148 PETRIFACTIONS AND THEIR TEACHINGS. CHAP. III. 



During the incalculable ages which the deposition of the 

 various systems of sedimentary strata must have comprised, 

 we find no evidence in the fossils hitherto observed, of the 

 existence of Birds and Mammalia as the characteristic types 

 of the faunas of the dry land. On the contrary, throughout 

 the immense accumulations of the spoils of the ancient islands 

 and continents, amidst innumerable relics of reptiles of various 

 orders and genera, portions of six or seven lower jaws, and a 

 few bones, of two genera of extremely small terrestrial quad- 

 rupeds, and the bones of a species of wading bird, are the 

 only indications of the presence of the two grand classes, Mam- 

 malia and Aves, which constitute the chief features of the 

 terrestrial zoology of almost all countries. 



The earliest indications of air-breathing vertebrata in the 

 ancient secondary formations, are the supposed footprints of a 

 chelonian reptile on the Potsdam limestone (Lower Silurian) of 

 North America, 1 and the bones of small* saurian reptiles in 

 the Carboniferous strata ; a few vestiges occur in the suc- 

 ceeding group, the Permian. In the next epoch, the Tr lassie, 

 colossal Batrachians (Labyrinthodons) appear ; and on some of 

 the strata of this formation are the footmarks of numerous 

 bipeds, presumed to be those of birds, which have already 

 engaged our attention ; but at present the evidence required 

 to establish the hypothesis is incomplete, for no bones of the 

 animals that made those imprints have been discovered. 



In the succeeding eras, the Liassic, Oolitic, Wealden, and 

 Cretaceous, swarms of reptiles of numerous genera and species 

 everywhere prevail ; reptiles fitted to fly through the air, to 

 roam over the land, to inhabit the lakes, rivers, and seas ; and 

 yet not one identical with any existing forms ! These beings 

 gradually decline in numbers and species as we approach the 

 close of the Secondary periods, and are immediately succeeded, 

 in the Tertiary epochs, by as great a preponderance of warm- 

 blooded vertebrata Birds and Mammalia as exists at the 

 present time, and an equal decadence in the Class of Reptiles. 

 With the Cretaceous Formation the " Age of Reptiles " may 

 therefore be said to terminate. 



1 A discovery recently made by Mr. Logan is supposed to establish 

 this fact. Casts of these very equivocal imprints may be seen in the 

 highly instructive and beautifully arranged Museum of Practical 

 Geology, in Jermyn Street, London. 



