r)f the Environs of Paris, 49 



But what characterizes more particularly this last system 

 of" strata of calcareous tbrmation, is the absence of every 

 shell and of every other fossil. 



It results froin the observations which we have related: 



1st, That the fossils of coarse limestone have been de- 

 posited slowly and in a calm sea, since these fossils are 

 deposited by regular and distinct strata; that they are not 

 indiscriniinatcly mixed, and that most of them are in a 

 Slate of perfect preservation, however delicate may be their 

 texture; the points of the prickly shells being very often, 

 unbroken. 



sdly, That these fossils are entirely diiTerent from those of 

 the chalk. 



Sdly, That in proportion as the strata of this 'formation 

 were deposited the number of the species of shells dimi- 

 nished until no more are found. The waters which formed 

 these strata either have not contained any, or have lost xh^ 

 property of preserving tb.em. 



There can be no doubt that things went on very differently 

 in these seas from what they do at present in the waters of 

 the j>resent day ; where no strata are formed, the species of 

 shells found in them are always the same in the same regions; 

 we do not find, for example, since we began to fish for 

 oysters on the shores of Concale, that this kind of shell-fish 

 has been replaced by other kinds. 



Art. IV. Gypsous Formation, 



The soil which we are now about to describe, is one of 

 the clearest examples of what is meant by the word forma- 

 tion. Here wc find strata very different from each other 

 ia their chemical nature, but evidently formed together. 



The soil which ^we call gypsous is not composed of gyp- 

 sum alone, it consists of alternate strata of gypsum ai?d of 

 argillaceous and calcareous marie. These strata have pursued 

 an order of superposition, which has been always the saiiie, 

 in the great gypsous girdle which we have studied, and 

 which extends from Meaux to Triel and Grisy. Some 

 strata are wanting in certain districts ; but those which re- 

 main are always in the same respective position. 



The gypsum is placed immediately above the limestone, 

 and it is impossible to doubt this superposition. The posi- 

 tion of the gypsum^quarrics of Clamart, Meudon, and Ville- 

 d'Avray, is above coarse limestone wrought in the same 

 places ; that of the quarries of the mountain of Triel, the 

 superposition of which is still more evident; lastly, a well 



Vol. 35. No. 14U*^/i. 1810, P dqg 



