south and an extensive land surface was produced. 



The lower members of the Karroo system, if present, were rapidly 

 removed by denudation, the rocks of the Cape system cut into, and 

 the pre-Cape rocks — slates, metamorphic rocks, and granite — laid 

 bare. It is possible that at this time, too, the extreme west of the 

 Karroo was dry land and contributed to the forming of the Storm- 

 berg series. 



At the close of the Molteno stage there must have been con- 

 siderable changes in the land surface due both to denudation and 

 to the continuance of the Zwartberg movements. Granite, and 

 quartzite still contribute largely to the derived rocks, but the abun- 

 dant red and purple sandstones, shales, and mudstones testify to the 

 denudation of an area in which ferruginous rocks, such as jaspers 

 and magnetite slates and schists were well represented. We have, 

 in fact, a return to the conditions which existed in pre-Stormberg 

 times, and instead of finding ferns and cycads as fossils in the rocks, 

 the remains are once more those of dinosaurian reptiles. 



The Zwartberg movements continued to modify the land surface, 

 and at the summit of the Bed beds red-coloured sediment ceased to 

 be deposited with marked abruptness. Instead, we get the fine- 

 grained arenaceous Cave sandstone, whitish or yellowish in colour, 

 sometimes with a pinkish or pale bluish tint. 



The change usually takes place within a few feet in vertical range, 

 but sometimes the dividing line is remarkably distinct. Occasion- 

 ally towards the base of the sandstone there are lenticular beds of 

 reddish clay and mudstone, but of small extent laterally. 



The mineralogical composition of the sandstone, described pre- 

 viously in this paper, shows that the rock has been derived 

 principally from quartzite and granite. The absence of marked 

 bedding in the sandstone is due to the great uniformity of the 

 material ; specimens from near Molteno are identical with samples 

 from Elliot, Matatiele, or even Harrismith. 



There is plenty of evidence to show that the Karroo lake was very 

 shallow, and in many places there must have been extensive sandy 

 fiats, sometimes hardly covered by the water. 



