268 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 4, 



that fine species. Great numbers of the Potamides margaritaceus of 

 Sowerby occur in these beds. The shells of the freshwater lime- 

 stones are the same as those of the Lower Headons, with the excep- 

 tion, perhaps, of a large Paludina and the ^o-c?i\[e.di Bulimus politus. 

 Melania muricata abounds. 



h. The Middle Headons, — This is what is usually called ' the 

 Upper Marine.' At Headon Hill this division is mainly brackish, 

 although Oysters, Cytherea incrassata, Nuctda deltoidea, Natica, 

 and Fifsus, are sufficiently common. Immediately above and below, 

 or rather forming the uppermost and lowermost portions of this sec- 

 tion, are brackish water beds abounding in Potamides ventricosus, 

 P. coiicavus, and P. cinctus; also in NeritincB and NematurtB. A little 

 way off, at Colwell Bay, a marine character is assumed by the same 

 bed, and large banks of Oysters are seen, with numerous marine 

 shells, many of them of Barton species. It was this difference be- 

 tween the conditions at Headon Hill and Colwell Bay that misled 

 M. Hebert. Judging from detailed sections, especially those pub- 

 lished by the Marchioness of Hastings and Dr. Wright, the ma- 

 rine character is fully maintained, though in beds of a very inferior 

 thickness, at Hordwell. Respecting that locality, however, there 

 is a serious discrepancy in the statements of the describers. The 

 section made by Lady Hastings appears to me to be the most cor- 

 rect, and to agree most accurately with the arrangements of the beds 

 on the opposite side of the Solent. At Whitecliff Bay the marine 

 character of the Middle Headons is still more extensively developed, 

 and the thickness of purely marine deposits much greater than 

 westward. 



c. The Lower Headons consist of fresh and brackish water beds, 

 abounding in fossils for the most part identical with those in the 

 upper division. At Headon Hill and Colwell Bay there are strong 

 limestones in this part of the series, but at Whitecliff all the beds 

 are clays and marls. They are more varied at Hordwell, where the 

 greater part of the fluvio-marine beds there seen belongs to the Lower 

 Headons. In them at that locality numerous remains of Vertebrata 

 have been found, especially by the Marchioness of Hastings, Mr. 

 Searles Wood, and Mr. Falconer ; and all the species appear to be 

 peculiar and distinct from those in the Bembridge and Hempstead 

 series, a fact to which attention was called strongly some years ago 

 by the noble lady just mentioned, before the geological differences of 

 the strata themselves had been suspected. 



The lower beds of the Headon series rest upon the Headon Hill 

 sands. No fossils have hitherto been recorded from these beds or 

 the Isle of Wight. At Whitecliff Bay, however, though to all ap- 

 pearance barren, they are highly fossiliferous, containing abundant 

 impressions of marine shells apparently of Barton species. The 

 shelly matter has entirely disappeared, and, owing to the loose and 

 friable condition of the sands, the specimens are quite untrans- 

 portable. 



These sands rest on the Barton clays, the relations of which at 



