The many inquiries that the author has received concerning his views upon the gold deposits of California, has induced him to add this chapter to his work.
It has been said by an earnest and astute observer, that “The cooled earth permits us no longer to comprehend the phenomena of the primitive creation, because the fire which pervaded it is extinguished,” and again that “There is no great foundation (of truth), which does not repose upon a legend.” There has been a tradition among the California Indians, that the Golden Gate was opened by an earthquake, and that the waters that once covered the great plain of the Sacramento and San Joaquin basins were thus emptied into the ocean. This legendary geology of the Indians is about as good and instructive as some that has been taught by professors of the science, and as scarcely any two professors of geology agree in their theories of the origin and distribution of the gold in California, I have thought it probable that a few unscientific views upon the subject will interest my readers.
The origin of the gold found in California seems to me to have been clearly volcanic. The varying conditions under which it is found may be accounted for by the varying heat and force of the upheaval, the different qualities of the matrix or quartz that carried the gold and filled the 320 fissures of the veins or lodes, the influence that resistance of the inclosing walls may have exerted when it was slight or very great, and finally the disintegrating influences of air, water, frost and attrition of the glaciers, and the deposition in water.
The theories of aqueous deposit (in the lodes) and of electrical action, do not satisfy my understanding, and I go back in thought to the ten years of observation and practical experience in the gold mines, and to the problems that were then but partially solved. Looking at California as it is to-day, it will be conceded that its territory has been subjected to distinct geological periods, and those periods greatly varying in their force in different parts of the State. Within the principal gold-bearing region of California, and especially along the line of or near the Carson vein or lode, coarse gold has been found, and in such large masses, free of quartz, as to force the conviction upon the mind that the gold so found had been thrown out through and beyond its matrix into a bed of volcanic ashes, very nearly assuming the appearance that lead might assume when melted and thrown in bulk upon an ash heap. Where the resistance was great, as when thrown through wall rocks of gneiss, or green stone, the liquefaction of the quartz seems to have been more complete, and the specific gravity of the gold being so much greater than that of the quartz, its momentum, when in large quantities, carried it out beyond its matrix, leaving the more diffused particles to be held suspended in the fast cooling quartz, or to settle into “pockets,” or small fissures.
Prof. Le Conte says: “The invariable association of metaliferous veins with metamorphism demonstrates the agency of heat.” Experiments of Daubre and others prove that water at 750° Fahr. reduces to a pasty condition nearly all rocks. Deposits of silica in a gelatinous form, that 321 hardens on cooling, may be seen at some of the geysers of the Yellowstone; the heat, no doubt, being at a great depth. Quartz, like glass and lava, cools rapidly externally when exposed to air, or a cool surface, and would very readily hold suspended any substance volatilized, or crudely mixed into its substance. Its difficult secondary fusion is no obstacle to a belief in the capacity of heat under great pressure, to account for the phenomena that may be observed in the gold mines. Ashes derived from lavas have been found rich in crystalline substances. Crystals and microliths, and pyrites in cubes are, no doubt, of volcanic origin. The eruptions of moderate character seem to be the result of igneous fusion, while those of an explosive type are probably aqu?-igneous.
It is altogether probable from experiments tried by Stanislas Muenier and others, that the sudden removal of pressure is a sufficient cause of superheated water and mineral substances flashing into steam and lava. The geysers are evidently formed by varying temperature and interruption of flow by removal of pressure. Mr. Fanques, in an article in the Popular Science Monthly for August, 1880, says: “Discovery of microliths enclosed in volcanic rocks is a proof of immediate formation of crystals.”
The phenomena attending the recent eruptions in Java demonstrate the incredible force and chemical effects of superheated steam. Modern researches and experiments in mechanical and chemical forces have greatly modified the views once entertained by geologists, and I think that it will now be conceded that repeated volcanic disturbances, taken in connection with the action of glaciers, will account for most, if not all, the phenomena discoverable in the gold fields and mountains of California. As a rule, gold-bearing veins in clay or talcose slates have the gold more evenly diffused than those found in the harder rocks, where 322 pockets of crystals, pyrites and gold will most likely be found. If gold is found in seams or masses it will be very free from impurities, and the quartz itself will be most likely white and vitreous. When gold is found in or near to a lode that has been decomposed, it will be found porous and ragged, but if it has been deposited some distance from its source it will be more or less rounded and swedged by contact with the stones and gravel that were carried with it by the stream of water or ice that conveyed it to its placer. In the beds of the ancient and more modern rivers the gold is much more worn than that found in the ravines or gulches, and the coarser gold will be found at the bottom, the scale gold in the gravel above, and the fine or flour gold in the mixture of clay, gravel and sand nearer the surface. The scale gold, no doubt, has been beaten by repeated blows of stones brought in contact with it while moving in the bed of the stream, and the flour gold is that reduced by the continual attrition of the moving mass upon the gold.
