80 I. C. RUSSELL — HANGING VALLEYS 



one cited above, the resulting valley is hung up in reference to the de- 

 pression which it faces, and this depression may be a narrow or wide 

 valley, a continental or an oceanic basin. 



The changes in topography produced by mountain-side glaciers in 

 the ways just cited may be likened to the excavation of valleys by tidal 

 glaciers, inasmuch as in each case a local baselevel is established above 

 the bottom of a depression into which the glacier in each instance would 

 have advanced if conditions had not intervened which led to the removal 

 of its distal end. 



The production of rock escarpments across young glacial valleys by 

 the method of " quarrying," as outlined by Willard D. Johnson, so well 

 illustrated in the glaciated canyon of the Sierra Nevada, Cascade moun- 

 tains, and elsewhere, also results in breaking a valley or trough into 

 parts, one of which is left hanging in reference to its next neighbor lower 

 down. It may seem far-fetched to consider the examples just cited as 

 hanging valleys, but in glaciated valleys like those of the Sierra Nevada, 

 etcetera, the highest segment of a glaciated trough frequently leads to 

 a cirque, and in many instances has essentially all the topographic 

 features which pertain to normal hanging valleys on the sides of sim- 

 ilar troughs. The only topographic difference between the two seems 

 to be that the last " tread " in the giant stairway a valley glacier makes, 

 and the hanging valleys recognized by Gilbert and others, is that the 

 tributary enters the main valley at its head and in a direct continuation 

 of its course, instead of from the side. 



In case a glacier originates in the upper portion and is extended down 

 the course of a previously stream-eroded valley, filling it, we will assume, 

 to a depth of 1,000 feet for a distance of many miles, local glaciers may 

 originate on the bordering valley slopes, either in previously stream-eroded 

 gorges or on the precipitous valley side after the manner of mountain-side 

 glaciers, and enlarge preexisting ravines or create new lateral troughs. 

 Such lateral glaciers might become tributary to the main valley glacier, 

 in which case they would have a baselevel of erosion determined by the 

 level of the receiving glacier, less the thickness of the tributary. In this 

 imaginary case, which, as it seems, could be paralleled in nature, the 

 side glaciers would excavate valleys, which, if the ice should melt, would 

 become hanging valleys, in reference to the main trough formerly occu- 

 pied by the receiving glacier, but the discordance between the two would 

 not be due entirely and possibly only to a small extent to differential 

 glacial erosion. 



As has been pointed out by several writers, a large valley glacier which 

 advances down a previously stream-eroded valley tends in an efficient 

 way to straighten and broaden it. By this process lateral valleys are ab- 



