Studies in the Sierra. No. V.-Post-Glacial Denudation.
STUDIES IN THE SIERRA* By John Muir no. v. post-glacial denudation 9 WHEN Nature lifted the ice-sheet from the mountains she may well be said not to have turned a new leaf, but to have made a new one of the old. Throughout the unnumbered seasons of the glacial epoch the range lay buried, crushed, an...
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| Language: | English |
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Scholarly Commons
1919
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| Online Access: | https://scholarlycommons.pacific.edu/jmb/409 https://scholarlycommons.pacific.edu/context/jmb/article/1408/viewcontent/357.pdf |
| Summary: | STUDIES IN THE SIERRA* By John Muir no. v. post-glacial denudation 9 WHEN Nature lifted the ice-sheet from the mountains she may well be said not to have turned a new leaf, but to have made a new one of the old. Throughout the unnumbered seasons of the glacial epoch the range lay buried, crushed, and sunless. In the stupendous denudation to which it was then subjected, all its pre-glacial features disappeared. Plants, animals, and landscapes were wiped from its flanks like drawings from a blackboard, and the vast page left smooth and clean, to be repictured with young life and the varied and beautiful inscriptions of water, snow, and the atmosphere. The variability in hardness, structure, and mineralogical composition of the rocks forming the present surface of the range has given rise to irregularities in the amount of postglacial denudation effected in different portions, and these irregularities have been greatly multiplied and augmented by differences in the kind and intensity of the denuding forces, and in the length of time that different portions of the range have been exposed to their action. The summits have received more snow, the foothills more rain, while the middle region has been variably acted upon by both of these agents. Again, different portions are denuded in a greater or less degree according to their relations to level. The bottoms of trunk valleys are swept by powerful rivers, the branches by creeks and rills, while the intervening plateaus and ridges are acted upon only by thin, feeble currents, silent and nearly invisible. Again some portions of the range are subjected every winter to the scouring action of avalanches, while others are entirely beyond the range of such action. But the most influential of the general causes that have conspired to produce ir- * Reprinted, as revised by the author, from the Overland Monthly of November, 1874. Studies in the Sierra 415 regularity in the quantity of post-glacial denudation is the difference in the length of time during which different portions ... |
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