740 GEOLOGY. 



below it ; and that large European tracts were the sites of lakes, rivalling in size those 

 of the American continent, into which rivers disembogued. Supposing the Niagara 

 Falls to be removed to Lake Erie, by the gradual gnawing away of the rock by the river, 

 the waters of the lake being consequently drained off, a vast plain would be opened to 

 examination, consisting of a base of ancient limestone covered with fresh-water formations. 

 The latter are now slowly accumulating from the sediment brought into the lake by 

 its feeders, or being more rapidly created as the effect of the streams occasionally rushing 

 into it in flood, and in these strata organic remains are deposited of the existing tenants 

 of the lake, of animals also and vegetables peculiar to the land, which are drifted into it. 

 The case imagined is precisely parallel to that of some of the fresh-water tertiaries, whose 

 fossil contents proclaim their fluviatile or lacustrine origin. The organisms of the entire 

 system constitute an immense assemblage, generally characterised by being widely 

 different from those of the secondary rocks, and exhibiting a marked analogy to the 

 existing forms of life. They consist of plants, a few marine, but others terrestrial, pre- 

 senting the true dicotyledonous structure ; molluscs in great abundance, many belonging 

 to living species ; fishes, mostly of extinct species, though some are referable to genera 

 common in tropical regions ; reptiles, among which are the remains of genuine crocodiles, 

 with prototypes of the frog tribe ; and mammalia, of which between fifty and sixty 

 species have been determined, of various orders, but chiefly belonging to the pachydermata 

 or thick-skinned division of the animal kingdom, having their nearest representative 

 in the existing tapir. M. Deshayes gives the following results respecting living and 

 tertiary molluscs : 



Number of living species examined - - ^ - 4780 



of fossil species in tertiary strata alone - 3036 - 'v - total 7816 



Of these there were found both living and fossil - - .,-* - - . 426 



Leaving for the total number of species examined - - - 1 . 7390 



The ratio of the species which are both living and fossil to the whole number is 5-7 to 100 0. 

 The 4780 living species consisted of univalves - 3616 ^ f75-6 



bivalves - - u 64 j or per cent, j^ 



The 3036 tertiary species consisted of univalves ... 20981 f60'l 



- bivalves- - 938 J r P ercent - \39-9 



Proceeding upon the warrantable assumption that the tertiary beds which contain the 

 greatest proportion of living species are the most recent, M. Deshayes thus classifies the 

 system : 



{Localities. Sicily; the Italian sub-apennine beds, with whose fossils 

 those of the Morea and Perpignan in the south of France agree ; the 

 crag of Norfolk and Suffolk. 

 General proportion of living species, 49 per cent. 



- Bourdeaux ; Dax ; Turin ; Touraine ; Baden ; Vienna ; Angers ; Rouen. 

 Middle group. The fossils of Baden a d Vienna are a general type for those of Moravia, 



Hungary, Cracovia, Volhynia, Podolia, and Transylvania. 

 . General proportion of living species, 18 per cent. 



" Paris ; London ; Hampshire ; Valognes ; Belgium. The fossils of Castel- 

 Lower group. gomberto and Pauliac are the same nearly as those of the Paris basin. 



. General proportion of living species, 3 per cent. 



Mr. Lyell, adopting the same principle of classification, proposes a division of the 

 system similar to the above, except that he gives an independent rank to the Sicilian 

 deposits, separates them from the upper group of M. Deshayes,and thus makes four terms 

 of the whole mass of tertiary strata, employing a Greek nomenclature to distinguish them. 

 Newer Pliocene. Sicilian deposits, with 95 per cent, of recent species. 

 Elder Pliocene. Italian and crag deposits, with 41 per cent, of recent species. 



