424 Glaciers. 



long symmetrical mounds lengthwise in the valley, and 

 were deposited at intervals at the side of the glacier 

 when it ceased to fill the valley from side to side, and 

 was gradually decreasing in size. There is also some 

 appearance of an inner terminal moraine where the lake 

 narrows towards its southern end. 



When the ice of these later glaciers of Llanberis and 

 Nant-ffrancon was thickest, in my opinion it could not 

 have been less than 1,300 feet thick in the former, and 

 from 1,000 to 1,200 feet in the latter. 



In Switzerland there is an offshoot of the glacier of 

 the Aletsch which, at the foot of the Aeggischhorn, 

 projects from the great glacier a short way into the 

 valley in which the little lake lies, well known as the 

 Marjelen See. This lake is drained by a small brook, 

 which tumbles down the rocky ground to pass under 

 the glacier of the valley of Viesch. The right and 

 left sides of the lake are bounded by mountains, but 

 the side opposite the outflowing brook is overlooked 

 by an ice-cliff of the Aletsch glacier, which was about 

 60 feet in height where highest when I first visited the 

 spot. The water was then 97 feet deep where deepest, 

 and this I proved by soundings from the edge of the 

 ice-cliff. Occasionally masses of ice fall from this cliff 

 and break up into numerous icebergs, some of them 

 large enough to float boulders of moderate size. The 

 bergs, floating hither and thither, melt by degrees, and 

 boulders and smaller stones are thus scattered over the 

 bottom of the lake. At intervals, it is said, of about 

 eight years, a crack or crevasse opens in the ice, and all 

 the water of the lake passes away under the glacier to 

 swell the river that flows from under its lower end. 



In the valley of Llanberis there are two well known 

 lakes, Llyn Padarn and Llyn Peris, and on a clear day, 



