424 THE BLACK REEF TRANSGRESSION 



Black Beef, or lie between the Black Reef and the 

 Campbell Rand group, proving that volcanic activity, of 

 the same kind as that which gave rise to the Pniel 

 lavas, continued during the early part of the Transvaal 

 period. 



The significance of the Black Eeef series, chiefly 

 arenaceous beds which stretch from the north of Bechu- 

 analand through Griqualand West into Prieska, is that 

 it implies a general invasion by water at the commence- 

 ment of the Transvaal period. In Bechuanaland and 

 Griqualand West the floor on which this series rests 

 seems to have been remarkably flat. The character of 

 the sediments, ripple marked sandstones, conglomerate 

 beds and flagstones is that of rocks laid down near 

 land. The direction whence the invasion came has not 

 yet been determined. 



The Black Eeef beds are followed conformably by a 

 great limestone formation, the Campbell Rand series, 

 which was very probably of marine origin. It is in- 

 teresting to note that an unconformity implying local 

 disturbance along a north- north-west axis of folding 

 has been found in the Campbell Rand series in the south 

 of Griqualand West (the Leij Fontein unconformity). 

 The strata above and below the unconformity are alike ; 

 had they been dissimilar the phenomenon would have 

 closely resembled the unconformities within the Ven- 

 tersdorp system. 



The beds of the Campbell Rand series maintain a 

 constant character over a large part of the Transvaal 

 and the north of Cape Colony as far west as the Koran- 

 naberg, therefore the sea inust at that time have ex- 



