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.