The Geology of tJte East Rand and Heidelberg. 249 



The Geology of the Far East Rand and the Heidelberg 

 District, Southern Transvaal. — A Retrospect. 



By F. H. Hatch. 



TTEIDELBERG, a town of insignificant j)roportions. lies 30 miles 

 -*-^ due south-east of Johannesburg at the foot of the Zuiker- 

 boschrand, a range of hills running south-west towards the Vaal 

 River and made up of the volcanic beds of the Ventersdorp System 

 and of the Elsburg series at the top of the Witwatersrand System. 

 Travelling south-east from the Zuikerboschrand, the whole of the 

 Witwatersrand formation is traversed m descending order. The 

 district, which extends south-west of Heidelberg toGoedv.erwachting, 

 a distance of 20 miles, and south-east to Grreylingstad, another 

 30 miles, has a complicated geological structure, the succession 

 being disturbed by faulting, broken by numerous igneous intrusions 

 and obscured by frequent outliers of the Karroo formation. It is 

 well known to the mining community on account of the fact that 

 a gold-bearing conglomerate bed has been worked profitably at 

 the Nigel Mine since the earliest days of the gold-fields, while 

 numerous other reef outcrops in different parts of the district have 

 induced much active prospecting, which has continued to the 

 present day. 



On coming to the Rand in 1892, one of the first tasks allotted 

 to me by my employers (the South African Trust & Finance 

 Company, then under the able direction of the late W. Y. Canipbell) 

 was to attempt to unravel the intricacies of this district and to see 

 what relation its auriferous conglomerates bore to those of the 

 Rand. In those days the Main Reef had only been traced, as such, 

 from Johannesburg eastward to Boksburg, where it disappears 

 imder an outlier of the Karroo formation. The workings of the 

 Kleinfontein, Van Ryn, Modderfontein, and Nigel companies were 

 considered to be on independent series of conglomerate beds. 



Starting at Johannesburg and going eastward, I mapped the 

 country immediately north of the mines, and was thus able to prove 

 the geological identity of the Kleinfontein conglomerates with those 

 of the Main Reef series. I then showed that the reefs worked by 

 the Kleinfontein, the Van Ryn. and the Modderfontein companies, 

 although apparently independent, were in reality faulted portions 

 of the same bed, although a higher horizon lying between the Main 

 and the Bird Reefs was also worked in places by the Van Ryu, 

 Chimes, and Modderfontein mines. (See Fig. 1.) 



In 1893 I reported to my employers as follows : — - 



" My recent visit to Heidelberg has made it appear probable 

 to me that the ' reefs ' worked at the Nigel and at the Heidelberg- 

 Roodepoort, as well as those exposed at Malans Kraal, Twee- 

 fontein and Rietfontein, and on Botha's Kraal and Poortje are 

 portions of the same series." 



