Passing on now to the period when the great chalk rocks which prevail so much in the southeastern counties of Great Britain were deposited, we find the land in many places submerged; the fossil remains are eminently marine in character, and the earth must literally have presented a "world of waters" to the view. Sponges, corals, star-fish, and marine reptiles inhabited the globe, and plants, chiefly of marine types, grew on its surface. Although, however, a great portion of the earth was under water, it must not therefore be supposed that it was returning to its ancient desolation and solitude. The author whom we last quoted, in speaking of this subject, says: "The sterility and solitude which have sometimes been attributed to the depths of the ocean, exist only in the fictions of poetic fancy. The great mass of water that covers nearly three-fourths of the globe is crowded with life, perhaps more abundantly than the air and the surface of the earth; and the bottom of the sea, within a certain depth accessible to light, swarms with countless hosts of worms and creeping things, which represent the kindred families of low degree which crawl upon the land." This era seems to have been one of peculiar tranquillity, for the most part undisturbed by earthquakes or other igneous forces. The prevailing characteristic of the scenery was flatness, and low continents were surrounded by shallow seas. The earth is now approaching the state when it will be fit for the reception of man, and in the next age we find some of the existing species of animals. It is worthy of observation, that at the different periods when the world had attained a state suitable for their existence, the various orders of animal and vegetable life were created. In the "dark ages" of geological history, when the globe had comparatively lately subsided from a state of fusion,[23] it was barren, sterile, and uninhabited; next, the waters having become cool enough, some of the lowest orders of shell-fish and zoophytes peopled them; subsequently, fishes were formed, and for ages constituted the highest order of animal life; after this we enter on the age of reptiles, when gigantic crocodiles and lizard-like forms dwelt in fenny marshes, or reposed on the black mud of slow moving rivers, as they crept along toward the ocean betwixt their oozy banks; and we now reach the period when the noblest order of animal life, the class to which man himself belongs, Mammalia, began to people the earth. The world now probably presented an appearance nearly similar to what it does at present. The land, which in the chalk formation was under water, has again emerged, and swarms with life; vast savannahs rich in verdure, and decked in a luxuriant garb with trees, plants, grasses, and shrubs, and inland lakes, to which the elephant, the rhinoceros, and the hippopotamus, with many extinct races of animals, came to slake their thirst, form the principal characteristics of this period.