PRE-CAPE ROCKS OF SOUTH AND WEST OF COLONY 23 



flakes of white or yellowish mica are often sufficiently 

 abundant to give a lustrous appearance to the cleavage 

 planes. The country occupied by these beds is rather 

 flat and has a regular rainfall ; the slates are usually de- 

 composed to a depth of many feet, giving rise to a clayey 

 or sandy material of white, yellow, brown or red colour, 

 and are hidden over wide areas by a thin clayey soil or 

 covered by other superficial deposits, often of consider- 

 able thickness. 



Outcrops are not abundant, and as the beds are nearly 

 always found dipping at high angles and are obviously 

 repeatedly folded, the true structure of the area has not 

 yet been ascertained ; only in Van Khyn's Dorp has any 

 definite order of succession been made out. 



The slaty rocks sometimes become very micaceous, 

 and such sericitic phyllites are well developed in the 

 Tulbagh valley, and to the south and east of Piquetberg. 

 They may pass into impure quartzites, as for instance 

 in the hills north-east of Moorreesburg and the Tiger- 

 berg group, but pure quartzites are not often met with. 

 Gritty rocks are common and by the presence of felspar 

 pass into felspathic grits, usually very much cleaved, as 

 for example on the Verloren Kiver in Piquetberg and in 

 Van Ehyn's Dorp. Schistose felspathic rocks, which 

 are perhaps sheared arkoses, occur immediately north 

 of the town of Worcester. In Van Khyn's Dorp l there 

 is greater lithological variation in the series, and it can 

 be divided into a basal group, black slates and phyllites; 

 a middle one, crystalline limestones with interbedded 

 black slates and limonite beds ; and an upper one, slates 



1 G. C.,ix.,p. 13. 



