PRE-CAPE ROCKS OF THE NORTH OF THE COLONY 81 



which is particularly characteristic of this series through- 

 out its known extent in Cape Colony. In places dark- 

 coloured cherts containing rhombohedra of carbonate of 

 iron are associated with the quartzites, e.g., Schmidt's 

 Drift and Klip Fontein near Prieska. The conglomer- 

 ates are irregularly distributed and individual beds can 

 rarely be followed far. The pebbles are of quartz, chert, 

 agate or chalcedony, granite, slaty rocks, lavas from the 

 Pniel and older volcanic beds, and occasionally schistose 

 rocks. 



The limestones and calcareous grits are just like many 

 beds in the Campbell Kand series. They usually occur 

 near the upper limit of the series, but in Prieska there 

 is a well-marked band of them near the base. 



Between Zwart Fontein and Geluk in Vryburg a band 

 of argillaceous sandstones and ferruginous cherty rocks, 

 the latter very like some of the beds in the Griqua Town 

 series, occurs near the top of the Black Beef series. 

 They give rise to a low ridge about twelve miles long 

 called the Zwart Kand. 



The volcanic rocks found in the Black Reef series 

 near Vryburg are blue amygdaloidal lavas and fine- 

 grained flags of the same kind as many rocks in the 

 underlying Pniel group. They occur some fifty feet be- 

 low the top of the Black Reef quartzite near Vryburg, 

 and again between the latter and the bulk of the Camp- 

 bell Rand limestones at Takwanen and other places 

 west of Vryburg ; in the latter case they are separated 

 from the quartzites by a few feet of limestone. These 

 volcanics are also present on the Transvaal border near 

 Mafeking. 



