Man's physical universe

xanabras

140 THE EARTH AS MAN'S ABODE

China owes its color to the loess which it picks up as it carves its

path through extensive plains of loess, all of which was probably blown

from the Gobi desert.

Inasmuch as about three fourths of the earth's surface is covered

by the ocean, it is to be surmised that tremendous quantities of land

have been carried by the winds over the oceans, where it settled.

In the drier sections of

the world the wind carries away the finer

particles and leaves the sand, blowing it up into dunes. The wind is

constantly changing the shape and size of the sand dunes, moving

them from place to place, and overwhelming everything in their paths.

Fig. 37. Half Dome in Yosemite National Park, an example of exfoliation.

(Courtesy of the U. S. Geol. Survey.)

Temperature Changes Bring About Disintegration of Rocks.

Inasmuch as rocks are poor conductors of heat, they heat unevenly

and set up strains which result in cracks, just as glassware cracks when

it is placed under such a strain. Water which gathers in the cracks of

rocks expands when it freezes and thus splits the rocks apart.

"Exfoliation" is the name given to the process in which sharp edges

and corners of rocks are rounded off and layer after layer peels off to

form rounded domes. Exfoliation is thought to be caused by chemical

action, weathering, and expansion due to the decreased pressure resulting

from removal of heavy overlying loads.

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