UPPER EOCENE FORMATIONS. 
255 
As the vertical range of particular species of quadrupeds, so 
far as our knowledge extends, is far more limited than that 
of the testacea, the occurrence of so many species at Bin- 
stead, agreeing with fossils of the Paris gypsum, strengthens 
the evidence derived from shells and plants of the synchro¬ 
nism of the two formations. 
Osborne or St. Helen’s Series, A. 2. —This group is of fresh 
and brackish-water origin, and very variable in mineral char¬ 
acter and thickness. Near Ryde‘, it supplies a freestone much 
used for building, and called by Professor Forbes the Nettle- 
stone grit. In one part ripple-marked flagstones occur, and 
rocks with fucoidal markings. The Osborne beds are distin¬ 
guished by peculiar species of Paludina^ Melania^ and Me- 
lanopsis^ as also of Cypris and the seeds of Char a, 
Headon Series, A. 3. —These beds are seen both in White- 
cliff Bay, Headon Hill, and Alum Bay, or at the east and 
west extremities of the Isle of Wight. The upper and lower 
portions are fresh-water, and the middle of mixed origin, 
sometimes brackish and marine. Everywhere Planorbis e,u- 
omphalus^ Fig. 175, characterizes the fresh-water deposits, 
just as the allied form, P, discus^ Fig. 170, does the Bem- 
bridge limestone. The brackish-water beds contain Pota- 
momya plana^ Cerithium mutabile^ and Potamides cinctus 
(Fig. 37, p. 56), and the marine beds Venus (or Cytherea) in- 
crassata^ a species common to the Limburg beds and Gres de 
Fig. 175. 
Planorbis euomphalus, Sow. Helix labi/o'inthica, Say. Headon Hill, Isle of Wight; 
Headon Hill. ^ diam. and Hordwell Cliff, Hants—also recent. 
Fontainebleau, or the Lower Miocene series. The prevalence 
of salt-water remains is most conspicuous in some of the cen¬ 
tral parts of the formation. 
Among the shells which are widely distributed through 
the Headon series are Neritina concara (Fig. 
Lyynnea caudata (Fig. 178), and Cerithi¬ 
um concavum (Fig. 179). Helix labyrinthica^ 
Say (Fig. 176), a land-shell now inhabiting the 
United States, was discovered in this series by 
'\T 1 TT-r T • TT 1 T • I*' Sow. Jleacion se- 
Mr. Searles Wood in Hordwell Clifl. It is also ries. 
Fig. 177. 
