e Ontario. (The latter, the greatest silver mine now
known in the country, lies in quartzite, and the trap is near, but not
in contact with the vein.)

_(i.)_ In Nevada, the ore deposits of Pioche, Tempiute, Tybo, Eureka,
White Pine, and Cherry Creek, on the east side of the State, with those
of Austin, Belmont, and a series too great for enumeration in the
central and western portions.

_(j.)_ In California, the Bodie, Mariposa, Grass Valley, and other
mines.[1]

_(k.)_ In Idaho, those of the Poor Man in the Owyhee district, the
principal veins of the Wood River region, the Ramshorn at Challis, the
Custer and Charles Dickens, at Bonanza City, etc.

[Footnote 1: See Redmond's Report _(California Geol. Survey Mining
Statistics, No 1),_ where seventy-seven mines are enumerated, of which
three are said to be in "porphyritic schist," all the others in granite,
mica schist, clay, slate, etc.]

In nearly all these localities we may find evidence not only that the
ore deposits have not been derived from the leaching of igneous rocks,
but also that they have not come from those of any kind which form the
walls of the veins.

The gold-bearing quartz veins of Deadwood are so closely associated with
dikes of porphyry, that they may have been considered as illustrations
of the potency of trap dikes in producing concentration of metals. But
we have conclusive evidence that the gold was there in Archaean times,
while the igneous rocks are all of modern, probably of Tertiary, date.
This proof is furnished by the "Cement mines" of the Potsdam sandstone.
This is the beach of the Lower Silurian sea when it washed the shores of
an Archaean island, now the Black Hills. The waves that produced this
beach beat against cliffs of granite and slate containing quartz veins
carrying gold. Fragments of this auriferous quartz, and the gold beaten
out of them and concentrated by the waves, were in places buried in the
sand beach in such quantity as to form deposits from which a large
amount of gold is now being taken. Without this demonstration of the
origin and antiquity of the gold, it might very well have been supposed
to be derived from the eruptive rock.

Strong arguments against the theory that the leaching of superficial
igneous rocks has supplied the materials filling mineral veins, are
furnished by the facts observed in the districts where igneous rocks are
most prevalent, viz.: (1.) _Such districts are proverbially barren of
usefu