PALAEONTOLOGY I FOSSIL ORGANIC REMAINS. 



tant relations have been discovered between families and 

 species (the latter always few in number) which have dis- 

 appeared, and those which are still living. All observations 

 concur in shewing, that the fossil faunas and floras differ 

 from the present animal and vegetable forms the more widely, 

 in proportion as the sedimentary beds to which they belong 

 are lower or more ancient. Thus great variations have suc- 

 cessively taken place in the general types of organic life ; 

 and these grand phsenomena, which were first pointed out by 

 Cuvier, ( 306 ) offer numerical relations, which Deshayes and 

 Lyell have made the object of important researches, by which 

 they have been conducted to decisive results, especially as re- 

 gards the numerous and well observed fossils of the different 

 groups of the tertiary formation. Agassiz, who has exa- 

 mined 1700 species of fossil fishes, and who estimates at 

 8000 the number of living species which have been de- 

 scribed or which are preserved in our collections, affirms in 

 his great work, that, with the exception of one small fossil 

 fish peculiar to the argillaceous geods of Greenland, lie 

 Las never met in the transition, secondary, or tertiary strata, 

 with any animal of this class specifically identical with any 

 living fish ; and he adds the important remark, that even 

 in the lower tertiary formations, a third of the fossil fishes 

 of the calcaire grossier, and of the London clay, belong to 

 extinct families. Below the chalk we no longer find a single 

 genus of the present period ; and the singular family of the 

 i3auroid fishes (fishes with enamelled scales, almost approach- 

 ing reptiles in some of their characters, and extending up 

 wards from the carboniferous rocks, where the larger species 

 among them are found, to the chalk, where only a few indi- 

 viduals are met with), presents relations with two species 

 which now inhabit the Nile and some of the American rivers 



