A river of ice, under the right conditions, flows as literally as a river of water, fastest in the middle, and slowest along its margins where the friction is greatest. The old ice-sheet, or ice sea, flowed around and over mountains as a river flows around and over rocks. Where a mountain rose above the glacier, the ice divided and flowed round it, and reunited again beyond it. One may see all this in Alaska at the present time. Water, of course, flows because of its own pressure; so does ice, only the pressure has to be vastly greater. A drop of water on the table does not flow, but, pile it high enough, and it will. The old ice sea flowed mainly south, not because it was downhill in that direction, but because the accumulation of ice and snow at the North was so great. If through any climatic changes, the snowfall were ever again to be so great that more snow should fall in winter than could melt in summer, after the lapse of thousands of years, we should have another ice age. VII THE FRIENDLY SOIL I never tire of contemplating the soil itself, the mantle rock, as the geologist calls it. It clothes the rocky framework of the earth as the flesh clothes our bones. It is the seat of the vitality of the globe, the youngest part, the growing, changing part. Out of it we came, and to it we return. It is literally our mother, as the sun is our father. The soil!--the residuum of the rocks, the ashes of the mountains. We know what a vast stretch of time has gone to the making of it; that it has been baked and boiled and frozen and thawed, acted upon by sun and star and wind and rain; mixed and remixed and kneaded and added to, as the housewife kneads and moulds her bread; that it has lain under the seas in the stratified rocks for incalculable ages; that chemical and mechanical and vital forces have all had a hand in its preparation; that the vast cycles of animal and vegetable life of the foreworld have contributed to its fertility; that the life of the sea, and the monsters of the earth, and the dragons of the air, have left their ashes here, so that when I stir it with my hoe, or turn it with my spade, I know I am stirring or turning the meal of a veritable grist of the gods.