attached,
viz., every strake is traversed longitudinally by a small gas-pipe
perforated at the bottom, discharging a perfect spray of water upon the
blankets, whereby the lighter sands are very effectually washed down
the strakes. Owing to the great prevalence of lime in the ores, these
tailings evince a great disposition to decompose in the open air, so
that it is not at all surprising to find tailings which have been
repeatedly treated, to repay for all the trouble and expense for
extracting the bullion they still continued to contain, after farther
manipulations.
Section VL—The Sutro Tunnel.
This
undertaking, now so near its completion (August, 1877*), has been
carried on, from its inception to the time I inspected it, with
determined energy, and as the work was performed in a very short time,
and in the face of many difficulties, the following sketch may be of
interest to us in Australia, where certain localities offer similar
facilities for such principal adits:—
In
some of the lower workings on the Comstock, the temperature exceeds 130
degrees Fahrenheit, and that in the face of a large number of
machines-which either exhaust (suck) the depraved air to the surface,
or others which add good wholesome air directly or indirectly to the
heated atmosphere* below. There is, besides, every reason to believe
that a yet greater heat will prevail, and which will consequently
render the future working of these mines almost an impossibility for a
much greater depth. The amount of work performed under these
circumstances cannot exceed 50-per cent, of what miners would do in a
cool and wholesome atmosphere,. and thus the working expenses are
increased at a rapid ratio with a corresponding decline of profits,
for which the^extraordinary richness of the ores could only compensate.
The cost of raising a ton of ore, for instance, in sueh mines as yield
profits or pay their way amounts to one dollar each; in mines where no
regularly payable ore is getting it costs probably as much as 4 dollars
per ton. And it should also be remembered, that mine timber lasts
longer in ventilated workings than in less wholesome mines, which
circumstance, in the first case, would on the Comstock make a deal of
difference, as the mines there have used for years an annual supply of
lumber measuring 16,000,000 feet (American measure). Added to this,,
comes the expensive pumping machinery for the drainage of the mines,
and also the increased cost of carriage for all kinds of miners'"
requisites delivered at a high and almost inaccessible part of the
Nevada Mountains.
Mr.
Adolph Sutro conceived the idea, sometime before 1869, to start a main
tunnel from the banks of the Carson River, at a distance of about four
miles east of Virginia City, for the deeper levels of the Comstock
lode, and after grappling successfully with legal and local
difficulties, ground was broken in the same year, since which time this
adit has been in full operation. The expenses have been, on the
average, at the rate of £200 per day, and its total length at the time
of my visit was 18,000 feet, leaving but 2,000 feet more before the
Savage Company's levels would be holed into. As soon as this is done,
there cannot be any doubt but what the miners, mines, and all
interested will be materially benefited, through a considerable
reduction in the working expenses and consequent larger margins of
profit, besides
* This tunnel has since been successfully connected with workings (at the 1,922-foot level)
on the Comstock lode.—(G. T.)
