Rivers flu whig upon Glaciers. 183 



glaciers had their greatest expansion the higher mountains were 

 in about their present condition. The increase in the volume of 

 the glaciers was felt almost entirely in their lower courses. 



Characteristics of Alpine Glaciers below the Snow-Ltne. 



The first feature that attracts attention on descending from the 

 neve region to the more icy portion of the glaciers is the rapid 

 melting everywhere taking place. Every day during the summer 

 the murmur and roar of rills, brooks and rivers are to be heard 

 in all of the ice-fields. The surface streams are usually short, on 

 account of the crevasses which intercept them. They plunge 

 into the gulfs, which are many times Avidened out by the flow- 

 ing waters so as to form wells, or moulins, and join the general 

 drainage beneath. The streams then flow either through caverns 

 in the glaciers or in tunnels at the bottoms. While traversing 

 the glacier one may frequently hear the subdued roar of rivers 

 coursing along in the dark chambers beneath when no other 

 indication of their existence appears at the surface. When these 

 subglacial streams emerge, usually near the margin of the ice, 

 they issue from archways forming the ends of tunnels, and per- 

 haj)s flow for a mile or two in the sunlight before plunging into 

 another tunnel to continue their way as before. 



The best example of a glacial river seen during our explora- 

 tion was near the western border of the Lucia glacier. It is 

 shown in the illustration forming plate 12, which is reproduced 

 mechanically from a photograph. This Styx of the ice-world 

 has been described on an earlier page. The lakes formed at the 

 southern end of nearly every mountain spur projecting into the 

 Malaspina glacier discharge through tunnels in the ice, which 

 are similar in every way to those formed by the stream already 

 mentioned. 



In the beds of the glacial streams there are deposits pf sand 

 and gravel, and when the streams expand into lakes these de- 

 posits are spread over their bottoms in more or less regular 

 sheets. When streams from the mountains empty into the 

 lakes, deltas are formed. While these deltas have the same char- 

 acteristics as those built in more stable water bodies, many 

 changes in detail occur, owing to the fluctuation of the water 

 level. 



