| Epochs and Formations. | Faunal Characters. | |
| Cainozoic or Tertiary | Post-Pliocene. Glacial Period. | Man. Mammalia principally of living species. Mollusca exclusively recent. |
| Pliocene, 3,000 feet. | Mammalia principally of recent genera—living species rare. Mollusca very modern. | |
| Miocene, 4,000 ft. | Mammalia principally of living families; extinct genera numerous; species all extinct. Mollusca largely of recent species. | |
| Oligocene, 8,000 ft. | ||
| Eocene, 10,000 ft. | Mammalia with numerous extinct families and orders; all the species and most of the genera extinct. Modern type Shell-Fish. | |
| Mesozoic or Secondary | Laramie, 4,000 ft. | Passage beds. |
| Cretaceous, 12,000 ft. | Dinosaurian (bird-like) Reptiles; Pterodactyls (flying Reptiles); toothed Birds; earliest Snake; bony Fishes; Crocodiles; Turtles; Ammonites. | |
| Jurassic, 6,000 ft. Oolite. Lias. | Earliest Birds; giant Reptiles (Ichthyosaurs, Dinosaurs, Pterodactyls); Ammonites; Clam- and Snail-Shells very abundant; decline of Brachiopods; Butterfly. | |
| Trias, 5,000 ft. New Red Sandstone. | First Mammalian (Marsupial); 2-gilled Cephalopods (Cuttle-Fishes, Belemnites); reptilian Foot-Prints. | |
| Paleozoic or Primary | Permian, 5,000 ft. | Earliest true Reptiles. |
| Carboniferous, 26,000 ft. Coal. | Earliest Amphibian (Labyrinthodont); extinction of Trilobites; first Cray-fish; Beetles; Cockroaches; Centipedes; Spiders. | |
| Devonian, 18,000 ft. Old Red Sandstone. | Cartilaginous and Ganoid Fishes; earliest and (snail) and freshwater Shells; Shell-Fish abundant; decline of Trilobites; May-flies; Crab. | |
| Silurian, 33,000 ft. | Earliest Fish; the first Air-Breathers (Insect, Scorpion); Brachiopods and 4-gilled Cephalopods very abundant; Trilobites; Corals; Graptolites. | |
| Cambrian, 24,000 ft. | Trilobites; Brachiopod Mollusks. | |
| Azoic | Archæan, 30,000 ft. Huronian. Laurentian. | Eozoön, (probably not a fossil). |
| Primeval. | Non-sedimentary. |
I submit, then, that so far as the largest and most general principles in the matter of palæontology are concerned, we have about as strong and massive a body of evidence as we could reasonably expect this branch of science to yield; for it is at once enormous in amount and positive in character. Therefore, if I do not further enlarge upon the evidence which we here have, as it were en masse, it is only because I do not feel that any words could add to its obvious significance. It may best be allowed to speak for itself in the millions of facts which are condensed in this tabular statement of the order of succession of all the known forms of animal life, as presented by the eminent palæontologist, Professor Cope[17].
Or, taking a still more general survey, this tabular statement may be still further condensed, and presented in a diagrammatic form, as it has been by another eminent American palæontologist, Prof. Le Conte, in his excellent little treatise on Evolution and its Relations to Religious Thought. The following is his diagrammatic representation, with his remarks thereon.
When each ruling class declined in importance, it did not perish, but continued in a subordinate position. Thus, the whole organic kingdom became not only higher and higher in its highest forms, but also more and more complex in its structure and in the interaction of its correlated parts. The whole process and its result is roughly represented in the accompanying diagram, in which A B represents the course of geological time, and the curve, the rise, culmination, and decline of successive dominate classes.
Fig. 59.—Diagram of Geological Succession of the Classes of the Animal Kingdom. (After Le Conte.)
I will here leave the evidence which is thus yielded by the most general principles that have been established by the science of palæontology; and I will devote the rest of this chapter to a detailed consideration of a few highly special lines of evidence. By thus suddenly passing from one extreme to the other, I hope to convey the best idea that can be conveyed within a brief compass of the minuteness, as well as the extent, of the testimony which is furnished by the rocks.
When Darwin first published his Origin of Species, adverse critics fastened upon the “missing-link” argument as the strongest that they could bring against the theory of descent. Although Darwin had himself strongly insisted on the imperfection of the geological record, and the consequent precariousness of any negative conclusions raised upon it, these critics maintained that he was making too great a demand upon the argument from ignorance—that, even allowing for the imperfection of the record, they would certainly have expected at least a few cases of testimony to specific transmutation. For, they urged in effect, looking to the enormous profusion of the extinct species on the one hand, and to the immense number of known fossils on the other, it was incredible that no satisfactory instances of specific transmutation should ever have been brought to light, if such transmutation had ever occurred in the universal manner which the theory was bound to suppose. But since Darwin first published his great work palæontologists have been very active in discovering and exploring fossiliferous beds in sundry parts of the world; and the result of their labours has been to supply so many of the previously missing links that the voice of competent criticism in this matter has now been well-nigh silenced. Indeed, the material thus furnished to an advocate of evolution at the present time is so abundant that his principal difficulty is to select his samples. I think, however, that the most satisfactory result will be gained if I restrict my exposition to a minute account of some few series of connecting links, rather than if I were to take a more general survey of a larger number. I will, therefore, confine the survey to the animal kingdom, and there mention only some of the cases which have yielded well-detailed proof of continuous differentiation.