CHAPTER IV. 



THE PBE-CAPE ROCKS OF THE NORTH (CONTINUED). 



1. THE VENTERSDORP SYSTEM. 



IN Cape Colony and also in the south-western part of 

 the Transvaal the Black Beef series usually lies uncon- 

 formably upon dark-coloured volcanic rocks. The latter 

 were first described by Stow 1 under the name of " The 

 amygdaloidal rocks of Pniel ". These lavas and the as- 

 sociated sedimentary beds usually rest with marked un- 

 conformity on very much older rocks, but in places there 

 are intervening groups largely made of either acid or 

 basic lavas, separated from each other and from the 

 Pniels by unconformities. These volcanic groups to- 

 gether make up the Ventersdorp system, 2 which is thus 

 subdivided in downward succession : 



C. The Pniel series. 



B. The Kuip series. 



A. The Zoetlief series. 



The unconformities between these three series are of 

 great importance locally, but none is so pronounced as 

 that at the base of the lowest group in any given 



1 Stow, Q. J. G. S., xxx., PI. xxxv. 



2 Also called the Vaal River system by Molengraaff, Geology of the 

 Transvaal, 1904; "Ventersdorp" system was introduced by Hatch, 

 T. G. S. S. A., 1904, vi., p. 95. 



67 5* 



