184 Dr. FiTTON on the Strata below the Chalk. 



Gault. — This stratum consists, in the Isle of Wight, of dark, bluish grey, harsh, sandy clay, in- 

 terspersed with minute particles of mica : but I did not discover, anywhere, the beds of light 

 bluish, plastic clay, like that of Folkstone, whicli abounds in the characteristic fossils, and which, I 

 believe, forms the lower part of tlie formation. The clay here, which seems not to exceed 70 feet 

 in thickness, contains very few fossils, and these, from their imperfect preservation, are difficult to 

 obtain. The tract, however, which this stratum occupies has been very little explored. One of 

 the best sections of the gault whicli I saw, was at East-End, between Luccombe and Bonchurch, 

 where the clay contains nodules, and branching crystalline rods of pyrites, some thin sliells in frag- 

 ments, and minute crystals of sulphate of lime, perhaps produced by decomposition. The top of 

 the sands beneath this stratum, here slopes both towards the west, and outward, towards the sea ; 

 so that on the melting away of the gault, everything favours the subsidence and ruin of the upper 

 part of the cliffs. 



Lower Green-sand. — This stratum, which forms the principal portion of Mr. Webster's ' Ferrugi- 

 nous Sands,' occupies a great part of the surface on the south of the Isle of Wight, and is 

 everywhere conformable to the chalk ; a ridge of highly inclined strata of sand parallel to that of 

 the central chalk, crossing the island, from the shore on the south of Bembridge Down to the foot 

 of Afton Down. The sands are then reflected southwards, and form tlie lower ground in the 

 interior, from Mottestone, through Brixton, Shorwell, Kingston, Godshill, and Newchurch, to 

 the coast. Tiiroughout the greater part of the shore at the ' back of the island,' this stratum is either 

 below the level of the sea, or concealed by the debris of the undercliff; but where it rises, — 

 westward from Rocken-End, and eastward from Bonchurch Cove, it exhibits the most distinct and 

 fully developed sections. 



When I examined the Isle of Wight, I was not aware of the subdivision of the Lower green-sand 

 into the groups, which I afterwards found to be so well displayed in Kent (16, &c.), and Western 

 Sussex (72.) ; but from the map of the island, and the characters of the strata on the coast, I have 

 no doubt that it exists also here. A range of heights from Kingston to Walpen, which in the Ord- 

 nance Map is a very prominent feature, and seems to be continued to the shore between Walpen 

 and Whale Chines, appears to be the outcrop of the upper member of the formation ; and the 

 heights on the south of Chale seem also to belong to this uppermost or ferruginous subdivision ; 

 while the darker beds of Shanklin and Blackgang Chines must represent the middle, or more 

 retentive group : and even among the highly inclined strata of the Red-cliff, in Sandown Bay, green, 

 mud-like, beds are distinguishable in the corresponding part of that escarpment. A bed at the 

 bottom of the cliffs, both at Atherfield, and on the east of Shanklin, which abounds in fossils, espe- 

 cially the Gryphcea sinuata, is probably the equivalent of the lowest group of stone at Hythe. The 

 total thickness of the Lower green-sand in the Isle of Wight may be considered as about 300 feet. 



(94.) The Wealden. — The Purbeck strata do not make their appearance in 

 the Isle of Wight; and the two remaining- members of the Wealden pass into 

 each other by insensible gradation^ the Weald clay constituting but a small 

 proportion of the whole. A valley or depression^ however^ corresponding 

 to the site of the clay, is still a well-marked natural feature : the escarpment of 

 the green-sands projecting over it on the one hand ; while on the other, the 

 Hastings sands rise into a small prominence, even in the compressed section 

 of Sandown Bay ; and form, on the west, an undulating, dome-shaped ridge, 

 between Barne's Chine and Compton-Grange Chine, the section of which 

 corresponds to that of these sands on the Sussex coast. 



