Part 6 (2/2)

Here we can see how the slopes are protected, for in making the road the workmen cut deep into the hillside. They first removed a layer of pine needles and decaying branches. Then they cut through a layer of soil about two feet thick which was completely filled with little roots of trees and bushes. Below this they came to the soft subsoil, which contained only a few roots, and at the bottom they reached the solid rock.

The layer of roots and soil at the top of the bank, you can see from the picture, now overhangs the road, because the raindrops which beat against the bank have washed away all that they could reach of the unprotected earth at the bottom. How plainly we can see the network of roots. What a hard task it must be for the water to get at the soil in which these roots are growing.

[Ill.u.s.tration: _H. W. Fairbanks_ The layer of roots holds the soil on the mountain side.]

We will now leave the road and, although it is still raining hard, we will walk a distance through the forest and see if there is anything more that we can learn. We are soon in the deep woods where, perhaps, no one has ever been before. Around us are trees of all ages and sizes, from little seedlings to great giants six feet through. Among them are the crumbling stumps of trees long dead. Their trunks lie on the ground, and many are so soft and rotten that we can kick them to pieces with our feet.

As we walk our feet never touch the real earth. It is always on the soft, yielding leaves and crumbling branches that we step. These leaves and branches form a thick layer completely hiding the soil. But the strangest thing is that, although the rain is still falling, we can discover no rivulets. What, then, becomes of the water? The soft, decaying vegetation on which we are walking and the rotting stumps and logs act like a great sponge. As long as this sponge can take up the falling drops, none have a chance to run away. If it rains a very long time and the sponge becomes saturated, the drops that creep away and finally unite in rivulets in the hollows do no harm to the soil, for they cannot get at it.

[Ill.u.s.tration: _H. W. Fairbanks_ The roots of the tree grip the soil like the fingers of a great hand.]

Long after the storm has pa.s.sed, the earth underneath the trees remains wet, while the ground out in the open has become dry. A part of the water held by the decaying vegetation evaporates. Another part creeps down through the earth to the crevices in the rocks and feeds the springs.

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?

[Ill.u.s.tration: _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.

CHAPTER TWELVE

WHAT HAPPENS WHERE THERE IS NO PROTECTING CARPET OF VEGETATION

Not all of the muddy streams are due to the carelessness of men. It is the business of some of the servants of Nature, as we have already learned, to tear down the mountains and fill up the hollows in the earth. It is the business of others to spread a carpet of vegetation over the surface, and wherever they have already succeeded in their work the waters run clear most of the time.

Where it is dry so much of the time that few plants can live, the destructive servants have their own way when the occasional rains come.

Where there is a warm sun and frequent rains, a green carpet is spread over all the slopes. But when men destroy the carpet and take no care of the soil underneath, the raindrops are able to do as much damage as they do during the cloudbursts in the deserts.

The Colorado is one of those rivers in the basin of which few people live. Much of its journey is through a land in which there is little vegetation. Here, the waters from the melting snows upon the lofty mountains about the basin and those of the occasional heavy rains have things their own way. They are always yellow with mud. The amount of mud which this river carries has been measured. You will hardly believe me when I tell you that it amounts to sixty-one million tons every year.

This is enough to cover 164 square miles one foot deep. We might call this the cream of the soil from all the slopes of the great basin of the Colorado River.

In other parts of our land, where abundant rains fall, the streams tell a different story. Before men came the water of these streams was clear throughout the greater part of the year. It was only when the rains were very heavy that the soil washed away, for the vegetation held it well.

Now the gullies on the hillsides and along the roads tell us as plainly as though they could speak that our country is losing wealth here.

[Ill.u.s.tration: _H. W. Fairbanks_ The roots of the tree form a wonderful network underground from which the water cannot tear the soil.]

The soil is our most valuable possession. The people of many lands are suffering from poverty today because their forefathers did not take care of the soil as they should. In such lands the people who live on the mountain sides are poor, because the best of their soil has been washed away. Those who live in the valleys are often poor because of the sands and gravels which floods have spread over their fertile fields.

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