2 Tlie Eocene Formation of Headon and Alum Bay. 



speak in detail, though I shall have occasion more than once to 

 refer to the two former ; as certain broad lines of similarity exist 

 between them, which 1 shall endeavour from time to time to 

 point out. 



A sectional diagram was here exhibited, by the help of which the 

 general geological structure of the Isle of Wight was explained. A range 

 of chalk hills, in which the strata are so highly inclined as to be nearly 

 vertical, extends across the island from Culver Cliff at its eastern, to the 

 Needles at its western, extremity. South of these hills appear in 

 succession the various secondary strata underlying the chalk, extending 

 as low as the Wealden Formation. — The paper continues : — 



Northwards the strata consist of a numerous alternating series 

 in a vertical position, composed chiefly of sand and clay, which 

 may be studied to most advantage in Alum Bay, where they form 

 cliffs of about 200 feet in height. 



The whole of the most north side of the island consists of 

 nearly horizontal strata, which come up abruptly against those 

 which are vertical, but are slightly curved at their juncture with 

 them. Several of these strata are composed of calcareous rock, 

 some loose, others compact, and when they are compared with 

 the strata of the opposite coasts of Hampshire, Dorset, and Sussex, 

 it becomes evident that the date of their origin was posterior to that 

 of the chalk. 



Further, the points of resemblance between these and the great 

 Paris basin are said to be very strong, both in their geognostic 

 characteristics, and in the similarity of their fossiliferous beds. The 

 calcareous beds contain petrefactions of freshwater shells, and in 

 others marine fossils are found agreeing with those existing in the 

 corresponding strata of the Paris basin. 



In tracing the margin of the cavity or escarpment of the chalk, 

 in which these depositions are found, I shall begin with the South 

 Side. This is formed by the middle range of chalk hills in 

 the Island. Sailing Westward from the Needles to Handfast 

 Point in Dorsetshire, we recognize the same picturesque vertical 

 chalk strata, which may be traced thence by Corfe Castle to 

 Lulworth. This range corresponds in direction with that of the 

 Isle of Wight, and the strata in the Isle of Purbeck, though 

 differing in the details, correspond generally to those in the Isle of 

 Wight. 



The clay, however, over the chalk in Dorsetshire, and part of 

 the chalk itself is horizontal, differing in this respect from their 

 position in Alum Bay, which seems to have been produced by some 

 twist in the chalk stratum. 



