203 ENGLISH MIDDLE EOCENE FORMATIONS. [Ch. XVI. 



UPPER EOCENE. 



Thickness. 



A. Hempstead beds, Isle of Wight, see above, p. 192 - - 170 feet. 



MIDDLE EOCENE. 



B. 1. Bembridge Series, — North coast of Isle of Wight - - 120 



B. 2. Osborne or St. Helen's Series, — ibid. 100 



B. 3. Headon Series,— Isle of Wight, and Hordwell Cliff, Hants - 170 



B. 4. Headon Hill sands and Barton Clay, — Isle of Wight, and 



Barton Cliff, Hants 300 



B. 5. Bagshot and Bracklesham Sands and Clays, — London and 



Hants basins -- 700 



LOWER EOCENE. 



C. 1. London Clay proper and Bognor beds, — London and Hants 



basins 350 to 500 



C. 2. Plastic and Mottled Clays and Sands (Woolwich and Beading 



series), — London and Hants basins 100 



C. 3. Thanet Sands, — Reculvers, Kent, and Eastern part of London 



basin .....-..-.90 



The true place of the Bagshot sands, B. 5 in the above series, and of 

 the Thanet sands, C. 3, was first accurately ascertained by Mr. Prestwich 

 in 1847 and 1852. The true relative position of the Hempstead beds, A, 

 of the Bembridge, B. 1, and of the Osborne or St. Helen's series, B. 2, 

 were not made out in a satisfactory manner till Professor Forbes studied 

 them in detail in 1852. 



Bembridge series, B. 1. — These beds are above 100 feet thick, and, as 

 before stated (p. 187), pass upwards into the Hempstead beds, with which 

 they are conformable, near Yarmouth, in the Isle of Wight. They con- 

 sist of marls, clays, and limestones of freshwater, brackish, and marine 

 origin. Some of the most abundant shells, as Cyrena semistriata var., 

 and Paludina lenta (fig. 175, p. 193), are common to this and to the 

 overlying Hempstead series. The following are the subdivisions described 

 by Professor Forbes : 



a. Upper marls, distinguished by the abundance of Melania turritissima, Forbes 

 (fig. 182). 



Fig. 182. Fig. 183. 



yJMteM 



Melania turritissima, Forbes. Fragment of Carapace of Trionyx. 



Bembridge. Bembridge Beds, Isle of Wight 



b. Lower marl, characterized by Cerithittm mutabile, Cyrena pulchra, <fcc, and by 



the remains of Trionyx (see fig. 183). 



c. Green marls, often abounding in a peculiar species of oyster, and accompanied 



by Cerithia, Mytili, an Area, a Kucvla, <fec. 



d. Bembridge limestones, compact cream-colored limestones alternating with 



