330 MR. F. W. PENNY ON THE TEEDEFOET GEANITE. [Dec. I914, 



'on the farm Vergenoeg 220,' and described by him as follows : — 



' The actual contact between the two rocks is exposed in a cutting- connecting- 

 two hills, the one consisting of Orange Grove Quartzites, and the other of old 

 granite. The Orange Grove Quartzites dip towards the granite, and are very 

 much laminated at the contact, no doubt due to the tilting and the sliding of 

 the beds. The granite, although much weathered, shows a strip of sericite- 

 schist separating it from the quartzites.' 



At the time of my visit, there was no cutting open exposing the 

 actual contact. On passing north-westwards towards the Zyfer- 

 fontein boundary, one notes that a thickness of diabase intervenes 

 between the arranite and the sedimentary beds. This is not at all 

 an unusual phenomenon, for it occurs to a varying extent all round 

 the granite margin. In this case the line of separation is remark- 

 ably sharp; no veins of the one igneous rock were observed to 

 penetrate the other. Several isolated masses of well-bedded 

 quartzite occur on the inner edge of the diabase, having apparently 

 been wedged off from the main mass of quartzite at the time of 

 the diabase intrusion. On the north, this quartzite-riclge and the 

 diabase come to an end suddenly against a fault, which must be 

 subsequent in age to the basic intrusion, and probably resulted at 

 the time of the intrusion of the granite. Proceeding northwards, 

 one observes the interesting phenomenon of the granite invading 

 the Witwatersrand Beds; the quartzite (Wl) is entirely absent, 

 and the granite finds itself in contact with some part of the slates 

 (W2) which overlie it, except for a narrow band of quartzite that 

 for a short distance defines the margin of the granite. The slates, 

 as also their continuation northwards and southwards, are to the 

 eye considerably changed from their normal appearance of reddish 

 or brownish-black, very ferruginous, flaggy beds ; but their well- 

 marked banding, and the coarse cleavage parallel to it, are still 

 well preserved. Certain horizons are very rich in magnetite, and 

 form prominent outcrops. In these magnetite-slates, thin bands 

 composed almost entirely of radiating actinolite-crystals occur, 

 separated by layers of magnetite with little or no actinolite visible 

 to the naked e} r e. Under the microscope large crystals of somewhat 

 decomposed staurolite were observed, frequently twinned, having 

 clear edges but centres cloudy with opaque dust "(PI. XL VI, fig. 2); 

 angular fragments of quartz and clear secondary felspar were de- 

 tected in the ground-mass among the magnetite-grains. The slates 

 are much shattered and faulted, as can be seen from the mapped 

 outcrop of a narrow band of felspathic quartzite (W2t>) which 

 occurs in the body of them. This band is very distinctive, and has 

 been traced for some distance north-westwards, while its position 

 relative to the granite margin affords a good idea of the amount of 

 sedimentary beds absent at any point. Farther on, another lenti- 

 cular mass of diabase intervenes at the margin of the granite, and 

 the quartzite (Wl) simultaneously makes its reappearance — first 

 as a narrow band between the slate and diabase, then as a thicker 

 contorted and faulted ridge, which finally develops into its normal 

 thickness and continues up to the Parijs road, where it terminates 



