GLACIERS 



219 



plane away the angularities of the surface, reducing and 

 smoothing the slopes. Where hilltops are worn, the tend- 

 ency is to reduce the relief. Where glaciers move along the 

 axes of valleys, they tend 

 to widen and deepen them, 

 and so to increase the re- 

 lief. 



Ice-worn hills and ba- 

 sins. Hills that have 

 been eroded vigorously by 

 ice sheets are usually of 

 characteristic form (Fig. 



232). The side against and FIG. 232. Lamberts Dome. A glaci- 

 i . i , i , ated hill of granite. Upper Tuolumne 



up which the ice moved Rivei , (Fa i rbanks .) 

 (the stoss side) suffered 



most wear, and was lengthened and smoothed. The side 

 away from and down which the ice moved (the lee side) is 

 commonly the shorter and steeper, and was sometimes left 

 rough and irregular by plucking. Where it crosses valleys 

 and basins, and erodes them, an ice sheet usually wears chiefly 

 the sides opposed to its advance, making them gentler and 

 smoother (Fig. 233). 



The shapes of glaciated rock hills and basins, then, record 

 the direction of movement of ancient glaciers, the longer 

 and smoother slopes facing the direction whence the ice 



came. Since minute projections 

 and depressions are similarly 

 the ice, the 



FIG. 233. - Diagram showing sha P ed 



change which may be made in tion of any Small Surface of glaci- 



the cross section of a valley by ated bedrock will usua lly snO w the 

 an ice sheet which moves across ~ 



it. Dotted line shows side of direction in which the ice moved. 



valley before glaciation. ( How much CQuld be tol( j CQn . 



cerning the direction of movement by the trend of the 

 stria3?) 



Ice-shaped valleys. Valley glaciers tend by erosion to 

 widen and deepen their valleys and to steepen and smooth 



