AGES OF NATURE. 



229 



with a great number of birds' tracks (Fig. 158, a, Z>) belong- 

 ing to this epoch, for the most part indicating birds of gigan- 

 tic size. These impressions, which he has designated under 

 the name of Ornithichnites, are some of them eighteen inches 



V 



a Fig. 158. 



in length, and five feet apart, far exceeding in size the tracks 

 of the largest ostrich. Other tracks, of a very peculiar shape, 

 have been found in the red sandstone of Germany, and in 

 Pennsylvania. They were probably made by Reptiles which 

 have been called Cheirotherium, from the resemblance of the 

 track to a hand, (c.) The Mollusks, Articulates, and Radiates 

 of this period, approach to the fauna of the succeeding period. 

 484. The fauna of the Oolitic formation is remarkable for 

 the great number of gigantic Reptiles which it contains. In 



a 



Fig. 159. 



this formation we find those enormous Amphibia, known 

 under the names Ichthyosaurus, Plesiosaurus, Megalosaurus, 

 and Iguanodon. The first, in particular, the Ichthyosaurus, 

 (Fig. 159, ,) greatly abounded on the coast of the continents 

 of that period, and their skeletons are so well preserved, that 

 we are enabled to study even the minutest details of their 

 structure, which differs essentially from that of the Reptiles 

 of the present day. In some respects they form an inter- 

 mediate link between the Fishes and Mammals, and may be 

 considered as the prototypes of the Whales, having, like 

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