138 



WORK OF SNOW AND ICE 



some places in bunches. These various relations are illustrated by 

 Figs. 140 and 141. 



Drainage. Some of the water produced by surface melting 

 forms little streams on the ice. Sooner or later they plunge into 

 crevasses or over the sides and ends of the glacier. In the former 

 case, they may melt or wear out well-like passages (moulins) in the 



Fig. 140. Side view of end of glacier. Southeast side of McCormick Bay, 

 North Greenland. Shows foliated structure of ice as well as position of debris. 



ice, and holes or "wells" in the rock beneath. Much of the surface 

 water sinks into the ice without forming streams. The depth to 

 which water penetrates is undetermined by observation, but it 

 doubtless goes down to the zone of constant temperature in all cases, 

 and still lower where there are crevasses, and where the temperature 

 is not below freezing. 



Once within the glacier, the course of the water is variable. 

 Exceptionally it follows definite englacial channels, as shown by 

 the springs and streams which issue from some glaciers above their 

 bottoms. More commonly it descends or moves forward through 

 the irregular openings which the accidents of motion have made. 

 If it reaches a level where the temperature is below 32 it freezes. 

 Otherwise it remains in cavities or descends to the bottom. The 



