will be as good as it was in the first
place.

Upon the Western prairies only grain has been raised for so many years
that in many places the soil will scarcely grow a crop worth gathering.
Many farmers have never thought of this, but the wise ones understand
that they must frequently add plant food to the soil to replace that
taken by crops. They understand also that it is a good thing to change
the crops grown upon any particular field from year to year, since
different plants take different substances from the soil.

[Illustration: _H. W. Fairbanks_
The miner in his search for gold ruins the beautiful valley, leaving it
a mass of boulders.]

Water goes through a ceaseless round. It rises from the sea and lakes to
form the clouds, falls as rain or snow, and then flows back down the
slopes to the sea. Although we have learned that we cannot change the
quantity of rain that falls in any place, we can influence the way in
which it runs back to the sea. This in turn affects the lives of people.
We can store water in reservoirs, and by building canals have it to use
on the land during the summer. We can also keep it from flowing back to
the sea as rapidly as it otherwise would, by leaving uninjured the
covering of vegetation which has been spread over the mountain slopes.
The water will run from bare rocks and bare soil much more quickly than
it will from soil that is covered with leaf mold and held by plant
roots. Do you not see, then, that we have almost as much control over
water and its distribution as though we could increase or decrease the
rainfall?

What about the forests? If we cut them down, will they ever come back?
All through the eastern part of our country and in the mountains of the
West are lands once forested which have been cleared and turned into
farms. Many of these farms, when abandoned, have in a few years been
covered with a growth of young trees. The scattering trees that had been
left in the vicinity of the clearings furnished the seed. The winds and
the birds carried the seed to the open fields and so the forests began
again.

[Illustration: _H. W. Fairbanks_
But Nature, after a lapse of fifty years, has spread a new carpet of
soil over the valley.]

It will be hundreds of years before the trees are as large and
valuable as those of the first forest. The "big trees" of the Sierra
Nevada Mountains are found nowhere else in the world, for they are the
last of their race. Some of