44G PALEONTOLOGY. 



It has been, however, objected that negative evidence can- 

 not satisfactorily establish the proposition that the mammalian 

 class is of late introduction, nor prevent the conjecture that it 

 may have been as richly represented in primary and more 

 ancient secondary as in tertiary times, could we but get re- 

 mains of the terrestrial fauna of their successive continents .* 

 To this objection it may be replied : in the palaeozoic strata, 

 which, from their extent and depth, indicate, in the earth's ex- 

 istence as a seat of organic life, a period as prolonged as that 

 which has followed their deposition, no trace of mammals has 

 been observed. Were mammals peculiar to dry land, such 

 negative evidence would weigh less in producing conviction of 

 their non-existence during the Silurian and Devonian aeons, 

 because the explored parts of such strata have been deposited 

 from an ocean, and the chance of finding a terrestrial and air- 

 breathing creature's remains in oceanic deposits is very remote. 

 But in the present state of the warm-blooded, air-breathing, 

 viviparous class, no genera and species are represented by 

 such numerous and widely-dispersed individuals, as those of 

 the order Cetacea, which, under the guise of fishes, dwell, and 

 can only live, in the ocean. 



In all Cetacea the skeleton is well ossified, and the vertebrae 

 are very numerous : the smallest Cetacean would be deemed 

 large amongst land-mammals ; the largest surpasses in bulk 

 any creatures of which we have yet gained cognizance : the 

 hugest ichthyosaur, iguanodon, megalosaur, mammoth, or 

 megathere, is a dwarf in comparison with the modern whale 

 of a hundred feet in length. 



During the period in which we have proof that Cetacea 

 have existed, the evidence in the shape of bones and teeth, 

 which latter enduring characteristics in most of the species 

 are peculiar for their great number in the same individual, 

 must have been abundantly deposited at the bottom of the 



* Lyell, "Anniversary Address," Geol. Soc, 1851, pp. 51-57. 



