230 GEOLOGY OF THE ISLE OF WIGHT. 



the deposit, and decreased in size in an upward direction, the 

 whole deposit resting on an uneven surface of the Potamomja 

 sands, which underlie the limntean limestone of Totland Bay. 

 Occasionally a layer of small angular flints intervened between 

 the tufa and the sands. 



Helix nemoralis, H. rotundata, Cyclostoma elegans, with 

 occasional Bulimus luhricus and Pupa muscorum are the most 

 abundant land-shells, and occur throughout ; in the loam are 

 Succinea and Limncea, and in the lower part a small Planorhis 

 and fragments of Unio. In addition to the above, the following 

 shells were noticed by Prof. E. Forbes, viz., Helix arhustorum 

 (or nejnoralis), H pulcjiella, H. ericetorum, H. cellaria, H. hispida^ 

 H. hortensis, Achatina ucicula, Clausilia, Pisidium^ Limncea 

 palustris, Succinea ohlonga, Cyclas, &c. 



The only other deposit of similar character is a small patch of 

 shelly tufa immediately below the limestone a quarter of a mile 

 further east. This tufa is seen in the road cuttino; east of York's 

 Farm, but occupies so small an area that it cannot be placed on 

 the map. 



b. The Coast from Freshwater to Blachgang. 



It has been previously explained that the streams which now 

 empty themselves into the sea between Freshwater and Blackgang 

 have once been tributaries of the old river Yar. In consequence 

 of the encroachment of the sea by which the river was intercepted, 

 some curious anomalies have been brought about in the position 

 of the alluvial deposits. 



It will be noticed that a long strip of Alluvium which com- 

 mences near Chilton Chine, only 50 yards from the edge of the 

 cliff, winds away westwards parallel to the coast, catching a 

 little land drainage in its course. At Brook it passes out to 

 the edge of the cliff, and the water from it, cutting through the 

 Alluvium and deep into the Wealden Beds, escapes by the chine 

 so formed to the sea. But a few yards west of Brook Chine 

 another strip of Alluvium appears on the top of the cliff, and, 

 winding round Hanover Point, passes out to the cliff again at 

 Shippard's Chine. This latter isolated strip is, without much 

 doubt, the continuation of the other which runs westward from 

 near Chilton Chine. The separation of the two strips has re- 

 sulted from a comparatively recent encroachment of the sea in 

 Brook Bay. 



The alluvial tract follows the centre of the Valley Deposits 

 of the old Yar, coinciding in position with what must have been 

 the course of that river. That any part of the Alluvium dates 

 back to the time when this river ran through the Freshwater 

 Valley is hardly probable. But it was probably deposited by a 

 diminished representative of the old Yar, gathering the drainage 

 of Brook, Chilton, and still earlier of Brixton and Shorwell, and 

 falling into the sea somewhere a little further south and west than 

 Shippard's Chine. 



