THK KARROO SYSTEM 221 



menced in the north-eastern part of the Colony. Near 

 Molteno there are a few hills capped by volcanic 

 rocks, outliers of a formation which is found covering 

 an enormous area in Barkly East, Herschel, the interior 

 of Basutoland, and along the boundary between that 

 country and East Griqualand and Natal. Volcanic 

 rocks, in all -likelihood belonging to this formation, are 

 found in the Lebombo Mountains, the Bushveld area of 

 the Transvaal, and Rhodesia. 



The volcanic beds form the highest parts of the 

 country in which they occur ; seldom indeed does their 

 base drop as low as 5,000 feet above sea level. They 

 constitute a plateau which has been greatly dissected by 

 the upper tributaries of the Orange Kiver. In places it 

 rises to over 10,000 feet above sea level. The Drakens- 

 bergen are the southern edge of the plateau and over- 

 look the Transkei, Griqualand East and Natal. The 

 escarpment extends over 350 miles, and rises from 2,000 

 to 6,000 feet above the country at its foot. 



In the Cape Colony the volcanic rocks rarely reach 

 3,000 feet in thickness, but near Ongeluk's Nek (Mata- 

 tiele) there must be quite 4,000 of them; while Mr. 

 Churchill measured a vertical thickness of 4,500 feet on 

 the Mont aux Sources in Natal. 



By far the greater part of the group is formed of lava 

 streams, but in Barkly East and Elliot sandstones, 

 bedded tuffs, and agglomerates are represented towards 

 the base of the formation. 



Although the relationship between the Cave sandstone 

 and the volcanic beds is a very intimate one, the former 

 containing in places intercalated lava- flows, there are 



