Icebergs differ a little in colour according to their solidity and distance, or state of the atmosphere. A very general appearance is that of cliffs of chalk, or of white or grey marble. The sun’s rays reflected from them sometimes give a glistening appearance to their surfaces. Different shades of colour occur in the precipitous parts, accordingly as the ice is more or less solid, and accordingly as it contains strata of earth, gravel, or sand, or is free from any impurity. In the fresh fracture, greenish grey, approaching to emerald green, is the prevailing colour. In the night, icebergs are readily distinguished, even at a distance, by their natural effulgence; and in foggy weather, by a peculiar blackness in the atmosphere, by which the danger to the navigator is diminished. As, however, they occur far from land, and often in unexpected situations, navigators require to be always on the watch for them. Though often dangerous neighbours, they have occasionally proved useful auxiliaries to the whale-fishers. Their situation in a smooth sea is very little affected by the wind; under the strongest gale they are not perceptibly moved, but, on the contrary, have the appearance of advancing to windward, because every other description of ice moves rapidly past them. From the iceberg’s firmness, it often affords a stable mooring to the ship in strong adverse winds, and the fisher likewise avails himself of it when his object is to gain a windward situation more open. He moors under the lee of the iceberg, loose ice soon forces past, the ship remains nearly stationary, and the wished-for effect seldom fails to result. Vessels have, however, often been staved, and sometimes wrecked, by the fall of their icy mooring; while smaller objects, such as boats, have been repeatedly overwhelmed, even at a considerable distance, by the vast waves occasioned by such events.