as items of Geological Time. 



343 



The connexion of this question with the principal subject of this 

 paper, that of the comparative value of different geological eras as items of 

 geological time, is obvious. I feel that this subject is one of great 

 difficulty ; and, as far as I know, this is the first time that any attempt 

 of the kind has been made to solve the problem. If my method be incor- 

 rect, it may yet help to suggest a better way to some one else ; and in the 

 meanwhile, even if partly heterodox, I hope it may deserve toleration. 



Classification of Faunas (Terrestrial, Freshwater, and Estuarine) 

 into Groups. 



Formations. 



Class. 



Order. 



Number of Genera. 



Old Eed Sandstone 

 /'Carboniferous . 



I Permian 



ian < 



2 Trias 



Jurassic .... 



Weald and 

 Neocomian 



Upper 

 Cretaceous 



Eocene. 



-Miocene .. 



Amphibia.. 



Eeptilia ... 



Amphibia.. 

 Eeptilia .. 



Mammalia , 

 Reptilia ... 



Mammalia 

 Reptilia ... 



Mammalia 



Labyrinthodontia 



Lacertilia 



Labyrinthodontia 



Crocodilia 



Lacertilia 



Anomodontia ... 



Deinosauria 



M 

 Marsupialia 



Chelonia . . 

 Crocodilia 



Lacertilia . . 

 Deinosauria. , 



Pterosauria . . 

 Marsupialia 



Chelonia 



Crocodilia 



Deinosauria . . . 

 Pterosauria 



Crocodilia 



Pterosauria 



Lacertilia 



Chelonia 



Crocodilia .... 



Ophidia 



Pachydermata. 



No Vertebrata known except fish 



11 E. 

 3 C. 

 3 E. 

 1 C. 

 1 E. 



3 E. 

 1 E. 



4 E. 



3 C. 



1 E. 



2 E. 



1 C. 



2 E. 



4 E. 

 4 E. 



1 C. 

 4 E. 



2 E. 



1 C. 



2 E. 

 15 E. 



1 C. 



4 E. 



8 E. 



9 E. 

 1 E. 



3 E. 



1 E. 

 9 E. 



4 E. 



3 E. 



2 E. 

 11 E. 



Many more in France. 



No Vertebrata certain in Eng- 

 land, but a large Mammalian 

 fauna on the Continent, chiefly 

 of modern type. The Pliocene 

 and Post-Pliocene terrestrial 

 faunas are of course still more 

 modern. 



The letter E. means English, C. Continental and not known in England ; but as the 

 physical phenomena connected with the Continental strata in which they are found are, in 

 the main, identical with those that affect the English rocks, the European Continental 

 genera are named in this Table. 



