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MINING IN CALIFORNIA AND NEVADA.
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sinkers
as well as to send mining timber below. When necessary, according to
the terms of contract, with the crushing mills, all three cages bring
up ore, and each drum is under the sole control of a special driver, so
as to expedite the work during eight hours shifts. At the new east
shaft— these two companies sink their shaft exactly over their boundary
lines, and term them "combination" shafts—which is much larger, viz.,
27 feet by 6 feet 6 inches, the shaft timber employed is sugar-pine,
squared to 15 and 20 inches diameter; the frames are placed 5 feet from
centre to centre with " studdles" at the corners and partitions.
Plate
IX. exhibits one compartment and a portion of the second, of which
there are four in this and most other shafts. Instead of the "bearers"
used with us in difficult ground, which require much time and expense
for cutting "hitches" in hard country, the Americans use diagonal stays
a a instead, tennoned and bolted to the studdles b b, and as the hitches can easily be cut obliquely forward, without undermining horizontally, as with us, such can be done quicker, and, when wedged up, stand as well, if not better, as a bearer.
Some of the American "stations," i.e., plats,
are secured with timber, " arch" fashion ; besides the sole and leg
pieces, there are not less than five trapezoid pieces used to complete
the " cap" which, it is unnecessary to say, is a very strong and
enduring method to secure their stations, which, on the average,
measure 30 feet wide, 40 feet long by 11 feet high in the clear. Nearly
all their levels and stations underground are lined or floored with
stout boiler plates, instead of tramways, in order to facilitate the
rapid transit of ore from the passes to the shafts. The main levels are
9 feet in height, the same as their first stopes, and the remainder of
the backs above the levels is taken away in stopes 7 feet high ; the
whole of the ground is systematically cut up into blocks from the two
main levels driven in the foot and hanging wall respectively.
As already stated, the filling of the stoped backs is accomplished by
solid piles of timber, thus explaining the enormous consumption of
500,000 feet per day (American measure, or about one-third of ours) by
these two proprietaries.
As
will be seen from Plate X., already referred to, the whole space
between the legs (cills), soles, and caps, is filled in with spars 10
inches square, and long enough to fill three sets of timber, or about
11 feet, and, in order to render this " bulk-heading" quite solid, wedges o o o o are
driven in wherever necessary. The next stope is secured similarly, but
not quite so close, the support of the cap being the chief
desideratum, as shown at d, besides which, the whole of this
timber, so systematically constructed, is strongly stayed against the
hanging wall. The shaded places above the tennons p p are left
open until it is necessary to timber the first stope, and then the
lower tennons of these higher cills are put into these mortices, their
proper places, and so on.
To describe the mode of working of another mine, I select one of a number inspected, viz., the Justice, situated
at Gold Hill, two miles south of Virginia City, also on the Comstock
line of lode, which employs 630 miners. Their shaft is vertical for 400
feet, whence it follows the usual underlay of the Comstock lode for
1,180 feet, or 1,580 feet in all. The shaft (20 feet long by 5 feet
wide) is worked by means of powerful winding engines, and the one
surface winding compartment is used for winding from 300 feet only; the
, remaining 100 feet vertical are used as an ore chamber, into which
the skips empty themselves as they are hoisted from the deep workings ;
proper shoots at the 400-foot level supply the trucks to be raised to
surface ; the skips are unusually large, containing not less than seven
tons, or more, at the time
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