300 GLACIAL GEAVELS OF MAINE. 



It is a matter of observation that even small surface streams generally 

 find no difficulty in flowing into crevasses and finding exit by subglacial or 

 englacial channels, whereas waters flowing against the sides of glaciers are 

 usually dammed by the ice until glacial lakes accumulate. One of the best 

 known of such lakes is the Maijelen See in Switzerland, found where the 

 G-reat Aletsch glacier flows past the mouth of a small lateral valley. The 

 lake is about a mile long and one-fourth as wide, its longer axis being at 

 right angles to the glacier. The water of the lake is warmed by the sun,, 

 and also receives the water of several small streams which, during several 

 months of the year, have been warmed on land bare of ice. Many small 

 icebergs fall from the glacier into the water and float about the lake. 

 Obviously the water of 39° must sink to the bottom, below the reach of 

 the smaller bergs, and it will slowly melt away the side of the glacier. 

 The fall of the berglets is probably due to the melting of the ice beneath 

 them. But although the side of the glacier is thus undermined as it flows 

 past the lake, it is not melted away sufficiently to prolong a channel down 

 the valley between the ice and the mountain. It is only after several years 

 that, to use Ly ell's language, owing to " changes in the internal structure of 

 the glacier," "rents or crevasses in the ice open and give passage to the 

 waters." The pressure is so great that the discharge takes place with a 

 loud roaring rush of waters along the central parts of the glacier. That it 

 is along the channel of a subglacial river is proved by the fact that toward 

 the lower end of the glacier a great quantity of water spouts upward 

 tlirough the crevasses and escapes down the steep slope on the surface of 

 the ice. It is evident that at the time of the discharge there is a large 

 opening into the permanent waterways of the glacier, but for some reason 

 the inflowing streams, though in summer warmed on land bare of ice, are 

 not able to maintain the channel. It soon closes, perhaps by being pushed 

 past the mouth of the lateral valley, and the lake is not able again to force 

 an outlet till after the lapse of several years. In the Alps, in Alaska, and 

 in most mountainous countries now glaciated, are many similar lakes 

 formed in valleys lateral to glaciers, and the Parallel Roads of _ Glenroy, 

 Scotland, and many similar raised beaches found in Sweden and Norway 

 mark the sites of ancient but now extinct glacial lakes of this class. 



The inference follows that streams flowing transversely against the 

 sides of glaciers do not readily form subglacial outlets beneath them. The 



