284 



UPPER EOCENE FORMATIONS. 



[Ch. XVI. 



our knowledge extends, is far more limited than that of the testacea, 

 the occurrence of so many species at Binstead, agreeing with fossils 

 of the Paris gypsum, strengthens the evidence derived from shells 

 and plants of the synchronism 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 character and 

 thickness. Xear Kyde, it supplies a freestone much used for building, 

 and called by Professor Forbes the Nettlestone grit. In one part 

 ripple-marked flagstones occur, and rocks with fucoidal markings. 

 The Osborne beds are distinguished by peculiar species of Paludina, 

 Melania, and Melanopsis, as also of Cypris and the seeds of Cham. 



Headon series, K. 3. — These beds are seen both in Whitecliff Bay 

 and in Headon Hill, or at the east and west extremities of the Isle 

 of Wight. The upper and lower portions are freshwater, and the 

 middle of mixed origin, sometimes brackish and marine. Everywhere 

 Planorbis euomphalus, fig. 221, characterizes the freshwater deposits, 



•Fig. 221. 



Planorbis euomphalus, Sow. 

 Headon Hill. £ diam. 



Helix labyrinthica, Say. Headon Hill, Isle of Wight; 

 and Hordwell Cliff, Hants— also recent. 



just as the allied form, P. discus, fig. 216, does the Bembridge lime- 

 stone. The brackish-water beds contain Potamomya plana, Ceritkium 

 mutabile, and Potamides cinctus (fig. 44, p. 30), and the marine beds 

 Venus (or Cytherea) incrassata, a species common to the Limburg 



Fig. 223. 



Neritina concava. 

 Headon series. 



Fig. 225. 



Lymnea caudata. 

 Headon beds. 



Ceritkium concavum. 

 Headon series. 



beds and Gres de Fontamebleau, or the Lower Miocene series. The 

 prevalence of salt-water remains is most conspicuous in some of the 

 central parts of the formation. Mr. T. Webster, in his able memoirs 



