290 



GEOLOGY. 



The deepening of a valley by glacial erosion may throw its tribu- 

 taries out of topographic adjustment. Thus if a main valley is lowered 

 100 feet by glacial erosion while its tributary is not deepened, the lower 

 end of the latter will be 100 feet above the former when the ice dis- 

 appears. Such a valley is called a hanging valley (Figs. 262 and 263). 

 Such valleys are of common occurrence in regions recently glaciated, 

 but now ice-free. Examples are common in the western mountains 

 of North America and elsewhere. 



Ice-caps which overspread the surface irrespective of valleys and 

 hills, tend to reduce the angularities of the surface. Hills and ridges 

 are cut down and smoothed (Figs. 264 and 265); but since valleys 

 parallel to the direction of movement are deepened at the same time, 



^•^ 



Fig. 262. — A hanging valley. East side of Lake Kootenai, B. C. All except the 

 highest summits glaciated. (Atwood.) 



it is doubtful if ^he rehef of the surface is commonly reduced by the 

 erosion of an ice-cap. 



Fiords. — A glacier descending into the head of a narrow bay may 

 gouge out the bay to a very considerable depth, causing its head to 

 recede. When the ice finally melts, the bay may be a fiord. Thus 

 have arisen the glacial features of many of the fiords of high-latitude 

 coasts, and many of the glaciers of those coasts are now making fiords 

 (Fig. 266). Fiords also arise in other ways. Coasts indented by 

 fiords are likely to be bordered by islands. 



The positions in which debris is carried. — As a result of the methods 

 by which a glacier becomes loaded, there are three positions in which 



