Royal Institution. 307 



ROYAL INSTITUTION OF GREAT BRITAIN. 



May 13, 1853. — On some New Points in British Geology. By Prof. 

 Edward Forbes, F.R.S., President of the Geological Society. 



Not many years ago it used to be said, that the geology of England 

 was done, and yet the best investigated localities are constantly 

 affording fresh discoveries. When the Lecturer last year exhibited 

 Captain Ibbetson's beautiful and accurate model of Whitecliff Bay in 

 the Isle of Wight, in illustration of his views respecting the distribu- 

 tion of species in time, he had not the slightest suspicion that this 

 particular locality, so often and apparently so thoroughly explored, 

 could yield new results and new interpretations. Nevertheless, 

 having had occasion, at the suggestion of Sir Henry De la Beche, 

 to examine the tertiary strata of the Isle of Wight for the purposes 

 of the Geological Survey of Great Britain, this very bay of White- 

 cliff proved to be a rich source of novel geological information. 

 Moreover, a great portion of the Isle of Wight, on further examina- 

 tion, turned out to belong to a division of the older tertiaries, that 

 had never been demonstrated to exist within the British Islands. 

 As a general statement of these results and of their bearings may be 

 more intelligible to non-professional lovers of geology than the de- 

 tailed memoirs about to be published on the subject, Professor 

 Forbes has taken this opportunity of communicating them to the 

 Members of the Royal Institution. 



The Isle of Wight is divided into two portions by a great chalk 

 ridge running east and west. This is the ridge of vertical chalk 

 beds. To the north of it, the country is composed of tertiary, to the 

 south, of older strata, as far down in the geological scale as the 

 Wealden. The Lower Greensand or Neocomian beds occupy the 

 greater part of the surface of the southern division, and freshwater 

 tertiaries that of the northern. At Alum Bay, on the west, and 

 Whitecliff Bay, on the east, the ends of the older tertiary strata, as* 

 they rise above the chalk, are seen truncated and upturned, being all 

 affected by the movement which caused the verticality of the chalk. 

 These tertiaries constitute the following groups, successively enu- 

 merated in ascending order : the Plastic clay, the Bognor series (equi- 

 valents of the true London clay), the Bracklesham series, and the 

 Barton series, upon which lie the Headon Hill sands, and those 

 freshwater strata that spreading out form the gently undulating 

 country, extending from near the base of the chalk ridge to the sea. 



Owing to the sections at Headon Hill near Alum Bay being so 

 clear and conspicuous, and their position being in the loftiest ter- 

 tiary hill that exhibits its internal structure in the island, the fresh- 

 water and nuvio-marine beds which compose that elevation have 

 long attracted attention and have been described by many observers, 

 the first of whom was the late Professor Webster. The apparent 

 slight inclination of these beds, as seen in the Headon section, 

 except at the point where they are suddenly curved in conformity 

 with the verticality of the chalk and the beds immediately above it, 

 appear to have led geologists to the notion that the nuvio-marine 

 portion of the Isle of Wight was composed entirely of continuations 

 of the beds forming Headon Hill. Two observers only suspected 

 a discrepancy, viz. Mr. Prestwich, who, in a short communication to 



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