74 THE PNIEL SERIES 



they thicken eastwards by the coming in of more lavas 

 and green flagstones. For a distance of some thirty 

 miles north-west of Vryburg they rest upon the Zoetlief 

 lavas and overlap them at each end. The Pniel beds 

 stretch continuously from Takoon to the Transvaal 

 border near Vryburg, a distance of nearly eighty miles. 



North of Vryburg the belt is thirty-seven miles wide, 

 and the rocks again rest upon granite and the Kraaipan 

 series. The older rocks come to the surface in the 

 drainage basin of the Molopo south of Maretsani, but 

 between Setlagoli and Mosita .an outlier consisting of 

 conglomerates and grits followed by lavas and breccias 

 has been preserved in a synclinal fold. Pniel beds, con- 

 sisting of both breccias and lavas, again occupy a large 

 tract of country from Maretsani to beyond Mafeking, 

 while the town itself is built on a massive coarse con- 

 glomerate at the base of the formation. 



A small patch of lavas and green flagstones has been 

 found near Morokwen. 



Immediately south of Vryburg the Transvaal forma- 

 tion and the Dwyka cover the volcanic rocks for some 

 distance, but the latter appear on the Transvaal border 

 and extend without a break in a south-south-westerly 

 direction past Barkly West. South of Barkly West they 

 are covered over wide areas by the Dwyka, which still 

 partly fills the Pre-Karroo valley now being re-excavated 

 by the Harts and Vaal Eivers. The series in this area 

 is bent into a very low anticline, trending south-south- 

 west ; at Kirnberley it reaches a thickness of nearly 

 1,580 feet, including some 700 feet of quartzite at the 

 base. The rocks are occasionally exposed along the 



