Golden Theories and Glaciers.
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 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 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 aquæ-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 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 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 today, 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 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 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 agent employed to do any such work. ** Much less can it be supposed that the peculiar form of the Yosemite is due to the erosive action of ice. ** Besides, there is no reason to suppose, or at least no proof, that glaciers have ever occupied the valley, or any portion of it. ** So that this theory, based on entire ignorance of the whole subject, may be dropped without wasting any more time upon it.
"The theory of erosion not being admissible to account for the formation of the Yosemite valley, we have to fall back on some one of those movements of the earth's crust to which the primal forms of mountain valleys are due. The forces which have acted to produce valleys are complex in their nature, and it is not easy to classify the forms, which have resulted from them, in a satisfactory manner." After describing the generally received theories of mountain and valley formations, Mr. Whitney says: "We conceive that, during the process of upheaval of the Sierra, or possibly at some time after that had taken place, there was at the Yosemite a subsidence of a limited area, marked by lines of 'fault' or fissure crossing each other somewhat nearly at right angles. In other and more simple language, the bottom of the valley sank down to an unknown depth, owing to its support being withdrawn from underneath, during some of those convulsive movements which must have attended the upheaval of so extensive and elevated a chain, no matter how slow we may imagine the process to have been. Subsidence over extensive areas of portions of the earth's crust is not at all a new idea in geology, and there is nothing in this peculiar application of it which need excite surprise. It is the great amount of vertical displacement for the small area implicated which makes this a peculiar case; but it would not be easy to give any good reason why such an exceptionable result should not be brought about amid the complicated play of forces which the elevation of a great mountain chain must set in motion. By the adoption of the subsidence theory for the formation of the Yosemite, we are able to get over one difficulty which appears insurmountable to any other. This is the very small amount of debris at the base of the cliffs, and, even at a few points, its entire absence." In the space allotted to this chapter, I am able only to quote a few passages from Prof. Whitney, but refer the curious to his recent work, "Climatic Changes of Later Geological Times."
In contrast to the conclusions arrived at by Prof. Whitney, I extract from Prof. Le Conte's Elements of Geology, pages 526 and 527, the following: "1st. During the epoch spoken of (the glacial) a great glacier, receiving its tributaries from Mount Hoffman, Cathedral Peaks, Mount Lyell and Mount Clark groups, filled Yosemite valley, and passed down Merced canyon. The evidences are clear everywhere, but especially in the upper valleys, where the ice action lingered longest. 2nd. At the same time tributaries from Mount Dana, Mono Pass, and Mount Lyell met at the Tuolumne meadows to form an immense glacier which, overflowing its bounds a little below Soda springs, sent a branch down the Ten-ie-ya canyon to join the Yosemite glacier, while the main current flowed down the Tuolumne canyon and through the Hetch-Hetchy valley. Knobs of granite 500 to 800 feet high, standing in its pathway, were enveloped and swept over, and are now left round and polished and scored in the most perfect manner. This glacier was at least 40 miles long and 1,000 feet thick, for its stranded lateral-moraines may be traced so high along the slopes of the bounding mountains." In an article by John Muir, published in the New York Tribune, and kindly furnished me by Prof. Kneeland, will be seen views differing from those of Prof. Whitney, but Mr. Muir has spent long years of study upon the glacial summits of the Sierras, and if an enthusiast, is certainly a close student of nature. The paper was written to his friend Prof. Kunkle, of Boston, who had views similar to his own. Mr. Muir says: "I have been over my glacial territory, and am surprised to find it so small and fragmentary. The work of ancient ice which you and I explored, and which we were going to christen `Glacial System of the Merced' is only a few tiny topmost branches of one tree, in a vast glacial forest.
"All of the magnificent mountain truths that we read together last Autumn are only beginning sentences in the grand Sierra Nevada volume. The Merced ice basin was bounded by the summits of the main range and by the spurs which once reached to the summits, viz.: the Hoffman and Obelisk ranges. In this basin not one island existed; all of its highest peaks were washed and overflowed by the ice--Starr King, South Dome and all. Vast ice currents broke over into the Merced basin, and most of the Tuolumne ice had to cross the great Tuolumne canyon.
"It is only the vastness of the glacial pathways of this region that prevents their being seen and comprehended at once. A scholar might be puzzled with the English alphabet if it was written large enough, and, if each letter was made up of many smaller ones. The beds of those vast ice rivers are veiled with forests and a network of tiny water channels. You will see by the above sketch that Yosemite was completely overwhelmed with glaciers, and they did not come squeezing, groping down to the main valley by the narrow, angular, tortuous canyons of the Ten-ie-ya, Nevada or South canyons, but they flowed grandly and directly above all of its highest domes, like a steady wind, while their lower currents went mazing and swedging down in the crooking and dome-blocked channels of canyons.
