and fishes of uncouth forms, also, have been. preserved from this time. In the devonian age the presence of fishes became a leading characteristic of the seas; corals, too, which were abundant in the waters of the preceding age, became extremely numerous; and land-plants were common. Some of these were sturdy trees, but all were of comparatively low organization. In the carboniferous age a further advance in animal life occurred; namely, the introduction of the first vertebrates higher than fishes. These earliest amphibians and reptiles were respectively frog-like animals and great sealizards. Plants of most luxuriant growth flourished among the extensive marshes which covered much of Europe and an immense area in Eastern North America. But though the forests of carboniferous time in their strange luxuriance exceeded any that have since covered the earth, our highest two divisions of plants were still lacking, and it was not till the reptilian age that these appeared. The reptilian age was characterized, not only by the advance in plant-life just mentioned, but also by the advent of hosts of strange lizardlike forms. There were reptiles that swam in the sea, reptiles that crawled and that walked along the beach, and reptiles that flew like so many gigantic bats. The Atlantosaurus, a reptile of this age, whose fossil remains were discovered by Professor O. C. Marsh, probably exceeded in size any known animal. It had a length of about a hundred feet, and a height of thirty feet or more. So characteristic were the peculiar plants of this age, called cycads, that it has even been known as the age of cycads. In the mammalian age, mammals for the first time become predominant; and the earth was peopled with such an assemblage of animals of this group as is not even approached by the great fauna of South Africa at the present day. Among plants, all the great groups now found were represented. In the earlier part of the age of man, the fauna and flora differed greatly from those now existent; but it will not be necessary to say more of the matter in this place, since it will again be referred to in a later chapter. Some of the facts just stated may be most clearly represented to the eye by the following diagram, altered from Dana's "Manual of Geology."1 1 P. 130. Some changes have been made in the names of the groups. 2. Age of Invertebrates, or Silurian. 5. Age of Reptiles, or Secondary. 3. Age of Fishes, or Devonian. 6. Age of Mammals, or Tertiary. 7. Age of Man, or Quaternary. This diagram is defective in many ways and not in accordwith modern classification, but it is not easy to chtain a In explanation of the diagram Professor Dana says, "The horizontal bands represent the ages in succession: the vertical correspond to different groups of animals and plants. The lower end of each vertical band marks the time when, according to present knowledge from fossils, the type it represents began; and the varying width in the same band indicates the greater or less expansion of the type." The grand question which the student of organic evolution has to ask of the science of palæontology is, "Does the general succession of life-forms on the earth tend to corroborate the doctrine of descent?" The answer to this question must be given somewhat at length. At the outset, one of the most striking facts to be gathered from the diagram just given is the very late appearance on the earth of mammals in general, and in particular of man; the latter, according to the time-ratios already cited, having appeared only after 15 of the time has elapsed from the beginning of the palæozoic to the present.1 Again: the reptiles and amphibians, and the fishes, which respectively constitute the next 1 Man may date back to the beginning of the cenozoic. See Chap. IX. |
