GLACIERS OF MOUNT RAINIER 



Gradually, also, the glacier covers itself with debris. 

 Angular rock fragments, large and small, and quan- 

 tities of dust, derived from the rock walls bordering 

 the ice stream higher up, litter its surface and hide the 

 color of the ice. At first only a narrow ridge of such 

 material a moraine, as it is called accompanies 

 the ice river on each side, resembling a sharp-crested 

 embankment built by human hands to restrain its 

 floods ; but toward the lower end of the glacier, as the 

 ice wastes away, the debris contained in it is released 

 in masses, and forms brown marginal bands, fringing 

 the moraines. In fact, from here on down it becomes 

 difficult to tell where the ice of the glacier ends at the 

 sides and where the moraines begin. 



The lower part of the glacier also possesses a peculiar 

 feature in the form of a debris ridge about midway on 

 its back a medial moraine. Most of the way it 

 stretches like a slender, dark ribbon, gradually nar- 

 rowing upstream. One may trace it with the eye up 

 to its point of origin, the junction of the two main 

 branches of the glacier, at the foot of a sharp rock spur 

 on the mountain's flank. 



In the last mile of the Nisqually's course, this medial 

 moraine develops from a mere dirt band to a conspicu- 

 ous embankment, projecting 40 feet above the ice. Not 

 the entire body of the ridge, however, is made up of rock 

 debris. The feature owes its elevation chiefly to the pro- 

 tective influence of the debris layer on its surface, which 

 is thick enough to shield the ice beneath from the hot 

 rays of the sun, and greatly retards melting, while the 

 adjoining unprotected ice surfaces are rapidly reduced. 



A short distance above the glacier's terminus the 

 medial moraine and the ever-broadening marginal 

 bands come together. No more clear ice remains 

 exposed, irregular mounds and ridges of debris cover 

 the entire surface of the glacier, and the moraine- 

 smothered mass assumes the peculiar inchoate appear- 

 ance that is so striking upon first view. 



