36 STEPHEN R. CAPPS 



seen from the White River Valley, all of the main range which lies 

 west of the international boundary and south of the White River is 

 capped with ice above an elevation of about 7,500 feet. As in the 

 Wrangell Mountains, all of the important valleys which head back 

 into the range are occupied by valley glaciers. 



NUTZOTIN MOUNTAINS 



A few small glaciers have survived in the more favorably situated 

 valleys of the Nutzotin Mountains between the Chisana River and 

 Suslota Pass. The largest of these is not more than three miles long. 



INFLUENCE OF PRESENT GLACIERS UPON THEIR VALLEYS 



Erosive effects. — The existing glaciers are now exerting a most 

 important influence upon the shapes of their valleys. By the rasping 

 of their beds with rock fragments held in the moving ice; by freezing 

 to the bed rock and plucking out blocks of it; and by" undermining 

 the valley walls and causing the material above to fall down upon 

 the glacier, the ice is enabled to remove great quantities of material 

 from the valleys in which it is confined. The result of this erosion 

 is to be seen in the characteristic shapes of the valleys in which it 

 has been effective. Instead of the usual V shape of stream-cut val- 

 leys in rugged, youthful mountains, we find everywhere a broad 

 U-shaped cross-section. The ice tends also to steepen the valley 

 gradient toward the glacier-head, but to reduce it toward the foot 

 of the glacier. In areas from which the ice has retreated, the bed- 

 rock often shows well-marked striations, or surfaces which have 

 been smoothed or polished by the grinding. There is also a notable 

 absence of sharp angular surfaces or protrusions of the bedrock, as 

 all such projections have been worn away by the ice. 



Effects on valleys belozv glaciers.' — Glaciers also have an important 

 influence upon the topography of the valleys below the ice-edge. All 

 of the material which a glacier carries, either inclosed in the ice, or 

 upon its surface, is ultimately carried toward the terminus and dropped 

 as the ice melts away. It often accumulates as considerable moraine 

 deposits, consisting of a heterogeneous mixture of angular or partly 

 rounded rock fragments with finer clays. Often striae can be found 

 upon the included bowlders. 



