1825.] Mr. Webster's Heply to Dr. Fitton. 47 



in the isle of Purbeck with shells quite as large as those of Pet- 

 worth, and apparently of the same species. In my examination 

 of the Hastings beds, I remarked the resemblance of the casts of 

 the univalves to those of the Purbeck and Petvvorth marbles, and 

 that the fossil shells were altogether different from those of the 

 green sand. 



I always considered the weald clay as intimately connected 

 with the Hastings beds, and \^ith the Purbeck stone, from the ana- 

 logy in the fossils,* and from the resemblance between the Platten 

 in the Isle of Wight, the Battle beds, and the Purbeck beds, 

 although I could not then determine to what part of the series 

 each of these should be referred. This led me originally to class 

 the weald clay as a subordinate bed of the Hastings ferruginous 

 sand, which contains several other beds of clay, although that 

 of the weald is the most considerable : and this arrano-ernent I 

 still adhere to. In my first examination of the Isle of Wio-ht, 

 the fossils of Shanklin escaped me ; and I owe my knov.'ledo-e of 

 them to Prof. Sedgewick's valuable paper on that island in the 

 Annals for May, 1822. Since that time I have perceived the 

 necessity for separating the upper from the lower ferruginous 

 sands. 



I agree v/ith Dr. Fitton, therefore, in the propriety of making 

 the separation between the two sands at the top of the weald 

 clay ; but I think I see zoological reasons why the latter ouoht 

 not to be called a distinct formation, but that it should be 

 formed into a group Vv'ith the Hastings and the Purbeck beds, 

 1 do not go so far however as to consider these as freshwater 

 formations, a term which I am accustomed to restrict to such beds 

 only as have been probably formed in freshwater lakes. 



I come now to consider the changes which Dr. Fitton has 

 proposed to make in the names of the beds which have been 

 treated of. 



With respect to the proposal to change the name of the rock 

 of the Underchtf from green sand to Jiresfojie, I am compelled 

 entirely to dissent from it. It has already been called green 

 sand by all geologists ; no arguments have yet shown that it is 

 not entitled to that appellation, and mere change is obviously 

 worse than useless. Firestone is a terni used by builders to 

 express a stone of a certain quality, that of resisting the fire, 

 and which is employed for hearths and covings to chinmeys ; 

 this name can, therefore, be applied with propriety only to a 

 stone having that property. As only a certain portion of this 

 bed, and that only in a few localities, is fit for such a purpose, 



' Tlic small organic body supposed to lie a, cyi>ris, I f'rmnd in t)ic weald rlay in San- 

 down I?ay, when on a visit to the Ixle of \Viglit, in IS 19, with Mr. l$Tooke, togpthcr 

 with paludin.e and the teeth of lisli. 1 also pointed out to Dr. Fitton the resemblance 

 of tlie Hollin<.^ton limestone (first observed by him in that locality) to the freshwater rock 

 at East Cowes. 



