Page:Encyclopædia Britannica, Ninth Edition, v. 7.djvu/300

282 282 ISTKIBUTION [ANIMAL. that an extensive series of fossiliferous deposits may have once existed, whose record of the earlier stages of the history of life upon the earth has been either destroyed by denudation or obliterated by internal heat. This being the case, we must carefully distinguish between positive and negative evidence ; and we may also fairly apply such principles as can be established by means of the fuller record afforded by the Tertiary deposits, to interpret the more scanty and fragmentary record with which we have to deal in the older rocks. We will now proceed to sketch very briefly the successive stages of the development of animal life as indicated by the materials at our command. The lowest and most ancient of all the stratified rocks is the Laurentiau, consisting of crystalline beds of gneiss, mica-schist, quartzite, and limestone, reaching in Canada the aggregate thickness of 30,000 feet. The whole mass was long thought to be destitute of organic remains, till in one of the beds of limestone in the lower part of the series a curious structure was discovered, which is held by Dr Carpenter and Professor Rupert Jones, who have made a special study of the Foraminifera, to be the fossilized remains of one of that group of the Protozoa. It has been named Eozoon canadense, and if really organic (which is denied by some naturalists of eminence) is by far the oldest trace of animal life. The Upper Laurentian deposits, 10,000 feet thick, lie unconforniably on the lower, and seem to be entirely destitute of fossils. The next formation is the Cambrian, largely developed in Wales, Scandinavia, Bohemia, and North America, and consisting of a variety of distinct deposits. But in the very lowest of these (the Longmynd group) abundant organic remains have recently been found, comprising perfectly developed brachiopodous and pteropodous Mollusca, entomostracous Crustacea, and Trilobites. In the overlying beds of the same formation similar forms abound, and are accompanied by sponges, annelids, graptolites (which are supposed to be peculiar extinct Hydrozoa), starfishes, and encrinites. Here also first appear lamellibranchiate Mollusca, belonging to the families Arcadce, Nuculidce, and Atlantidce, and there are even some Orthoceratidce, belonging to the highest order of molluscs Cephalopoda. The Trilobites are already wonderfully varied, the smallest and largest kinds being found here (one 2 feet long), species with the least and with the greatest number of rings, blind Trilobites, and others with the most largely developed eyes. (Lyell s Students Elements of Geology, pp. 483, 485, 634.) We next come to the Silurian formation, in which we first meet with corals, of the three great divisions Rugosa, Tabulata, and Perforata, ostracode Crustaceans, Trilobites in enormous variety, Merostomata extinct Crustaceans of gigantic size, Echinoidea (Palcechinus), and true gastero- podous Mollusca. And lastly, in the Upper Silurian deposits, we find vertebrates, whose first representatives are several genera of fishes belonging to the Ganoid and Plagiostomous groups. In the succeeding Devonian formation we find an abundance of new families of fishes, a fresh-water mussel of the living genus Anodon, and no less than six forms of winged insects. These have been found in the Devonian rocks of New Brunswick, and are considered by Mr Scudder to be ancient forms of Neuroptern. The Carboniferous formation is very rich in animal as well as vegetable remains ; and, along with most of the animals already met with, we find several higher types of great interest. The higher rnacrurous Crustacea (Anthra- palcemon) are here first met with, as are true air-breathing molluscs, numerous specimens of the living genera, Pupa and Zonites, having been found in the coal-fields of Nova Scotia. Along with these are insects of various orders Myriapoda, scorpions, spiders, Orthoptera, Neuroptera, Coleoptera, and even Lepidoptera. Here, too, we meet with .air-breathing vertebrates the Labyrinthodonts, ancient forms of Amphibia which occur in considerable abundance and variety. (Lyell s Students Elements, p. 408; Annales de la Society Entomologique de Helyique, 1875, torn xviii., where a wing from the coal-measures, closely resembling those of moths belonging to the family Saturniidce, is photographed.) In the Permian formation, which closes the series of Palaeozoic rocks, we have the important addition of true Lacertian reptiles (Protorosaurus), which, according to Professor Huxley, differ wonderfully little from some living groups, What are supposed to be Chelonian footprints have been discovered in the Permian sandstones of Dumfriesshire. (Huxley s American Addresses, p. 41.) Entering the Secondary period with the Triassic forma tion, we at once meet with higher forms of life. Among Crustacea we first find traces of the brachyuruus division of Decapods (Etheridge, in Lyell s Students Elements, p. 632) and many new forms of Mollusca. Among reptiles the Dinosauria, Dicynodontia, Plesiosauria, and Crocodilia, appear; what seem to be undoubted footprints of birds have been found in the New Red Sandstone of Connecticut (see figures in TuyelYs Students Elements, p. 371, and Nicholson s Paleontology, p. 389) ; and all improbability of this early appearance of birds is removed by the fact that a little higher in the same formation remains of a true Mammalian have been undoubtedly discovered. This is the Microlestes, founded on well-preserved teeth from a bone bed in the Upper Trias of Wiirtemberg, and since found also hi the Rluetic beds of Somersetshire ; while in rocks supposed to be of the same age in North Carolina tho lower jaw of an allied form (Dromatheri-um) has been obtained. Both are believed to be Marsupials, and most nearly allied to the Myrmecobius of Australia. In the Jurassic or Oolitic period, the main forms of life which have already appeared are further developed. In sects of all orders are found, and they can mostly be classed in existing families and even genera, as Locusta, frepa, Sphinx, Termcs, Ephemera, Ayrion, yEshna, Ayrion, Prionus, Libellula. (Rev. P. B. Broclie, in Proc. Warwick shire Nat. Hist. Soc., 1873.) Among reptiles, Chdonia and Ichthyosauria are added. Of birds we have the long tailed and feathered Archoeopteryx ; while no less than eight genera of small Mammalia have been discovered, must of them Marsupials, though some may have been ancestral forms of Insectivora. Many living genera of shells, both marine and fresh-water, first appear ; and among fishes, true sharks of the existing family Notidanidae, In the Cretaceous period, we make a still further approach to living forms. The highest Crustacea (Bra- chyura) are tolerably abundant, and the living genus Cancel appears. Mollusca (Lamellibranchiata and Gasteropoda) are represented by a number of living genera. Malacop- terous fishes now appear. Reptiles are still mostly of extinct types Pterosauria, Ichthyosauria, Dinosauria, &c. ; but among birds we find some allied to existing waders, as well as the curious extinct group of Odon- tornithes, or toothed birds. (Marsh, in American Jour. of Science and Arts, vol. x. 1875.) When we pass over the great asm of time which separates the Mesozoic from the Cainozoic or Tertiary period, we at once come upon a host of new forms closely resembling those which now live upon the earth. The majority of living genera of Mollusca now appear, with a gradually increasing proportion of living species, as we pass from the Eocene to Miocene and Pliocene times ; the highest forms of Crustacea are plentiful ; Insecta of all orders, and almost all of living genera, abound ; fishes of