38 
ECONOMIC GEOLOGY 
of New Zealand and at Nome in Alaska : but the most im- 
portant is the Witwatersrand Goldfield in the Transvaal, 
the most productive goldfield in the world. The South 
African goldfields have been worked from prehistoric times 
in Rhodesia, which is often regarded as the Ophir, whence 
Solomon obtained the gold for his temple. The gold in the 
Rand ore, though very rich, is in such minute particles that 
it is rarely visible and produced no noticeable alluvial de- 
posits. The ore was discovered in 1885, at Langlaagte, near 
Johannesburg, and the auriferous conglomerate was followed 
SW - 
2 
_ = 
~~ 
XX 
IYI 
~ 
2: 
pu 
a ————— 
cr TF 
Karroo beds. 
Pretoria system, 
Ventersdorp system. 
Upper part of Witwatersrand system. 
— 
en 
‘~ 
NE 
io >| 
| 
Z. 
nA 
><, 
F1a. 19.—SkcrioN Across THE RAND GoOLDFIELD, 
during 1886 for miles E. and W. Johannesburg was founded 
in 1887. A boom in 1888 was followed in 1889 by a panic 
due to the discovery that much of the ore was low grade, 
and that the minuteness of the gold rendered its recovery 
difficult by the methods then used. The local coal discovered 
in 1887, the regularity of the ore in bulk, and the opportune 
discovery of the cyanide process, rendered the mining easy 
and profitable. 
The Rand Goldfield is a large synclinal basin (Fig. 10) 
of pre-Paleozoic rocks. Both to N. and to S. are granites, 
of which the northern is intrusive into schists containing