The Geology of the Gold District of California, with the probable
cause of the production of Gold to the surface of the earth.
The rocks of Golden California, in common with the whole western
declivity of the Sierra Neveda mountains, are principally composd of
primary, stratified, slate rocks. Some of these rocks are talcose slate.
Others are more silicious, approaching even to coarsish sandstone slate,
of various colors.
Before confining the reader expressly to the gold district, a few
remarks relative to that portion of California lying west of the Neveda
mountains to the valley of the great Sacramento and St. Waukeen, may
afford some light on the subject of that part of the western declivity
lying within the seat of mining operations. The slate rock on the
western side of the mountain range, from its axis to its base, is tilted
up a little more than perpendicularly outward from the axis of the
mountain, a distance of more than 60 miles in width, and traverses the
whole range, as far north and south as the present mines extend, in
lines parallel to the course of the mountain’s axis.
At the base of the mountain, commences a tertiary deposit of about 20
miles in width, which, with an alluvial deposit of about 20 more in
width, to the great rivers of the valley, hides from sight the remaining
portion of tilted rocks, so that the entire width of the tilted strata
can never exactly be ascertaind. But if a mountain range like the one
under consideration, is formd by the furrowd and ridgd condition of the
earth’s crust, by conforming to a diminishd molten nucleus within, from
refrigeration of its heat, it may be expected that the whole declivity,
from its axis or highest point to its lowest or mid valley, may be all
of it tilted up in the same manner as that portion which is presented to
sight. If this be fact, we are then apprizd that a portion of the
earth’s crust must have had a thickness of full 100 miles, by measuring
across the tilted rocks, from the central valley, to the top of the
mountain, eastward,—a fact not hitherto believd by geologists, from
experiments made upon the increase of downward heat, to where the crust
must necessarily become molten.
As so many and various opinions of the tilted condition of primary
stratified rocks have been advancd among the visitants of the gold
district of California, a few conflicting opinions may serve in some
degree to satisfy the mind of the curious.
It is the belief of some, that rocks cannot have become tilted without
the expansive powr of volcanic agency. Hence, on viewing the country
around, they imagine they see successions of craters, formd all over the
western declivity of the Neveda mountains, and in some places,
profusions of scoria bestrewing the ground. For my own part, I must
confess that I have seen nothing in my ramblings to justify a belief
that volcanic agency any where has existed so as to produce the present
appearance of those rocks.
Those persons imagining volcanic agency in those parts, are not aware
that intense heat destroys stratification, for in the middle of the
craters of some of their imaginary volcanoes, the stratification is as
perfect as in any other portion of the tilted district, and they are not
apprizd that in such case a discrepancy must therefore exist.
After the tilting of those rocks had occurd, it would not be improbable,
with such an enormous crust resting entirely upon a liquid, molten
nucleus, that many undulations in it should occur, and in many instances
the crust should become weakend and even sunderd apart by the severe
strain. Into fissures so formd, granite, sandstone and conglomerated
rocks, may have subsequently been intruded, presenting, therefore, to
persons unacquainted with such rocks, the appearances of craters,
scoria, &c. In some parts of New England, primary stratified rocks are
tilted up confusedly, having no regular line of strike. In some cases,
the dynamics employd may have been volcanic, or they may have been
paroxysmal, acting from time to time, till those rocks were thrown into
their present condition. But tilted rocks that have a regular line of
strike, must have a regular agency to place them in such condition.
Hence, then, considering the perfect parallelism of the tilted rocks of
Golden California with the mountain axis, it seems to follow, that an
exceedingly slow and regular movement of the tilting of those rocks must
have occurd.
Another consideration of the western declivity of the Neveda mountains,
is in relation to the formation of its rivers.
Almost invariably, the rivers of Oregon were formd by an expansive force
from beneath, but the rivers of California were formd by undulations in
the earth’s crust, which is well proven by the entire passage of
unbroken strata across the beds of streams. Such condition of its rocks,
is also another proof against volcanic agency in those parts.
* * * * * * * *
The inquiring mind may now be led to the subject of Quartz Rock,
containd among the slate rock of the gold district.
