HEADON HILL AND COLWELL BAY IN THE ISLE OF WIGHT. 



99 



denuded away in the centre of Totland Bay. It cannot, however, 

 have been many feet above the present cliffs near Widdick Chine, 

 while a little south of that it exists in the cliff. At the 1N".E. corner 

 of Headon Hill we noted it at a height of 70 feet above the sea ; it 

 is well seen also in the cliffs near Heatherwood Point, where it has 

 a somewhat higher elevation. 



There is evidence of an anticlinal in Totland Bay, as indicated in 

 E. Porbes's sketchy diagram ; the summit of the anticlinal we infer 

 to be near the old wooden pier. 



If we add up, we obtain a thickness for the Lower Headon exposed 

 in Warden Cliff of 71 1 feet (supposing no interruption at the point 

 specified above). It remains to settle the relation of the lowest bed 

 here seen to the Upper Bagshot Sands. 



The junction of the Lower Headon with the Upper Bagshot is well 

 seen north of Alum-Bay Chine; immediately above the Upper Bagshot 

 sands come greenish-grey clays ; then, in ascending order, alternation 

 of clays and sands ; next, pale greenish-grey sands ; then a stiff marly 

 clay : total 16 feet. Above is a purplish red cla3 T -ironstone band; 

 and succeeding that is the first thin Limnaea-limestone. 



If we consider this red iron-band to be at the same horizon as 

 that noticed under Weston Chine, as is extremely probable (though 

 it is some 4 feet nearer to the lowest Limnasa-limestone), then we 

 must add 12 or 16 feet to the 71 feet obtained for the Lower Headon 

 in Warden Cliff, making a total of 83 or 87 feet before we reach the 

 yellowish sand of the Upper Bagshot. 



Knowing now the full thickness of the Lower Headon, we are 

 able to test the argument as to the position of the Upper Bagshot, or 

 Headon sands, as they were once called by E. Forbes (Hem. p. 34-6), 

 in Totland Bay. It is stated (op. cit. p. 147) that the Survey 

 actually represent these as occurring, in both the Yertical and Hori- 

 zontal Sections, near the summit of the anticlinal in Totland Bay*. 



There seems a little inconsistency in the Survey Yertical Sections 

 concerning both boundaries of the Lower Headon ; if we may classify 

 these green clays in the Lower Headon, and then read off by scale from 

 the top of the How-Ledge bed, the Survey Section would give a thick- 

 ness of 85 ft. for the Lower Headon in Totland Bay. 



It is urged "that the Headon-Hill sands do uot occur in the 

 position indicated by the Geological Survey ;" and the crucial test of 



* We pointed out above that the Survey Yertical Section [edition 1870] shows 

 them only just above the sea-level at a point some way inland. The Yertical 

 Section we are inclined to interpret in this way — that the beds denoted Upper 

 Bagshot in Totland Bay are what we have classed in the Lower Headon ; for the 

 legend states, below the "clay-ironstone " are 6 inches sand in " Totland Bay," 

 then " green clay with lenticular patches of sand " 15 feet, so that the de- 

 scription agrees fairly with our lowest beds at Heatherwood Point. The Survey 

 Section does not state that these were exposed in the centre of Totland Bay ; but 

 as Heatherwood Point is the western point of the bay, we may assume that 

 they may have been seen anywhere short of that point along the base of Headon 

 Hill, where it is quite certain that they exist, and must have been open at that 

 time at more points than one ; for the white glass-house sands were then being 

 actively worked in Headon Hill, and the yellower sands above them may still 

 be seen about a mile from the N.E. corner of Headon Hill. 



