the Environs of Paris. S3 



Glen, and forms well defined elevations on both banks of 

 the Loire, enclosing the small tongue of freshwater lime- 

 stone along this river from Gien to Cosne ; so that the Pari- 

 sian formations which so long predominate over the chalk, 

 which afterwards confound themselves with it under the 

 same level, terminate in the end in a valley lower than the 

 chalk hills that surround it. 



If, setting out from this SE. extremity, we resume the 

 continuation of the limits of the Paris basin, we shall see 

 that they are not better defined along the canal of Briare 

 than in the vicinity of the Loire, but they can afterwards be 

 distinguished on the north of Montargis, and especially in 

 the environs of Nemours, where the sandstones without 

 shells appear. 



Such is the extent of the Paris basin considered as a whole ; 

 for the different formations of which it is composed send off 

 ramifications of greater or less extent, beyond the limits I 

 have mentioned. The freshwater formation especially ex- 

 tends to considerable distances. I have already had occasion 

 to .remark, that it extends along the banks of the Loire and 

 the Allier, and over the platforms of Berry.* It is known 

 to form a new and very extensive basin in the Limagne d'Au- 

 vergne. It is found, but in small quantity, towards Tours 

 and Mans. 



The second marine formation also constitutes some isolated 

 patches beyond the limits of the basin ; at least I conceive 

 that I can refer to this formation, the deposit of white sand.< 

 stones occurring in the plains of Picardy, and as far as the 

 departments of the North, and Jemappe, as also those exist-? 

 ing in the chalk country between the Seine and the Loing. 



Plastic clay, under the form of black pyritous earth, is 

 also found in detached patches upon the chalk on the north 

 of the Seine ; and it appears that there are other argillaceous 

 deposits far distant from the Paris basin, which, though 

 resting upon older rocks, may still belong to this formation. 



The true calcaire a cerites appears, on the contrary, cir^ 



■* Journal des Mines, tome 32. p, 43, 



