34 GEOLOGY OF THE ISLE OP WIGHT. 



It will be noticed that the fossiliferous <2;roup described above 

 corresponds to beds at Bhickgang, in which only a few fossils 

 occur. On the other hand, the strata between Little Stairs and 

 Sandown, though corresponding to richly fossiliferous beds at 

 Blackgang, have yielded no fossils. These differences are princi- 

 pally due to the condition of the rock. Fossils are seldom pre- 

 served in any part of the series near the surface of the ground, 

 but only in the deep-seated strata that are exposed at the foot of 

 the cliffs, and the weathering of the beds, which has reached a 

 depth varying according to local circumstances, has extended 

 below the level exposed in the Sandown cliffs. This weathering 

 consists chiefly in the replacement of carbonate of lime by car- 

 bonate of iron, and the conversion of the latter into peroxide of 

 iron, the effect being to destroy the coherence of the rock and 

 to impart to it a brown colour. The original condition of the rock 

 was probably that of the hard greyish and calcareous concretions, 

 in which alone fossils are found in perfection, even at Atherfield. 



Tlie Sand-rock Series. 



This division is finely exposed in the cliffs from Bonchurch to 

 Knock Cliff. Its base is very clearly marked by the ledge or 

 undercliff formed by the clay last described. A second, but 

 smaller ledge, is formed by a bed of very green clayey grit, at 

 times more clay than grit, which lies about 20 feet higher up. A 

 descending section is as follows : — 



Sand-rock Series at Luccomh and Knock Cliff. 



Carstone (p, 59). IFt. 



f Bright yellow and white sand with laminse 

 { of blue clay in planes of current -bedding. 

 I A few bands of very green sand throwing 



Sand-rock Series ^^^^*«^^Jy^^^*^^^^*^^ " " "^S 



\ W hite and grey sand - - - 50 



I Very green clayey grit, forming a ledge in 



i' the cliff, and throwing out water - 8 



l^White and ashy grey sand and sand-rock - 20 



Ferruginous Sand, &c. 



113 



The lower part of the series may be most conveniently studied 

 at the top of Knock Cliff, and in Luccomb Chine. The upper 

 beds are accessible in the cliff between Luccomb and Bonchurch, 

 the last exposure being in Monk's Bay. The inland sections of 

 these beds in the neighbourhood of Shanklin :ire unusually good, 

 and will be described subsequently (p. 46). 



Sandown to Culver Clijpjp. 



The position of the base of the Lower Greensand is marked 

 here as in Compton Bay by a great founder of the cliff, and at the 



