Icebergs. Are immense bodies of ice, extending occasionally two miles long by one broad, and some hundreds of feet high, which are found floating in the polar seas, and are formed in two ways - in the sea itself, by the accumulation of snow and ice, or on precipitous shores, in glaciers, which are ultimately broken off by their own weight and often carry with them enormous pieces of rock. These, as the icebergs melt, when floated into warmer regions, are dropped, with all their lesser earthy contents of gravel, etc, to the bottom of the ocean, and so help to raise its bed. The erratic masses of stone called boulders, found scattered in various parts of the world, on the surface, without any apparent connexion with the rocks in the crust beneath, are supposed to have been thus deposited in some remote time, when the locality was covered with the deep waters.