52 J. PRESTWICH ON THE QUATERNARY PHENOMENA 



Hope's Nose near Torquay, and then taking a nearly direct line across 

 Bridport Bay to the south end of Portland. Thence, at some distance 

 beyond, it passed more inland, ranging near Fareham and Chichester, 

 to Brighton, and to the Straits of Dover. Up this channel the shingle 

 was drifted, as to a certain extent at present, from the westward, 

 while floating ice transported the larger blocks found in places on the 

 Sussex coast from more distant localities. 



In the mean time an east and west anticlinal disturbance slowly 

 elevated the Weymouth district, and with it part of the Purbeck and 

 Portland area — succeeded or accompanied by a denudation which 

 not only levelled but deeply channelled the uplifted areas. At the 

 close of this period Portland must have presented nearly the same 

 features as at present, only that the surface was varied by the presence 

 of hills of the Middle Purbeck strata. The final submergence of 

 which we have before spoken, and the subsequent emergence, buried 

 the old cliff and sea-line under the mass of angular debris washed 

 down from the adjacent land (denuding possibly some areas more 

 deeply), and left the district much as we now see it, with its pleasant 

 variety of hill and dale, its well-marked and bold escarpments, and 

 its diversified geological features. 



Note on the Fossil Shells. By J. Gwtn Jeffreys, Esq., P.R.S. 



I have examined the shells and washed shell-sand from the raised 

 beach at Portland, collected by Mr. Prestwich. The shells are 

 rather northern than southern ; but but I have not detected any 

 peculiarly arctic species, and certainly none of a Mediterranean or 

 Lusitanian type. All the species inhabit the British coasts from 

 Shetland to Yorkshire, except one, which I consider un described, and 

 propose to name Bissoa subcylindrata. I subjoin a description of 

 this species. Another species (Trochus helicinus) has not, so far 

 as I am aware, been found south of Yorkshire and Dublin Bay. The 

 most northern known locality for another species (Trochus umbili- 

 catus) is Stornoway in the outer Hebrides; and it occurs in a 

 raised beach at Portrush*. 



The freshwater bed which overlies the raised beach contains 

 very few species of Mollusca. These shells I am disposed to re- 

 gard as northern, although the species have an extensive distri- 

 bution southwards. 



J. Gwyn Jeffreys. 

 Ware Priory, 

 9th June, 1874. 



Bjssoa subcylindrata, Jeffreys. 



Shell somewhat cylindrical, solid, opaque, glossy: sculpture none, 

 except occasional lines of growth : colour whitish : spire rather short ; 

 apex blunt : whorls 4-5, convex, regularly increasing ; the last 



* All the shells belong to the littoral zone. The sand and its contents appear 

 to have formed part of a beach or strand in the neighbourhood of rocks. 



