640 GEOLOGY. 



The dawn of organic life the morning twilight of the era of living beings appears in 

 certain slaty rocks of North Wales, which are variously regarded as upper beds of the 

 clay-slate system, as lower Silurian, and as a distinct formation under the name of 

 Cambrian. Zoophytes, molluscs, and traces of annelidans, are occasionally detected. In the 

 following table, the more important remains of animal and vegetable life, characteristic of 

 great geological eras, are indicated : 



SILURIAN PERIOD. 



Fossils eminently marine. Zoophytes in great abundance and of 

 many species, among which the chain-pore coral (Catenipora, 

 escharoides), is a beautiful example ; encrinites of several varie 

 ties ; crustaceans, particularly trilobites ; and molluscs in great 

 numbers. True vertebrated fishes, towards the close of the 

 period. Sea- weeds and aquatic plants. 



OLD RED SANDSTONE PERIOD. 



Remarkably uncouth fishes common, many covered with bony 

 plates. First trace of reptiles, apparently allied to the 

 lizards. Land-plants appear akiu to the tree-ferns, and 

 other vegetation of the succeeding period. 



CARBONIFEROUS PERIOP. 



Marine life exuberant. Fishes of large size and of sauroid 

 character. Fragments of laud-shells, and skeletons of minute 

 reptiles of the frog-kind, indicate a terrestrial fauna. An 

 abundant and gigantic flora forms the grand feature of the 

 period, consisting of araucarian-like pines, palms, tree-ferns, 

 enormous reeds, equisetums, club-mosses, and other kindred 

 plants. 



LOWER NEW RED 8VNDSTONF, Oil PERMIAN PERIOD. 



Land-plants allied more or less to those of the preceding era. 

 True air-breathing, land-inhabiting creatures more distinctly 

 indicated, of the frog and lizard families the Palceosaurus 

 (ancient saurian), Protorosaurus (first saurian), Thecodonto- 

 saurus (sheath-tooth saurian), the latter allied to the living 

 monitor. 



UPPER NEW RED SANDSTONE, OR TRIASSIC PERIOD. 



A limited flora indicated, both as to species and individuals, 

 but more allied to that of the present era than of the 

 preceding epochs. Frog-like reptiles, of huge size, appear, 

 and new families of saurians. Ichnolitcs (foot-prints on 

 stone), those of reptiles ; and Ornithicknites (stony bird 

 tracks), the imprints of birds, some of gigantic size, are 

 characteristic memorials of the period. 



OOLITIC PERIOD. 



Organic remains extremely numerous and well-preserved. The 

 most remarkable are reptiles, many of enormous size, as the 

 Ichthyosaurus (fish-like saurian), Plesiosaurus (akin to the saurian), 

 and the intermediate Pliosaurus, inhabitants of the ocean ; the 

 Pterodactyle (wing-fingered reptile), a flying saurian ; the Hylceosaurus 

 (forest-saurian) ; the Meyalosaurus (great saurian), a gigantic carni 

 vorous terrestrial reptile ; and the Jguanodon, a huge herbivorous 

 reptile, allied to the existing iguana. Among molluscs, Ammonites 

 occur in prodigious numbers, of many species, and varying size. 

 liisects also appear, beetle-like and dragon-fly-like ; and a specimen 

 or so of birds. Fragments of small marsupial animals proclaim the 

 existence of warm-blooded terrestrial mammalia. 



Sphsnopteris Hscninghausi. 



Encrinites Moniliformis. 



Ammonite Catena. 



