GENERAL RELATIONS OF FOSSIL FISHES. 73 



with the enamelled covering so often alluded to, and why these 

 races should have given place at a later period to others so differ- 

 ently constituted, we have no certain means of knowing. It has 

 been suggested by Dr. Buckland, that the purpose of this cuirass 

 may have been, to defend the bodies of the animals against waters 

 that were warmer, or subject to more sudden changes of tem- 

 perature than could be endured by animals, whose skin was pro- 

 tected only by such thin and often disconnected coverings, as the 

 membranous and horny scales of most modern Fishes. Such 

 changes of temperature were more frequent, there is good reason 

 to believe, in the earlier epochs of the Earth's history, than they 

 are at the present time, for reasons which will be elsewhere 

 explained. (See Treatise on GEOLOGY.) 



592. It may be further remarked, that the history of the 

 Fossil Fishes most clearly proves, that the first-created forms of 

 Animal life were not the least perfect, as some have maintained; 

 and that there is not a regular succession of new races, increasing 

 in elaborateness of structure, from the oldest to the most recent 

 formations. For among the earliest races of Fishes, we find that 

 those of the Sauroid family, which had many characters of eleva- 

 tion, held a conspicuous place ; and that, when these were 

 replaced by the class of Reptiles, which was called into existence 

 as soon as there was any land for its habitation, they ceased to 

 exist, and were succeeded by races of Fishes which must be 

 regarded as lower in the scale. 



