  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 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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