NEGATIVE EVIDENCE. 447 



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 verte- 

 brates 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 fishes which have superseded the ganoid orders of mesozoic 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 Plesioscmrus, been represented by species in the 

 same ocean that was tempested by the Balaenodons, and Dio- 

 plodons of the miocene age, the bones and teeth of those 

 marine reptiles would have testified to their existence as 

 abundantly as they do at a previous epoch in the earth's 

 history. But no fossil relic of an enaliosaur has been found 

 in tertiary strata, and no living enaliosaur has been detected in 

 the present seas : and they are consequently held to be extinct. 



In like manner does such negative evidence testify to the 

 non-existence of marine mammals in the liassic and oolitic 

 times. In the marine deposits of those secondary or mesozoic 

 epochs, the evidence of vertebrates governing the ocean, and 

 preying on inferior marine species, is as abundant as that of 

 their air-breathing successors in marine tertiary strata ; but 

 in the one the fossils are exclusively of the cold-blooded rep- 



