The fertile plain and valley and the rounded hill are of slow growth, immensely slow. But any given stage of the earth has followed naturally from the previous stage, only more and more and higher and higher forces took a hand in the game. First its elements passed through the stage of fire, then through the stage of water, then merged into the stage of air. More and more the aerial elements--oxygen, carbon, nitrogen--have entered into its constituents and fattened the soil. The humanizing of the earth has been largely a process of oxidation. More than disintegrated rock makes up the soil; the air and the rains and the snows have all contributed a share. The history of the soil which we turn with our spade, and stamp with our shoes, covers millions upon millions of years. It is the ashes of the mountains, the leavings of untold generations of animal and vegetable life. It came out of the sea, it drifted from the heavens; it flowed out from the fiery heart of the globe; it has been worked over and over by frost and flood, blown by winds, shoveled by ice, --mixed and kneaded and moulded as the house-wife kneads and moulds her bread,--refining and refining from age to age. Much of it was held in solution in the primordial seas, whence it was filtered and used and precipitated by countless forms of marine life, making a sediment that in time became rocks, that again in time became continents or parts of them, which the aerial forces reduced to soil. Indeed, the soil itself is an evolution, as much so as the life upon it. We probably have little conception of how intimate and cooperative all parts of the universe are with one another,--of the debt we owe to the farthest stars, and to the remotest period of time. We must owe a debt to the monsters of Mesozoic and Caenozoic time; they helped to fertilize the soil for us, and to discipline the ruder forces of life. We owe a debt to all that has gone before: to the heavens above and to the earth-fires beneath, to the ice-sheets that ground down the mountains, and to the ocean currents. Just as we owe a debt to the men and women in our line of descent, so we owe a debt to the ruder primordial forces that shaped the planet to our use, and took a hand in the game of animal life. The gods of evolution had served a long apprenticeship; they had gained proficiency and were master workmen. Or shall we say that the elements of life had become more plastic and adaptable, or that the life fund had accumulated, so to speak? Had the vast succession of living beings, the long experience in organization, at last made the problem of the origin of man easier to solve? One fancies every living thing as not only returning its mineral elements to the soil, but as in some subtle way leaving its vital forces also, and thus contributing to the impalpable, invisible store-house of vital energy of the globe.