THE SIERRA NEVADA MOUNTAINS.
The Virginia range of mountains, of which Mount Davidson is the
principal peak, is separated from the Sierra Nevada Mountains by a
series of small valleys, the principal of which are Washoe Valley, Eagle
Valley, Steamboat Valley, and the Truckee Meadows. The range can be
traced for a distance of about one hundred miles from the point where it
diverges from the Sierras, as they trend to the northwest, to where it
finally dies out in the Mud Lake region. The average width of the range
is about eighteen miles, though it is quite irregular. The great mass of
the mountains composing the range is made up of volcanic rocks, the
accumulation of several successive outpourings.
On the eastern face of Mount Davidson, about 1,500 feet below the
summit, are found the croppings of the Comstock lode. The rock on the
west side of the vein—called the “country rock” by mining men, because
it is the general rock of the country outside of the lode—is syenite,
a rock which forms the mass of Mount Davidson; on the east side of
the vein the country rock is propylite, a volcanic rock of much more
recent origin than the syenite. (Syenite is much the same as granite,
and propylite is a rock of a porphyritic character.) Between these
two rocks, by some throe of nature, was formed the immense fissure in
which lies the Comstock vein—a fissure known to be nearly four miles in
length and from one or two hundred to nearly fifteen hundred feet in
width. This vast chasm was undoubtedly formed by volcanic action. It is
not one fissure, but more properly speaking, a series of rents running
parallel with the main opening. The smaller parallel fractures are
principally in the propylite or east country rock. It is but natural
that they should be in this, as it was the stratum that was lifted up
and shattered when the main fissure was formed. In depth, all of these
rents will be found to be lost in the principal opening.
After the rending apart of the rocks and the formation of the chasm,
there doubtless burst up through the opening immense volumes of hot
mineral waters, steam, and gases, from solfataras or hot springs
underneath, and these charged the vein with its rich sulphurets and
other ores of silver.
Signs of hot springs are seen everywhere on the hills to the eastward of
the vein, and hot springs that are still active are found in various
directions, at the distance of a few miles, the most remarkable of which
are those known as the Steamboat Springs; which, even at this day, are
briskly sending up hot water, steam, and columns of heated gases through
a fissure over a mile in length, in fact are actively engaged in the
formation of a metallic lode.
It is not improbable that the fissure in which the Comstock lode was
formed was originally rent by the upward pressure of the confined steam
and gases of hot springs formed between the syenite and propylite far
beneath the surface of the earth. Be that as it may, the rent was
formed, and afterwards was charged with its present mineral contents.
When the rocks were rent apart, fragments from the edges of the
chasm—principally from the east or propylite side, the side reared
up—fell into the opening, and sliding down the smooth slope of the
syenite, blocked the fissure, preventing its closing. Some of these
fragments were at least one thousand feet long and from three to four
hundred feet in thickness, and many of them were from fifty to one
hundred and fifty feet in length, with a proportionate thickness. These
still rest in the vein, the ore, quartz, etc. having formed about them.
By the miners these are called “horses.” They are generally composed of
propylite (commonly spoken of as porphyry in the mines, owing to its
inclosing crystals of feldspar and fragments of hornblende), but there
are some that came from the west side of the fissure and are syenite.
After the fissure was thus propped open, still other fragments of
propylite fell from its roof during the time the vein was filling with
its present precious contents, and these are found to be surrounded on
all sides by ore of the richest character. The cavities caused by their
displacement were also filled with quartz and ore. This makes the east
wall or propylite side of the vein very jagged and uneven, while the
less disturbed west or syenite wall is quite regular, descending to the
eastward at an angle of from thirty-five to fifty degrees, being
throughout quite smooth and covered with a heavy coating of clay.
The fragments of rock that fell into the chasm during the time it was
being charged with the precious metals, formed each a nucleus about
which the quartz and ores collected. In all parts of the vein are to be
seen pieces of country rock, from the size of a filbert to many pounds
in weight, about which quartz has formed, and with the quartz ore.
After the vein was filled, it appears to have again several times
opened, when fresh fragments fell into the newly formed fissures, and
were surrounded by quartz and ores by the action of the waters and gases
forced up from below. These several convulsions pulverized the quartz
and ore previously formed in the vein, leaving it in such a condition
that in most of the mines the greater part of it can be dug down with
picks.
