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It means that we shall not kill the birds that destroy harmful insects and thus invite the insects to destroy the crops that we have cultivated with such care.

It does not mean that we shall let our mines of coal and iron lie unused, as the miser does his gold, but that we shall, while taking what we need, leave as little waste in the mine as possible, and shall use what we take in the most economical way. This means a saving of money to the user, as well as a conservation of resources. It means, too, that we shall not allow our water-power to remain unused, while we burn millions of tons of coal in doing the work that water-power would do better.

It means that we shall not allow enough natural gas to escape into the air every day to light all the large cities in the United States. It means that we shall take better care of the life and health of the people.

This is the true conservation.

In the following chapters we shall take up each of the great resources in turn, shall see what we have used, what we have wasted, what remains to us, how long it will continue at the present rate, how it may be used more wisely, and how it may be replaced, if that be possible, or what may be used instead of those which can not be renewed.

We shall study how we may make the most of all that nature has given us and develop our country to the highest possible point, how we may rise far above our present level in comfort, convenience, and abundance, and yet do all these things with much less waste than we now permit.

CHAPTER II

THE SOIL

The soil is the greatest of our natural resources. We may almost say that it is greater than all the others combined, for from it comes all of our food; a large part of it directly as plants which grow in the soil and which we eat in the form of roots, leaves, grains, berries, fruits, and nuts; and a part of it indirectly as animals, which have received their food supply from the plants.

But this is not all. The soil supplies almost every known need. We build our homes from the trees of the forest; combined with the iron that comes from the soil they furnish our fuel, our ships, our cars, our furniture, and countless other things. Our clothing is made from the cotton or flax which grows from the soil, the wool from the sheep that feed on the pastures, or from the silk-worms that feed on leaves.

So it is to the earth that we turn for every need, and Mother Nature supplies it. But it is of the soil as it gives us our food supply that we shall speak in this chapter, and we must first learn the nature of the soil, and the process of its making, in order to understand the need of extraordinary care in its management, and also how to use it so that it will not wear out, or become exhausted, but will increase in value for years and even centuries, as it will if properly cared for.

The earth's surface is constantly being renewed. Although the great formative movements occurred ages ago, yet earthquakes, volcanic action, wind, frost and water are working continual changes. Hills and mountains have been thrown up, and nature has gone to work at once to shave down the mountains and fill up the valleys. The whole earth is as carefully adjusted and balanced as the wheels of a watch, but these adjustments take place in long periods of time. In a lifetime, or even a century, the changes of the earth's surface seem few and small, but they are none the less sure.

The soil or humus, that is, the upper layer of the earth's crust which is used in farming, has an average depth of about four feet, and has been formed by decay, first and most important of all by rock decay which is constantly going on under the surface of the earth and in exposed places everywhere, and is caused by the action of air and water. This process is very slow. In places where the rock is already partly ground up, or, disintegrated, as we sometimes say, it is more rapid, but the average growth of the soil from beneath by rock decay is scarcely more than a foot in ten thousand years.

Some waste of this upper layer is constantly taking place from above, caused by wind and floods, and considerable additions are made to it by the decay of animal and vegetable matter, but in order to keep the soil at its best, the average soil waste should not amount to more than an inch every thousand years.

When this humus is once exhausted there is no way to repair the damage but to wait for the slow rock-decay. In the river valleys there is no immediate danger of exhausting the entire body of the soil, but on the hills and in the higher regions the soil-depth is very much less than four feet, and the danger of waste much more serious. There are parts of the earth that were once almost as fertile as ours where great cities once stood, but where now nothing is left but the bare rock.

So we know that the end is sure, even for the life of man upon earth, unless we learn to conserve our soil.

The value of our farm crops can not be overestimated. In food value they are the life of the nation; in money value, our greatest national wealth. For the year 1909 the total value of farm products was the amazing sum of $8,760,000,000. It may give some idea of this vast amount to say that if we could have it in the form of twenty-dollar gold pieces, stacked in one pile, the column would reach seven hundred miles high. If they were laid flat, edge to edge, they would extend from Alaska to the Panama Canal, with enough left over to reach from New York to San Francisco. If the money could be distributed, it would give us all, every man, woman and child in the United States, one hundred dollars apiece. The corn crop was worth $1,720,000,000; the cotton $850,000,000; wheat comes third with a value of $725,000,000; then come hay, oats, and other crops in vast amounts worth hundreds of millions of dollars. The cotton alone was worth more than the world's output of gold and silver combined. The corn would pay for the Panama Canal, for fifty battleships, and for the irrigation projects in the West, with a hundred million dollars left over.

And this is all new wealth. If we build a house, we have gained the house, but the trees of which we build it are gone. The same thing is true of every article we manufacture. Something is taken from our store in the making. But after we have taken these wonderful crops from our farms the land is still there, and the soil is just as ready to produce a good crop the next year, and the next, and the next, if we treat it properly.

This matter of soil conservation is of the greatest importance to every one of us. If you are to own a farm, or rent a farm, or till a garden, or plant an orchard ten years from now, it will make a great difference to you whether the man who owns it from now until then knows how to care for it so as to make it produce well, or whether, by neglect, he allows it to become poorer each year. It will make a far greater difference if twenty years elapse.

It makes a difference to the farmer whether he gets twelve bushels of wheat to the acre, or whether he gets twenty, for the cost of producing the smaller amount is just as great as the cost of producing the larger, and the extra bushels are all profit. It makes a difference whether a garden furnishes all the fruit and vegetables needed by the family, or whether it does not even pay for cultivation, and the food must be bought at high prices. It makes