100 A. 8. Lucas — T/ie Headon Beds of the Isle of Wight. 



above it show a similar but reverse transition from fresh-water to 

 marine conditions. 



Near the N.E. angle of Headon Hill we have another very definite 

 section, which can be verified more or less at any time, directly 

 under the cottage. This has been fully done by Messrs. Keeping 

 and Tawney,^ the former of whom lived for many years in the 

 neighbourhood. We made some measurements which entirely con- 

 firm their observations, though we had not seen their section at the 

 time. "We found the Bembridge Limestone reaching 21 ft. below 

 the base line of the cottage, and traced the red and green mottled 

 Osborne marls some 19 ft. below the limestone in the vertical cliff, 

 and they gave no evidence of coming to an end. The "Brocken- 

 hurst " beds should be about here according to Prof. Judd's section,^ 

 but we could see nothing of them. The Great Limestone rested on 

 a deficiency of sands here. The upper brackish beds of the Middle 

 series were alone exposed in situ, as mentioned above, at a height 

 of 110 ft. above sea-level. The marine beds had slipped down, and 

 we obtained manj'- of the typical shells on the slopes just above the 

 Lower Headon Limestone, where Prof. Blake describes them as 

 in situ. We did not even venture on measuring the height of the 

 Lower Limestone, as it seemed to us uncertain whether it was 

 exactly in position, or whether portions had advanced en masse in 

 a roll seawards. This certainly confirms the Rev. 0. Fisher's sug- 

 gestion as to the cause of a previous erroneous interpretation. Putting 

 together then these four vertical Headon Hill sections, we have a 

 very clear succession of strata. The one bed which thins out in the 

 Hill is the Osborne Limestone. The rest are continuous. 



The extensive denudation N. of Widdick Chine, and the gentle 

 dip of the strata, forbid any further comprehensive vertical sections 

 at particular spots. The next step is to tabulate the beds, on their 

 successive emergence above sea-level as we proceed N. to Cliff End. 

 The beds claimed as Headon have been measured carefully by Dr. 

 Wright, and by Messrs. Keeping and Tawney, and the Osborne beds 

 by Edward Forbes, and the main divisions are so conspicuous even 

 as one walks over the ground, that about the succession here there 

 can be no dispute. Then there comes the question as to how far 

 the succession in the standard Colwell-Totland Bays section tallies 

 with that of the standard Headon Hill section. The upper limit 

 to both, the Bembridge Limestone, is most useful as restricting 

 possibilities to accessible ground in both cases. It is universally 

 admitted as occurring at the top of both sections. The Osborne series 

 of the two localities are tabulated successively by Forbes (Mem. p. 

 78 and p. 81), and the general agreement (minus at Cliff End the 

 limestone of Heatherwood Point) is evident. These Osborne marls 

 may still be seen under the grass behind the cliff immediately S. 

 of the Battery, as we found by a little digging. That the series was 

 an unprofitable one we had keenly felt in Museums, with its ill- 

 preserved and poorly characteristic fauna, but its great use as a 



1 Q.J.G.S. vol. xxxTO. pp. 88, seq. * Q.J.G.S. vol. xxxvi. pi. vii. fig. 2. 



