Let us now put aside our storm clothes and journey, in imagination, far away to where it seldom rains—to that land which we call the desert. Here the bare rocks of the mountain slopes are burned brown by the hot sun. Here there is little soil and only a few little bushes that somehow manage to live. Why does not the soil gather over the rocks as it does in other places? The rocks are surely crumbling, for we can crush some of the pieces in our hands.
Once in a long time it rains in this desert. Then the drops descend furiously. The water gathers in rivulets and these turn to torrents which sweep down the slopes. They carry away the particles of sand and clay which would in time, if there were plant roots to hold them, turn to soil.
The winds also help keep the desert rocks bare and free of soil. Have you ever been in a dust storm or have you read of caravans caught in such storms in the Sahara Desert? The fierce wind picks up the particles of sand and clay from the bare earth and sweeps them along as it does the snow in winter, or it whirls them in clouds high in the air. The dust clouds are often so dense that they hide the sun and all landmarks by which the traveler can guide his way. But have any of us ever seen the winds pick up much dust from the green fields where the vegetation protects the surface?
H. W. Fairbanks
The vegetation prevents the wind from blowing the sand away, so that wherever the roots obtain a hold there a little mound is formed.
If we turn now to a very wet country, such as that upon our northwest coast, where often nearly eight feet of rain falls in a year, we shall find the vegetation so dense that it hides both soil and rocks. Here water can do little in wearing away the soil, even upon the steepest slopes, while the wind cannot get a peep at the earth.
Does it not seem strange that where little rain falls the earth washes a great deal faster than where it rains very heavily? The reason is that the more it rains the more dense becomes the carpet of vegetation. If we wish to preserve the soil, we must preserve the natural growth on the hillsides.