REVOLUTIONS. 97 



point of view, an approximation to the truth. In the beds 

 of the transition class, (the oldest rocks which are known to 

 contain petrifactions), the remains both of radiate and mol- 

 luscous animals occur ; yet the organization of the latter is 

 considered more perfect than that of the former. In the 

 transition class, however, no remains of vertebrose animals 

 have been detected. In the independent coal-formation, (one 

 of the oldest groups of the flcetz class,) in addition to the re- 

 lics of radiate and molluscous animals, those of several an- 

 nulose animals occur, as species of the genera Trilobites, 

 Dentalium and Spirorbis ; together with fishes, both osseous 

 and cartilaginous. In the newer groups of the floetz series, 

 relics of amphibia make their appearance, and in the newest 

 groups those of birds and quadrupeds. In the oldest al* 

 luvial deposits are found the bones of extinct quadrupeds ; 

 in the newer beds, those of such as still survive. From the 

 period, therefore, at which petrifactions appear in the old- 

 est rocks, to the newest formed strata, the remains of the 

 more perfect animals increase in number and variety ; and 

 it is equally certain, that the newest formed petrifactions 

 bear a nearer resemblance to the existing races, than those 

 which occur in the ancient strata. The older remains are 

 much altered in their texture, and more or less incor- 

 porated with the matter of the rock, while the newer 

 are but little altered. These circumstances lead us to be- 

 lieve, that the strata containing petrifactions were once in a 

 state of mud ; and that the same process which altered the 

 imbedded relics, communicated to the surrounding matter 

 its present compact or crystalline structure. 



These facts, in the history of animals, which have been 

 ascertained by the researches of the geologist, lead the in- 

 quisitive mind to investigate those circumstances which have 

 operated in bringing about such mighty revolutions. In 

 conducting the inquiry, it is necessary to impose restraint up- 

 on the imagination, and deliberately to examine the existing: 



VOL. ir. 



