North Wales. 



423 



symmetrical moraine crosses the valley in a crescent- 

 shaped curve. 



Another striking example of the moraines of a 

 retreating glacier may be seen in Llyn Idwal, first 



FIG. 88. 



Glacier of the Pass of Llanberis. 



described by Mr. Charles Darwin in 1842. Below an 

 amphitheatre of steep hills and cliffs lie the waters of 

 Llyn Idwal, which are dammed up by ice- worn rocks 

 strewn with moraine. Below the moraine, down to the 

 Ogwen, the rocks are strikingly moutonnee, the striations 

 gradually curving round NW. to take the direction of 

 the main valley. On either side of Llyn Idwal lie several 

 moraines, four in number on the west. They run in 



