BELOW THE SURFACE.
In order that the reader may get a proper idea of the underground works
of a mine, I shall now give a detailed description of all that is worthy
of special mention. Drifts are openings or galleries from four to six
feet in width, and from six to eight feet in height, opened along the
course of the vein. They are generally run along one of the walls of the
vein, in the “country rock,” (rock outside of the vein) as that contains
no lime, and therefore stands best, and does not swell and crush the
timbers. In some drifts the rock stands without being timbered. The main
north and south drift, generally the first reached after leaving a
station in a mine, is the highway of the level in which it is opened. It
has a car-track running through its whole length, and, in some cases, as
in the main drift on the 1500-foot level of the consolidated Virginia
and California mines, contains a double car-track.
The cross-cuts are the same kind of openings as the drifts, but they are
smaller and run across the course of the vein—run east and west. They
start from the main drift, and are pushed out into the vein and
ore-body, if ore-body there be. Pushed out in this way from the main
drift at intervals of about 100 feet, they cut through and “prospect”
the vein. The progress of the cross-cuts on a new level in a leading
mine on the Comstock is always watched with great interest by all the
“mining experts,” “stock sharps,” and mining men generally.
Car-tracks are laid in all of the cross-cuts, and connect with the track
of the main drift by means of turn-tables. The cross-cuts are pushed
through the vein to its opposite wall, in order that the whole of the
ground may be thoroughly explored and its boundaries defined. In order
to secure a free circulation of air on the level, they are frequently
connected at various points by cross-drifts.
Winzes are small shafts sunk from one level to another in the mine. They
are sunk in any place where they may happen to be required. Some are
sunk vertically, but many follow the foot-wall of the vein, and thus go
down at an angle of from thirty-five to forty-five degrees. All are of
great use for the purpose of ventilation, and those that are sunk at an
angle are very frequently properly planked up, and used as chutes
through which to send ore or timbers to a lower level. In all mines will
be found a great number of these chutes. Sometimes the men fall into
them. When this happens they are always to be found at the bottom, on
the level below, immediately after. Generally, men are not very badly
hurt by sliding through an ordinary chute, yet not a few have been
killed by such a fall, and many have had bones broken.
In going down a chute much depends upon the angle of the opening—the
steeper, the more danger there is in making the trip. On the surface of
the earth all the vertical winzes would be called shafts, and what are
called drifts and cross-cuts below would be called tunnels, were they
where their mouths came out on the surface. An “upraise” is where the
miners begin on a lower level and dig upward toward a higher. While it
is going up, it is an upraise, but when it is connected with the level
above it is a winze. Should it never reach the level for which it was
started it remains an upraise for all time.
Winzes are very often thus made—one set of miners being engaged below at
digging up, while above another set are digging down. The progress made
by the men below is always much more rapid than that of the men above,
as every ounce of dirt loosened at once falls down out of the way.
When the ore-body has been properly opened, explored, and ventilated by
means of drifts, cross-cuts, and winzes, the work of extraction is
commenced.
The first opening is made on the “track-floor” of the level—the floor on
which are run the drifts and cross-cuts wherein are laid the
car-tracks—and in the bottom of this opening or chamber are put down the
sills for the first “square-set” of timbers.
The timbers used as supports in a mine are from twelve to fourteen
inches square. The posts are six feet, and the caps five feet, in
length. The upper ends of the posts are framed in such a manner that the
ends of four caps may rest upon each, and leave a mortise in the centre,
in which to insert the tenon of the post of the next “set”; on the top
of this is a place for another post, and so the work of building up sets
goes on to any height that may be required.
As the ore is extracted at the sides of the first set, the same squares
of timbers are built up in those places, and there is formed a sort of
pyramid of cribs, rising constantly as the work of extracting the ore
proceeds. The top sets of this pyramid are secured closely against the
ore, by means of large wooden wedges, and the side sets are also wedged
up against the ore in the same way, as they are carried up. In this way
the mass of ore overhead is supported at all points by the cribs of
timbers, except here and there where chambers are being excavated in the
ore-body for new sets.
