GEOLOGY OF THE SOUTH AFRICAN REPUBLIC is 
The facts presented by Hatch, who devotes much less con- 
sideration to geological than to economic questions, lead one to 
conclude that there is one large and several smaller synclinal 
basins, none of which can be fully traced on the surface, and 
which are undoubtedly much broken by dynamic movements 
which have been accompanied by the intrusion of igneous rocks, 
mostly on the fault planes, but to a certain extent as intrusive 
sheets and laccolites. It seems not unlikely that the apparent 
basin structure indicated by outcrops, will be found to be much 
broken in depth by these igneous intrusions. 
The auriferous conglomerates of the Rand—The area within 
which is the principal development of auriferous conglomerates 
is estimated at 2000 square miles. Gold deposits occur also in 
other beds assumed to belong to the Cape formation, notably in 
the dolomites of the Malmani district, as vertical quartz veins, 
and in the sandstones of the Lydenburg district, which rest on 
dolomites. None of these have yet assumed any considerable 
economic importance, however, and it is the area called for short 
the “Rand” that produces over nine-tenths of the South African 
gold. 
In this area, though gold is found in most all of the several 
reef series enumerated above, it is rarely in paying quantities out- 
side of the Main reef series, upon which most of the mines near 
Johannesburg are working. In this series are several beds of 
conglomerate known respectively as the north, main, middle, and 
south reefs, and main and south reef leaders (this name is given 
to thin beds of conglomerate) not more than two or three of 
which are usually productive in the same mine. Schmeisser says 
the tenor in gold varies inversely with the thickness of the 
beds, and in many mines the principal values are obtained from 
the main reef leader, which averages only 15 inches in thickness 
while some of the reefs average six feet. Although there is con- 
siderable variation in the richness of the different beds, and of 
the same beds from one point to another, yet taking the district 
as a whole the gold seems to be distributed with remarkable uni- 
formity, as compared with other mining districts. Schmeisser 
