ed rocks, perhaps the
same that inclose the vein above, by highly heated solutions which
deposited their load near the surface. On the other hand, Becker
supposes the concentration to have been effected by surface waters
flowing laterally through the igneous rocks, gathering the precious
metals and depositing them in the fissure, as lateral secretion produces
the accumulation of ore in the limestone of the lead region. But there
are apparently good reasons for preferring the theory of Richthofen:
viz., first, the veinstone of the Comstock is chiefly quartz, the
natural and common precipitate of _hot_ waters, since they are far more
powerful solvents of silica than cold. On the contrary, the ores
deposited from lateral secretion, as in the Mississippi lead region, at
low temperature contain comparatively little silica; second, the great
mineral belt to which reference has been made above is now the region
where nearly all the hot springs of the continent are situated. It is,
in fact, a region conspicuous for the number of its hot springs, and it
is evident that these are the last of the series of thermal phenomena
connected with the great volcanic upheavals and eruptions, of which this
region has been the theater since the beginning of the Tertiary age. The
geysers of Yellowstone Park, the hot springs of the Wamchuck district in
Oregon, the Steamboat Springs of Nevada, the geysers of California, the
hot springs of Salt Lake City, Monroe, etc., in Utah, and the Pagosa in
Colorado, are only the most conspicuous among thousands of hot springs
which continue in action at the present time. The evidence is also
conclusive that the number of hot springs, great as it now is in this
region, was once much greater. That these hot springs were capable of
producing mineral veins by material brought up in and deposited from
their waters, is demonstrated by the phenomena observable at the
Steamboat Springs, and which were cited in my former article as
affording the best illustration of vein formation.

The temperature of the lower workings of the Comstock vein is now over
150 deg.F., and an enormous quantity of hot water is discharged through the
Sutro Tunnel. This water has been heated by coming in contact with hot
rocks at a lower level than the present workings of the Comstock lode,
and has been driven upward in the same way that the flow of all hot
springs is produced. As that flow is continuous, it is evident that the
workings of