of ice, swimming on the surface of the water, or even with its base sunk considerably below it, to furrow in a straight line the summits and sides of the hills, and the bottoms of the intervening valleys. It would be carried over the inequalities of the country without touching the lowest depressions. Instead of ascending the mountains, it would remain stranded against any elevation which rose greatly above its own base, and, if caught between two parallel ridges, would float up and down between them. Moreover, the action of solid, unbroken ice, moving over the ground in immediate contact with it, is so different from that of floating ice-rafts or icebergs that, though the latter have unquestionably dropped erratic boulders, and made furrows and striæ on the surface where they happened to be grounded, these phenomena will easily be distinguished from the more connected tracks of glaciers, or extensive sheets of ice, resting directly upon the face of the country and advancing over it. There seems thus far to be an inextricable confusion in the ideas of many geologists as to the respective action of currents, icebergs, and glaciers. It is time that they should learn to distinguish between classes of facts so different from each other, and so easily recognized after the discrimination has once been made. As to the southward movement of an immense field of ice, extending over the whole North, it seems inevitable, the moment we admit that snow may accumulate around the pole in such quantities as to initiate a pressure radiating in every direction. Snow, alternately thawing and freezing, must, like water, find its level at last. A sheet of snow ten or fifteen thousand feet in thickness, extending all over the northern and southern portions of the globe, must necessarily lead, in the end, to the formation of a northern and southern cap of ice, moving toward the equator.