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POPULAR SCIENCE MONTHLY 



Fig. 5. Hanging Valley, Grenville Channel, Inside Passage. The forest-covered lip 

 is solid rock, but it looks like a dam. Doubtless if one went to the crest of this lip he would 

 find the broad valley extending, with moderate grade up the distant mountain. Note the 

 waterfall near center of picture. Photograph by Lawrence Martin. 



of the main valley to which they are tributary, instead of entering at 

 grade, as is normal. 



Where these Alaskan hanging valleys are most typically developed, 

 the appearance is quite remarkable. The valley wall of the long, 

 straight ' Beach ' or ' Canal ' is broken by a broad U-shaped tributary 

 valley, whose cross section, if explained by ordinary methods of valley 

 formation, would require a long period of time for its formation. 

 The stream occupying the hanging valley flows with moderate grade 

 up to the point where the tributary valley is intersected by the straight 

 wall of the main i Beach.' Then, instead of continuing into the main 

 valley with the same grade, it tumbles over the lip of the hanging valley 

 and descends to the fiord in a succession of leaps, sometimes on the 

 very face of the main valley wall (Fig. 4), sometimes in a shallow 

 gorge (Figs. 3 and 5). 



In these most typical cases, there is such an absolute discordance 

 of conditions as to cause comment from even the most casual observers, 

 as I had occasion to observe in many instances in sailing through the 

 Inside Passage. The first feature to attract attention was the water- 

 fall. It was then noticed that the stream emerged from a broad valley, 

 far up which one could look, though without seeing its bottom (Figs. 

 3-5). This produced the impression that the lip of the hanging 

 valley was really a dam across the mouth of a broad tributary valley. 



