OLIGOCEXE STRATA OE THE HAMPSHIRE BASIN. 171 



When the beds of the Headon group are traced over to the oppo- 

 site coast of Hampshire, they are found at Hordwell, apparently 

 diminished in thickness ; and here we have evidence of the existence 

 of numerous reptilian and mammalian forms of life which do not 

 occur in the Isle-of- Wight strata. Unfortunately, however, the 

 exposure is incomplete, only the lowest 100 feet of the group being 

 seen in the cliff section. The correspondence both of the freshwater 

 and brackish forms of the MoUusca at Headon Hill and Hordwell is 

 perfect, and leaves no room for doubt that the two series of strata 

 are upon the same geological horizon. 



When we pass to the eastern extremity of the Isle of Wight, we find 

 at Whitecliff Bay a very different series of strata from that exposed 

 at Headon Hill. Immediately below the well-marked Broekenhurst 

 series at Whitecliff Bay we have a series of clays and lignites with 

 some bauds of ironstone, which appear to be entirely of freshwater 

 origin. These are estimated by Mr. Prestwich at 92 feet in thick- 

 ness ; but the officers of the Survey make them only 40 feet. My 

 own measurements indicate a thickness intermediate between these 

 two amounts, namely about 60 feet. Below these we have 200 

 feet of sands usually identified with the Headon-Hill sands, but 

 which I cannot but regard as representing all the lower part of the 

 Headon group. Unfortunately they do not contain any fossils, with 

 the exception of the casts of a few undeterminable bivalves. As is 

 well known, the Barton series is very imperfectly represented at 

 Whitecliff Bay, and it is difficult to draw a boundary either between 

 the Bracklesham and the Barton beds or between the latter and 

 the overlying fluvio-marine strata. 



The Broekenhurst series is represented at Whitecliff Bay by 100 

 feet of purely marine strata. The identity of these with the beds 

 of the !N"ew Forest, so well worked out by Mr. Edwards and Herr 

 Von Konen, has already been recognized by Mr. Fisher * and by 

 Messrs. Jenkins and Codringtonf. At Colwell Bay this marine 

 series is reduced to a thickness of 25 feet ; but the number of its 

 fossils is so great as to render its correlation with the Broekenhurst 

 beds unquestionable. In the New Forest, unfortunately, we have 

 no clear sections showing the thickness and succession of the Broek- 

 enhurst series. A well-section, observed by Mr. Henry Keeping and 

 recorded by Mr. Wise in his work on the New Forest, shows that 

 the thickness of this marine series is certainly not less than at 

 Colwell Bay. Considering the wide area over which the fossils of 

 this horizon have been found, the thickness of the Broekenhurst 

 series in the New Forest is probably very considerable. 



The Bembridge group consists of a series of beds which at the 

 western end of the Isle of Wight attain a thickness of more than 

 250 feet. In the midst of the series occurs the well-known lime- 

 stone of Bembridge, having a thickness of about 25 feet. We may 

 distinguish the beds above and below the Bembridge Limestone 

 respectively as the Upper and Lower Bembridge Marls. The Lower 



* Quart. Journ. Geol. Soc. vol. xviii. (1862) p. 67. 

 t Ibid. vol. xxir. (1868) p. 519. 



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