FOSSIL INVERTEBRATED ANIMALS. 467 



From observations on the tract to the south of Fontenai- 

 aux-Roses^ we may believe that a great part of certain steep 

 and rugged hills have been carried away by waters, the 

 current of which was not above them. The bottom of the 

 valley is covered with a thick stratum of argillaceous earth. 

 Ascending these to the fountain of the mills, on each side of 

 the way, you may see the oyster bed, which follows the move- 

 ment of the stratum, and which was already in a state of in- 

 clination when those animals existed in this place. On pro- 

 ceeding to the summit of the hill, the quartzose sand is found 

 under the superficial soil, disposed in horizontal strata, which 

 could not have had this disposition if the valley had not been 

 filled with them, at least in part, when the deposition took 

 place. 



As to the disappearance of these sands, whose origin must 

 be attributed to the waters which covered those places when 

 the valley in which the Seine flows was filled, it may be like- 

 wise referred to the same waters which deposited the sands, 

 and which, on return, must have carried them away in 

 part. 



The deposition of tenuous substances, which compose the 

 argillaceous earth, appears to be one of the last in the neigh- 

 bourhood of Paris ; and it would seem that, from the period of 

 its deposition, this substance has not been in circumstances 

 favourable to crystallization ; at all events, it has not been 

 found in that state in any part of those environs. All its strata 

 seem to be owing to some torrent, whose waters, though 

 troubled, were turned aside, and became comparatively tran- 

 quil. It is yet to be desired, that, by ulterior observations on 

 the position of the strata of rolled flints found in so great a 

 number of places, we may ascertain if all the depositions of 

 argillaceous earth have been furnished by torrents which have 

 deposited rolled flints. 



The marine sandstone being found at the summit of all the 

 heights of the environs of Paris, we may be assured that the 



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