464 FOSSIL JNVERTEBRATED ANIMALS. 



fied. It exhibits, however, in the plain of Grenelle, some sili- 

 ceous agglomerations, which are found at a tolerable depth. 

 Its thickness varies, and probably in proportion to the more or 

 less elevated situation of the stratum on which it reposes. It 

 commences on the road to Orleans, near the Grand Montrouge, 

 by some inches of thickness, and proceeds, increasing, to above 

 eighteen feet of depth, in the plain of Grenelle, near Vaugirard. 

 Afterwards, it extends, ascending towards the north of the 

 other side of the basin, as far as the forest of St. Germain. 



All that is observed from this forest, as far as Montrouge, 

 proves that the waters have filled this space ; and they could 

 not fill it without doing the same to very extensive distances, 

 to east and west in the basin, the lowest parts of which are oc- 

 cupied by the Seine. Neither can it be doubted that the same 

 is true of the basins of the Marne and Oise, since they are 

 caused by a similar stratum. 



It is extremely probable that these basins were formed when 

 they were filled with water by the event, whatever it was, which 

 deposited the stratum there, as it is equally probable that they 

 were more deep and extensive, since there is a stratum depo- 

 sited, the thickness of which, in some places, is more than 

 eighteen feet ; unless we may suppose that, in the commence- 

 ment of the irruption, the waters had carried off some portions 

 of the strata over which they had flowed, and that those were 

 replaced by the bodies, carried on by the torrent, when it dimi- 

 nished in intensity. This supposition assumes some degree of 

 probability, when we find that all these bodies are foreign to 

 the place in which they are deposited ; and that, near the bridge 

 of Sevres, are seen prodigious blocks of pudding-stones, of 

 nearly thirty-six cubic feet, and which have been torn from 

 strata indubitably very remote, since nothing similar is known 

 in the environs of Paris. Almost the whole of the bodies thus 

 deposited are either quartzose or siliceous ; the calcareous 

 fragments have been bruised. Some fossil shells and lime- 

 stones have been found there, dependent on the formation of 



