Mr. Webster on the Strata lying over the Chalk, 169 



with the vertical beds without suffering any considerable change in 

 their dip, it should seem that they have been deposited on the sides 

 of this basin subsequently to the disturbance of the strata already 

 spoken of. 



The above conclusions are confirmed by other circumstances. 



These horizontal beds have no agreement with any of those 

 beneath the chalk, nor indeed with any others yet observed in Great 

 Britain ; their mineralogical characters, and their fossils, are peculiar 

 and distinctive. The calcareous beds contain numerous petrefactions 

 of freshwater shells, and in others are found marine fossils agreeing 

 with those described by Lamarck in the strata of the Paris basin. 

 But fortunately, the inspection of specimens from the basin of Paris 

 enabled me no longer to depend upon conjecture only as to the 

 similarity of these formations. They had been given by M. Brong- 

 niart himself, in illustration of his memoir, to the Count de Bournon, 

 who had deposited them in the museum of the Geological Society. 

 The agreement of the strata of the two basins, not only with re- 

 spect to the external characters of the calca'ire d'eau douce^ but also 

 to its fossils, was thus rendered evident : and these specimens, so 

 well authenticated, added one more proof (if more could be want- 

 ing) of the utility of such collections, and of the advantages to be 

 derived from a liberal communication between men of science. 



It is unnecessary to inform the Society that this circumstance 

 produced another visit to the Isle of Wight and its vicinity, for the 

 purpose of examining more particularly its basin, and the remains 

 of its antient lake. From this, compared with my former survey, I 

 was enabled to add to the British strata the following, of later for- 

 mation than the London clay. 



1. A calcareous stratum, containing only freshwater shells. 



2. Greenish marl, with marine shells. 

 Vol. II. Y 



