1853.] FORBES — ISLE OF WIGHT. 26/ 



Paludina. At St. Helens Cyclostoma mumia is frequent. Of its 

 freshwater pulrnonifera, Limneus longiscatus and Planorbis discus 

 are the most abundant and generally distributed species. The latter 

 takes the place of the Planorbis euomphalus of the Headon series. 

 Chara tubercidata is the characteristic gyrogonite. From these 

 beds, especially at Binstead near Hyde, have been procured the re- 

 mains of Anoplotheria, PalcBotheria, and other mammals, many of 

 them specifically identical with species of the gypseous series at 

 Montmartre. 



C. The St. Helens Beds. (Figs. 1 & 3, d.) 



These lie between the Headon series proper and the Bembridge 

 limestones. They are very variable in mineral character and thick- 

 ness on the western side of the island, consisting entirely of about 

 60 feet of soft marls and shales, whilst between Ryde and St. Helens 

 they thicken and assume the forms of strong freestones, sandstones, 

 and loose sands ; the first constituting an excellent and much-used 

 building-stone. These beds are of fresh and brackish water origin. 

 They contain numerous remains of mollusks, chiefly Paludina: and 

 Melanice, some of the latter peculiar to the beds ; abundance of a 

 carinated Melanopsis, and peculiar Cyprides. Chara Lyellii is the 

 gyrogonite of this limestone band, which on the eastern side of the 

 Isle of Wight divides the upper or Nettlestone beds from the lower 

 division, or St. Helens sands. 



D. The Headon Series. (Figs. 1 & 3, e,f.) 



These beds are 170 feet thick, or thereabouts. They are seen best 

 at Headon Hill and Colwell Bay, at WhiteclifF Bay, and their 

 lower divisions only at Hordwell. Everywhere Planorbis euompha- 

 lus characterizes their freshwater bands, accompanied by peculiar 

 Limnei. Potomomya plana and Cerithium cinctum abound in the 

 brackish water belts ; and Venus incrassata, accompanied by many 

 sea-shells, some peculiar, more of them common to the Barton series, 

 occurs in the marine division. The group may be subdivided into 

 three sections, all however more intimately connected by their fossils 

 than the subdivisions of the higher series are among themselves. 



a. The Upper Headons. — These form the greater part of what 

 was usually termed the Upper Freshwater, and in Headon Hill were 

 confounded with the superincumbent beds of the St. Helens series. 

 The strongest masses of freshwater limestone in Headon Hill belong 

 to this section, but a little way to the north they thin out consider- 

 ably, and are represented in the WhiteclifP Bay section by a few very 

 thin and inconspicuous sandy concretionary bands. It was the 

 strength of these and the limestones of the lower beds at Headon 

 Hill that seems to have misled former observers into the belief that 

 all the conspicuous limestones in the island belonged to the Headon 

 series. The upper Headon beds consist in their highest part of 

 brackish water bands abounding in Potomomyce and a large variety 

 of Cyrena obovata. At Cliflfend they contain a Cyrena, which, 

 though usually regarded as C. pulchra, appears to be distinct from 



