THE WITWATERSRAND GOLD REGION 739 
especially true of the conglomerates of the Black Reef series of the 
Potchefstroom system, which belongs considerably higher up in the 
geological column than the Witwatersrand system. A number of 
attempts have been made to work the Black Reef gold, but so far the 
success has been small, though in a few instances a certain amount of 
profit is said, at least temporarily, to have been obtained. 
Besides its occurrence in conglomerates, gold is found under 
various other conditions in various places in the Transvaal, but these 
Fic. 2.—Photograph of surface workings in the Crown Reef Mine, Witwatersrand 
District, Transvaal. Thesteeply dipping strata underneath the hoisting works on the 
right-hand side of the picture are the outcrop of the gold-bearing conglomerate. 
occurrences are not within the scope of this article. Among them, 
however, may incidentally be mentioned the auriferous quartz veins in 
rocks of the Swazieland series in the Barberton region and near 
Pietersburg; the quartz veins in the rocks of the Dolomite series near 
Lydenburg and at Malmani; the quartz veins in rocks of the Pretoria 
series west of Pretoria and west of Krugersdorp as well as elsewhere; 
the placer workings in many places. The importance of all these 
occurrences, however, has proved small compared with the gold in the 
conglomerates of the Main Reef series of the Witwatersrand, the 
