Who can tell when the last great revolutions of the earth-rind took place, which, by the upheaving of mighty mountains or the disruption of isthmuses, drew the present boundaries of land and sea? or who can pierce the deep mystery which veils the future duration of the existing phase of planetary life? So much is certain, that the ocean of the present day will be transformed as the seas of the past have been, and that “all that it inhabit” are doomed to perish like the long line of animal and vegetable forms which preceded them. We know by too many signs that our earth is slowly but unceasingly working out changes in her external form. Here lands are rising, while other areas are gradually sinking, here the breakers perpetually gnaw the cliffs and hollow out their sides, while in other places alluvial deposits encroach upon the sea’s domain. However slowly these changes may be going on, they point to a time when a new ocean will encircle new lands, and new animal and vegetable forms arise within its bosom. Of what nature and how gifted these races yet slumbering in the lap of time may be. He only knows whose eye penetrates through all eternity; but we can not doubt that they will be superior to the present denizens of the ocean. Hitherto the annals of the earth-rind have shown us uninterrupted progress; why, then, should the future be ruled by different laws? At first the sea only produces weeds, shells, crustacea; then the fishes and reptiles appear; and the cetaceans close the vista. But is this the last word, the last manifestation of oceanic life, or is it not to be expected that the future seas will be peopled with beings ranking as high above the whale or dolphin as these rank above the giant Saurians of the past? THE FLOOR OF THE OCEAN --JOHN JAMES WILD If we wish to form a perfect idea of the distribution of land and water, we must consider not only the length and breadth of the areas occupied, but also the height of the land and the depth of the water; in other words, the volume of those portions of the solid crust of the earth which are raised above the level of the sea, and the volume of the masses of water which fill up the depressed portions of the earth’s crust. We are thus led to regard the surface of the solid crust of our planet as composed of heights and hollows, of areas of elevation and areas of depression, and, as a next step, to discriminate between these areas--not according to the usual standard of the level of the sea, but according to their relative distance from the centre of the earth. In this sense we may conceive an area of elevation--_i. e._, a raised portion of the earth’s surface, which may be partially or entirely covered with water, and an area of depression--_i. e._, a hollow in the same surface, which may be raised above the level of the sea, and from dry land or the basin of an inland sea or lake.