AGES OF NATTJBE. 403 



vrith air-breathing animals, as insects, scorpions, and rep- 

 tiles. At the same time, land-plants first make their ap- 

 pearance, namely, ferns of great size, club-mosses, and other 

 fossil plants. Fig. 381 exhibits some of the most typical 

 forms of the flora of this period. This abundant vegetation 

 corroborates what has been already said concerning the inti- 

 mate connection existing between the animals and the land- 

 plants of all epochs. The class of crustaceans has also improved 

 during the coal period. It is no longer composed exclusively 

 of Trilobites, but the type of horse-shoe crabs also appears, 

 with other gigantic forms. Some of the mollusca, particularly 

 the bivalves, seem also to approach those of the Oolitic period. 

 6/2. In the Trias period, which immediately succeeds 

 the Carboniferous, the fauna of the Secondary age acquires 

 its definitive character ; here the reptiles first appear in con- 

 siderable numbers, consisting of huge crocodilian animals, 

 belonging to a peculiar order, the Rhizodonts (Protosaurus, 

 Notosaurus, and Labyrinthodori). The well-known discoveries 

 of Professor Hitchcock, in the red sandstone of the Con- 

 necticut Valley, have made us acquainted with a great number 

 of birds' tracks belonging to this epoch, for the most part indi- 

 cating animals of gigantic size. These impressions, which he 

 has designated under the name of Ornithichnites, are some of 

 them eighteen inches in length, and five feet apart, far exceed- 

 ing in size the tracks of the largest ostrich. Other foot-marks 

 of a very peculiar shape, have been found in the red sandstone 

 of Germany (fig. 382), and in Pennsylvania. They were 

 probably made by reptiles, which have been called Cheiro- 



Fig. 382. Line of footmarks on a slab of sandstone, from 

 Hildburghausen, in Saxony. 



to the palaeozoic epoch. But there are reasons which induce us to unite 

 the carboniferous period with the secondary age, especially when we 

 consider that a luxuriant terrestrial vegetation was developed at this epoch; 

 that here land animals first appear in any considerable number, whereas, 

 in the palaeozoic age, there were chiefly marine animals, breathing by gilis, 

 and a few reptiles known only by their foot-marks. 



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