Page:Popular Science Monthly Volume 85.djvu/75

Rh sawing of corrasive forces. The pinnacled Cathedral Spires and Rocks, the wrinkles of the Three Graces and the creases of Three Brothers most distinctly illustrate the differentiation of zones of more friable, granitic materials. Beneath one's feet is the remarkable floor of the valley, whose gradient is but little more than a foot of fall to the mile. Far above the rim of the main gorge of the Merced are dozens of "hanging valleys" cut off abruptly by the transverse trend of the precipitous walls of the Yosemite Basin. Above and beyond rise an ascending series of polished domes and U-shaped troughs culminating in the serrated crest of the High Sierra. Its eastern slope affords a most striking contrast to the gentler gradient towards the Pacific. The sunrise-fronting spurs of the Sierra plunge abruptly at a high angle down to the Mono plain seven thousand feet below. Alternating with steep escarpments, are deep-carved canons descending giant staircases, whose hollowed treads are frequently filled with azure lakelets. Beyond, over the drab desert, arise an array of dead "fire-mountains," recording an important chapter in the history of the High Sierra.

According to Professor Joseph Le Conte, this mighty range was born out of the ocean during the Jurassic period, the strata bulging, mashing and crumpling as it yielded to horizontal pressure. Its first physical appearance in the poetic diction of John Muir was as "one vast wave of stone in which a thousand mountains, domes, canons and ridges lay concealed." Geologists agree that the original crest of the Snowy Range was in the vicinity of the Yosemite Valley, but, at the end of the Tertiary and the beginning of the Quaternary periods, the Sierra block was tilted upward by volcanic upheavals which burst forth all along its eastern border. The Sierras were pitched en masse in a steep slope toward the west, while a great fault system produced the precipitous escarpment towering above the desert. Consequently, the crest of the range was transferred to its eastern rim. Throughout the Quaternary period, a newer system of rivers, accelerated by the increased inclination of their watersheds, cut their beds deeper and deeper along the lines of least resistance. Then followed an "over-deepening" of these stream courses by corrasive forces of far greater potentiality than the agency of running water.

The fact that no concordance in the conjectures of geologists exists is probably due to their different earlier environment and experience. Some were more familiar with the phases of stream erosion, others had studied the folding of sedimentary rocks, while certain savants were so carried away with their theory of glaciation that, in their imagination, they could only see the Sierras buried beneath a sea of ice a thousand fathoms deep. More who came to guess at its genesis, remained firm in their faith that "the bottom of the Yosemite dropped