102 A. 8. Lucas — The Headon Beds of the Isle of Wight. 



the Warden Cliff, mtist have been of the same age with that of 

 Headon Hill, hy the least equivocal of all geological tests, continuity 

 of strata. Messrs. Keeping and Tawney assert that the sequence is 

 identical in Warden Cliff and the N.E. corner of Headon Hill. 

 The thickness they obtain for the series — with a definite C. ventri- 

 cosuni band above and a definite fresh- water limestone below in both 

 cases— is in the N. '34^ ft., in the S. 31 ft. 9 in. to 33 ft. And they 

 state, moreover, that the lithological and palEeontological details of 

 these two near sections were so far identical that repetition was 

 useless. Owing to the state of the Headon Hill beds above mentioned 

 during our stay, we cannot offer any fresh evidence on this point, 

 though we found the general succession at Warden Point much like 

 that of the S.W. of Headon Hill, with Ostrcea v-elata most abundant 

 in a middle zone. We took the height above the sea of this oyster 

 band at four points. 



rr ii 11, 1-1, • (At "Warden Point under the fort 55 ft. 



lotiand brackisn-marine i' t ^.-u -u • i j rn .i j tt j. i ta^^j. 



I In the brickyard near iotland Hotel .... 70 it. 



TT 1 T, 1 • 1, • ( Below the cottasre at N.E. corner 94 ft. 



Headon brackish-marme Wt ^ at t> j. o -nr mojij. 



( jST. of Alum Bay at S. W . corner 128 ft. 



These measurements are strongly in favour of the continuity of 

 the series, for the anticlinal is grossly exaggerated in Forbes's 

 diagram. 



The correspondences continue as we proceed downwards. Prof. 

 Blake admits fully that the How Ledge Limestone was continuous 

 with that at the top of the Lower Headon in Headon Hill. Thej"^ 

 agree in thickness, in appearance, with abundance of Limnea and 

 scarcity of Planorbis. The How Ledge Limestone is continuous 

 from the Ledge nearly to Weston Chine ; the Lower Headon Lime- 

 stone is continuous throughout the Hill ; there is but this hiatus for 

 half a mile caused by palpable denudation. As to the beds below 

 this Limestone, there is no discrepancy in published evidence. Prof. 

 Blake admits that the succession at Headon Hill (noted at some 

 point on the W. face) '•' is perfectly in accordance with that at 

 Totland Bay." ^ The details of Headon Hill agree essentially with 

 the full section of the Totland Bay strata between Warden Point 

 and Weston Chine, published by Messrs Keeping and Tawney.* 



It may be said then, in support of the Survey view, that we 

 traverse the same succession of strata as we climb Headon Hill from 

 the shore, and as we walk from Widdick Chine to Cliff End, that 

 there is no break or unconformity in either series, that where the 

 beds of the two series are adjacent, certain are practically identical, 

 and that divergences in what are claimed as corresponding beds are 

 found when they are compared at greater distances, that the con- 

 spicuous Bembridge Limestone and Osborne Marls cap both series 

 above, and that the correspondences both in general order and in 

 detail, are such as to bring possible errors of correlation between 

 very narrow limits. 



We now turn to the palaeontological evidence of the brackish- 

 marine strata. Such evidence is naturally not considered by Prof. 

 ^ Proc. Geol. Assoc, vol. vii. p. 158. ^ op. cit. p. 98. 



