Joseph Le Conte—Genesis of Metalliferous Vems. 15 
matters. Most other forms are accounted for by subsequent 
changes in these. ut there are some metals which occur 
in a native condition, as, for example, gold, platinum, etce., 
nearly always; mercury and silver frequently ; copper some- 
times. It is well to observe that the occurrence in a native 
condition is common just in proportion to the feeblerress 
of the affinities of the metal. In the case of mercury, silver 
to me most probable, therefore, that the gold, like and along 
with other metals, was in solution as a sulphide, and deposited 
at the same time, but that on account of its feeble affinities it~ 
gave up its sulphur to the alkali at the moment of its deposition. 
Auriferous quartz veins have been filled, like other veins, by 
deposit from hot alkaline carbonate and alkaline sulphide wa- 
ters, holding in solution metallic sulphides, among which was 
gold sulphide. The deposit took place probably by loss of 
heat and pressure, the gold giving up its sulphur to the alkali, 
either forming alkaline persulphide, or else displacing carbonic 
acid at the moment of its deposition. If the gold sulphide was 
the only metallic sulphide present, then the gold would be found | 
_ We have preferred to ascribe the deposit to loss of heat and 
Pressure, but any one of the reactions given on p. 5 may accom- 
