354 SPECIAL GEOLOGY. 



6. Finally, owing to their position at the surface, and 

 having undergone less pressure than the rocks beneath, they 

 constitute a vast depository of fossil shells, which are pre- 

 served in such number and perfection, as to form a scale 

 by which the relative ages of these formations may be deter- 

 mined. 



M. Deshayes, whose work on the fossil shells of the Paris 

 beds will long remain a monument of his profound know- 

 ledge of conchology, divided the European tertiary strata into 

 three groups, founded upon the proportion of existing species 

 which they contain. The following table exhibits the groups, 

 the per-centage of the recent species, and the localities where 

 they are developed : 



STAGES. LOCALITIES. 



Upper Group, J" Sicily ; the stib-apennine beds ; Perpignan, Morea, and the 

 49 per cent. \ Norfolk crag. 



("Faluns of Touraine ; Dax ; Bordeaux; Suffolk Crag; 



Middle Group, I Turin ; Baden; Vienna; Angers; Rouca. The Viennese 



18 per cent. | and Baden fossils are typical of those of Moravia, 



^ Hungary, Cracovia, Volhynia, Podolia, and Transylvania. 



.. p f Paris; London ; Hants ; Isle of Wight, Valognes; Belgium. 



l,owe -oup, I The fogs . l8 of Cagtel Gomberto and pjmliac are near]y 



1 [ the same as the Parisian series. 



By independent investigations on the tertiary strata of 

 Europe, Sir C. Lyell* grouped the beds into four divisions, 

 founded on the proportion of existing species they seve- 

 rally contained. The result of our distinguished country- 

 man's labours confirmed those of M. Deshayes. 



In certain deposits he found that out of a hundred shells 

 there were no more than three which were identical with 

 living forms ; in other beds the proportion increased to 

 seventeen ; while, in others, the numbers varied from about 

 thirty-five to upwards of ninety per cent. Inferring, there- 

 fore, that the relative age of these deposits might be deter* 

 mined by the number of existing shells they respectively 

 contained, he assigned the three per cent, beds to the oldest 

 term, calling them eocene, from fas, aurora, and KCUI/OP, recens, 

 indicating the dawn of the new or recent period ; the seven- 

 teen per cent, to the miocene, or middle, from nfiwv, minor, 

 and Kaivos, recens, signifying that these beds contained a 



* Principles of Geology, 2nd Edition. 



