. Guide leaflet. right angles to thedirection of the tilting, have not yet intrenched themselves and stilldrop into the canyons from hanging valleys. The conditions showncorrespond in a general way to those that prevailed for some time after the first great uplift mentioned in the text pulled down. After a great lapse of time in the latterhalf of the Tertiary period- the slant of the block wassteepened and the eastern edge was raised to a moun-tain crest several thousand feel high. Still later, aboutthe dawn of ihe Quaternary period—the last great MATTHES, THE YOSEMITE VALLEY 11 division of ge
. Guide leaflet. right angles to thedirection of the tilting, have not yet intrenched themselves and stilldrop into the canyons from hanging valleys. The conditions showncorrespond in a general way to those that prevailed for some time after the first great uplift mentioned in the text pulled down. After a great lapse of time in the latterhalf of the Tertiary period- the slant of the block wassteepened and the eastern edge was raised to a moun-tain crest several thousand feel high. Still later, aboutthe dawn of ihe Quaternary period—the last great MATTHES, THE YOSEMITE VALLEY 11 division of geologic time, which embraced the [ce Age and witnessed the rise of man a scries of thrusts morevigorous than any that had preceded it tilted the Sierrablock still more strongly and lifted it to its presentgreat height -to altitudes ranging from 7,000 feet at thenorth to more than feet at the south. One effect of the tilting was, naturally, to bring abouta rearrangement of the waters on the surface of the. Fig. 3. Section of the two-story valley which the Mercedhad cot by the end of the tertiary period. A-A is the profile of a side stream which was unable to trench asrapidly as the Merced and whose valley has therefore remained hang-ing. B-B is the profile of a side stream that succeeded in catchingup with the trenching of the river. This diagram and the two follow-ing are drawn to scale and represent the successive stages in the develop-ment of the Yosemite Valley in their true proportions. Sierra block. The main streams originally flowed indiverse directions, but when, early in the Tertiaryperiod, the Sierra block acquired a considerable slant,they changed their courses and began to flow in thedirection of the slant. A series of parallel rivers thuscame into existence, all heading at the eastern edge anddraining westward, into the Pacific Ocean. The Mercedwas one of these new rivers. 12 AMERICAN MUSEUM GUIDE LEAFLET In the long period of quiet that followed the earlier
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectnatural, bookyear1901
