“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 In other and more simple language, the bottom of the valley sank down to an unknown depth, owing to its support being withdrawn from underneath, during some of those convulsive movements which must have attended the upheaval of so extensive and elevated a chain, no matter how slow we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.”