104 The Anierican Geologist. August, is% 
Antimony unci arsenic sulf)hids TS-OBOSg 
Oxide of iron 3.5924 
Galenite , 0.0720 
Cinnabar 0.0070 
Gold 0.0034 
Silver 0.0012 
That the gold was undoubtedly deposited by the hot waters 
was shown by the fact that in 15 pounds of decomposed gran- 
ite arsenic, antimony, lead and copper were detected, but no 
mercury or gold. In what form the gold was held in solution 
was not ascertained, and a physical condition is as likely as 
a chemical one. 
The hot springs of Nevada are the last manifestations of 
an eruptive era that has not long since ceased. If we look 
around for eruptive rocks in the famous gold districts we find 
that the principal gold fields of California, Australia and 
South Africa are cut in all directions by dykes of eruptive 
rocks of the dioryte and diabase group. The inference is not 
far to seek, that gold was present in the siliceous waters which 
accompanied the eruption of these as well as other deep- 
seated or surface flows, and that it was precipitated in the 
adjacent rocks by the agency of sulphids which already ex- 
isted there or were sublimed by the eruptions, This hypothe- 
sis seems to be in harmony with the geological relations of 
the better known gold districts. 
In recent times the Witwatersrand has become familiar to 
us through the works of Schenk and Molengraaf and the thor- 
ough investigation of Schmeisser. In what follows I have for 
the most part made use of Schmeisser's description. 
In South Africa we can distinguish two varieties of gold 
deposits: The gold-bearing quartz veins and the auriferous 
conglomerates. The quartz veins belong for the most part to 
the steeply folded Swazi formation Avhich has been highly 
metamorphosed by eruptives. The characteristics of these 
veins in different districts may be summed up as follows: 
The quartz veins are principally genuine bedded veins. They 
are numerously cut by greenstone dykes, chiefly of dioryte, 
which are also sometimes found to have a course parallel to 
the veins. Besides gold, pyrite is almost always present, but 
has very often been largely altered into limonite antl iron 
ocher. Some veins contain large amounts of gold at the o ut 
