1818.] the Strata of the Environs of Paris, 93 



4. Second fresh-water Formation. — This fonnation, to which, 

 for reasons before given, I associate the buhr-stones without 

 shells, forms the fourth series (etage). It covers almost all the 

 basin of Paris ; but throughout the parts where the lower forma- 

 tions are found, it is often interrupted, and is not sufficiently 

 powerful to give a character to the face of the country. It 

 becomes thicker as we proceed on the left bank of the Seine ; 

 and when once we pass the line from Chartres to Nemours, 

 where we have seen that the sand-stone without shells termi- 

 nates, this alone remains of all the Parisian formation, and 

 reposes immediately on the chalk, as we may perceive by exa- 

 mining it on the edges of the basin; for in the interior the 

 deposit of the fresh-water lime-stone is of such thickness that 

 we cannot see any other strata. This is certainly the most 

 considerable deposit of this nature that has yet been described. 

 It is also worthy of attention from the solidity of the stones it 

 furnishes, the variety of the siliceous matters it contains, and 

 the quantity of its fresh-water and land shells. 



The part of this formation near to the Loire, and generally all 

 that is to the south of Montargis, Neuville, 8cc. is covered by a 

 sandy deposit, which might, in some degree, be considered as a 

 fifth series connected (qui vient se confondre avec) with the sands 

 that cover the northern part of the Solagne. These sands are in 

 general composed of pretty large sized grains of white hyaline 

 quartz, accompanied with rounded fragments of the same quartz : 

 there are also found on the surface, at least in the neighbourhood 

 of the Loire, rolled pebbles of pale silex (silex blond). I shall 

 again notice this sandy deposit ; of which, however, I will not 

 venture to fix positively the geological situation. I shall content 

 myself with stating the different opinions that may be enter- 

 tained respecting it, after I have related some facts in the course 

 of this memoir which may assist in directing those opinions. 



The geographical Disposition of these Formations divides the 

 Paris Basin physically into different Regions. 



We see, by what has been stated, that the principal forma- 

 tions of the Paris basin, notwithstanding their successive super- 

 position, have in reality a geographical disposition which divides 

 the country into different regions, distinguished by their aspect 

 and agricultural productions. 



In the first place, we may have remarked that the lime-stone 

 with cerithia prevails in the part of the basin to the north of the 

 Mams and the Seine, and in a large band to the south of the 

 latter river between Versailles and Houdan. Considering this 

 country in respect to its physical and agricultural character, we 

 shall observe, that its face is uneven, being furrowed into many 

 large and small valleys. The soil is dry, and produces much 

 wine. 



The country between the Marne and the Seine, commonly 



