106 M. B. de Basterot's Obse7vations on Fossil Shells. 



they do, the forms of our domestic animals and cultivated 

 plants ; would not the differences of bottom, depth, tempera- 

 ture and agitation of the waters in which they live, vary the 

 mhabitants of the sea ? 



It may not, perhaps, be useless to state an opinion here, 

 which an examination of many shells contained in the more 

 ancient beds has enabled me to entertain : I have observed an 

 uniformity in their exterior characters not found among those 

 from the more recent rocks, an uniformity which becomes the 

 more striking, as the total number of species diminishes ; in 

 other words, that identical species are the more generally spread 

 in direct proportioii to the antiquity of the rock containing 

 them*. 



In fact, the transition limestone of England, France, and 

 North America, presents us with the same species of Trilo- 

 bite. Impressions, very remarkable for their forms and as- 

 sociation, are found with the same characters in the transi- 

 tion slates of Wales, Northumberland, Finisterre, the Co- 

 tentin, the Ardennes, the Hunsdruck, the Hartz, the county 

 of la Mark (Colombia), New York (Pennsylvania), and the en- 

 virons of lake Oneida, in North America. I should not, how- 

 ever, omit noticing that an attentive examination of fossils from 

 the carboniferous or mountain limestone, in places distant 

 from each other, has not presented me so perfect a resem- 

 blance ; yet identical species are still found in Ireland, En- 

 gland, the Pays-Bas, France, and Norway. The species should, 

 however, be more varied in this than in a more ancient rock, 

 even according to the rule I have proposed. 



The catalogue which I have formed of the fossil shells of the 

 environs of Bordeaux, is not, doubtless, perfectly complete; 

 it is however sufficiently so, to give rise to some remarkable 

 approximations in ancient zoology. 



It is there seen, that, notwithstanding the loose nature of the 

 beds in these environs, notwithstanding the resemblance they 

 still bear to a coast recently abandoned by the waters, — the 

 Bordelais soil owes its origin to an order of things anterior to 

 the last revolution of our planet. The action of our present 

 seas accumulates sand-hills on one side of this basin, which 

 advance slowly into the interior. These are, however, much 

 circumscribed, antl possess no analogy with the great sandy 

 deposit of the Landes. In fact, the catalogue here presented, 

 shows, that out of three hundred and thirty species of shells, 

 found fossil in the latter sands, forty-five only are analogous 



* This is not exactly a new opinion : every additional confirmation of it 

 is, however, valuable. — Trans. 



to 



