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 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 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.