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Page:Popular Science Monthly Volume 89.djvu/430

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416

��Popular Science Monthly

��The photograph with the man stand- ing i)esi(Je a rork shows a perched granite boulder left on a sandstone base by a glacier which melted on a slope of the famous Yosemite Valley, California, a \ast gash in the Sierra Nevada, now believed to have been largely cut out by glacial action. Since the boulder was so de- posited it has changed but little. The sandstone pedestal, however, is greatly weather- ed and in the natural course of events, in a few hundred or a thou- sand \earspcrha]),s, will further disin- tegrate. Tiien the boulder will be pre- cipitated down the steep slope of the gorge into the can- yon below.

What are now the beautiful Tuolumne Mead- ows of California were formed by billions of tons of rock and soil, including many great boulders as large as houses, which were trans- ported by glaciers from the Sierra Nevada. Most of this material has been formed into soil and grass, trees and running streams all to make a beautiful natural park. A few great granite boulders still remain to be a witness to the might of a glacier which melted away long ago.

One of the pictures shows a large boulder which is beginning to dis- integrate, wiiile the smaller boulder — weighing perhaps a ton — is perched on top of it, having rested in this position for probably the better part of a thou- sand centuries. Another of the photo- graphs shows a large erratic boulder resting on a rock outcrop in Mono Valley, California. Undoubtedly it was transported to this point from the nearby Sierra at a lime when the ice streams flowed strongly down the eastern

���A rypir;il Crevasse Cruiseii by the Earth- quake Which Demolished San Francisco

��slope of this range to levels much lower than those reached by the feeble glacier remnants now existing near the summits of the range. This boulder could have been brought to its present position only by some agency not now present and one that would disregard topogra- phy, riding over irregularities in land surface and leaving erratic rock fragments perched in positions to which water could not transport them.

The famous Balanced, or Rock- ing, Stone of the Garden of the Gods in Colorado was deposited in a similar way by the glaciers of the Rocky Mountains. It is a stone of very large dimensions, and so exactly does it balance that un- til lately it could be swayed easily. The continual rocking to which it was subjected by thousands of tourists ground away the base to such an extent that to i)reser\e it as a curiositj' it was cemented in place.

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��One of the Pranks of the San Francisco Earthquake

^BOVE is one of the crevasses caused by the eartluiuake which almost destroyed San I'rancisco. Earthquakes are always terrif>ing e\ents, but they are only excessively destructive of life and property in case the territory affected is thickly populated and highly imjiroved. At this uninhabited point the great eartluiuake of i()ofi resulted only in a natural curiosity, but imagine this rift occurring beneath the business block of a pr<is(X'rous town! In another place a quartiT of a mile of wagon road was boilily removed ten or twelve feet from tlic rest of the road.

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