The quartz rock of the gold region is mostly white, though some of it is
of the carnelian order, whilst some is translucent, and other specimens
are entirely transparent. The carnelian appearance of some of the quartz
seems to have been nothing more than the circulation of water containing
the red oxide of iron, through the cracks of the broken quartz, till the
rock became tingd with it. The transparent variety is crystalizd, and is
found only sparingly.
Quartz is found interstratified amongst the tilted slate, varying from
less than one quarter of an inch in thickness to several feet, and in
some places even to rods, penetrating the slate indefinitely downward.
Although quartz is mostly seen lying in a position parallel with the
stratified slate rock, yet in some instances it is found crossing it
diagonally.
To account for the formation of quartz and its occupying its present
position in the gold district, is to account also for the formation and
production of gold to the surface of the earth, as is satisfactorily
believd by all. It is hard to account for much of the works of nature.
If it be considerd, that the quartz veins of the gold district be of
aqueous origin, that is, formd by infiltration, or the percolation of
silicious water into unoccupied spaces, till they are completely filld
with silicious sediment, so as to become rock, we then have to account
for its existing there in a friable state, which is hard to conceive,
since a formation by aqueous agency would most likely produce solid
rock.
It is equally hard to see how gold can be found imbedded in solid masses
in those quartz veins, since, if by the percolation of the water, quartz
was producd there, so also must the gold have been producd by
infiltration—and in such case, it must have been disseminated through
the whole rock, giving hues of various shades, as is the case with iron
in a soluble state.
Another objection to the formation of the quartz of the gold district by
infiltration, is, that it is not generally transparent, since the
percolation of silicious water through cold and silent places will most
naturally produce such result. It is most probable that the crystalizd
portion of those rocks was formd from silicious water, after the
original deposit.
It has been asserted by some miners, that they have seen gold in a state
of formation, by the percolation of water over quartz rock. Those men
are probably such as believe that quartz is the mother of gold—and by
the way, I should like to have them tell me also what the father was.
They say that the yellow appearance of the mud and other sedimentary
matter, which they have seen passing through quartz veins, is gold in a
state of formation. Perhaps they might allow of a correction in their
minds on that subject, if they were told that the yellow appearance they
saw was nothing more than decomposd iron—probably the chromate of it.
Another view of the subject may be taken, somewhat like the following.
It may be considerd that the quartz of the gold district was formd
previous to the tilting up of the slate rock, by alternations of tabular
masses with the slate.
Some objections to this mode also naturally arise. One objection is,
that there are instances of quartz veins traversing the stratified slate
rock diagonally. Another is, that it cannot well be conceivd that so
thin layers, as is the case with some of the quartz rock, can well be
formd in a tabular way. And if the quartz had been formd by alternate
layers with the stratified slate, it must of necessity have been of
aqueous origin, and also the gold.
The last view I shall take of the quartz, as found interstratified with
the slate rock, is, that the slate rock is of aqueous origin, and the
quartz rock of igneous origin, intruded from beneath after the tilting
up of the slate.
In the formation of stratified rocks, the planes of stratification, or
sides facing each other, are never firmly united together, being formd
by depositions from water at different times, so that by subsequent
movements they are liable to be sunderd apart. If it now be considerd
the enormity of a massive crust of earth resting upon a molten nucleus,
it becomes easy to see how intrusions upward of melted matter can take
place amongst stratified rocks, and the many undulatory movements of the
rocks, as appear in the mining district, only give facility to its
accomplishment.
If it be taken for fact, that the quartz of the mining district was
intruded in a melted state, it must also be considerd that gold was
intruded with it. To account for the friable state of the quartz,
moisture must be supposd to have been present, whilst the quartz was in
a heated state.
Such a state of things would produce a disintegration of the quartz
rock, and set at liberty the imbedded gold, to be carrid downward by
gravitation from the hills into ravines, creeks and rivers. To account
next, for the difference between massive imbedded gold in quartz rock,
and gold disseminated in small particles, needs only to consider the
quartz acting as a flux during a state of fusion, to bring the gold
together, in the same manner as borax, glass or quartz will do in the
artist’s crucible—and the only probable difference between the gold of
California and that of Georgia, is, during a melted state of the quartz,
a higher degree of heat existed in the quartz of California than that of
Georgia, thereby bringing about a more perfect work of separation
between the quartz and the gold.
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