UPPER EOCENE (bARTON AND UPPER BAGSHOT FORMATIONS). 599 



feet of green clay mottled with 

 shells, and 6 or 7 feet of com- 

 pact pale green sand, the com- 

 bmed horizontal extent being 

 700 yards. This must, we 

 believe, represent the beds im- 

 mediately below, as well as 

 partly the Unio-heds of our 

 Hordwell section, for the Middle 

 Headons occur somewhere in 

 the next rising ground on the 

 Brockenhurst side. 



The Alum-Bay Section (fig. 7). 



The section at Alum Bay is 

 but 6 miles from Barton, and 

 being through lofty cliffs with 

 vertical bedding, is extremely 

 easy to measure and under- 

 stand. Measurements taken 

 by Prof. Prestwich were pub- 

 lished in his " Memoir on the 

 Isle of Wight Tertiaries," in 

 1846, the entire series forming 

 the 29th and 30th beds of his 

 section, with a thickness of 

 380 feet*, inclusive of 100 feet 

 of siliceous sand. In 1857 he 

 separated the formation into 

 three not very well character- 

 ized beds as group a, and made 

 the overlying siliceous sands 

 his division h. Mr. Bristow, 

 with Mr. Gibbs, measured it 

 again, the results published in 

 the Survey Memoirs of 1856 

 and 1862 showing a total thick- 

 ness of 300 feet, exclusive of 

 the siliceous sands. We think 

 that this is a little over-esti- 

 mated and that the measure- 

 ment of 380 feet is nearly 

 correct. Mr. Pisher, in 1861, 

 reduced the thickness shown by 

 Prestwich by 43 feet, placing 

 the beds below the Nummulites 

 elegans, var PrestwicTiiana, in 



* Quart. Journ. Geol. Soc. vol. ii. 

 109. 



