78 DR. F. H. HATCH GEOLOGY OF THE [Feb. 1 898, 



portant point in connexion with following: up the auriferous conglo- 

 merates of the Main E.eef Series bej'ond Klipfontein. The outcrops 

 of this formation on Uitkyk, Erischgewaagd, and Kuilfontein closely 

 resemble those of Hospital Hill, and, like the latter, the beds are 

 faulted up against the granitic rocks of the Archaean formation. 



Another important occurrence of these beds is north of the Yaal 

 River granite on the farms Xodoeslaagte, Kodoesfontein, AVit- 

 koppiefontein, etc. The dip here is south, namely, towards the 

 granite, the contact-line being here also a faulted one. 



There remain to be noted several small inliers of the Hospital 

 Hill Series in the Heidelberg district, as for instance on Modder- 

 fontein and Klipfontein, some 12 miles south of Heidelberg. 



Description of the Rocks. 



The rocks of which this formation is composed consist of granular, 

 sugary quartzites, and banded, highly ferruginous shales. As 

 already pointed out, the quartzites generally appear as ridges, while 

 the shales, on account of their feebler resistance to the weather, 

 are hollowed out into valleys. Occasionally, however, when the 

 shales are very highly impregnated with iron, the beds resist rapid 

 weathering, and ridges are formed. The quartzites are generally of 

 a white saccharoidal type, consisting of subangular quartz-grains 

 which, under the microscope, are seen to be in close juxtaposition, 

 there being no interstitial matter, a result brought about, no doubt, 

 by a secondary accretion of crystalline silica on to the original 

 quartz-grains. 



The iron in the ferruginous shales is present, partly in the form of 

 specular ore, partly as magnetite. The shales are occasionally striped 

 or banded, ferruginous layers alternating with bands of jaspery 

 quartz. They show much diversity in colour, dependent on the 

 state of oxidation of the iron. 



W. H. Penning^ and D. Draper" attach considerable importance to 

 certain of the magnetite-beds as a clue to, and as a means of identi- 

 fying, the Main Reef, the idea being that they are continuous and 

 always present at practically the same distance from the outcrop of 

 the Main Reef. As, however, changes in the dip of the beds cause 

 a great variation in the distance between the outcrops, and further, 

 since there are many such ' magnetite-beds,' no one of which can 

 be traced continuously for any great distance, the proposed method 

 of prospecting is of no practical utility. 



With regard to strati graphical relations, the junction of the 

 Hospital Hill Series with the Archaean formation is always a faulted 

 one. As to the overlying strata, I see no reason to assume 

 (with Molengraaff ^) an unconformity between this series and the 

 quartzites and conglomerates of the Witwatersrand Beds. Wherever 



- * A Contribntionto the Geology of the Soutbern Transvaal,' Quart. Journ. 

 Geol. Soc. vol. xlvii (1891) p. 455. 



Trans. Geol. Soc. S. Africa, vol. ii, pt. i (1897) p. 7. 

 Neues Jabrb. Beilage-Bd. ix (1895) p. 178. 



