The classification of the Eocene formations into Upper, Middle, 

 and Lower, adopted in the first edition of the Memoir, has been 

 modified. The so-called " fiuvio-marine beds " of the Isle of 

 Wio;ht are now classed as Oligocene. 



The most important alteration of the Map of the Tertiary part 

 of the Island has been in the tract occupied by the Hamstead 

 (Hempstead) Beds. These strata have been detected by Mr. 

 ileid %' means of a boring apparatus over a large area, so that 

 instead of covering a space of only two or three square miles, they 

 really spread over half of the Tertiary district of the Island. 

 They also prove to be of considerably greater thickness than has 

 been supposed, their actual thickness being 260 feet instead of 

 170 feet. The sections in the Tertiary districts have been re- 

 measured where it was thought desirable. The Chapters on the 

 Tertiary rocks in the present Memoir have been largely extended 

 and in great part re-written. 



In the recent re-survey of the Isle of Wight the superficial 

 deposits have been mapped out in detail. They have been 

 arranged in four groups which are based, as far as possible, on 

 chronological order. Excluding the angular flint-gravel of the 

 Chalk Downs, the age of which is doubtful, the oldest group, that 

 of the Plateau Gravels, is shown to be probably as old as, and 

 perhaps contemp iraneous with, some of the Glacial deposits of 

 the Midlands, But no conclusive evidence has been obtained 

 in the Isle of Wight of the co-operation of coast-ice or land-ice 

 in the formation of these deposits. 



The later groups (Valley Gravels and Alluvia) contain the 

 records of successive stages in the excavation of the present 

 system of valleys. This chapter of geological history possesses a 

 special interest and value from the insular position of the Isle of 

 Wight and the changes that have resulted from the cutting back 

 of the coast-line by the sea. The di-ainage system of the Island, 

 like that of the South of England generally, has been determined 

 by the great lines of anticlinal and synclinal folds into which the 

 Secondary and Tertiary strata have been thrown. Each main 

 anticline became a line of watershed, but in the subsequent 

 gradual denudation of the general surface of the land the forms 

 and elevations of the topography have resulted, not from these 

 underground movements, but from the relative durability of the 

 rocks. The areas of maximum elevation at the present day are not 

 those where the greatest amount of upheaval took place in past 

 time. 



Mr. Strahan's survey of the superficial deposits in the south o£ 

 the Isle of Wight affords a glimpse of an older and different 

 topography before the Chalk Downs of that region had been 

 reduced to their present limited area. An extensive sheet of 

 river-gravel in the south-west of the Island marks the course of 

 what must at one time have been a considerable stream, taking its 

 rise among the Southern Downs which then stretched southwards 

 into the English Channel. As Mr. Codrington has suggested, 

 this stream flowed westwards and northwards by Freshwater to 



