GLACIER-FORMED HANGING VALLEYS 81 



breviated,and when the glacier melts a discordance in gradient between 

 the main valley and its tributary valleys would become manifest. This 

 result would follow under the process referred to, no matter whether 

 the tributary valleys were occupied for a time by secondary glaciers 

 or not. 



Still another manner in which glaciers may give origin to hanging 

 valleys without the aid of differential ice erosion is illustrated about the 

 northern border of the Malaspina glacier, where several alpine glaciers 

 are tributary to a widely expanded ice sheet at the foot of the mountains 

 from which they flow. The surface of the feeding ice streams near their 

 mouths are not at present well adjusted to the surface level of the re- 

 ceiving ice field, but make more or less sharp descents in order to join it. 

 During a previous and higher stage of the glaciers, however, their sur- 

 faces were more nearly in adjustment than at present. The point I wish 

 to make is that a tributary to a piedmont glacier would have its base- 

 level determined by the horizon of the receiving ice field less the thick- 

 ness of the tributary, and, given time enough, would excavate down to 

 that level. Should the glaciers meet after this result had been reached, 

 hanging valleys would appear about the border of the basin or plain 

 formerly occupied by the piedmont glacier. 



To summarize : There appears to be at least six sets of conditions or 

 processes each of which may produce glaciated hanging valleys without 

 necessitating a conspicuously great measure of differential ice erosion. 



To generalize more widely, as I think is justified from the considera- 

 tions presented in the preceding pages, there are at least five sets of con- 

 ditions each of which may produce hanging valleys without the assistance 

 of glaciers and at least six sets of conditions under which glaciated hang- 

 ing valleys may originate. 



Most common Type of Hanging Valleys 



chief characteristics 



As is well known, hanging valleys are a characteristic feature of many 

 formerly glaciated mountains, such as the Sierra Nevada, Cascades, the 

 Alps, the Southern Alps, etcetera. In such mountains conspicuously 

 straight or broadly curved trough-like valleys, U-shaped in cross-profile 

 and several thousand feet deep, are of common occurrence and frequently 

 have tributary glaciated valleys opening into them along their sides at 

 elevations of perhaps 1,000 and in some instances 2,000 or more feet 

 above their bottoms. In the most typical instances the gradients of 

 both the receiving and tributary valleys are low, and the descent from 

 the mouth of a tributary to the bottom of its main valley is precipitous 