Prof. Le Conte says: “There are in many parts of California two systems of river beds—an old and a new.... The old, or dead, river system runs across the present drainage system in a direction far more southerly; this is especially true of northern members of the system. Farther south the two systems are more nearly parallel, showing less movement in that region. These old river beds are filled with drift gravel, and often covered with lava.” The lava referred to is relatively of modern origin, and the molten streams have in many instances covered the ancient streams, and in others cut them in twain. The “Blue Lead” is a very old river bed that has been the principal source of supply of the placer gold of the northern mines, and it must have existed as a river long anterior to the more modern upheavals that disturbed its course by forming 323 mountain torrents to rend its barriers and cut across its channel. That channel crosses some of the present tributaries of the Sacramento and San Joaquin and contains fossil remains of trees, plants and fruits not now indigenous to California.
The well rounded boulders and pebbles found in the beds of these ancient rivers render it probable that they were of considerable length, and that they may have been the channels of very ancient glaciers. It is also probable that the region covered by glaciers at different epochs is much more extensive than has been generally supposed. To me it appears probable, that during some of the eras of formation, they may have stretched across the entire continent. I have not space to give in detail the evidences of glacial action, but will simply state that remains of glaciers may be seen by an observing eye at intervals from the Atlantic to the Pacific; in Minnesota and in the Rocky Mountains, they are especially abundant. Prof. Le Conte says: “The region now occupied by the Sierra range was a marginal sea bottom, receiving abundant sediments from a continent to the east. At the end of the Jurassic, this line of enormously thick off-shore deposits yielded to horizontal thrust, was crushed together and swollen up into the Sierra range. All the ridges, peaks and canyons, all that constitutes the grand scenery of these mountains are the result of an almost inconceivable subsequent erosion.”
I have no doubt of the truth of this theory of formation as it relates to the Sierra Nevada ranges as they exist to-day, for the intrusion of the granite into the slate formations suggests a force far greater than can be ascribed to volcanic action alone. The previous condition of the “continental mass” can not be so well imagined; yet reasoning from what we know of the present condition of the Sierras we may with propriety assume that great changes had occurred 324 in the territory embracing the Sierras Nevada long prior to their upheaval. The changes that have occurred since are too abundant and enduring to require more than a reference to the localities. The “glacier pavements” of the Sierras are so conspicuous that, as Mr. John Muir says: “Even dogs and horses gaze wonderingly at the strange brightness of the ground, and smell it, and place their feet cautiously upon it, as if afraid of falling or sinking.” These glacier-smoothed rocks “are simply flat or gently undulating areas of solid granite which present the unchanged surface upon which the ancient glaciers flowed, and are found in the most perfect condition in the sub-alpine region, at an elevation of from 8,000 to 9,000 feet. Some are miles in extent, only interrupted by spots that have given way to the weather, while the best preserved portions are bright and stainless as the sky, reflecting the sunbeams like glass, and shining as if polished every day, notwithstanding they have been exposed to corroding rains, dew, frost and snow for thousands of years.”
This statement of Mr. Muir will especially apply to the “glistening rocks” at the sources of the Merced and Tuolumne rivers, in view on this trail through the Mono Pass. The evidences of past glacial action in polishing the domes, mountains and valleys above the Yosemite valley, are too undeniable for controversy, but how much of the Yosemite itself may have been produced by glacial action will probably always remain a theme for discussion among geologists.
Prof. Samuel Kneeland, the well known author of “Wonders of the Yosemite,” in a letter to me upon the subject, says: “I think there can be no doubt that the valley was filled, and 1,000 feet above, by ice—that while the mass above, moved, that in the valley, conforming to its configuration, was comparatively stationary, lasting much longer 325 than the first, gradually melting to a lake, now represented by the Merced river.
“I agree with Prof. Whitney that the valley was the result of a subsidence, long anterior to the glacial epoch, and that the valley itself, except upon its edges and upper sides, has not been materially modified by the glacier movement.” Prof. J. D. Whitney, in his geological report says: “The Yosemite valley is a unique and wonderful locality; it is an exceptional creation; ... cliffs absolutely vertical, like the upper portions of the Half Dome and El Capitan, and of such immense height as these, are, so far as we know, to be seen nowhere else.... How has this unique valley been formed, and what are the geological causes which have produced its wonderful cliffs, and all the other features which combine to make this locality so remarkable? These questions we will endeavor to answer, as well as our ability to pry into what went on in the deep-seated regions of the earth in former geological ages will permit.” Mr. Whitney explicitly states his belief that most of the great canyons and valleys have resulted from aqueous denudation and erosion and cites the cutting through the lava of Table Mountain at Abbey’s Ferry on the Stanislaus river as proof, and, continuing, to the exception, says: “It is sufficient to look for a moment at the vertical faces of El Capitan and the Bridal Veil Rock turned down the valley, or away from the direction in which the eroding forces must have acted, to be able to say that aqueous erosion could not have been the agen............