They have been known to drift from Baffin’s Bay to the Azores, and from the South Pole to the Cape of Good Hope.[33] As they approach the milder climate of the temperate zones, the ice gradually melts away, and thus the moraines of arctic and antarctic glaciers are deposited at the bottom of the deep sea. In this way, submarine mountains and valleys and table-lands are strewn over with scattered blocks of foreign rocks, and gravel, and mud, which have been transported hundreds of miles across the unfathomable abysses of the ocean.
Though we are chiefly concerned with Glaciers and Icebergs as agents of Denudation, yet we cannot pass away from the subject without referring to the Geological theory of an ancient Glacial Period. This little digression from the main purport of our present argument will not be unacceptable, we hope, to our readers. The theory is in itself interesting and ingenious; and it offers an admirable illustration of the kind of reasoning by which Geologists are guided in their speculations.
It is well known that the action of moving ice leaves a very peculiar and characteristic impress on the surface of the rocks, and even on the general aspect of the country over which it passes. This is no mystery of science, but a plain fact which any one that chooses may observe for himself. Every Glacier carries along in its course a vast quantity of loose gravel, hard sand, and large angular stones. A considerable proportion of these materials in course of time fall through crevasses in the ice, and become firmly embedded in the under surface of the Glacier. Then, as the moving mass slowly descends the valley, they are shoved along under enormous pressure, and the surface of the rocks beneath is furrowed, scratched, and polished, in a remarkable and unmistakable manner. The furrows and scratches are rectilinear and parallel to an extent never seen in the marks produced by any other natural agency: and they always coincide more or less in their direction with the general course of the valley. A reciprocal action often takes place: the large blocks of stone, frozen into the under surface of the Glacier, are themselves scored and polished by friction against the floor and sides of the valley.