CHAP. XIII.] PLEISTOCENE EPOCH. 265 



of subsidence, and the modern river-gravels one of 

 emergence. 



England and Wales. 



Glacial Deposits. In the mountain districts, as in Scot- 

 land, there are traces of Boulder-clays and morainic de- 

 posits which contain local debris and have other special 

 characters, and sometimes these are seen to pass beneath 

 newer clays which contain far-travelled boulders and are 

 associated with sands containing marine shells. These two 

 sets of Glacial deposits are well developed in Lancashire, 

 Cheshire, and North Wales, and their differences have been 

 described by Mr. Mellard Eeade 1 and Mr. A. Strahan. 2 



So long ago as 1852 Sir Andrew Ramsay showed that 

 in North Wales there had been an early glaciation by 

 glaciers, followed by a submergence of at least 1,400 and 

 probably of 2,000 feet, and that when the land again 

 emerged from the sea it was once more occupied by a sys- 

 tem of glaciers which have left their terminal moraines in 

 many of the valleys. The proofs of submergence consist 

 in the existence of stratified marine deposits at high levels ; 

 thus, on Moel Tryfaen in Carnarvonshire there are sands 

 and gravels containing shells and overlain by Boulder-clay 

 at a level of 1,350 feet. Most of the stones and boulders 

 are of local rocks, but among them are pieces of granite 

 from Eskdale in Cumberland, and flints probably derived 

 from the Chalk of Ireland. In the county of Flint, between 

 levels of 1,100 and 1,250 feet, there are gravels contain- 

 ing broken shells and erratics which have come from the 

 Snowdon and Arenig ranges to the eastward, while close 

 by are trains of boulders which have come from the north- 

 ward. What relation these deposits bear to the low-level 



1 " Quart. Journ. Geol. SOP.," vol. xxxix. p. 83. 



2 Ibid., vol. xlii. p. 369. 



