SUCCESSION OF CLASSES 409 



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 vertebras 

 are very numerous : the smallest Cetacean would be deemed 

 large amongst land-mammals ; the largest surpass in bulk any 

 creatures of winch 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 

 sea; and as cachalots, grampuses, dolphins, and porpoises are 

 seen gambolling in shoals in deep oceans, far from land, their 

 remains will form the most characteristic evidences of verte- 

 brate life in the strata now in course of formation at the 

 bottom of such oceans. Accordingly, it consists with the 

 known characteristics of the cetacean class to find the marine 

 deposits which fell from seas tenanted, as now, with vertebrates 

 of that high grade, containing the fossil evidences of the order 

 in vast abundance. 



The red crag of Suffolk and Essex contains petrified frag- 

 ments of the skeletons and teeth of various Cetacea, in such 

 quantities as to constitute a great part of that source of phos- 

 phate of lime for which the red crag is worked for the manu- 

 facture of artificial manure. The scanty and dubious evidence 

 of Cetacea in secondary beds seems to indicate a similar period 

 for their beginning as for the soft-scaled cycloid and ctenoid 

 fishes which have superseded the ganoid orders of mesozoic 

 times. 



We cannot doubt but that had the genera Ichthyosaurus, 

 Pliosaurus, or Plesiosauriis, been represented by species in the 



