1916.] THE DEPOSITS. 387 



the author is in favour of the view that the boulder clays and 

 the associated gravels result from the action of floating ice. 



This view is well supported by the evidence which we 

 have here, for the deposits of clay, as already said, are best 

 described by an ice-cap lifted, but not removed, by a sea-level 

 approximately at the level of the top of the island. 



THE EVIDENCE OF SUBMERGENCE. 



1 think it will be justifiable for me to produce both local 

 and collateral evidence of the submergence, for it is a point 

 which has and will be strongly debated. 



If we find that there are reliable authorities who hold 

 that belief for the south of England, and we may, I think, 

 take it that their conclusions also apply to the islands, for it 

 is inconceivable that the submergence of the south of England 

 could have occurred without the islands being involved. 



Dr. Nils Olof Hoist, in a paper on " The Ice Age in 

 England," in discussing the brick earth or what we here speak 

 of as the Upper Clay, says " The deposits from the two stages 

 of depression, the pre-glacial or raised beach stage and the 

 glacial stage (this author only formulates one glacial period, 

 A.C.) demand special attention. After discussing the nature 

 of the " brick earth," which agrees with our upper deposit, 

 our author describes a depression of the land which was filled 

 with water. " This loam contains no fossils. If this basin 

 had been filled with sea water this would be quite impossible. 

 Almost equally impossible would it be if it contained fresh 

 water. There remains, therefore, no other possibility than 

 that the water was glacial, coming from the inland ice (of the 

 continent) and the tundras, that the basin was closed in the 

 north by inland ice and in the south by an elevation of the 

 sea-floor from Finisterre north-westwards." 



However caused we have here the opinion of one who 

 has carefully reviewed the whole evidence that at least two 

 submergences have occurred. 



Prestwich also indicates two submergences, for he 

 describes (op. cit.) a pre-glacial series of beaches to a 

 height of nearly 200 feet (see ante) and also a submergence 

 causing the drift of post-Mousterian times. I think, however, 

 that the " Head " described as proof of the post-Mousterian 

 submergence is here a composite one including the deposits 

 of a pre-Mousterian submergence. 



To account for the different deposits, Prestwich, instead 

 of placing them in different submergences, formulates one 

 only and a succession of rapid thrusts of the land upwards out 



J 



