Ch. XVI.] MIDDLE EOCEXE FORMATIONS OF FKAXCE. 



305 



Fiff. 269. 



Nerita conoidea, Lam. 

 Syn. JV Schmidelliana, Chemnitz. 



it accompanies the nummulitic formation from Europe to India, hav- 

 ing been found in Cutch, near the mouths of the Indus, associated 

 with Nummulites scabra. No less than 33 shells of this group are 

 said to be identical with shells of the London clay proper, yet, after 

 visiting Cuisse-Lamotte and other localities of the "Sables inferieurs" 

 of Archiac, I agree with Mr. Prestwich, that the latter are probably 

 newer than the London clay, and perhaps older than the Bracldesham 

 beds of England. The London clay seems to be unrepresented in the 

 Paris basin, unless partially so, by these sands.* One of the shells 

 of the sandy beds of the Soissonnais is adduced by M. Deshayes as 

 an example of the changes which certain species underwent in the 

 successive stages of their existence. It seems that different varieties 

 of the Cardium porulosum are characteristic of different formations. 



Ear. 270. 



Cardium porulosum. Paris and London basins. 



In the Soissonnais this shell acquires but a small volume, and has 

 many peculiarities, which disappear in the lowest beds of the calcaire 

 grossier. In these the shell attains its full size, with many distinctive 

 characters, which are again modified in the uppermost beds of the 

 calcaire grossier ; and these last modifications of form are preserved 

 throughout the " upper marine " (or Lower Miocene) series.f 



LOWER EOCEXE FORMATIOXS OF FRANCE. 



Argile plastique (C. 2, p. 298). — At the base of the tertiary system 

 in France are extensive deposits of sands, with occasional beds of clay 



* D'Archiac, Bulletin, torn. x. ; and Prestwick, Geol. Quart. Journ., 1847, p. 377. 

 \ Coquilles caracteristiques des Terrains, 1831. 

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