THE KARROO SYSTEM 



167 



Karroo 

 system 



Stormberg 

 series 



Beaufort 

 series 



Ecca series 



Dwyka 

 series 



Approximate 

 maximum 

 thickness. 



Drakensberg beds (volcanic) 4000 ^ 

 Cave sandstone . . . 800 [ Q Arkf \ 

 Red beds .... 1600 f 

 Molteno beds . . . 2000 J 

 Upper (Burghersdorp) beds ^ 



Middle .... [6000 



Lower .... 



2600 



Upper shales . . 600 ^ 



Boulder-beds . . . 1000 [ 2300 

 Lower shales . 700 J 



19,300 



The maximum thickness of the Karroo formation is 

 not less than 15,000 feet, excluding the volcanic beds, 

 although it is uncertain whether the full thickness is 

 now, or ever was, developed in ,any one locality. This 

 great bulk of sedimentary rocks nowhere contains evi- 

 dence of marine conditions having prevailed during its 

 deposition ; on the contrary, nearly all the fossils known 

 from the Karroo beds were undoubtedly land or fresh- 

 water forms. The accumulation of so great a thickness 

 of beds under such conditions is a very interesting fact, 

 and we shall return to the subject in a later chapter. 



1. THE DWYKA 

 Everywhere round the borders of the central basin a 

 rock with very peculiar characters crops out. For a 

 long time it was more or less of a puzzle to geologists, 

 and the formation was given such names as " trap-con- 

 glomerate " or claystone-porphyry," and by some ob- 

 servers was considered to be of sedimentary and by 



1 A full historical account of the views regarding the nature of the 

 Dwyka will be found in Corstorphine, " The History of Stratigraphical 

 Investigation in South Africa," Rept. S. A. A. S., 1904, p. 153. 



