148 GEOLOGY OF THE ISLE OF WIGHT. 



CHAPTER XI. 



OLlGOGENE—contiimed. 



Osborne Beds. 



Between the Upper Headon beds, containing Potamomya and 

 the Bembridge Limestone, intervenes a series of strata to which the 

 name of " St. Helen's Series " was originally applied by Professor 

 Forbes in consequence of the " conspicuous features presented by 

 them between St. Helen's and Ryde." This designation was, 

 however, subsequently changed by Professor Forbes to " the 

 Osborne Series," on account of their being displayed in the cJifFs 

 and grounds of the Royal demesne, — a small distance to the east 

 underlying the Bembridge Limestone, and a little to the west in 

 conjunction with the Upper Headon beds, with which they do not 

 appear in connexion at the locality after which they were named 

 in the first instance. 



The total thickuess of the Osborne Beds varies from about 80 

 feet at each end of the island to 110 feet at Cowes and Newport. 



Commencing at the western end of the island it will be per- 

 ceived, on comparing the sections of the Osborne beds at Headon 

 Hill with those at Cliff End, that the thick bed of concretionary 

 limestone seen in the former locality altogether disappears in the 

 latter, where it is most probably represented by the mottled clays 

 and marls in which the remains of Turtle are found, and by the 

 clays with pale-green nodular concretions containing LimncBa 

 longiscata, Paludina globuloides, &c. 



Osborne Series at Headon Hill. 



Ft. In. 



"Whitish (passing into red and bhie) marls, with occasional hard 

 bands, and courses of nodular concretions of light-grey argil- 

 laceous limestone in which occur traces of shells and turtle bones. 

 In the concretions are Limncea longiscata, Planorbis discus, 

 P. obtusus, P. oligyratus, Paludina, sp. - 



Grey shale, with crushed Paludina lenta, fish-vertebra3, &c. 



Ferruginous and nodular band . - . . 



Grey shale, Paludina lenta, Melanopsis carinata. Melania costata. 

 The Fish and Plant Beds - - - - 



Yellow, red, and blue sandy clays - - . - 



Thick concretionary limestone, with silicious concretions sometimes 

 of large size and used for building. This band almost disappears 

 northward. Fossils scarce. Limncea longiscata, Planorbis euom- 

 phalus, P. lens, Paludina lenta - - - . 



Greenish-white calcareous clay - - . . 



Sandy ferruginous band - - - - . 



