and Eastern Canada were completely covered, and probably deeply buried, in sheets of ice and snow. In the British Islands and Norway the inscriptions made by ancient glaciers are scarcely less broad and profound, and it is even conjectured that the bed of the shallow North Sea is itself glaciated throughout. These evidences of vast accumulations of ice and snow on the borders of the Atlantic have led some theorists to suppose that the Ice period was attended, if not in part caused, by a far more abundant evaporation from the surface of the Atlantic than takes place at present; and it has even been conjectured that submarine volcanoes in the tropics might have loaded the atmosphere with an unusual amount of moisture. This speculation seems to me, however, both improbable and superfluous; improbable, because no traces of any such cataclysm have been discovered, and it is more than doubtful whether the generation of steam in the tropics, however large the quantity, would produce glaciation of the polar regions. The ascent of steam and heated air loaded with vapor to the altitude of refrigeration, would, as it seems to me, result in the rapid radiation of the heat into space, and the local precipitation of unusual quantities of rain; and the effect of such a catastrophe would be slowly propagated and feebly felt in the arctic and antarctic regions. The hypothesis is superfluous, because all we want, to restore the conditions recorded in the glaciated area, is simply a depression of temperature; by this the climate of Greenland, with all the attending phenomena, would be brought down on both sides of the Atlantic to the lowest point where the average annual temperature of Greenland prevailed.
This is, I think, proved by the condition of Greenland itself; remote as it is from evaporating surfaces of warm water, the precipitation of moisture upon that continent is, however, sufficient to cover it deeply under sheets of snow and ice; the whole interior being occupied by a continental glacier; and it is easy to see that, with a depression of the average annual temperature 10°, the highlands of Labrador would be brought into the same condition. With a still further depression the elevated portions of New England, the Adirondacks, and the highlands north of the lakes, would be completely encased in snow and ice. If the flow of the St. Lawrence were arrested, and the annual precipitation of the region drained by it were congealed, and retained from year to year, glaciers would soon form, and creep down from the highlands into the valleys, until the basins of the great lakes and the troughs of the Hudson and St. Lawrence would be completely filled with ice. On the eastern side of the Atlantic this state of things would be still more rapidly reached, inasmuch as, from the effect of the Gulf Stream, the coast climate is considerably more moist.
So far, then, as the region bordering the North Atlantic is concerned, a simple depression of temperature from any cause whatever,
