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This great ice-sheet not only covered our northern farms with rocks and stones, and packed the soil with rounded boulders, but it also carried away much of the rock decay that goes to the making of the soil, so that the soil is of greater depth in the non-glaciated than in the glaciated areas of the country. The New-Englander or New-Yorker in traveling in the Southern States may note the enormous depth of soil as revealed by the water-courses or railroad cuts. The ice-sheet was a huge mill that ground up the rocks in the North probably as fast or faster than the rains and the rank vegetation reduced them in the South, but the floods of water which it finally let loose carried a great deal of the rock-waste into the sea.

The glacier milk which colors the streams that flow from beneath it finally settles and makes clay. Off the great Malaspina Glacier in Alaska the ocean is tinged by the glacier milk for nearly fifty miles from the shores. Very few country people, even among the educated, are ready to believe that this enormous ice-sheet ever existed. To make them believe that it is just as much a fact in the physical history of this continent as the war of the Revolution is a fact in our political history is no easy matter. It certainly is a crushing proposition. It so vastly transcends all our experience with ice and snow, or the experience of the race since the dawn of history, that only the scientific imagination and faith are equal to it. The belief in it rests on indubitable evidence, its record is written all over our landscape, but it requires, I say, the scientific imagination to put the facts together and make a continuous history.

Three or four hundred feet above my cabin, five or six hundred feet above tidewater, there is a bold rocky point upon which the old ice-sheet bore heavily. It has rubbed it down and flattened it as a hand passing over a knob of soft putty might do. The great hand in this case moved from the northeast and must have fairly made this rocky prominence groan with its weight. The surface, scratched and grooved and planed by the ice, has weathered away, leaving the rock quite rough; its general outlines alone tell the tale of the battle with the ice. But on the east side a huge mass of rock, that had been planed and gouged by the glacier, was detached and toppled over, turning topsy-turvy before it had weathered, and it lies in such a position, upheld by two rock fragments, that its glaciated surface, though protected from the weather, is clearly visible. You step down two or three feet between the two upholding rocks and are at the entrance of a little cave, and there before you, standing at an angle of thirty or forty degrees, is this rocky page written over with the history of the passing of the great ice plane. The surface exposed is ten or twelve feet long, and four or five feet wide, and it is as straight and smooth, and the scratches and grooves are as sharp and distinct as if made yesterday. I often take the college girls there who come to visit me, to show them, as I tell them, where the old ice gods left their signatures. The girls take turns in stooping down and looking along the under surface of the rock, and feeling it with their hands, and marveling. They have read or heard about these things, but the reading or hearing made little impression upon their minds. When they see a concrete example, and feel it with their hands, they are impressed. Then when I tell them that there is not a shadow of a doubt but that the ice was at one time two or three thousand feet thick above the place where they now stand, and that it bore down upon Julian’s Rock with a weight of thousands of tons to the square foot, that it filled all the Hudson River Valley, and covered the landscape for thousands of miles around them, riding over the tops of the Catskills and of the Adirondacks, and wearing them down and carrying fragments of rock torn from them hundreds of miles to the south and southwest,–when I have told them all of this, I have usually given them a mouthful too big for them to masticate or swallow. As a sort of abstract proposition contained in books, or heard in the classroom, they do not mind it, but as an actual fact, here in the light of common day on the hill above Slabsides, with the waters of the Hudson glistening below, and the trees rustling in the wind all about us, that is quite another matter. It sounds like a dream or a fable. Many of the processes that have made our globe what we see it have been so slow and on such a scale that they are quite beyond our horizon–beyond the reach of our mental apprehension. The mind has to approach them slowly and tentatively, and become familiar with the idea of them, before it can give any sort of rational assent to them. It has taken the geologist a long time to work out and clear up and confirm this conception of the great continental glacier which in Pleistocene times covered so large a part of the northern hemisphere. It is now as well established as any event in the remote past well can be. In Alaska, and in the Swiss Alps, one may see the ice doing exactly what the Pleistocene ice-sheet did over this country.