6 GEOLOGICAL SYSTEMS 



ably upon various older formations in the south of the 

 Colony. Marine fossils of Devonian age occur in about 

 1,100 feet of rock in the middle of the system. Unfor- 

 tunately these beds have not been recognised in the 

 north, though one of the northern formations, the 

 Matsap series, has been supposed, on quite inadequate 

 grounds, to represent the lower part of the Cape system. 



The Cape system is overlain conformably by the 

 Karroo formation along the southern edge of the Kar- 

 roo, but northwards it is overlapped unconformably by 

 that formation and finally disappears at the north end 

 of the Bokkeveld Mountain in Calvinia, where the Kar- 

 roo beds lie directly upon Pre-Cape rocks. 



The Karroo system, including the Dwyka series, 

 mainly of glacial origin at its base, and the volcanic 

 group of the north-east at its summit, is over 19,000 

 feet thick, and it covers a greater area in the Colony 

 than any other formation. Consisting chiefly of sand- 

 stones and shales without marine fossils this group of 

 rocks is a striking example of that class of formations 

 called continental, and it is of extreme interest on ac- 

 count of the numerous reptiles, ranging in age from 

 Permian to Jurassic, preserved in it. Though of con- 

 tinental origin, an expression which merely implies that 

 the rocks were not formed under the sea, this system does 

 not resemble such rocks as the Bunter and Keuper series 

 of the British Trias ; the characteristic red marls and 

 sandstones of the latter are unlike any beds in the Kar- 

 roo formation, in which red and purple shales play a 

 subordinate part. 



The Cretaceous beds have only been found near the 



