There was a time when men of science, and, amongst others, the French philosopher St. Pierre, believed that icebergs were the snow and ice of ages accumulated upon an Arctic sea, which, forming at the Poles, detached themselves from the parent mass. Such an hypothesis naturally gave rise to many theories, not less ingenious than startling, as to the effect an incessant accumulation of ice must produce on the globe itself; and St. Pierre hinted at the possibility of the huge “domes of ice”--which, as he supposed, rose to an immense height in the keen frosty heavens of the Poles--suddenly launching towards the Equator, dissolving under a tropical sun, and resulting in a second deluge! In simple language Professor Tyndall furnishes an explanation of the origin of icebergs, which we may transfer to these pages as supplementary to the preceding remarks. [Illustration: ORIGIN of ICEBERGS--EXTENSION OF A GLACIER SEAWARDS.] What is their origin? he asks; and he replies, as we have done, the Arctic glaciers. From the mountains in the interior the indurated snows slide into the valleys, and fill them with ice. The glaciers thus created move, like the Swiss ones, incessantly downward. But the Arctic glaciers descend to the sea, and even enter it, frequently ploughing up its bottom into submarine moraines. Undermined by the continuous action of the waves, and unable to resist the pressure of their own weight, they break across, and discharge enormous masses into the ocean. Some of these drift on the adjacent shores, and often maintain themselves for years. Others float away to the southward, and pass into the broad Atlantic, where they are finally dissolved. But a vast amount of heat is demanded for the simple liquefaction of ice, and the melting of icebergs is on this account so slow that, when large, they sometimes maintain themselves till they have been drifted two thousand miles from their place of birth. Icebergs, then, are fresh-water formations, and though they are found on a colossal scale only in the Polar seas, yet they are by no means uncommon among the lofty Alpine lakes. The monarch of European ice-rivers is the great Aletsch glacier, at the head of the valley of the Rhone. It is about twenty miles in length, and collects its materials from the snow-drifts of the grandest mountains of the Bernese Oberland--the Jungfrau, the Mönch, the Trugberg, the Aletschhorn, the Breithorn, and the Gletscherhorn.