PREFACE. 



The onward progress of geological science during more than a 

 quarter of a century since the first edition of the present Memoir 

 appeared has not left the Isle of Wight unaffected. The 

 geological formations on which the beauty of that fair Island so 

 largely depends have been studied in great detail in all parts of 

 the South of England, as well as in foreign countries. The coast- 

 sections of the Isle of Wight have even become subjects of discus- 

 sion and controversy. When, therefore, the first edition of this 

 Memoir was nearly exhausted, and it became necessary to under- 

 take the preparation of a second edition, I felt that no satisfactory 

 progress could be made in this task until the Map of the Island 

 had been first revised and brought abreast of the present con- 

 dition of Geology. The publication of the large Ordnance Survey 

 Maps on tlie scale of six inches to a mile supplied for such a 

 revision a far more accurate and convenient basis than was 

 available at the time when the Island was originally mapped by 

 the Geological Survey. 



Accordingly, Mr. Bristow, the Senior Director, to whom 

 science is mainly indebted for the first Survey Map of the Isle of 

 Wight, and for the Memoir descriptive of the structure of the 

 Island, undertook the serious labour of superintending the pre- 

 paration of new editions, both of Map and Memoir. 



In the following Prefatory Note supplied by him he has stated 

 how this work has been carried on under his general supervision. 

 The revision of the Map became in fact a re-survey of the Island, 

 as all the lines were retraced on the ground. It is, however, due 

 to Mr. Bristow to add that the main geological lines remain 

 nearly as he mapped them more than 30 years ago. 



In the preparation of the present edition of the Memoir so many 

 and important have been the changes required that the work 

 might not unfairly be described as a new one. The revision alike 

 of Map and Memoir has been made under Mr. Bristovv's direction 

 and with his co-operation, by two of the officers of the Survey, 

 Mr. C. Reid, who took the Tertiary area, and Mr. A. Strahan, who 

 had assigned to him the Secondary Kock.-\ I have also myself 

 personally visited the Island with Messrs. Reid and Strahan, and 

 read over on the grovmd the proofs of the following chapters. 

 I will here briefly mention some of the more important alterations 

 and additions. 



In discussing the relations of the Wealden to the Upper 

 Neocomian Rocks it is shown that these two groups are separated 

 by a sharply-defined lithological demarcation, accompanied by a 

 paljeontologicnl break. 



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