It is clear, then, that the second great agency of soil formation,
which always acts in conjunction with temperature changes, is
_freezing water. _The rock particles formed in this manner are often
washed down into the mountain valleys, there caught by great rivers,
ground into finer dust, and at length deposited in the lower
valleys. _Moving water _thus becomes another physical agency of soil
production. Most of the soils covering the great dry-farm territory
of the United States and other countries have been formed in this
way.
In places, glaciers moving slowly down the canons crush and grind
into powder the rock over which they pass and deposit it lower down
as soils. In other places, where strong winds blow with frequent
regularity, sharp soil grains are picked up by the air and hurled
against the rocks, which, under this action, are carved into
fantastic forms. In still other places, the strong winds carry soil
over long distances to be mixed with other soils. Finally, on the
seashore the great waves dashing against the rocks of the coast
line, and rolling the mass of pebbles back and forth, break and
pulverize the rock until soil is formed.
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