238 THE GEOLOGY OF THE ISLE OF WIGHT. 



darker towards the lower part. It contains numerous existing 

 land-shells, among which are Helix aspersa, H. nemoralis, H. 

 cricetorum, H. virgata, H. rotundata, Bulimus luhricus, &c.* 

 It rests on the northern slopes of a small outlier of the Chalk 

 Marl, but extends a few yards beyond the boundary of the Chalk, 

 so as to touch the Upper Greensand. It is made up almost 

 enth*ely of small fragments of Chalk and Chalk mud, but con- 

 tains a little Upper Greensand, and a very few fragments of 

 chert. It is clearly a rain-wash from the slopes of a hill of Chalk, 

 which must have once existed, to the south, but of which the 

 small outlier is the only surviving fragment. The remainder of 

 the hill has slipped down to various positions in the Undercliff, 

 one of the most striking; features of which is the o^reat slices of 

 Chalk and Upper Greensand, still retaining their relative posi- 

 tions. 



The inland limits of the deposit are altogether indefinite, but pre- 

 sumably tend to follow the boundary of the Chalk, though slightly 

 overlapping it as in the cliff. Similar deposits would probably be 

 seen along the greater part of the base line of the Chalk, were 

 there any sections to show them. Agriculturally they are im- 

 portant, for they produce a chalk-soil over the outcrop of the 

 Upper Greensand. In the same way the guttering down of the 

 Gault, described on p. 58, has spread a clay-soil over the 

 outcrop of the Carstone, and part of the Sandrock Series. 



* Helix aperta also appeared in the list in the 1st edition of the Memoir. But as 

 the authority is not forthcoming, and the occurrence of this continental shell is im- 

 probable, it is now omitted. 



