HEADON HILL AND COLWELL BAY IX THE ISLE OF WIGHT. 



101 



half; the result is that the dip is considerably exaggerated. Again, 

 in Headon Hill an exaggeration of dip is produced by the error of 

 105 ft. in plotting the marine beds. The effect is that the identical bed 

 (Middle Headon) is split into two beds separated by 120 ft. of beds. 

 Prom our point of Yiew this could only be done by counting more 

 than 100 ft. of beds twice over. In the legend attached to the diagram 

 section fig. 2, " new interpretation," the beds g are, in our opinion, 

 the Lower Headon ; f is the Middle Headon ; e the Upper Headon ; 

 d and c are the Lower Headon; b is the Middle Headon again. 

 According to the old view, which we certainly should prefer, this last 

 105 ft. has no existence in fact*. 



Loiuer Headon of Colwell Bay. — The section in Colwell Bay is 

 continuous with that of Warden Cliff ; but in the bay, as we go 

 north, a few lithological changes occur in the marine beds f , as 

 noticed below, and which cause the marine beds at one part of Col- 

 well Bay to differ far more from the same beds at the centre of the 

 bay than the latter do from the marine beds of Headon Hill. On 

 rounding Warden Point, beyond the sea-wall, is a small rifle-target ; 

 and from here the beds are fairly well exposed throughout the bay, 

 though tumbled portions or a diminutive undercliff may conceal 

 some of the beds in places, sufficiently to give considerable trouble 

 in measuring the beds. 



The Unio-Solandri bed with Melania turritissima has been fre- 

 quently worked by one of us below the How-Ledge limestone here 

 but this summer we could only find tumbled portions of it. The said 

 limestone rises from beneath the sea-level at How Ledge t, whence 

 its appellation, and crosses Colwell Chine ; here and at the target it 

 has the same lignitic band and clays beneath it as on the south side 

 of Warden Cliff ; it thins down to 3 ft. north of the chine. We 

 mention these upper beds of the Lower Headon to show that the 

 Colwell-Bay marine bed, as at Warden Cliff, reposes on the same 

 succession of beds as in Headon Hill. 



Middle Headon of Colwell Bay. — The lowest or Neritina-bed at 

 the S.W. end of the bay, by the target, is now covered by tumbled 

 matter, but is well seen a little further on about 50 yards short of 

 Colwell Chine. Here, i. e. between the target and the chine in the 



* The diagram in Forbes's posthumous work is so schematic that it omits 

 the higher part of Headon Hill, and, perhaps for clearness sake, the effect of 

 the anticlinal is exaggerated. It is rather severe to treat it as if it were drawn 

 to scale, and, because the Upper Bagshot Sands were brought up too much in 

 the centre of the roll, to say that E. Forbes was "mistaken in his interpretation" 

 (op. cit. p. 176) of the beds. Forbes's diagram, in fact, with this qualification, 

 represents the beds in their right position ; thus the Lower Headon, no. 6, occu- 

 pies the summit of the cliffs in the centre of Totland Bay, while no. 7, Middle 

 Headon, is denuded from above it — all which, is perfectly correct. 



t Since Warden Battery has been built it is forbidden to search for fossils 

 on the slopes at Warden Point. Many years ago one of the authors was in the 

 habit of frequently exploiting the beds here for fossils, and many of them are 

 incidentally described by Dr. Wright, Proc. Cotsw. Club, i. pp. 91, 92 (1850). 

 The engineers, however, have not succeeded in grassing all the slopes, and fallen 

 fossils may still be picked up at the base. 



% Bed 18 of Dr. Wright, who describes it correctly in Warden Cliff, but 

 appears to have mistaken its position in Headon Hill {ib. p. 95). 



Q. J. G. S. No. 146. i 



