268 



and fragments of minute planorbes among decidedly marine 

 shells, and supplies a list of forty-eight river and land shells 

 found by Lamarck among the fossil sea shells of Grignon. 



But this mixture of these supposed land and fresh-water 

 with sea shells, is not confined, according to M. Brard, to 

 the lately discovered formations of the environs of Paris ; 

 since he has ascertained that they are found together in 

 several other parts of France, at a considerable distance 

 from Paris. Buxweiller, Mayence, Caen, Francfort, Or- 

 leans, Gergovia, the Brecciae of Nice, the volcanico-marine 

 valley, as it is called by St. Fond, of Ronca, and the island 

 of Sheppey, are among those places in which he states them 

 to have been found. Whilst speaking of the Brecciae of 

 Nice, he reprehends Cuvier for having entirely omitted to 

 mention the sea shells which are found there, although he 

 particularized the land shells, and this, after Faujas St. 

 Fond had stated his having found there turbinites and ser- 

 pulce, both marine shells. 



The shells of the valley of Ronca, as noticed by the Abbe 

 Fortis, are very interesting, they being mostly filled with 

 very minute shells. Their substance, too, is changed into 

 lamellar carbonate of lime ; and they are found to have ac- 

 quired a considerable increase of thickness. From this 

 frequent discovery of sea, river, and land shells thus mixed, 

 M. Brard hopes that the opinion of their all having lived 

 originally in a similar fluid is confirmed. 



M. Brongniart, anxious to support the position, that the 

 shells in the fresh-water and accompanying formations were 

 separately deposited by the alternation of fresh and sea 

 water, experienced, however, a considerable difficulty from 

 Lamarck having already admitted that, among the accumu- 

 lation of fossil sea shells in the environs of Paris, there were 

 nearly fifty species which w r ere referrible to land or fresh- 

 water shells. To meet this, we have seen that he admits 

 that these may have been derived from the mouths of rivers, 



