1818.] the Strata of the Environs of Paris. 89 



beds ; I have found only some detached fragments of white 

 lime-stone containing the casts of the inside of ' cyclostoma mumin, 

 which, from some indications, I imagine to belong to the lower 

 beds. Building stones containing great numbers of cerithhun 

 lapidum are also used in these cantons, principally in the neigh- 

 bourhood of Dormans. It is a whitish, fine-grained lime-stone, 

 rather porous, like the fresh-water (calcaire d'eau douce) lime- 

 stone, and appears to me to be obtained from some beds situated 

 between the true lime-stone containing cerithia, and that con- 

 taining the cyclostomse. As it resembles the latter much more 

 than the common marine lime-stone, I should be tempted to 

 think that it also was a fresh-water formation, and that those 

 two beds belong to the same set of beds as the clicart of Mantes- 

 la- Ville, described at p. 329 of the Mineralogical Geography of 

 the Environs of Paris.* 



The green marls are covered with another white lime-stone 

 a little less compact than the preceding, and having the tubular 

 cavities which are characteristic of certain parts of the fresh- 

 water formation. It contains a large quantity of shells, among 

 which are particularly distinguished two species of lymnaeae, and 

 a small bulimus. (B.pusil/us, Brong.) 



Lastly, the whole is surmounted with the buhr-stone (meu/ieres) 

 without shells, with the sands and clays which commonly accom- 

 pany them, and which cover all the elevated plains of the neigh- 

 bourhood. 



This order of superposition, interesting from the series of beds 

 it presents, is still more remarkable from the constancy and 

 uniformity of its occurrence throughout the country that extends 

 from Chateau-Thierry to near Rheims. 



I consider all the strata situated above the lime-stone con- 

 taining cerithia to belong to the fresh-water formation. This is 

 sufficiently evident with respect to the beds which contain lym- 

 naesR, and even for those of the lower white lime-stone, which are 

 easily recognised as agreeing with the lower part of the gypseous 

 formation near Paris ; but some explanation seems requisite in 

 respect to the green marls, and the burh-stones without shells. 



I think that I have shown f that the siliceous lime -stone 

 belonged to the same formation as that which contains the lyn:- 

 naeee and other fresh-water shells.! ^ n ' s opinion gives an addi- 



* Many geological circumstances, as welt as the zoological agreements, induce 

 me to suspect that the ecrilhium lapidum ought to he classed with the potauiidcs of 

 M. Brongniart, or cerithia of the fresh-water formations. This shell, which differ* 

 but little from the Putamides T.amarleii, seems to me to have this peculiarity, that 

 it is found in the later marine beds, and in the earliest beds of fresh-water for ma. 

 tion, and that it is the only fossil of the marine formation which exists in situ in 

 that of fresh-water. 



t Notice on the existence of a lime-stone of fresh-water formation in the depart- 

 ments of the Cher, &c. (Journal del Mines, vol. xxxiP p. 43.) 



{ Further observations which will be published in the second edition of the 

 Mineralogical Geography of the Knvirons of Paris, induce us to agree entirely 

 with this opinion of M. D'Halloy. We have now direct proof that the siliceous 



