466 FOSSIL INVERTEBRATED ANIMALS. 



angular in consequence of their hardness, and of rounded 

 debris of calcareous substances^ which render it probable that 

 this sand also is a dependence of the stratum carried into the 

 basin by the torrent. It is very likely that this sand always 

 descends more and more, for fresh supplies of it may be drawn, 

 in those places where it appeared to have been exhausted. 



It is indubitable that when the water was above the elevation 

 of Montrouge that it covered a very considerable extent of 

 soil, both to the right and left of the course of the Seine, and 

 especially in the valleys where those streams and rivers flowed 

 which are received by the Seine. But the total absence of 

 any deposition of rolled fragments beyond the limit of Mont- 

 rouge seems a convincing proof that the torrent did not pass 

 that limit, and that the waters spread through the valleys 

 pretty nearly in a tranquil state. It is, doubtless, to those 

 tranquil waters, which deposited the most tenuous par- 

 ticles of the earths, and other bodies, carried down by the 

 torrent, and which they held in suspension, that are to be 

 attributed the considerable strata of argillaceous earth which 

 cover the environs of Sceaux, of Bagneux, of Arcueil, of 

 Chatenay, and probably of all the places where the tranquillity 

 of those waters permitted a similar deposition. 



Had the waters of the torrent been so elevated as to cover 

 all the heights in the neighbourhood of Paris, a current must 

 have been established above them, which would have trans- 

 ported the rolled flints beyond Montrouge, and even into the 

 valley of the river of Bievre, on that side. It would have 

 carried off the entire of the marine depositions of fine and 

 quartzose sand which cover the summits of the little hills of 

 the neighbourhood, and of which they are even sometimes 

 composed ; neither would it have permitted the deposition of 

 fine substances composing the argillaceous earth. We may 

 believe, however, that they were high enough to have formed, 

 in retiring, the ravines which are seen in those depositions of 

 sand. 



