If you will examine with a glass--an ordinary hand-glass will do--one of these decaying pebbles lying embedded in the grass you can trace on it a number of wrinkly lines--sometimes even a network. These are the marks, the "finger-prints," of little roots. Little roots, as we have seen, are very wise. They always know what they are about, and the fact that they cling to the pebbles in this way means that they are getting food out of them. And that's right where the cows of Wisconsin come in. The rootlets of the grasses get a steady supply of food from the decaying surfaces of these pebbles scattered through the pastures, and then pass it on to the cows. [Illustration: HOW PEBBLES HELP FEED THE COWS You'll think I'm joking at first, but it's the truth: _Pebbles are good for cows._ Otherwise how are you going to account for the fact that in the counties in Wisconsin where there are plenty of pebbles the production of cheese and butter is something like 50 per cent greater than it is in regions where there are comparatively few pebbles? Examine, with a hand-glass, the "finger prints" of the little roots on a decaying pebble, and see if you can't guess why. Then read the explanation in this chapter.] TEAMWORK BETWEEN MOUNTAINS AND PEBBLES But now, going from little things to big things again, notice how the mountains and the pebbles are linked together in this chain of service. The mountains, too, continually feed the plains. Ruskin, in speaking of this great service, says: "The elevations of the earth's surface provide for it a perpetual renovation. The higher mountains suffer their summits to be broken into fragments, and to be cast down in sheets of massy rock, full of every substance necessary for the nourishment of plants. These fallen fragments are again broken by frost and ground by torrents into various conditions of sand and clay--materials which are distributed perpetually by the streams farther and farther from the mountain's base. Every shower which swells the rivulets enables their waters to carry certain portions of earth into new positions, and exposes new banks of ground to be mined in their turn. The turbid foaming of the angry water--the tearing down of bank and rock along the flanks of its fury--these are no disturbances of the kind course of nature; they are beneficent operations of laws necessary to the existence of man, and to the beauty of the earth; ... and each filtering thread of summer rain which trickles through the short turf of the uplands is bearing its own appointed burden of earth to be thrown down on some new natural garden in the dingles below." [Illustration: THE MILL OF THE EARTHWORM AND THE EARTH MILLS OF THE SEA