HEADON HILL AND COLWELL BAY IN THE ISLE OF WIGHT. 



107 



&c. (1. c. p. 148). Of the brackish-water genera which are supposed 

 to be found in Headon Hill only, we may remark that we found 

 Ceritliium, Cyrena, Hydrobia, Limiicea, Paludina, Planorbis, Melania, 

 and Melanopsis fully as plentiful in the marine series of Colwell 

 Bay as at Headon Hill ; e. g. in a quarter of an hour we turned out 

 half a dozen specimens of Limncea longiseata * from the richest 

 nine inches of the Venus-bed, the best zone for Voluta, Cancellaria, 

 Murex, Cytlierea, (fee. It has always been the opinion of one of us, 

 who has worked these beds for so long, that these freshwater forms 

 were either drifted down by flood-waters or were dead shells washed 

 out of lacustrine or brackish deposits. They cannot have lived in the 

 waters depositing the marine bed at Headon Hill any more than at 

 Colwell Bay. 



Another argument brought forward in opposition to the views of 

 the Geological Survey is, that certain species of Ceritliium are 

 confined to Headon Hill and do not occur in Colwell Bay ; and by 

 this means have been " detected the serious errors which have crept 

 into our classification and correlation of the strata we are now con- 

 sidering " (op. cit. p. 149). Ceritliium ventricosum and C. concavum 

 are said to be entirely confined to the Headon Hill and Hordwell 

 localities. We cannot agree with the statement as to the distri- 

 bution of C. ventricosum in the Headon-Hill beds and its " prodigious 

 abundance." It is there, as far as we have observed, found only in 

 one bed ; moreover, it is equally abundant in a bed in a precisely 

 similar position at Colwell Bay, viz. at the top of the Middle Headon. 

 Its analogous position in these two localities we consider as fossil 

 evidence confirmatory of the stratigraphical. 



Nor do our observations confirm the statement of "prodigious 

 abundance " of 0. ( Vicarya) concavum at Hordwell Cliff in the Middle 

 Headon. One of the authors who worked that bed when a special 

 excavation was made for the purpose f, considers that V. concava 

 was extremely rare in the Hordwell bed ; but, as is well known, it 

 occurs abundantly in the Upper Bagshot sands further west at Long 

 Mead End. 



As to the supposed absence of V. concava from Colwell Bay, we 

 remark that we had not been many minutes at work on the richest 

 portion of the Venus -bed before we found a specimen, subsequently 

 followed by a dozen more. It can scarcely be maintained, therefore, 

 that the Colwell-Bay bed does not belong to the C -concavum zone. . 

 This species is here, however, not so common as at Headon Hill %. 



* Also noticed by Mr. Bristow, F.R.S. (Mem. 10* p. 61), as well as by previous 

 writers. 



t The Middle marine or Middle Headon bed at Kook Cliff, Hordwell, has not 

 been exposed for the last twenty-eight years ; it is covered up by a great thick- 

 ness of gravel, and its precise position is known but to few geologists. It was 

 quite a thin bed, but rich in fossils, especially minute forms. Fossils in 

 existing collections were all obtained about a quarter of a century ago. 



\ This species exists, however, in the Edwards collection, labelled as from 

 Colwell Bay. The absence of a shell in the Edwards collection from Colwell 

 Bay is no proof that it did not occur there ; the local dealers might not have 

 thought of picking up V. concava at Colwell Bay. For this species they went 

 to Headon Hill, where it was more abundantly found and in better preserva- 



