269 



and from the marshes adjoining the sea ; and that it is 

 therefore necessary that the genera already formed should 

 be so subdivided, that genera should be established for the 

 complete separation of sea, river, and land shells ; a labour 

 in which he said M. Lamarck was already engaged. 



The editor of the Journal de Physique for 1811 ob- 

 served, " Les Naturalistes des autres Contrees, et particu- 

 lierement la Societe Geologique de Londres, ne manqueront 

 pas de faire des recherches analogues." The supposition of 

 M. de la Metherie was soon verified by the interesting dis- 

 coveries of similar formations in the Isle of Wight, by the 

 highly judicious and zealous exertions of Mr. Webster, who 

 not only pointed out a basin, probably of some ancient lake, 

 formed in a depression in the chalk stratum, corresponding 

 with that of Paris ; but also showed that a very close agree- 

 ment existed between the respective beds of the two basins, 

 and that the beds in the Isle of Wight basin were lying 

 above the London clay. He ascertained that the beds of 

 shells of the several formations are to be found distinctly 

 separate, but, as might be expected, sometimes mingled. 

 He also pointed out the great basin of the London clay, and 

 noticed the mixture of fresh-water shells with sea shells, 

 which it contains ; observing on lymnecB^ melani(E, and other 

 fresh-water shells, being found in the Sheppey clay, " These 

 shells (he says), which are however very few in number, 

 do not prove the existence of fresh-water formations in 

 this place similar to those in the basins of Paris and of the 

 Isle of Wight. Being found among the remains of vege- 

 tables and marine animals, we may suppose that they were 

 carried down together with the branches of trees and fruits, 

 by the numerous streams and rivers that must have flowed 

 into this gulph." * 



* Geological Transactions, Vol. \\.\ 

 t In a paper, read at the meeting of the Geological Society, on 

 Nov. 2, 1821, it appears, that Mr. Webster having recently exa- 



