CORRASION BY GRAVITY STREAMS. 311 



(v) Still younger valley cutting. 



(vi) Ice visitation with the formation of cwms, cribs, 

 facetted spurs, hanging valleys and lake basins. 



There appear to have been at least two ice visitations of 

 importance in the locality of Snowdon. The older and 

 more important one buried the shoulders of the moun- 

 tain in the vicinity of the Orib Goch. The moutonneed 

 appearance of these shoulders is well seen during a walk 

 from Snowdon down the cwm (cirque) under the summit to 

 the Llanberis Pass. A "schrund line "* appears to exist 

 on a shoulder to the left of the track. At a later date 

 a smaller ice stream occupied the lower portions of the 

 valleys. The well defined moutonnees and ice scratched 

 rock masses mark the upward limits of this later ice visita- 

 tion. In the valley constriction near the head of the 

 Llanberis Lake, the mountain spurs may be observed to 

 have been torn away, 2 while steep and rugged cliff slopes 

 or wide spur facets have been left in their place. At the 

 foot of the old steep channel slope of pre-glacial age the 

 long Llanberis Lake occurs. This was evidently made by 

 slow headward recession of the ice fall from an initial 

 basin formed lower downstream. The lake is in just such 

 a position, and is of such a shape as to suggest formation 

 by a stream (See Part I of this Series). With the exception 

 of one of ice, no other stream large or strong enough to 

 excavate such a rock basin in recent times appears to have 

 visited this locality. 



In association with the valley over deepening or lake 

 basin formation, one may see numerous examples of hang- 

 ing valleys and facetted spurs. At the valley heads 

 magnificent cwms (cirques) may be seen. These cwms, for 

 example, the one under the Snowdon hut and down which 

 the track winds to Llanberis Pass, are evidently definite 



1 Gilbert, G. K., (a) p. 582. 2 See also Davis, (a) pp. 338-339. 



