It may be said of polar countries, that they form a transition state between land and sea, for water is always present, although in a solid state; the surface is always at a very low temperature; snow does not melt as it falls, and the sea is thus sometimes covered with a continuous sheet of frozen snow; sometimes with enormous floating blocks of ice which are driven by the currents. Meeting with these floating masses of ice is one of the dangers of polar navigation. Captain Scoresby has given a very detailed description of the different kinds of ice met with in the Arctic Seas. The ice-fields of this writer form extensive masses of solid water, of which the eye cannot trace the limits, some of them being thirty-five leagues in length and ten broad, with a thickness of seven to eight fathoms; but generally these ice-fields rise only four to six feet above the water, and reach from three to four fathoms beneath the surface. Scoresby has seen these ice-fields forming in the open sea. When the first crystals appear, the surface of the ocean is cold enough to prevent snow from melting as it falls. On the approach of congelation the surface solidifies, and seems as if covered with oil; small circles are formed, which press against each other, and are finally soldered together until they form a vast field of ice, the thickness of which increases from the lower surface. The water produced from melted ice is perfectly fresh--the result of a well-known physical cause. When a saline solution like sea water is congealed by cold, pure water alone passes into the solid state, the saline solution becomes more concentrated, increases in density, and, sinking to the bottom, remains liquid. Blocks of ice, therefore, in the Polar Seas, are always available for domestic use. There are, however, salt blocks of ice, which are distinguished from fresh-water ice by their opaqueness and their dazzling white colour: this saltness is due to the sea water retained in its interstices. Scoresby amused himself sometimes by shaping lenses of ice, with which he is said to have set fire to gunpowder, much to the astonishment of his crew. The ice-fields, which are formed in higher latitudes, are driven towards the south by winds and currents, but sooner or later the action of the waves breaks them up into fragments. The edges of the broken icebergs are thus often rising and continually changing: these asperities and protuberances are called _hummocks_ by English navigators; they give to the polar ice an odd, irregular appearance. Hummocks form themselves of the stray, broken icebergs which come in contact with each other at their edges, and thus form vast rafts, the pieces of which may exceed a hundred yards in length.