Travels in Alaska 



July 20. I kept wet bandages on my eyes last night 

 as long as I could, and feel better this morning, but all 

 the mountains still seem to have double summits, 

 giving a curiously unreal aspect to the landscape. I 

 packed everything on the sled and moved three miles 

 farther down the glacier, where I want to make meas- 

 urements. Twice to-day I was visited on the ice by a 

 hummingbird, attracted by the red lining of the bear- 

 skin sleeping-bag. 



I have gained some light on the formation of gravel- 

 beds along the inlet. The material is mostly sifted 

 and sorted by successive rollings and washings along 

 the margins of the glacier-tributaries, where the sup- 

 ply is abundant beyond anything I ever saw else- 

 where. The lowering of the surface of a glacier when 

 its walls are not too steep leaves a part of the margin 

 dead and buried and protected from the wasting sun- 

 shine beneath the lateral moraines. Thus a marginal 

 valley is formed, clear ice on one side, or nearly so, 

 buried ice on the other. As melting goes on, the 

 marginal trough, or valley, grows deeper and wider, 

 since both sides are being melted, the land side 

 slower. The dead, protected ice in melting first sheds 

 off the large boulders, as they are not able to lie on 

 slopes where smaller ones can. Then the next larger 

 ones are rolled off, and pebbles and sand in succession. 

 Meanwhile this material is subjected to torrent-action, 

 as if it were cast into a trough. When floods come it is 

 carried forward and stratified, according to the force 

 of the current, sand, mud, or larger material. This ex- 

 poses fresh surfaces of ice and melting goes on again, 



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