§ 30. REVIEW OF THE AGE OF REPTILES. 583 



( Two genera of very small land animals (ante, 



AMMALIA . • . I p 51 q ^ 



{One species, indicated by a few mutilated bones 

 in the Wealden (ante, p. 440). 

 Many species, inferred from footprints on sand- 

 stone of the Triassic period (ante, p. 556) ?? 



Marine; — Ten genera, including above fifty-two 



Reptiles ) species. ; j _ . , m 



Terrestrial and Jo luviatile ; — Twenty-four genera, 



comprising between forty and fifty species. 



Flying; — One genus, containing sixteen species. 



Here, then, the classes Mammalia and Apes, which con- 

 stitute the essential features of the existing terrestrial faunas 

 of almost all countries, are represented through a period of 

 time of incalculable duration, by two diminutive qua- 

 drupeds, and by uncertain vestiges of one genus of birds, 

 and problematical foot-prints of bipeds on the rocks ; while 

 every where, bones, teeth, and entire skeletons of rep- 

 tilian forms, adapted for aerial, terrestrial, and aquatic 

 existence, afford unequivocal proofs that the air, the land, 

 and the waters, were tenanted by cold-blooded vertebrate 

 animals. In the succeeding tertiary ages, the fossil remains 

 of reptiles belong to species of existing types, and are asso- 

 ciated with those of mammiferous quadrupeds ; thus, in 

 the eocene strata of the Himalayahs, bones of living species 

 of gavials and tortoises are imbedded with the skeletons 

 of elephants, horses, and deer. 



Now, if we admit to the utmost extent, the effect of 

 causes that may be supposed to have operated to the exclu- 

 sion of the remains of mammalia from the secondary for- 

 mations, still the overwhelming preponderance of the reptile 

 tribes, both on the land and in the waters, is most striking. 

 And here we may inquire whether this remarkable pheno- 

 menon warrants the hypothesis which some eminent geolo- 

 gists have advanced, namely, that during the periods 



