from Minnesota to Cape May, on the shore of the Atlantic, a distance of about fifteen hundred miles. At scarcely any point was I out of sight of the red clay and gravel of the Drift: it loomed up amid the beach-sands of New Jersey; it was laid bare by railroad-cuts in the plains of New York and Pennsylvania; it covered the highest tops of the Alleghanies at Altoona; the farmers of Ohio, Indiana, Illinois, and Wisconsin were raising crops upon it; it was everywhere. If one had laid down a handful of the Wisconsin Drift alongside of a handful of the New Jersey deposit, he could scarcely have perceived any difference between them.
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Here, then, is a geological formation, almost identical in character, fifteen hundred miles long from east to west, and reaching through the whole length of North and South America, from the Arctic Circle to Patagonia.
Did ice grind this out of the granite?
Where did it get the granite? The granite reaches the surface only in limited areas; as a rule, it is buried many miles in depth under the sedimentary rocks.
How did the ice pick out its materials so as to grind nothing but granite?
This deposit overlies limestone and sandstone. The ice-sheet rested upon them. Why were they not ground up with the granite? Did the ice intelligently pick out a particular kind of rock, and that the hardest of them all?
But here is another marvel--this clay is red. The red is due to the grinding up of mica and hornblende. Granite is composed of quartz, feldspar, and mica. In syenitic granite the materials are quartz, feldspar, and hornblende. Mica and hornblende contain considerable oxide of iron, while feldspar has none. When mica and hornblende are ground up, the result is blue or red clays, as the oxidation of the iron turns the clay red; while the clay made of feldspar is light yellow or white.
Now, then, not only did the ice-sheet select for grinding the granite rocks, and refuse to touch the others, but it put the granite itself through some mysterious process by which it separated the feldspar from the mica and hornblende, and manufactured a white or yellow clay out of the one, which it deposited in great sheets by itself, as west of the Mississippi; while it ground up the mica and hornblende and made blue or red clays, which it laid down elsewhere, as the red clays are spread over that great stretch of fifteen hundred miles to which I have referred.
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Can any one suppose that ice could so discriminate?
And if it by any means effected this separation of the particles of granite, indissolubly knit together, how could it perpetuate that separation while moving over the land, crushing all beneath and before it, and leave it on the face of the earth free from commixture with the surface rocks?
Again: the ice-sheets which now exist in the remote north do not move with a constant and regular motion southward, grinding up the rocks as they go. A recent writer, describing the appearance of things in Greenland, says:
"The coasts are deeply indented with numerous bays and fiords or firths, which, when traced inland, are almost invariably found to terminate against glaciers. Thick ice frequently appears, too, crowning the exposed sea-cliffs, from the edges of which it droops in thick, tongue-like, and stalactitic projections, until its own weight forces it to break away and topple down the precipices into the sea."[1]
This does not represent an ice-sheet moving down continuously from the high grounds and tearing up the rocks. It rather breaks off like great icicles from the caves of a house.
Again: the ice-sheets to-day do not striate or groove the rocks over which they move.
Mr. Campbell, author of two works in defense of the iceberg theory--"Fire and Frost," and "A Short American Tramp"--went, in 1864, to the coasts of Labrador, the Strait of Belle Isle, and the Gulf of St. Lawrence, for the express purpose of witnessing the effects of icebergs, and testing the theory he had formed. On the coast of Labrador he reports that at Hanly Harbor, where
[1. "Popular Science Monthly," April, 1874, p. 646.]
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the whole strait is blocked up with ice each winter, and the great mass swung bodily up and down, "grating along the bottom at all depths," he "found the rocks ground smooth, but not striated."[1] At Cape Charles and Battle Harbor, he reports, "the rocks at the water-line are not striated."[2] At St. Francis Harbor, "the water-line is much rubbed smooth, but not striated."[3] At Sea Islands, he says, "No striæ are to be seen at the land-wash in these sounds or on open sea-coasts near the present waterline."[4]
Again: if these drift-deposits, these vast accumulations of sand, clay, gravel, and bowlders, were caused by a great continental ice-sheet scraping and tearing the rocks on which it rested, and constantly moving toward the sun, then not only would we find, as I have suggested in the case of glaciers, the accumulated masses of rubbish piled up in great windrows or ridges along the lines where the face of the ice-sheet melted, but we would naturally expect that the farther north we went the less we would find of these materials; in other words, that the ice, advancing southwardly, would sweep the north clear of débris to pile it up in the more southern regions. But this is far from being the case. On the contrary, the great masses of the Drift extend as far north as the land itself. In the remote, barren grounds of North America, we are told by various travelers who have visited those regions, "sand-hills and erratics appear to be as common as in the countries farther south."[5] Captain Bach tells us[6] that he saw great chains of sand-hills, stretching
[1. "A Short American Tramp," pp. 68, 107.
2. Ibid., p. 68.
3. Ibid., p. 72.
4. Ibid., p. 76.
5. "The Great Ice Age," p. 391.
6. "Narrative of Arctic Land Expedition to the Mouth of the Great Fish River," pp. 140, 346.]
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away from each side of the valley of the Great Fish River, in north latitude 66°, of great height, and crowned with gigantic bowlders.
Why did not the advancing ice-sheet drive these deposits southward over the plains of the United States? Can we conceive of a force that was powerful enough to grind up the solid rocks, and yet was not able to remove its own débris?
But there is still another reason which ought to satisfy us, once for all, that the drift-deposits were not due to the pressure of a great continental ice-sheet. It is this:
If the presence of the Drift proves that the country in which it is found was once covered with a body of ice thick and heavy enough by its pressure and weight to grind up the surface-rocks into clay, sand, gravel, and bowlders, then the tropical regions of the world must have been covered with such a great ice-sheet, upon the very equator; for Agassiz found in Brazil a vast sheet of "ferruginous clay with pebbles," which covers the whole country, "a sheet of drift," says Agassiz, "consisting of the same homogeneous, unstratified paste, and containing loose materials of all sorts and sizes," deep red in color, and distributed, as in the north, in uneven hills, while sometimes it is reduced to a thin deposit. It is recent in time, although overlying rocks ancient geologically. Agassiz had no doubt whatever that it was of glacial origin.
Professor Hartt, who accompanied Professor Agassiz in his South American travels, and published a valuable work called "The Geology of Brazil," describes drift-deposits as covering the province of Pará, Brazil, upon the equator itself. The whole valley of the Amazon is covered with stratified and unstratified and unfossiliferous
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Drift,[1] and also with a peculiar drift-clay (argile plastique bigarrée), plastic and streaked.
Professor Hartt gives a cut from which I copy the following representation of drift-clay and pebbles overlying a gneiss hillock of the Serra do Mar, Brazil:
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DRIFT-DEPOSITS IN THE TROPICS.
a, drift-clay; f f, angular fragments of quartz; c. sheet of pebbles; d d, gneiss in situ; g g,