STKATA OF THE HAMPSHIBE BASIN. 141 



of the "Hempstead Series"*. In the second place Forbes demon- 

 strated, by both stratigraphical and palaeontological evidence, that 

 the thick freshwater limestones seen at Bembridge Ledge and in 

 Headon Hill respectively, are not, as had been supposed by all pre- 

 vious writers on the subject, on the same horizon, but that the 

 former of these belongs to a much more recent period than the 

 latter. 



As the result of his observations of the strata and study of their 

 fossils in 1853, Edward Porbes proposed the total abandonment of 

 Webster's classification, and the division of the fluvio-marine strata 

 of the Isle of Wight into four series — the Headon, the Osborne and 

 St. Helens, the Bembridge, and the Hempstead f. This is the 

 classification which was adopted in the publications of the Geological 

 Survey, and is now generally received among geologists. 



Unfortunately, Edward Eorbes's life was not spared sufiiciently 

 long to enable him to complete his study of this important forma- 

 tion. While his observations on the three higher divisions of the 

 formation are very full and detailed, it is evident, from an exami- 

 nation of Eorbes's posthumous work, that he had been able to devote 

 far less attention to the study of the succession of beds and the 

 fossils of the lowest or Headon series. With regard to these strata 

 Forbes maintained, as almost all previous observers had done, that 

 the beds of Colwell and Totland Bays are on the same horizon as 

 those at the base of Headon Hill and at Hordwell Clifi". 



It will be seen that Webster made the mistake of placing all 

 marine bands in the fluvio-marine formation upon one horizon. 

 Prestwich made the first rectification of this error by proving that 

 the Hamstead strata are superior to all the other fluvio-marine 

 strata ; and Forbes followed in the same direction, by showing that 

 the oyster-beds of Bembridge are on a distinct and much higher 

 horizon than those of either ColweU Bay or Headon Hill. I 

 shall now demonstrate that the Colwell-Bay marine beds are not, 

 as has hitherto been supposed, the equivalent of those of Headon 

 Hill and HordweU Cliff, but that they occupy a distinct and much 

 higher horizon. 



Since Edward Eorbes's premature removal from our midst, very 

 great and important additions have been made to our knowledge of 

 the fauna and flora of the fluvio-marine beds of the Hampshire basin. 

 To no one do we owe more for valuable additions to our knowledge 

 of the palaeontology of this formation than to the late Mr. Frederick 

 E. Edwards and Mr. S. V. Wood+, who have collected and described 



* In the choice of this name Forbes was singularly unfortunate. The name 

 of the farm near which the beds are exposed is " Hamstead," though it is mis- 

 printed "Hempstead" on the old 1-inch map of 1810. This name, as it now 

 stands, is not only quite unknown in the Isle of Wight, but runs the risk of 

 being confounded with localities in Essex and Hertfordshire. 



t " On the Fluvio-marine Tertiaries of the Isle of Wight," Quart. Journ. 

 Geol. Soc. vol. ix. p. 259 ; " On some new Points in British Geology," Edin. 

 New Phil. Journ. vol. Iv. p. 263. 



J ' A Monograph of the Eocene Mollusca, Cephalopoda and Gasteropoda,* 

 by F. E. Edwards, supplemented by S. V. Wood ; ' Bivalves,' by S. V. Wood. 

 Palaeontographical Society, 1848-1877. 