In most places in the ore-bodies in the lower levels, appearances
indicate that while the ore and quartz were in this shattered and
pulverized state, floods of hot water poured in upon it and boiled it as
in a caldron, and that at the end of this cooking operation it finally
settled down, assuming a horizontally stratified position. In this way
must have been formed the occasional streaks of clay and the numerous
strata of various shades of color and degrees of fineness of subdivision
of component parts seen in the ore as it now rests in the vein. It is as
plainly sedimentary in form as any gravel deposit seen on the surface.
This is not seen everywhere in the lower levels, but in such places as
were most subject to dynamical action.
All who have visited the lower levels of the mines on the Comstock lode
must have observed, even upon the most cursory examination of the ores,
the peculiar stratification of which I speak. The chasm in which is
formed the Comstock lode was doubtless at one time a seething caldron,
and at the great depths now attained, not only great quantities of hot
water are found, but the rock itself is in many places sufficiently hot
to be almost painful to the naked hand.
The course or “strike” of the Comstock vein is a little east of the
magnetic meridian, about north twenty-five degrees east. The lode crops
out in several places along the face of Mount Davidson, throwing up huge
piles of quartz at intervals of from three hundred to five hundred or
one thousand yards, as it takes its course southward across the
“Divide,” and through and beyond Gold Hill; also, to the northward, in
the direction of Cedar Hill and Seven-mile Cañon. When the ledge crops
out it has a first or false dip to the west, but after being followed
down it becomes straight, then turns, and takes its regular dip to the
east at an angle of from thirty-five to fifty degrees. In the Ophir,
when the true dip was first discovered, the vein turned to the east at
the depth of three hundred and thirty feet. The croppings of the vein
being above and to the west of Virginia City, this eastern dip carries
it under the whole length and breadth of the town, and it also passes
under the town of Gold Hill, a mile further south in the same way.
The lead follows the curved outlines of the hills on the surface,
swinging in at the ravines and bearing out on the points of the ridges,
but as depth is attained it will doubtless be found to straighten in the
direction of its present general course. The only gangue of the vein is
quartz, though, in places, there are found detached patches and masses
of gypsum and carbonate of lime. The ore contains native gold, native
silver, sulphuret of silver (silver glance), stephanite, chloride of
silver, some rich galena and antimony, and a few rare forms of silver in
small quantities; also, mingled with the whole mass of the ores, iron
pyrites, copper pyrites, zinc-blende, and a few other minerals.
The early miners began the work of opening their claims along the
Comstock by sinking shafts on the croppings and by running short tunnels
to pass under these croppings and tap the vein at depths varying from
two hundred to six or seven hundred feet. The shafts were mere circular
holes precisely like an ordinary well, and a common windlass, rope, and
bucket, constituted all there was coming under the head of machinery.
When more water was encountered than could be hoisted out with a bucket,
these early miners were at the “end of their string.” Those who were
running tunnels, however, were not incommoded by the water they tapped
during the progress of their work, as it flowed out as fast as it came
in.
The Ophir mine was at first worked by means of an incline which followed
the dip of the vein to the west. They soon began to be bothered with
water and were obliged to set up a small pump, as has already been
stated. All of those who had locations on the Comstock, however, were
able to find means for the erection of machinery as soon as it was found
necessary to use it, though much of the first hoisting and pumping
apparatus was too light and was badly arranged. But almost any kind of
steam machinery was better than hoisting by the hand-windlass or with
the horse-whim.
After starting up with steam hoisting-works, it was not long before a
number of companies began to extract ore from the upper series of
bonanzas, and these being exhausted, carried their work to lower levels
and searched out new bodies of ore. It often happened that when the ore
in sight was exhausted, the company was obliged to drift in all
directions for a long time before again finding paying ore. In case a
level was opened and explored in all parts without finding ore, sinking
was resumed in the main shaft, and a new level was opened at a greater
depth in the vein. The miners are never discouraged so long as they find
a good width of quartz and other vein-matter between the two walls of
the lode, as there is then always a chance of finding ore somewhere in
the mass. What they do not like, however, is to find the walls coming
together—“pinching,” as they call it. The coming together of the walls
pinches out or cuts off the vein; yet, even at the “pinch,” there is
always left a seam of clay, or some such sign, by which the lead may be
followed until the pinch has been passed and the vein again widens and
becomes ore-producing.
[Illustration: HOISTING-WORKS.]