282 



Sierra Club Bulletin. 



South 



to those at the head. Figure i shows diagrammatically 

 the ground plan of a glacier flowing northward. The 

 greatest snow accumulation is in the cirque, AA, where 



precipitation is at a maximum, 

 where depletion through solar 

 influences is at a minimum, 

 and where circling cliffs pro- 

 tect against removal by the 

 wind. There is great accumu- 

 lation also along the west 

 margin, BB, where the snow 

 drifted by the westerly winds 

 comes to rest in the shelter of 

 the west wall of the glacier 

 trough. Along the eastern bor- 

 der, CC, the snow deposit is 

 comparatively small, because 

 of exposure to the westerly 

 winds. The resulting lines of 

 ice-flow are as drawn. Mov- 

 ing directly away from the 

 walls of the cirque, the glacier 

 makes and annually renews 

 the bergschrund ab. Moving 

 obliquely away from the west 

 wall of the trough, the gla- 

 cier similarly produces the minor bergschrund be, and 

 this minor bergschrund leads to sapping and the produc- 

 tion of a cliS, just as the major bergschrund causes the 

 cirque cliff. Thus the west wall of the trough is kept 

 steep, and is thereby contrasted not only with the east 



Fig. I. — Diagrammatic ground 

 plan and section of a glacier. 

 The heavy line abc marks the 

 position of the bergschrund. Dotted 

 lines show direction of ice flow. 

 The broken line marks the crest of 

 the spur separating the glacier from 

 its neighbor on the west. 



