12 



PLIOCENE GLACIERS, ETC. OF WALES. 



Other 



moraines 



The mouth of a 



GailIet. strikin S examples of this phenomenon. 

 - - — ' dam up lakes in a more peculiar manner. 

 in Recess 41. valley is surrounded by a mound or series of united mounds 



curving outwards, formed of earth, angular, subangular 

 and sometimes smoothed and scratched stones, so truly 

 moraine-like in their arrangement, that their origin and 

 the places whence they came are unmistakeable. A deep 

 clear lake lies inside, and the drift of the glacial sea, full of 

 boulders, slopes right up to the outside base of the moraine, 

 with a long smooth outline, showing that the glacier de- 

 scended to the sea level, and pushing for a certain dis- 

 tance out to sea, formed a marine terminal moraine, while 

 ordinary drift detritus, partly scattered by floating ice, was 

 accumulating beyond. In the meanwhile the space on and 



kept 



glacier 



was 



surrounding 



beyond the sea level occupied by the 



clear of debris ; and when the land arose, and the climate 



ameliorated, the hollow within the terminal moraine became 



replenished with the water -drainage of the 



hills, just as in earlier times it was filled with ice formed 



by a drainage of snow. Such, in Caernarvonshire, are the 



lakes of Lly n Dulyn, Melynllyn, Ffynnon Llugwy, Marchlyn- 



mawr, and Marchlyn-bach ; and in Scotland it would not 



be difficult to find parallel cases. Judging by the present 



o 



Welsh 



that confine them were formed, the highest parts of the 

 mountains of Caernarvonshire (the snow drainage of which 

 gave birth to the glaciers) could not have been more than 

 from 1,400 to 2,000 feet above the sea. The average great 

 intensity of cold maybe inferred from this circumstance, for 

 the sea then flowed through some of the greater valleys 

 between the Menai Straits and Cardigan Bay, across the 

 present watersheds of the Passes. The principal of these 

 are the Vale of Conwy, and its upper branches to Capel 

 Curig, &c. ; the Pass of Nant Francon, and its continuation 

 between Llyn Gwynant and Capel Curig ; the Pass of Llan- 

 beris, opening into Cwm Gwynant (about 1,000 feet high 

 at the watershed) ; and the Valley of Afon Gain, between 





it: 



