448 PALEONTOLOGY. 



tilian class ; in the other, of the warm-blooded mammalian 

 class. The Enaliosauria, Cetiosauria, and Crocodilia, played 

 the same part and fulfilled similar offices in the seas from 

 which the lias and oolites were precipitated, as the Belphinidce 

 and Bcdcenidce did in the tertiary, and still do in the present 

 ocean. The unbiassed conclusion from both negative and 

 positive evidence in this matter is, that the Cetacea succeeded 

 and superseded the Enaliosauria. To the mind that will not 

 accept such conclusion, the stratified oolitic rocks must cease 

 to be trustworthy records of the condition of life on the earth 

 at that period. 



So far, however, as any general conclusion can be deduced 

 from the large sum of evidence above referred to, and con- 

 trasted, it is against the doctrine of the Uniformitarian. 

 Organic remains, traced from their earliest known graves, are 

 succeeded, one series by another, to the present period, and 

 never re-appear when once lost sight of in the ascending 

 search. As well might we expect a living Ichthyosaur in the 

 Pacific, as a fossil whale in the Lias : the rule governs as 

 strongly in the retrospect as the prospect. And not only as 

 respects the Vertebrata, but the sum of the animal species at 

 each successive geological period has been distinct and pecu- 

 liar to such period. 



Not that the extinction of such forms or species was sudden 

 or simultaneous : the evidences so interpreted have been but 

 local : over the wider field of life at any given epoch, the 

 change has been gradual ; and, as it would seem, obedient to 

 some general, continuously operative, but as yet dimly dis- 

 cerned law. In regard to animal life, and its assigned work 

 on this planet, there has, however, plainly been " an ascent 

 and progress in the main." 



Although the mammalia, in regard to the plenary develop- 

 ment of the characteristic orders, belong to the Tertiary division 

 of geological time, just as " Echini are most common in the 



