INTRODUCTION. 39 



had already led, that it is not land animals only 

 which have undergone a change during the revolu- 

 tions of the globe ; hut that the inhabitants of the 

 ocean likewise, have not withstood their effects ; 

 and that when the sea formed on our continents 

 those prodigious deposits filled with shells which 

 are now almost unknown, the great mammalia which 

 it nourished were not those which people it at 

 present ; and that in spite of the strength which the 

 immensity of their size apparently conferred upon 

 them, they had no more power to resist the catas- 

 trophies which disturbed their element, than had 

 the elephant, the rhinoceroses, the hippopotami, &c. 

 to withstand those upon land; and that in the 

 absence of the arts of man, which, of course, could 

 not be brought to bear against them, their races 

 must have been exterminated by the general revo- 

 lutions of nature alone/' (Oss. Foss. v. 398.) Many 

 of the fossile varieties will be incorporated into our 

 Survey, each being introduced in connexion with 

 those genera and species with which it stands most 

 nearly allied. 



We must not conceal from our readers that the 

 ascertainment and description of the existing Ce- 

 tacea is a work of great difficulty and uncertainty. 

 " It is," says Cuvier, " concerning large animals that 

 the greatest errors and confusion exists ; and for this 

 reason, that we can know and distinguish only those 

 species which we can examine under our eye and 

 carefully compare with each other ; and this remark 

 applies especially to the great Cetacea. They as- 



