94 Mr. Webster on a Fresh-water Formation in Hordwell Cliff, ^c. 



had perceived, in connexion with the lower fresh-water formation, some alter- 

 nations of beds containing marine and fresh-water shells, and in some places 

 even mixtures of these. These mixtures are to be seen at Cowes; and at 

 Hordwell I met with one specimen of a Cerithium : but the examination of 

 this cliff, which is of great height and of difficult access, will no doubt afford 

 traces of the passage to the upper marine formation. The imperfect lignite 

 of Hordwell resembles that of Headen ; and the Melania of Hordwell is to be 

 met with in abundance in Thorness Bay, Isle of Wight. But it would be 

 tedious to enumerate all the circumstances of resemblance that strike the ob- 

 server, and which on the spot produce a conviction of the identity of this bed 

 at the two places, very difficult to convey to others. The strongest argument, 

 however, is derived from the subjacent strata : since in the Isle of Wight, a 

 bed of white sand rests upon the London clay ; and over this sand is the lower 

 fresh-water formation ; \vith the intervention, in some places, of a bed in 

 which a mixture of marine and fresh-water shells is to be found. 



The agreement of this series with that just described at Barton and Hord- 

 well Cliffs furnishes a strong confirmation of the opinion I formerly advanced, 

 with respect to the extent of what I have called the Isle of Wight Basin. 

 And from the great thickness of this fresh-water formation in HordwellCliff, 

 it cannot be doubted that it extends to a considerable distance inland ; but 

 how far I have yet had no opportunity of determining*. 



* Since the preceding paper was read, Charles Lyell jun. Esq. has beeu so obliging as to 

 transmit to me a specimen of shell marl, obtained from pits at a hill called Acres Down, and which 

 is used for manure in the neighbourhood of Lyndhurst; from which it is evident, that the upper 

 marine formation may be traced thus far : this marl consisting entirely of fragments of the same 

 shells as are found in such numbers in that formation in the Isle of Wight. 



