Eocene (dawn of recent life), consisting of sandstone, limestone, sands, clays, marls, coral rags, and lignites, and containing fossil equine forms, birds, reptiles, bats, and marsupials. Meiocene (less recent life), consisting of arctic coal, limestone, sands, clays, and lignites, and containing fossil apes and marsupials. Pleiocene (more recent life), the white and red crags of Britain, containing fossil apes, bears, and hyenas. Pleistocene (most recent life), consisting of glacial accumulations of all kinds of earths, and containing fossil remains of apes and men, and implements of stone, bone, and horn, and later still of remains of lake-dwellings, shell-mounds, etc. These different layers of stratified rocks have not always kept their proper positions with regard to each other in the order they were originally laid down; but, owing to volcanic eruption, have frequently intruded upon each other, so that, at first sight, it would sometimes appear as though the regular order of deposition had not been adhered to; but that this is not so has been made apparent by careful investigation over large areas. The depth of the Secondary and Tertiary is from twenty to twenty-five miles. We see, therefore, that the first life-forms made their appearance as marine organisms in the Laurentian, or first stratified rock period; but whether the animal or the vegetable form first appeared, or whether both were developed from one primordial organism, it is impossible at present to say. In each successive layer of rock we meet with fossil remains of animal and vegetable life, which steadily develop into more highly organised forms, through the different periods, until, at last, they assume the exquisite phases we now behold around us. The vegetable kingdom was the first to exist upon the land, the first land-plant being found in the fossil state in the Cambrian layer, at the same time that marine animal life was assuming the forms of worms, shell-fish, and star-fishes. In the Silurian period the first vertebrate animals made their appearance in the form of lowly-organised fishes, from which, in the Carboniferous age, developed amphibious creatures, the first breathing animals, living both in and out of water, and the progenitors of the large kingdom of land animals, including man.