"Glaciers have made every mountain form of this whole region; even the summit mountains are only fragments of their pre-glacial selves.
"Every summit wherein are laid the wombs of glaciers is steeper on its north than its south side, because of the depth and duration of sheltered glaciers, above those exposed to the sun, and this steepness between the north and south sides of summits is greater in the lower summits, as those of the Obelisk group. This tells us a word of glacial climate. Such mountains as Starr King, Cloud's Rest, and Cathedral Peak do not come under this general law because their contours were determined by the ice which flowed about and above them, but even among these inter-basin heights we frequently find marked difference of steepness between their north and south sides, because many of the higher of these mountains and crests extending east and west, continued to shelter and nourish fragmentary glacierets long after the death of the main trunk to which they belonged.
"In ascending any of the principal streams of this region, lakes in all stages of decay are found in great abundance, gradually becoming younger until we reach the almost countless gems of the summits with basins bright as their crystal waters. Upon the Nevada and its branches, there are not fewer than a hundred of these lakes, from a mile to a hundred yards in diameter, with countless glistening pondlets about the size of moons. Both the Yosemite and the Hetch-Hetchy valleys are lake basins filled with sand and the matter of morains easily and rapidly supplied by their swift descending rivers from upper morains. The mountains above Yosemite have scarce been touched by any other denudation but that of ice. Perhaps all of the post glacial denudation of every kind would not average an inch in depth for the whole region.
"I am surprised to find that water has had so little to do with the mountain structure of this region. None of the upper Merced streams give record of floods greater than those of to-day. The small water channel, with perpendicular walls, is about two feet in depth a few miles above the Little Yosemite. The Nevada here, even in flood, never was more than four or five feet in depth. Glacial striæ and glacial drift, undisturbed on banks of streams but little above the present line of high water mark, is sufficient proof."
The views entertained by Mr. Muir are, for the most part, in consonance with my own. That the valley was originally formed as supposed by Prof. Whitney I do not doubt, but to suppose that the vast bodies of ice, stated by Mr. Whitney to have existed at the sources of the Merced river, could have halted in their glacial flow down the steep declivities of its canyons, seems as absurd as to suppose one entertaining opposite views "ignorant of the whole subject." As a matter susceptible of eternal proof, I will state that in the canyon below the Yosemite there are existing to-day, large, well rounded bowlders that I think a geologist would say had been brought from above the valley; and if so, water alone could scarcely have brought them over the sunken bed of the valley, or if filled to its present level of about thirty-five feet descent to the mile, the laws that govern aqueous deposits would have left those huge masses of rock far above their present location in the canyon. Some of the bowlders referred to will weigh twenty tons or more, and, in connection with flat or partially rounded rocks fallen, probably, from the adjacent cliff, form waterfalls in the middle of the canyon, of from fifty to one hundred feet of perpendicular height. The fall through the canyon averages over two hundred feet to the mile. Well rounded bowlders of granite and other hard stones may be seen for long distances below the Yosemite, on hillsides and flats far above the present bed of the river, and, in some instances, deposited with those bowlders, have been found well rounded and swedged masses of gold. The experiments and observations of Agassiz, Forbes and others, render it probable that the valley of the Yosemite was filled with ice, but that the upper surface moved more rapidly, carrying down most of the material brought from mountains above the valley. The observations of Prof. Tyndall render it almost certain that a glacier does not move as a rigid mass or on its bed, but as a plastic substance, as asphalt for instance.
(Height, 325 feet; circumference, 100 feet.)
If it were possible, for the reconciliation of geologists, to believe that the subsidence in the valley occurred at about the close of the glacial flow, thereby changing the appearace of the inclosing walls, yet still leaving material to fill the chasm, a great part of the mystery that will always remain as one of the "Wonders of the Yosemite," would then disappear. As it is, we are compelled to believe, not in miracles, but that the glacier that flowed over the Yosemite was so great in depth as to leave, like some deep sea or ocean, its bottom undisturbed by the tumultuous aeriel strife upon its surface.
Now, those glacial heights have, at times, a solitude unutterly profound! Not a bird or beast to break the stillness, nor disturb the solemn charm. Nor does the Indian, even, loiter on his way, but hastens on down to his mountain meadows or wooded valleys. There, if anywhere, the poet's idea can be realized, that: "Silence is the heart of all things; sound the fluttering of its pulse,Which the fever and the spasm of the universe convulse.Every sound that breaks the silence only makes it more profound,Like a crash of deafening thunder in the sweet, blue stillness drownedLet thy soul walk softly in thee, as a saint in heaven unshod,For to be alone with silence, is to be alone with God."