Yol. 70.] Mil. F. W. VEJSttTY OX THE TEEDEFORT OEANITE. 333 



granules of quartz, the whole being deeply stained with limonite. 

 No other minerals were observed. This is so different a rock from 

 the staurolite-actinolite-magnetite slate found in contact with the 

 granite, but derived from the same type of rock, that it is reason- 

 able to assume that the latter variety is intimately connected 

 with the granite intrusion, and has not been produced by the diabase. 



The extent of the disturbance caused by this intrusion of diabase 

 can be appreciated by tracing the band of quartzite (W3), which in 

 the southern part of the area forms its eastern boundary. After 

 being completely cut through three times by the diabase, north of 

 the Parijs road it is duplicated, forming two parallel outcrops for a 

 considerable distance, the one thrust behind the other. 



Coming now to the correlation of these sedimentary beds, one can 

 draw no exact parallel with those cropping out along the Band ; 

 but it seems highly reasonable to assume that the division Wl 

 corresponds to the Orange Grove Quartzite, W2 to the Water-Tower 

 Slates, W4 to the Hospital Hill Slates, with the contorted magne- 

 tite-quartz band in the middle of it, and W5 to the Hospital Hill 

 Quartzite. The vertical section appended to the map (PI. XLYII) 

 shows that two subsidiary quartzites (the lower one felspathic. and 

 both somewhat impersistent) occur in the mass of "W2 ; while AY 5 

 is made up of several alternating bands of quartzite and slate, with 

 a thick mass of quartzite at the top. The total thickness of the beds 

 to the top of W5 can approximately be estimated at 4800 feet. 



Summary. 



To sum up: In this paper it is maintained that the Yredefort 

 Granite is intrusive, not only into the Witwatersrand Beds, but 

 also into the basic intrusions associated with them. It is shown 

 that along its margin the granite has removed— possibly by absorp- 

 tion, but more probably by overhead stoping, varying amounts of 

 the sedimentary beds from point to point ; that it has reacted with 

 the basic intrusions in the sedimentary beds, with the production 

 of hybrid rocks ; that in one place a subsidiary intrusion of granite 

 occurs in the middle of the diabase : and finally that the granite has 

 induced a definite type of metamorphism in the adjacent slates, 

 which is of a type distinct from that induced by the diabase. 



With regard to the age of this granite, it has been suggested to 

 me by Dr. Hatch that the diabase, which is sometimes amygda- 

 loidal, may be genetically connected with the Yentersdorp Beds, in 

 which case the granite would be of post- Yentersdorp age. In 1903, 

 Dr. Molengraaff was impressed with the fact that the sediments 

 surrounding the granite boss, up to and including the Pretoria 

 Beds, were highly inclined, and, with the granite, were overlain by 

 the practically horizontal Karroo Beds. Being of the opinion then 

 that the steep clip of these beds was caused by the intrusion of the 

 granite, he postulated a post-Pretoria-pre-Karroo age for this 

 intrusion. I suggest, therefore, that the Yredefort Granite is, if 

 not contemporaneous with, at least connected with the same epoch 

 of igneous activity as, the Red Granite of the Northern Transvaal. 



