Page:Popular Science Monthly Volume 85.djvu/80

76 Survey to study the eastern slope of the High Sierra and particularly the basin of Mono Lake, he devoted several summers during the early eighties to extended observations of the adjacent region. Although he mapped the ramifications of a vast system of Quaternary glaciers, flowing down from the cirques of the Snowy Range, he adopted in toto the theory first advanced by Professor Whitney that dislocations of the cross-fractured granite, comprising the former bulk of the Yosemite Basin, had caused the orographic block to subside to an unknown depth, forming an appalling abyss.

"Those who seek to account for the formation of the Yosemite," Professor Russell wrote, "by glacial erosion should be required to point out the moraines deposited by the ice streams that are supposed to have done the work." It is evident that he did not seriously consider the four reputed moraines on the floor of the valley which King first discovered. "The glaciers of this region," he continued, "were so recent that all the coarse debris resulting from their action yet remains in the position where it was left when the ice melted." In reply to this reasoning, John Muir insisted that sufficient time had elapsed since the recession of the glacier from the Yosemite to permit the disintegration of most of the detritus and its transportation to the lower levels by the Merced River. And Mr. Muir has strengthened his argument by demonstrating the rapidity with which aqueous and aerial agencies transform loose granite into sand. The extreme depth of the alluvium in the San Joaquin Valley far below is undeniable evidence of the decomposition of thousands of cubic miles of igneous rock, crushed by the mills of the glaciers and conveyed by the ground-sluices of the streams. A general conclusion reached by Professor Russell was, in his words, that

The main work of sculpturing the Sierra Nevada and the production of the variety of scenery for which these mountains are remarkable is to be attributed to water erosion; while only minor features, such as the rounding and broadening of the bottom contours of valleys, the smoothing of the higher mountain slopes, the polishing and striation of rock surfaces are to be referred to glacial action.

Still, the relative importance to be attached to each of the several agencies at work in this wonderland remains to be estimated accurately by the geological engineer.

Joseph Le Conte, the eminent geologist, author of the "Elements of Geology," a standard manual for two generations, was one of the first to survey the valley with the vision of an engineer. In his "Ramblings in the High Sierra," an account of his first visit to this region in 1870, appear his preliminary observations. His practical eye discerned the peculiar petrography of the walls of the Yosemite. "Already, I observe,"