If we know anything of the earth’s past history, we know that the continents were long in forming, that they passed through many vicissitudes of heat and cold, of fire and flood, of upheaval and subsidence—­that they had, so to speak, their first low, simple rudimentary or invertebrate life, that they were all slow in getting their backbones, slower still in clothing their rock ribs with soil and verdure, that they passed through a sort of amphibian stage, now under water, now on dry land, that their many kinds of soils and climes were not differentiated and their complex water-systems established till well into Tertiary times—­in short, that they have passed more and more from the simple to the complex, from the disorganized to the organized.  When man comes to draw his sustenance from their breasts, may they not be said to have reached the mammalian stage?

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.