HEADON HILL AND COLWELL BAT IN THE ISLE OF "WIGHT. 105 



the lists at the end of this communication. These have been drawn 

 np from an inspection of the Edwards collection of Tertiary fossils 

 in the British Museum f , while we have added many occurrences 

 from our researches this summer, and we believe our list to be fairly 

 correct. 



We do not admit that the Edwards collection is sufficient for a 

 full knowledge of the distribution of English Tertiary fossils : e. g. if 

 a certain shell does not exist in the Edwards collection from Colwell 

 Bay, it is no proof that it does not occur there, but simply that 

 Mr. Edwards had better specimens of it from Headon Hill, which 

 was considered, as, indeed, it is, an equivalent bed. The greater 

 part of the Edwards collection was made by the hands of one of the 

 authors ; but we do not think it possible to establish from this col- 

 lection that Colwell Bay contains so many marine forms which do 

 not occur in Headon Hill, and therefore that the marine beds at these 

 localities are not on the same horizon. 



The following reasons induce us to say this : — It was the habit of 

 the local collectors to exploit the Colwell-Bay bed far more than the 

 Headon-Hill locality, because it was more accessible and showed 

 a larger extent exposed ; the fossils were better preserved, and in 

 every respect it was easier to collect from. Again, some species 

 which one of us supplied to Mr. Edwards from Headon Hill were 

 not incorporated in this collection, probably owing to his having 

 better ones from Colwell Bay ; and doubtless they were exchanged 

 with foreign correspondents or given away. These two con- 

 siderations would serve to account for his Colwell-Bay collection 

 being richer than his Headon-Hill one. Corroborative of this is 

 the fact that in a few days' . search this summer we have found 

 several species in the marine bed at Headon Hill which do not exist 

 in the Edwards collection from that locality. 



Moreover we hold that the best test as to the contemporaneity 

 of these beds is not to be obtained from the rarer forms, which may 

 be evidenced only by a single example, but from a comparison of the 

 commoner, which we should consider the more characteristic forms. 

 Accordingly we add a list of the species obtained by us this summer 

 from the Middle Headon of both localities : H indicates Headon 

 Hill ; C the equivalent bed at Colwell Bay. 



List of all the Shells obtained on the ground by the authors for the 

 purposes of this paper (Aug. 1880). 



(Those with an asterisk pass up from Barton beds.) 



*Lamna contortidens (Ag.) ... C,H. 



Marginella vittata (Edw.) H. 



*Voluta spinosa (Lam.) 0, H. 



Pleurotoina headonensis (Edw.).C, H. 



* denticula (Bast.), var. 



odontella (Ed.) C,H. 



*Borsonia sulcata (Bou.) C. 



*Riinella rimosa {Sol.) C, H. 



Murex sexdentatus (Sow.) C, H. 



sp H. 



Pisania labiata (Sow.) C, H. 



*Cominella fiexuosa (Ed. 31S.) C, H. 



t "We are greatly indebted to the Keeper of the Geological Department, Dr. 

 H. Woodward, F.P.S., for his courtesy in allowing us access to the collection, 

 even during the laborious process of packing np and moving the national col- 

 lection to the new building at South Kensington. 



