1822.] Geology of the Isle of Wight ^ S^c. 345 



remote from each other, may probably have extended over the 

 greater part of the Isle of Wight basin. 



The sihceous beds which in the neighbourhood of Paris are 

 often found between the calcaire grossier and the lower freshwater 

 formation, are strikingly analogous to the beds we have been 

 describing*. Whether the Bagshot sand which rests immediately 

 on the London clay can be referred to the same epoch may admit 

 of doubt, because the time of its deposition is not, I beheve, 

 limited by any known succession of newer beds. The proper 

 data for solving the question will probably be given in the next 

 volume of the Geological Transactions. 



VII. Horizontal Beds in the North of the Isle of 



Wight, 8cc. 



Since the publication of Mr. Webster's letters to Sir H. Engle- 

 field, it has been universally admitted that all the northern 

 region of the Isle of Wight is composed of nearly horizontal beds, 

 of later origin than any of those which have been enumerated. 

 As the separation of these beds into three distinct formations is 

 founded simply on zoological considerations, without any primary 

 reference to the nature of their component parts ; the propriety 

 of such a separation can only be established by a rigid determi- 

 nation of the fossil species contained in them. With the com- 

 pletion of this task Mr. Webster has been for some time 

 employed ; especially since the objection to his arrangement, 

 which appeared in the Annals of Philosophi/ for last September. 

 Every thing may be expected from the zeal and talents of one to 

 whom we are already so much indebted. Those facts, connected 

 with this subject, which have fallen under my own observation, 

 will be given without any details, except such as are absolutely 

 necessary to make them understood. The classification published 

 by Mr. Webster will be adopted without any reserve. 



1. Lower Freshwater Formation. During a visit to the Isle of 

 Wight, made by Mr. Henslow and myself in the year 1819, we 

 verified almost all Mr. Webster's observations on the portion of 

 this formation which extends from Headen Hill to Colwell Bay. 

 In the northern part of Totland Bay, we found alternating with 

 the indurated lower freshwater marl, several thin beds of clay, 

 one of which contained many specimens of a small shell we 

 considered a cerithium. Not only from its associates, but also 

 from its specific characters, w^e are now convinced that it is a 

 freshwater shell. According to the modern nomenclature, it 

 must, therefore, be called a potamides. In some of the upper 

 beds of the formation (more especially in Colwell Bay, near the 

 place where they descend to the beach and disappear) we found 

 undoubted proofs of the mixture of marine and freshwater species, 

 not only in the argillaceous marls, but in the masses of fresh- 

 water rock. A single specimen struck off from one of these 

 masses contains examples of the following genera : 



