Elsewhere the same writer speaks of this glacier as a line of cliff, rising in a solid glassy wall to a height of three hundred feet above the water-level, and with an _unfathomable_ depth below it; and its curved face, sixty miles in length, from Cape Agassiz to Cape Forbes, vanished into unknown space at not more than a single day's rail-road travel from the pole. The interior with which it communicated, and from which it issued, was an unsurveyed _mer de glace_, or sea of ice, of apparently boundless dimensions; and from one part of this great cliff he _saw_ long lines of huge bergs floating slowly away. Here, we think, is ice enough and of sufficient dimensions to account for the largest bergs that were ever beheld. It will be at once seen, then, that icebergs, though found floating in the sea, are not necessarily of the sea. They are composed entirely of fresh water, and arctic ships can at any time procure a plentiful supply of good soft drinkable water from the pools that are formed in the hollows of the bergs. The risk of approaching icebergs in the arctic regions is not so great as when they are found floating further south; because when in their native regions they are comparatively tough, whereas on their southern journeys they become more or less disintegrated--in fact, the blow of an axe is sometimes sufficient to cause a rent, which in its turn will induce other rents and failings asunder, so that the whole mass runs the risk of being entirely broken up. Hence the danger of ships, in certain circumstances, venturing to anchor to them. Nevertheless this is a common practice--sometimes a necessity--among discovery ships and whalers. It is a convenient practice too; for many a vessel has been saved from absolute destruction by getting under the lee of a good sound iceberg, where she has lain as safely, for the time being, as if in a harbour. When Captain McClure was endeavouring to make the north-west passage in 1851, he was saved, from what appeared to be at least very probable destruction, by a small iceberg. On the 17th of September he writes: "There were several heavy floes in the vicinity. One, full six miles in length, passed at the rate of two knots, crushing everything that impeded its progress, and grazed our starboard-bow. Fortunately there was but young ice upon the opposite side, which yielded to the pressure; had it otherwise occurred, the vessel must inevitably have been cut asunder. In the afternoon we secured to a moderately-sized iceberg, drawing eight fathoms, which appeared to offer a fair refuge, and from which we never afterwards parted."