CRETACEOUS FORMATION. 



85 



er ages, there was a parity of conditions for animal life 

 over a vast tract of the earth's surface. To European 

 reptiles, the American formation adds a gigantic one, 

 styled the saurodon, from the lizard-like character of its 

 teeth. 



We have seen that footsteps of birds are considered to 

 have been discovered in America, in the new red sand- 

 stone. Some similar isolated phenomena occur in the 

 subsequent formations. Mr. Mantell discovered some 

 bones of birds, apparently waders, in the Wealden. The 

 immediate connexion of that set of birds with land, may 

 account, of course, for their containing a terrestrial or- 

 ganic relic, which the marine beds above and below did 

 not possess. In the slate of Glarus, in Switzerland, cor 

 sponding to the English gait, in the chalk formation, the 

 remains of a bird have been found. From a chalk bed 

 near Maidstone, have likewise been extracted some re- 

 mains of a bird, supposed to have been of the long- winged 

 swimmer family, and equal in size to the albatross. These, 

 it must be owned, are less strong traces of the birds than 

 we possess of the reptiles and other tribes ; but it must be 

 remembered, that the evidence of fossils as to the absence 

 of any class of animals from a certain period of the earth's 

 history, can never be considered as more than negative 

 Animals, of which we find no remains in a particular for- 

 mation, may, nevertheless, have lived at the time, and it 

 may only have been from unfavorable circumstances that 

 their remains have not been preserved for our inspection. 

 The single circumstance of their being little liable to be 

 carried down into seas, might be the cause of their non- 

 appearance in our quarries. There is at the same time a 

 limit to uncertainty on this point. We see, from what re- 

 mains have been found in the whole series, a clear pro- 

 gress throughout, from humble to superior types of being. 

 Hence we derive a light as to what animals may have ex- 

 isted at particular times, which is in some measure inde- 

 pendent of the specialties of fossilology. The birds are 

 below the mammalia in the animal scale ; and therefore 

 they may be supposed to have existed about the time of 

 the new red sandstone and oolite, although we find but 

 slight traces of them in those formations, and, it may h? 

 *aid, till a considerably later period. 



