Man's physical universe

xanabras

THE GRADATION OF THE EARTH 139

The molecules of the gases that make up the atmosphere are so

small that they produce little friction except when they are moving

very fast. Strong winds seldom, if ever, wear down rocks without any

abrasive agents. The great disintegrating power of winds is due

largely to the particles of sand or dust which they carry.

Motor cars caught in a sand storm in the Mojave Desert have had

all of the paint blasted from their bodies and the glass windshields

and windows "frosted" by the flying sharp particles of sand. In only

eleven years the telegraph wires of the Trans-Caspian Railway were

worn to one half of their original diameter by wind-driven sands. This

Fig. 36. Dust storm, Johnson, Kansas, April 14, 1935.

action of wind is applied in the sandblast, which is used to cut designs

into stone or wood or to clean off old stone buildings.

Winds produce many grotesque forms as they wear away the less

resistant portions of rock formations. The beautifully colored rock

formations in the Garden of the Gods at Colorado Springs were formed

by wind erosion.

Winds also act as great transporting agents. Sometimes single

wind storms in the southwest portion of the United States pick up a

million tons of dust and scatter it over a dozen states. No one who

lived in the Middle West during the drought of the summer of 1934

will forget the terrible dust storms.

In the United States, Europe, and especially in China, the wind has

heaped up deposits of rock particles that are larger than clay but

smaller than sand. Such detritus is called loess. The Yellow River in

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