ICEBERG, a floating mass of ice, which has broken off from such ice-sheets as cover Greenland, Spitzbergen, and other polar lands, constituting vast glacier systems ever creeping out and down from the central heights to the shores. As the glacier is pushed out to sea, the lower margin is exposed to the destructive action of the waves, and breaks up into fragments of endless variety of form. These severed blocks, many of which are hundreds of millions of tons in mass, drift to lower latitudes under the influence of polar currents, and gradually melt away in the warmer water. Such is the natural history of icebergs, which, in their freshwater origin, are to be distinguished from the ice-fields, ice-floes, pack ice, and ice-hummocks, so familiar to the polar voyager. The iceberg, as it drifts along, melts most rapidly under water; and this unequal wasting must be accompanied by a change in the position of the centre of mass and a consequent shifting of the iceberg into its new position of equilibrium. Undermining and fracture also result; so that at length the mass of ice, however square-shaped or symmetrical it may have been originally, assumes a form irregular and fantastic in the extreme. The densities of ice and sea-water are nearly ∙92 and 1Ό3 respectively, so that only τ 1 π 1 κ or nearly ⅜th of the iceberg is above water and visible. An iceberg observed by Sir John Ross and Lieutenant Parry was 2j miles long, 2⅜ miles broad, and 153 feet high. Assuming the form to have been approximately a cone erected upon an elliptic base, the mass above water would be roughly 150 million tons—giving a total mass of nearly 15 hundred million tons. This iceberg, however, was by no means of extraordinary dimensions. In the southern seas, great fleets of icebergs have ...