Thus are squares of timbers constantly added, and the pyramid carried up
till the ore has been worked out to the level above. If the level above
has been worked out, it is already filled with the same square sets as
are being built up from below, and the latter rise into their proper
places and fit as neatly as the squares on a checker or chess-board.
The sets are six feet in height by five feet in width, and as they rise,
floors of strong plank are laid upon each set. Thus there are seen
floors some six feet apart from the bottom to the top of the level.
In these floors are square openings as for trap-doors, with short
flights of steps leading from floor to floor. The floors are pushed out
against the breasts of ore on all sides as the stope is extended. A
light blast of giant-powder being exploded in the face of the
ore-breast, the mass is shattered, and is then easily pulled down by the
picks of the miners.
As the ore is dug down it falls upon the floors, from which it is easily
shovelled into the wheelbarrows, by means of which it is carried to the
chutes. These chutes lead down to ore-bins on the track-floor, where the
cars are loaded which carry the ore to the main shaft and finally up to
the surface, and out along a track which leads to the ore-house, from
which it is sent to the mills. This is the method of timbering mines
that was invented by Mr. Philip Deidesheimer, in the early days of
Washoe, when he was superintendent of the old Ophir mine. The building
up of timbers in square sets or cribs is found to be exactly what is
required, as a cavity of any size, however great, can by this plan be
filled up and its roof supported.
In order to still further secure the mine, it is usual to plank or
timber up a section of four of these square sets, and fill them in from
bottom to top with waste rock. Thus is provided a large column of stone
reaching up to and supporting the roof of the mine. Such columns are
constructed in a number of places, at suitable intervals throughout each
level of the mine, and they are found to stand more strain than would
all of the timber that could be piled into a level. Being built up of
loose rocks they gradually yield for a time, but still stand as firmly
in their places as before, whereas a solid column of stone would be
crushed into a thousand fragments, and would let down the whole upper
part of the mine.
In some mines many blocks of porphyry and other barren rock are found
with the ore, making it necessary to do a great deal of assorting, but
in the Consolidated Virginia mine there is no work of this kind to be
done, at least not on the 1500-foot level, where they are sloping out in
the bonanza. There is nothing to do but dig down the rich masses of
black sulphuret and chloride ores, shovel them into the cars, and send
them to the surface to be taken to the mills, and the same is the case
in the California mine.
Samples are taken from each car-load of ore down in the mine, when it
reaches the main shaft; at the surface other samples are taken, and at
the mills samples are taken of the pulp, every hour, as it runs from the
batteries—in short, the ore is sampled everywhere, and at all stages in
the handling, from the ore-breasts till it has passed through the mills,
and finally appears in the shape of large, shining silver bricks, each
weighing a hundred pounds or more. All the samples thus taken are
carefully assayed, and the results compared and noted.
An incline is simply an inclined extension of the main shaft, from some
convenient point below, or rather at or near the point where the shaft
strikes the west wall of the vein. The Comstock lode dips to the
eastward at an angle of from thirty-five to forty-five degrees, and as
the main working shaft of a mine is always sunk to a considerable
distance—a thousand feet or more—to the eastward of the croppings [_i.
e._ that part of the lode which comes to the surface of the earth], the
west wall is not reached until the shaft has attained a depth of from
1000 to 1500 feet, depending upon how far east of the croppings it was
sunk.
