Would the icebergs have carried it over the face of the continents? Mr. Croll has shown very clearly[1] that the icebergs nowadays usually sail down into the oceans without a scrap of _débris_ of any kind upon them. Again: how could the icebergs have made the continuous scratchings or striæ, found under the Drift nearly all over the continents of Europe and America? Why, say the advocates of this theory, the icebergs press upon the bottom of the sea, and with the stones adhering to their base they make those striæ. But two things are necessary to this: First, that there should be a force great enough to drive the berg over the bottom of the sea when it has once grounded. We know of no such force. On the contrary, we do know that wherever a berg grounds it stays until it rocks itself to pieces or melts away. But, suppose there was such a propelling force, then it is evident that whenever the iceberg floated clear of the bottom it would cease to make the strive, and would resume them only when it nearly stranded again. That is to say, when the water was deep enough for the berg to float clear of the bottom of the sea, there could be no striæ; when the water was too shallow, the berg would not float at all, and there would be no striæ. The berg would mark the rocks only where it neither floated clear nor stranded. Hence we would find striæ only at a certain elevation, while the rocks below or above that level would be free from them. But this is not the case with the drift-markings. They pass over mountains and down into the deepest valleys; they are [1. "Climate and Time," p. 282.] {p. 16} universal within very large areas; they cover the face of continents and disappear under the waves of the sea. It is simply impossible that the Drift was caused by icebergs. I repeat, when they floated clear of the rocks, of course they would not mark them; when the water was too shallow to permit them to float at all, and so move onward, of course they could not mark them. The striations would occur only when the water was; just deep enough to float the berg, and not deep enough to raise the berg clear of the rocks; and but a small part of the bottom of the sea could fulfill these conditions. Moreover, when the waters were six thousand feet deep in New England, and four thousand feet deep in Scotland, and over the tops of the Rocky Mountains, where was the rest of the world, and the life it contained? {p. 17} CHAPTER V. WAS IT CAUSED BY GLACIERS? WHAT is a glacier? It is a river of ice, crowded by the weight of mountain-ice down into some valley, along which it descends by a slow, almost imperceptible motion, due to a power of the ice, under the force of gravity, to rearrange its molecules. It is fed by the mountains and melted by the sun.