CHAP. XIII.] PLEISTOCENE EPOCH. 283 



following are points which call for explanation : (1) that 

 the lowest Boulder-clays are not persistent sheets, but are 

 lenticular beds seldom more than ten feet thick, and sepa- 

 rated by laminated and ripple-marked sands and clays, and 

 these beds are broken off and worked up into contor- 

 tions of the overlying beds to the northward of Trimming- 

 ham ; (2) that the Contorted Drift contains the spoils of a 

 sea-bottom, together with boulders which probably came 

 from Scandinavia, while the upper Chalky clay does not ; 

 (3) that the inland sands and gravels often include 

 irregular and contorted masses of Boulder-clay similar to 

 the Chalky clay which overlies them, and also contain 

 broken marine shells ; (4) that the upper Boulder-clay con- 

 tains Lower Cretaceous and Jurassic detritus, the quantity 

 of which increases north-westward, a fact which proves 

 the ice which formed it to have come chiefly from that 

 direction. 



Passing to the later Glacial deposits described on pp. 

 267 and 268, it may be remarked that the abolition of the 

 old classification of these beds deprives the author of " Pre- 

 historic Europe " of the basis on which he constructed his 

 account of the conditions which prevailed during the forma- 

 tion of the Purple and Hessle Clays (op. cit., pp.266, 267), 

 and adds force to the objections which have already been 

 urged against his theory of the formation of Boulder- 

 clays. 



The presence of the sea during the period of their forma- 

 tion is still more marked than in the case of the East 

 Anglian Drifts, and the materials of which they consist 

 have all been transported from a greater or less distance, 

 so that they contrast strongly in this respect with the older 

 Chalky Boulder-clay, but whether they were accumulated 

 during the uprise of the land from a previous great sub- 

 mergence, or whether a fresh land surface was first formed 

 and a second submergence took place, cannot yet be deter- 



