In order fully to appreciate the power and magnitude of this ice-movement, it must be borne in mind that a very large proportion of the ice is of very ancient formation,--old floes or ice-fields of immense thickness and miles in extent, as well as of icebergs discharged from Humboldt Glacier. These vast masses, tearing along with the current in the early winter through the sea as it is closing up and new ice is making rapidly, are as irresistible as a tornado among the autumn leaves. As an illustration, I will give the dimensions of an old field measured by me while crossing the Sound. Its average height was twenty feet above the sea level, and about six by four miles in extent of surface, which was very uneven, rising into rounded hillocks as much as eighty feet in height, and sinking into deep and tortuous valleys. To cross such a floe with our sledges was almost as difficult as crossing the hummocks themselves; for, in addition to its uneven surface, like that of a very rough and broken country, it was covered with crusted snow through which the sledge-runners cut continually, and which broke down under the foot. I estimated its solid contents, in round numbers, at 6,000,000,000 of tons, its depth being about one hundred and sixty feet. Around its border was thrown up on all sides a sort of mountain chain of last year's ice, the loftiest pinnacle of which was one hundred and twenty feet above the level of the sea. This ice-hill, as it might well be called, was made up of blocks of ice of every shape and of various sizes, piled one upon the other in the greatest confusion. Numerous forms equally rugged, though not so lofty, rose from the same ridge, and from every part of this desolate area; and if a thousand Lisbons were crowded together and tumbled to pieces by the shock of an earthquake, the scene could hardly be more rugged, nor to cross the ruins a severer task. [Sidenote: ORIGIN OF A FLOE.]