87 



A Str<iti<jf<ij)Jii<nl Account of the Section from Round Tower 

 Point to Alum Bay, on the North-west coast of the Isle of 

 Wight. By Thomas Wright, M.D. 



Read 1/tii September 1850. 



Tn i publication of Cuvier and Bronguiart's celebrated ' Descrip- 

 tion Geologique des Environs de Paris' formed an important 

 epoch in the history of geology in general, and of the tertiary 

 system of the Isle of Wight in particular. The appearance of 

 this work induced the late Mr. Thomas Webster, Secretary to the 

 Geological Society of London, to make in 1813 a minute exami- 

 nation of the structure of the island, with the view of comparing 

 the beds at Headon Hill with those described by the French 

 naturalists in the environs of Paris. He adopted the classifica- 

 tion of these authors, and divided the coast section at Alum Bay 

 in a descending order into — 



5. Upper freshwater formation. 



4. Upper marine formation. 



3. Lower freshwater formation. 



2. London clay. 



1. Sands and plastic clay. 



In 1816 Sir Henry Englefield published his splendid work on 

 the Isle of Wight, which contains numerous coast sections most 

 accurately drawn by Mr. Webster, together with a series of letters 

 by the same accurate observer written from the island whilst 

 on a tour made expressly for collecting materials for Sir Henry's 

 work. 



In 1821 Mr. G. B. Sowerby visited Headon Hill, to collect 

 fossil freshwater shells for the illustration of Ferussac's great 

 work on 'Land and Freshwater Mollusca/ and to obtain a re- 

 gular series of the strata above the chalk. He published a cri- 

 ticism* on Mr. Webster's paper, in which he dissented from many 

 of that author's descriptions, but especially from that part which 

 related to the upper marine formation. He described what he 

 supposed to be a mixture of shells belonging to freshwater and 

 marine genera in this bod, and inferred therefrom its estuary 

 and not its marine origin as stated by Webster. He pointed out 



* Annals of Phiiosopln . vol. ii. 1821, p. 216. 



i 2 



