208 ENGLISH MIDDLE EOCENE FORMATIONS. [Cn. XVL 



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 Reading 



series), — London and Hants basins 100 



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



basin 90 



The true place of the Bagsliot 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. 



Beijihridge 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, bracldsh, and marine 

 oiigin. Some of the most abundant shells, as Cyrena semistriata ym',^ 

 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). 



Eis. 1S2. Fig. 183. 



3felania turritissima, Forbes. Fragment of Carapace of Trionyx. 



Bembridge. Bembridge Beds, Isle of Wight. 



h. Lower marl, characterized by Cerlthnim mutabile, Cyrena pulchra, &c.^ and by 

 the reinains of Trionyx (see fig. 183). 



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



by CerWna, Mi/tili, an Area, a JVucuIa, &c. 



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