The main incline of a mine is of about the same dimensions as the main
shaft, and is timbered in much the same way. In the Consolidated
Virginia mine there is as yet no incline, but at the Crown Point mine is
to be seen one that is a model in every respect. This incline starts at
the 1100-foot level, from the bottom of the vertical shaft, and goes
down with the dip of the vein (at an angle of about thirty-five
degrees), to the 1700-foot level, its present terminus. A track is laid
on its bottom, of ordinary railroad iron, and as neither cages nor a car
of the usual pattern can be used in an incline, recourse is had to
another device. A kind of car called a “giraffe” is used for hoisting
through an incline. It has low wheels in front and high ones behind;
thus the body of the giraffe stands level, the same as a common ore-car
on an ordinary track.
The giraffe is capable of carrying eight tons of ore—more than eight
ordinary car-loads. It is lowered down the track to the bottom of the
incline, and hauled up to the foot of the shaft by means of a round
steel-wire cable which runs upon a reel at the surface.
The cable passes over a large iron pulley at the top of the vertical
shaft, and _under_ a second pulley of the same kind at its bottom. The
cable is also supported by rollers, placed in the centre of the track,
as it travels up and down the incline, otherwise its great weight would
cause it to drag upon the ground. From the upper side of an incline,
stations are made, the same as they are made at intervals along a
vertical shaft; drifts are then run, and the work of cross-cutting and
prospecting the vein goes on in the same way as when the ore-body is
approached by means of a shaft. The giraffe has in front and on the
“outside” two seats, facing each other, on which six passengers can ride
very comfortably. Sometimes there is hitched behind the giraffe a second
car of the same pattern, called the “back-action.”
There is not a little of novelty in a ride up an incline on a “giraffe.”
The conductor of the “train,” who is seated by our side, gives the
signal for starting by pulling a wire and striking upon the engineer’s
bell—far away up the incline and up the vertical shaft, and some
distance beyond that again in the engine-house—a certain number of
strokes. Instantly we start, and soon are darting up the steep iron way
at a terrific rate of speed. Lamps are placed at intervals on the sides
of the incline; besides, we carry lanterns, and there are lights burning
at all the stations. Thus our underground railroad is well lighted up.
We have a good view of the track, and can see the rails glistening far
ahead of and above us.
We rush up this steep road so rapidly that the posts along the sides of
the incline resemble a fine-toothed comb. To look ahead and see before
you, and high above you, a hundred yards or more of semi-vertical
railroad, up which you are thundering at whirlwind speed, is strikingly
the reverse of natural. Going down does not in any way interfere with
your notions of the “eternal fitness of things,” for it is quite natural
for anything that is loose to run down hill, but this fierce darting up
the steep iron rails somewhat unsettles you.
Up this queer railroad you are hurled through the caverns of the gazing
Troglodytes, till you reach the foot of the vertical shaft, when they
transfer you to a cage, and you are shot out at the top, much as the
“Red Gnome,” in the play, is shot up through the trap in the stage-floor
of a theatre.
A giraffe is provided with a safety-apparatus somewhat similar to that
on a cage. A large wooden rail runs the whole length of the track.
Extending from the side of the giraffe, and almost clasping this rail,
are two toothed, eccentric wheels. Should the cable break, these wheels
would instantly grasp and clasp the rail, and the greater the weight
upon the car the more fiercely they would bite into the wood, and retain
their hold upon it. This invention has been the means of saving scores
of lives.
The “sump” is the well or hole sunk below the bottom of a shaft, for the
purpose of holding the water flowing in from above. In this is placed
the “suction” of the pump, and into it is collected the water from all
parts of the mine. Although “sump” is now considered an English word, it
was doubtless derived from the German word, “sumpf,” which means a
marsh, pool, bog, or fen. When miners fall down a shaft it is frequently
necessary to fish their mangled remains out of the sump with grappling
irons.
As some persons may desire to know how sinking can be carried on in the
bottom of a shaft where there is a strong influx of water, it may be
well to explain the matter. On the end of the pump-column or tube which
comes down near to the bottom of the shaft, is a piece of flexible hose,
the same as the “suction” of a fire-engine, and this is moved about from
side to side in the shaft, always keeping the end of it in the low
places where the water collects.
[Illustration]