522 BEPORT— 1882. 



Ledge limestone. Between Warden Battery and "Weston Chine the Colwell Bay 

 marine bed (Middle Headon) is maintained in all its integrity. 



Middle Headon of Colwell Bay. — ' The Neritina bed at the south-west end of 

 the Bay is well seen a little short of Colwell Chine. Above this comes the richest 

 part of the "Venus bed" — the fossils in which {Cytherea incrassata) strew the 

 tumbled clays and commingle witli recent shells on the shore.' Osfrea velata, as at 

 Headon Hill, is abundant above the part richest in Cytherea. This oyster occurs 

 in vast abundance in the centre of the bay between Colwell and Bramble Chines, 

 crowding out other fossils and forming a massive oyster bank about 20 feet thick. 

 The Venus bed here is altered in character, and abundantly occurring with Cy- 

 therea incrassata axe Miif-e.v sexdentatus, Pisania labiata, Natica labeUata, Nerita 

 aperta, Ceritkium variahile, and Osfrea velata.'' 



Upper Headon of Colwell Bay. — The horizon of Cyrena Wiyhtii is a marked 

 feature here, associated with Corbicida nhovata ; Cerithium trizoiiatum also occupies 

 one horizon just below the bull-coloured Lymupea limestone forming a narrow band 

 with green clays; ,Serpui< (nuis is equally characteristic, occurring at the same 

 horizon both here and at Headon Hill, viz. in the Upper Potamomya clay just above 

 the Lymnsean limestone. 



PALiEONTOLOGICAI EVIDENCE. 



Having noticed the stratigraphical succession of the several divisions in the 

 beds at Headon Hill and Colwell Bay, I now proceed to draw attention to the 

 distribution of the fossils. 



The authors of the paper have discussed the question as to whether the 

 Colwell Bay has any more affinity with the Brockenhurst fauna, than has the 

 Headon Hill bed ; and they compare the fauna both of the Colwell Bay and 

 Headon Hill marine beds. This they do by separating in tabular form the 

 fauna of all the localities which are to be compared togetlier. The splendid 

 collection of Tertiary fossils belonging to the late Mr. F. Edwards, and now in the 

 British Museum, has formed the basis of their comparison, while their own researches 

 have added occurrences still more conclusive as to the correlation of species in 

 the areas imder examination and consideration. The authors obtained during 

 their research in the Isle of AVight many species in the marine bed at Headon 

 Hill which do not exist in the Edwards collection from that locality. ' The test 

 as to the contemporaneity of the beds in question is not to be obtained "from the 

 rarer forms only, but from a comparison of the commoner and more characteristic 

 species.' No less than fifty-eight species were obtained by the autliors from the 

 Middle Headon of two localities, Colwell Bay and Headon Hill, nineteen of which 

 appeared in and came up from the Barton beds, and with seven exceptions all the 

 fifty-eight forms came from both horizons. 



It has been stated that the ' strata at Colwell Bay are of 2}iirely marine oriyin, 

 tohile the so-called Middle Marine beds of Headon Hill and Hordwell Cliff' are 

 of totally different character.' But Messrs. Tawney and Keeping obtained from 

 the marine series at Colwell Bay the brackish -water genera Cerithium, Cyrena, 

 Hydrobia, Lymncea, Paludina, Planorbis, Melania, and Melanopsis, although said to 

 be found only at Headon Hill. It has also been stated that certain species of 

 Cerithium are confined to Headon Hill, and do not occur in Colwell Bay, and 

 that through this discovery serious errors in our classification have been detected, 

 as well as in the correlation of the strata under consideration. 



The presence of Cerithium concavum in the Venus bed abundantly at Colwell 

 Bay — and we may add from private information from Mr. Keeping that he has 

 found it also at Whitecliff Bay in the same position — removes all doubt as to the 

 non-occurrence of the zone in that locality. As has been stated, the species is not 

 so common at Colwell Bay as at Headon Hill. 



There is but one marine bed, and that is known only in the Middle Headon. The 

 place of the Brockenhurst bed is at the lowest horizon in the Middle Headon, but 

 it does not appear at Colwell Bay, or anywhere in the west end of the island, but 

 only at WhitecliflP. 



