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PLIOCENE GLACIERS, ETC. OF WALES, 



13 



Caernarvon and Beddgelert, The country was thus broken tjppee 

 into a group of islands, each one of which in great part had GALLERr - 

 its covering of snow and ice, permanent till large changes . T; L bl e-case 



® iii Recess 41 



(perhaps of physical geography) produced a decided ame- 

 lioration of climate. 



■ This amelioration did not, however, take place till after 

 the re-clcvation of the land, and after this upheaval, in 

 the greater valleys large glaciers were formed which in 

 Wales ploughed the drift cut of the Passes of Nant Francon 

 and Llanberis, and left untouched the marine drift deposits 

 that cover the broad spreading table lands that lie on the 



►raine, whi sides of these valleys at their mouths 



Another proof of the former existence of glaciers is to be 

 space on ani found in the polishing, scratching, grooving, and deep fur- 

 r was kep: rowing of the rocks over which the glaciers flowed, mag- 

 tile climffi nificent examples of which occur in many a Highland valley, 

 aine becai in Cumberland, Wales, Ireland, and the mountains of the 



Vosges. These precisely resemble what formerly took place 

 by the greater extension of the Alpine glaciers, and what 

 is now produced underneath and at the sides of glaciers 

 that still exist. In Wales, wherever a tributary glacier 

 has flowed into a valley, a series of lines is to be found, 

 branching from the general direction of the grooves that 

 mark the bottom and sides of the main valley. In Nant 

 Francon, for example, in the main valley, the striaB follow 



its course (20° to 25 



N 



in the tributary 



valleys they run east and north-easterly, according to their 

 curves ; while in entering Cwm Idwal from Nant Francon 

 they curve gradually round from E.S.E. to N.N.E. The 

 same is equally striking in the neighbourhood of Snowdon, 

 where, in the Pass of Llanberis, the grooves and stria? first 

 strike from 30° to 35° south of cast, and gradually curve 

 round to the south, as a portion of them pass into the high 

 tributary valley of Cwm Glas ; or, again, in Nant Gwynant, 

 where, in the main valley, they strike to the south-west, 

 and branch off first to the north-west, and gradually curve 

 round to the north in the higher part of Cwm-y-Llan : and 



