144 ALASKA GLACIERS 



200 to more than 1,000 feet. The immediate walls are 

 1,000 to 2,000 feet high, curving back to rounded sum- 

 mits. On the mainland side the fiord is joined by many 

 troughs of similar depth and character, and by a few 

 hanging valleys. From Vancouver Island it is joined by 

 many hanging valleys. The sills of the hanging valleys 

 best seen lie from 200 to 500 feet above tide and are evi- 

 dently carved from the rock. Below each sill the con- 

 tours of the main trough are continuous, without any de- 

 flection toward the side valley, and the draining stream has 

 only begun the work of grading its channel. A shallow 

 trench is cut on the edge of the sill, and escaping from 

 this, the water tumbles down the open face of the fiord 

 wall. Other valleys hang so high that from our low point 

 of view we could not look into them. At a moderate 

 estimate the highest seen are 1,000 feet above the water, 

 and as these occur opposite the deeper part of the chan- 

 nel it is probable that the maximum discordance of valley 

 floors is not less than 2,000 feet. All the hanging valleys 

 appeared to be steep-sided glacial troughs, and those we 

 saw best are at least several miles in length, with moun- 

 tains behind them. 



For this complicated system of troughs I have not been 

 able to suggest an origin that does not involve an immense 

 amount of excavation by ice. The hypothesis demanding 

 least of the ice is one which assumes the main fiord to 

 follow a belt of weak rock, in which pre-glacial streams 

 had sunk their beds rapidly, outstripping such small trib- 

 utaries as had strong rocks to contend with. Under 

 such conditions, all pre-glacial valleys, with the possible 

 exception of those in the weak rock, would have been 

 narrow gorges, and the work of the ice in enlarging them 

 to existing dimensions would be at least as great as the 

 preceding work of the streams. While this work was be- 

 ing done by the tributary glaciers, the trunk glacier may 



