98 



DE. F. H. HATCH — GEOLOGY OE THE 



[Peb. 1898 



Certain mineralogical changes are likewise observable as a con- 

 sequence of tbe dynamic influences. Thus a white silvery mica or 

 sericite is commonly developed in the conglomerates ; this mineral 

 is found in filmy layers round the pebbles, and in those portions of 

 the beds where differential movement has been sufficiently great 

 to develop schistose structure. The pebbles themselves have 

 occasionally been fractured, or even completely shattered, and the 

 fragments re-cemented by secondary quartz. The silicification of 

 the quartzites by the deposition of secondary quartz, as described 

 above, is probably also a consequence of dynamic metamorphism. 

 The alteration of the dolerite- dykes, first to epidiorites, thence to 

 hornblende-schists, and finally to chlorite-schists must be ascribed 

 to the same influences. 



Pig. 6. — Reversed fault in the Croivn Deep Mine? 



fiS cS 0^ Oj- 



^ S -col;.^ 



K^^W 



Scale of Feet 



(00 200 30O <-ro 500 



The curiously complicated structure of the Yenterskroon district, 

 near Potchefstroom, on the Vaal, where the normal succession of 

 the members of the Cape System is reversed, is undoubtedly caused 

 by reversed or overthrust-faulting on a large scale (see PI. YI). 

 We find here, as already pointed out, the Magaliesberg and Gatsrand 

 Series dipping apparently under the Dolomite, the Dolomite under 

 the Witwatersrand Beds, the AYitwatersrand Beds under the Hospital 



