GEOLOGY OF THE SOUTH AFRICAN REPUBLIC 17 
to be secondary. Gold is sometimes found also in the sand- 
stones between the reefs. 
Numerous dikes and some intrusive sheets traverse the beds ; 
the intrusive rocks are generally basic; diabase, olivine and 
bronzite-diabase, gabbro and olivine-norite being among the vari- 
eties recognized. The dikes generally follow fault planes. The 
faults, which are quite frequent, are both dip, strike and reversed 
faults. Quartz veins are said to cross the gold-bearing beds, and 
at the intersection the quartz becomes quite rich. 
Origin of the gold—¥rom the very earliest discovery of these 
deposits the question as to how the gold came to be distributed 
in such quantities over such great areas and in so many different 
beds has been one that has occupied the attention of all geolo- 
gists who have visited the region. Probably the largest number, 
certainly among the earlier observers, have considered that the 
gold, like the pebbles of which the beds consist, results from the 
degradation and concentration by sea waves of material from an 
ancient landmass of Swasi-schists. They have seen in the quartz 
of the pebbles a resembiance to that of the veins which are so 
abundant in these rocks in the De Kaap and other outlying dis- 
tricts. A few have held that the gold was chemically deposited 
from the waters of the ocean; and another, and in late years an 
increasing, number believe that it has been deposited from ascend- 
ing or descending thermal solutions. 
Schmeisser brought back specimens of the conglomerate ore 
from six of the principal mines of the Rand, which were sub- 
mitted to Dr. Koch for microscopical examination. The main 
results of this examination are as follows: 
The pyrite shows the effects of wear in rounded edges, etc., 
and also occurs within the quartz pebbles; hence it is undoubt- 
edly of primary origin. The same is true of the magnetite and 
zircon. The rutile is, however, not original, and the muscovite 
and chlorite are evidently formed from the alteration of other 
minerals. Secondary quartz occurs both in the matrix and filling 
the cracks in the pebbles that result from dynamic action; it con- 
tains fewer inclusions than the primary quartz. The gold con- 
