460 G. P. Becker—New Feature in the ‘Comstock Lode.” 
economical standpoint, as the source for many years past of an 
immense proportion of the silver, and a considerable fraction of 
the gold added to the circulation of the world; and the details 
of its geological character as developed, therefore acquire an 
importance not possessed by those of less prominent deposits. 
The Virginia Range is a due north and south branch of the 
Sierra Nevada system of mountains. On the eastern slope 
of Mt. Davidson, the chief peak of the range, were found the 
outcroppings of the vein which have been followed somewhat to 
the north, and a long distance to the south of that mountain, 
and shown to possess a total length of four miles in the general 
direction of the Virginia Range. Decidedly the most important 
portion of the Lode—that in which the celebrated “ Gould and 
Curry,” “Hale and Norcross,” “ Ophir,” “ Consolidated Virginia” 
and ‘ California” mines as well as others have been opened—ties 
at the base of Mt. Davidson, and is included within the limits 
of Virginia City. 
It is well known to those who have had occasion to make 
themselves familiar with the Comstock lode* that throughout 
that portion of the vein which lies in Virginia City, the west or 
foot wall is a continuation of Mount Davidson, and consists, like 
the mass of that mountain, of syenite, while the east wall isa 
porphyry, more nearly described as trachytic greenstone, or pro- 
pylite, with which the country was overflowed during the Ter- 
tiary period. The direction of the fissure subsequently filled by 
the vein matter of the Comstock, was plainly determined by the 
previously existing surface of contact between the syenite and 
propylite, which naturally offered less resistance to rupture than 
the solid mass of either adjoining rock. This is clear from 
the fact that for over a thousand feet from the surface, only 
insignificant masses of either rock were found on the side of the 
vein opposite to that of which they are especially characteristic. 
So strong was the influence of the direction, both in strike and 
in dip, given to the fissure by the presence of this com aratively 
weak surface of contact in he rocky mass, that the fissure ¢X 
tending in both directions away from Mount Davidson into solid 
propylite, unaccompanied by syenite, retained the strike, (nearly 
north and south,) and the dip (from 35° to 50°,) of the Virginia 
rtion, almost unaltered. 
This very clearly defined influence of the contact surface, was 
of itself good reason for supposing that the fissure in Virginia 
von Richthofen, “The Comstock Lode, San Francisco, 1865,” and “ U. 8. 
ical Exploration of the 40th Parallel,” Vol. III. ore 
