66 THE GRANITE AND GNEISS 



the granite is traversed by planes of shear, and in places 

 it has been converted into a flaggy rock scarcely dis- 

 tinguishable from a fine-grained quartzite. The minerals 

 have broken down to form a granular ground mass 

 containing occasional "eyes" of felspar and quartz; 

 these crushed bands of rock can be called mylonites. At 

 Prieska Poort glaucophane and epidote have developed 

 in such rocks. This structure was of course given to 

 the rock long after its consolidation, but the gneissose 

 structure was produced before it became solid, and though 

 the two kinds of structure have parallel strikes there is 

 often considerable divergence between them in places. 



As mentioned in connection with the Kheis series, the 

 granite has invaded the latter, and peculiar rocks have 

 been produced by the mixing of the granitic material 

 with the quartzose sediments of the Kaaien beds on the 

 one hand and with the basic lavas of the Marydale beds 

 on the other. As a result there are streaky rocks, 

 usually with granulitic structure, varying in composition 

 from extremely siliceous types to basic, and often con- 

 taining garnet. In many places it is difficult to deter- 

 mine the boundary of the intrusive rock. 



Pegmatites are very frequently seen, especially in the 

 formations invaded, and in the south-eastern corner of 

 Kenhardt the crystals are of such gigantic dimensions 

 that one can walk for many yards over continuous 

 masses of white microcline felspar. Graphic granite is 

 abundant. These pegmatites contain muscovite and 

 occasionally garnet and haematite. Tourmaline is of 

 rare occurrence ; it is found in quartz veins in the 

 Marydale beds west of Uitspansberg, but it is reported 

 to be plentiful in the north-west of Kenhardt. 



