Sec. 9. The third great use of mountains is to cause perpetual change in the _soils_ of the earth. Without such provisions the ground under cultivation would in a series of years become exhausted and require to be upturned laboriously by the hand of man. But 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, as we shall see presently, 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. That turbid foaming of the angry water,--that tearing down of bank and rock along the flanks of its fury,--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. The process is continued more gently, but not less effectively, over all the surface of the lower undulating country; 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. And it is not, in reality, a degrading, but a true, large, and ennobling view of the mountain ranges of the world, if we compare them to heaps of fertile and fresh earth, laid up by a prudent gardener beside his garden beds, whence, at intervals, he casts on them some scattering of new and virgin ground. That which we so often lament as convulsion or destruction is nothing else than the momentary shaking of the dust from the spade. The winter floods, which inflict a temporary devastation, bear with them the elements of succeeding fertility; the fruitful field is covered with sand and shingle in momentary judgment, but in enduring mercy; and the great river, which chokes its mouth with marsh, and tosses terror along its shore, is but scattering the seeds of the harvests of futurity, and preparing the seats of unborn generations.