It is in this true soil that the roots gain their nourishment, and not only roots, for whole populations of worms, of germs, of insects, even of birds and the higher animals, live upon it. To it return the dead leaves, the bodies of dead insects, and waste products of all kinds. Within it, they are broken to pieces and worked up again by the roots of other plants in order to form new leaves, new insects, and food for bird and beast. Just as in engine-works, you may see old engines, wheels, and scrap-iron being smashed into pieces; they are melted down and again worked up into engines of some improved design. [Illustration: THRASHING CORN IN CHILE Mares are driven at the gallop round the circle, and so beat the corn out of the ear with their hoofs. They do this for twenty minutes at a time, and are then made to go the other way round.] On a chalk-cliff, which dates from the long-distant Cretaceous period, the entire thickness formed by the yearly work of plants for millions and millions of years is often less than a foot in depth, and probably only four to five inches are true soil. But this is an exceptionally thin stratum, although it is capable of producing rich turf, fat snails, and excellent mutton. In peat-mosses and in those buried forests which form the coalfields, vegetable matter may accumulate in deposits of thirty feet of coal. Yet these stores of carbonaceous matter seem to be at first sight miserly and selfish, at least from a vegetable point of view. They resemble the gold and silver withdrawn from circulation in the world by some Hindoo miser and buried deep within the earth. Yet somebody is pretty certain to find out and make use of such stores eventually. In the case of the peat and coalfields, an animal of sufficient intelligence to utilize them has already been produced, and now they are used by man as fuel. It is very important to remember that the soil is a sort of last home to which the particles of carbon, of nitrate, and minerals always return after their wanderings in the bodies of plants, of insects, or of other animals. They probably rest but a short time before they again set off on new adventures. One might say the same of the water, and of the carbonic acid gas and oxygen of the atmosphere, for the water, falling as rain upon the earth, trickles down to the underground water-level. Then it immediately begins to rise up between the particles of earth and is promptly caught and sucked in by the roots, only to be again given out by their leaves. The carbonic acid gas and oxygen also are always entering and leaving the foliage. Even the nitrogen of the air is not left alone in the atmosphere. There are small germs in the soil which are able to get hold of it and make it into valuable nitrates. More curious still is the fact that electric charges can be used to change the comparatively useless air-nitrogen into useful manures. Probably the farmer will some day make his own nitrates by electricity.