S. V. Wood, Jun. — Bepli/ to Mr. James Geikie. 175 



and of the seas by a moUuscan assemblage, not merely all of living 

 species, but one that differs in but a slight degree from that inhabit- 

 ing the English coast near at hand. Mr. Harmer and I, in 1870, 

 called attention to the character of the mollusca of the Lancashire 

 middle sand, and to the possibility suggested by this character, that 

 such sand, and the Upper Boulder-clay of the North-west of England, 

 might belong to the Hessle group ; for the mollusca of this middle 

 sand (which I have now got from Wales, Cheshire, and Lanca- 

 shire) is all of the same modern and contiguous English-coast 

 character as that of the Hessle (Kelsea Hill) gravel, and of some 

 Norfolk and Cambridgeshire post-glacial beds. In these two 

 counties we have beds yielding a moUuscan fauna of the same 

 British-coast character, — viz., at March and several other places in 

 that neighbourhood, at Hunstanton, and at several places in the 

 Nar Valley, — and these occupy spaces from which the Glacial beds 

 have been removed by denudation. Erom the knowledge since 

 gathered by us as to these beds, and from the various evidence 

 which has reached me from the North-west of England, and from 

 the Severn valley, the possibility suggested by Mr. Harmer and my- 

 self in 1870 has grown in our minds into a probability of some 

 strength. One fact which weighed with us adversely to this view 

 was the limited thickness of the Hessle clay, and the comparative 

 paucity and usually small size of the boulders in it ; although one 

 from this clay at Hessle, now in the Museum of the Literary and 

 Philosophical Society at Hull, is of considerable size, and deeply 

 grooved by parallel striae. This, however, seems to me capable of a 

 satisfactory explanation by reference to the geographical conditions 

 attending the occurrence of this clay ; for under the limited amount 

 of submergence indicated by it, when compared with that under 

 which the true Glacial deposits were accumulated, its nearest source 

 of supply would be the higher parts of the Chalk Wold, then an 

 island, and the next the island formed by the Eastern Moorlands — 

 sources far more limited than the entire shed of one side of the 

 Pennine chain. On the other hand, the lower elevations of the 

 North-west of England, over which the Upper Boulder-clay of that 

 region extends, would receive the entire material brought down by 

 the glaciers occupying the valleys on the Western side of the Pen- 

 nine Chain during that part of the Post-glacial period to which the 

 Hessle clay belongs, when, as it seems to me, a high degree of cold 

 returned upon Europe, bringing with it the Eeindeer, and eventually 

 also bringing about the extinction of the great Pachydermata. In a 

 similar way the lower parts of North Wales, over which this Upper 

 Boulder-clay and its underlying sand with modern British coast 

 mollusca extends, and the Severn Valley, which is occupied with 

 thick gravel-beds, yielding a similar modern British-coast moUuscan 

 fauna, would receive the entire material brought down by the 

 glaciers occupying the valleys of the Welsh mountain district. In 

 the North-east of England Mr. Eome and I, subsequently to the 

 publication of our paper, traced an Upper Boulder-clay and under- 

 lying sand through the Vale of York into that of the Tees, which 



