1853.] ‘OF THE ROYAL INSTITUTION. 317 
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 section 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 fluvio-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 fluvio-marine 
portion of the Tsle 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 
the British Association at Southampton, expressed his belief that 
Hempstead Hill, near Yarmouth, would prove to be composed of 
strata higher than those of Headon ; and the Marchioness of Hastings, 
who, having given much time to the search for the remains of fossil 
vertebrata in the tertiaries of the Isle of Wight and Hordwell, 
declared her conviction that these remains belonged to distinct 
Species, according as they were collected at Hordwell, Hempstead, 
and Ryde, and that these three localities could not, as was usually 
understood, belong to the same set of strata. The recently pub- 
lished monograph of the pulmoniferous mollusks of the English 
Eocene Tertiaries, by Mr. Frederic Edwards, afforded also indications 
of the shells therein so well described and figured having been col- 
lected in strata of more than one age. 
A few days’ labour at the west end of the island convinced Pro- 
fessor Forbes that the surmises alluded to were likely to prove true, 
and that the structure of the north end of the island had been in the 
main misunderstood. After four months’ constant work at both 
extremities and along the intermediate country, he succeeded in 
making out the true succession of beds, with most novel and gratifying 
results. During this work he was greatly aided by his colleague, Mr. 
Bristow, and by Mr. Gibbs, an indefatigable and able collector 
attached to the Geological Survey. 
