nd where the winds go down the dust particles settle again to
the earth. After a long, long time, enough dust collects to form a
thick layer of the richest soil. This is called aeolian soil, from the
word _AEolus_, meaning the "wind."

There is one more kind of soil which we ought to know about; that is
_peat soil_. It is found in marshy or swampy lowlands and is formed
largely of plant remains. When lands with such soil are drained, they
prove very rich.

CHAPTER ELEVEN

HOW VEGETATION HOLDS THE SOIL

[Illustration: _H. W. Fairbanks_
What the rivulets did to the hillside pastures where the grass was
destroyed.]

A walk up the mountains on a rainy day is not a pleasant one. There are
mud and water under our feet, and overhead are the dripping branches
which, if touched, send down a shower of drops. But if we keep our eyes
open we shall learn something which will be of great value to us. We
shall learn how it is that Nature holds the soil on the slopes--the
wonderful soil which it takes her so long a time to make and which is
the source of all our wealth.

Our way up the mountains is by a winding road. We first pass the
foothills upon which there are scattered oaks. The rain is steadily
pouring down and rivulets loaded with mud are eating little gullies all
over the slopes. Along the roadside, where they have united, the
rivulets form a torrent which is making a deep ditch that threatens to
render the road impassable.

These slopes were once covered with grass and the rivulets ran down them
without doing any harm. But so many sheep were pastured here that the
grass was killed. The roots, which once formed a thick protecting sod,
are now decaying. How quickly the rivulets have taken advantage of the
unprotected slopes!

The road leads still upward until it brings us to where there were once
pine forests. The lumbermen cut off all the trees, and then fire came
and burned the decaying vegetation which once lay spread over the
ground. Now all that remains is bare earth and blackened stumps.

What are the raindrops doing here? They gather in rivulets just as they
do on the once grassy hillside; but because there are so many roots
still remaining in the ground they have not done much work. They are not
loitering, however, and by and by, when the roots have rotted, they will
seize their chance and begin tearing away the soil from the mountain
side.

But this is not the end of the road. Farther up we