HEAD0X HILL AXD COL WELL BAY IN THE ISLE OF WIGHT. 



89 



from the chine on the west side (private grounds interfere with 

 examination nearer the chine). 



We should say, from our examination of the ground which inter- 

 venes between the escarpment of the thick Upper Headon Limestone 

 and the Benibridge, that there is no difficulty in seeing what beds exist 

 there. It is true they are sufficiently interrupted by local taluses to 

 cause trouble in making a continuous measurement ; but the tumbled 

 portions are partial and affect only a few feet of beds at a time, so 

 that by moving the observer's position laterally it is possible to see 

 all the beds in turn. This we claim to have done ; we do not pretend 

 that our measurement of the beds is any thing but rough, though 

 controlled by repetition, because we had no le veiling-instruments with 

 us, and in shifting horizontally from one spot to another there might 

 be frequently a slight error in picking up the next bed to be 

 measured. We might describe the beds immediately below the Bern- 

 bridge Limestone, in descending order, as follows : — yellowish and 

 ochry marls, red aud grey mottled marls, marly clays with nodular 

 bands, greenish-grey clays, pale greyish clays, grey and ochry clays, 

 stiff pale or whitish clays with calcareous lenticular bands, red and 

 green mottled marls, " cherry marl " with calcareous bands. These 

 are the Osborne beds of the Survey ; and they come in the precise 

 position assigned to them in the Survey Memoirs. They are well 

 characterized by the " cherry marl " — the mottled red and pale 

 greenish marl which distinguishes the group from the Upper 

 Headon ; and we consider the subdivision a very useful one in the 

 classification of beds. Their thickness here, by our comparatively 

 rough way of measurement, is 70 feet. The vertical section of the 

 Survey Sheet 25 gives 71 feet, reading off by scale down to the bed 

 which we have taken as our boundary ; their measurement seems to 

 have been taken near Heatherwood Point, where this series contains 

 a thick limestone of 18 feet ; as noticed by previous observers, this 

 limestone thins out to the east, and is only represented by nodular 

 calcareous bands at the east end of the hill ; its loss will probably be 

 compensated by an increase in the clays. Our results are perhaps suffi- 

 ciently near to those of the Survey to prove that the same series of 

 beds has been examined in both cases. We should remark that from 

 the lower red beds it is perfectly easy to draw a continuous vertical 

 section to the beds below ; and from here our measurements to the 

 Lower Headon are uninterrupted in a vertical line. The Osborne 

 beds yield few interesting fossils ; Limncea is abundant in the 

 calcareous bands ; but, as noticed by Forbes (Mem. p. 81), the shell- 

 substance is not preserved. These beds are identical lithologically 

 with the mottled red and pale green series at Cliff End. 



The beds next below the red series are grey and ochry clays, very 

 rich in Potamomya gregaria and Paludina lenta beautifully pre- 

 served : we place these in the Upper Headon ; they are about 15 

 feet thick * 



* In the Survey Section no. 5, at Headon Hill (sheet 25, Yert. Sect.), these 

 clays are included in the Osborne series ; but in the Vert. Section, no. 4, at Col- 

 well Bay, the boundary is so drawn that analogous clays are put into the Upper 

 Headon. 



