128 GEOLOGY OF THE ISLE OF WIGHT, 



Owing to the high dip and absence of any topographical feature, 

 it has been found impossible to separate the Osborne from the 

 Headon Series on the Map. These two series are therefore shown 

 by a single colour, though described separately in this Memoir, 



Headon Beds. 



This series, as a whole, consists of a mass of beds of fresh- 

 water, estuarine, and marine origin, the total thickness of which 

 varies from 147 feet at Headon Hill to 212 feet at WhiteclifF 

 Bay. It is only at the western extremity of the Island, between 

 the river Yar and the sea, that the Headon series covers an 

 extensive area, elsewhere it is comprised in a narrow belt of 

 land, between the Headon Hill Sands and the Osborne Series. 

 These beds are best displayed at Headon Hill, in Totland and 

 Colwell Bays, and in Whitecliff Bay. There is also a small 

 section of the upper portion — now almost entirely overgrown or 

 hidded by the sea-wall — on the coast close to Norris Castle and 

 Osborne. 



The Fluvio-marine formation, which extends over the northern 

 portion of the Island, forms an undulating tract of country, the 

 scenery of which presents a marked difference to that of the more 

 open district covered by the Cretaceous rocks on the south, owing 

 to the greater abundance of woods with which the surface is in 

 many places covered. The land situated on the limestones is of 

 a more fertile description than that based upon the clays or sands, 

 but over a considerable part of the Island mapped as Fluvio-marine 

 there is a thick deposit of flint gravel spread over the surface, 

 which conceals the underlying strata, and causes the agricultural 

 nature of the soil to bear no relation whatever to the rocks 

 beneath. From the highly inclined position of the beds in the 

 neighbourhood of the Chalk, the lower members of the formation 

 are comprised, for the most part, within comparatively narrow 

 limits, and the chief portion of the superficial area occupied by 

 the Fluvio-marine series consists of the upper members of that 

 group. The thick beds of limestone in this formation thin out 

 towards the north, and nearly disappear in an easterly direction. 



The Headon Series was subdivided by Edward Forbes into : — 

 J J fjjp^evmost inavhi \fith. Cerifhium lapidian? 



Lipper ^Upper Headon freshwater and brackish beds. 



2. Middle ; Headon intermarine. 



3. Lower Headon fresh and brackish-water beds. 



The following sections, measured during the original survey 

 of the Island, will give a good idea of the nature and fossils of 

 these beds. It must not be Ibrgotten, lioweAcr, that each of the 

 minor divisions is extremely variable, and many of them are 

 found to die out or entirely change their character in short 

 listances. 



