1922] EDWARDS, GEOLOGICAL WORK AT RAINER NATIONAL PARK 67 



sheet is covered with rock debris. The whole length of the glacier is 

 sHghtly over six miles and for over half of that distance it is sunk into 

 a steep-walled canyon which it has carved for itself. At the snout of 

 the glacier, the Muddy Fork of the Cowlitz river is formed and flows 

 southeastwardly to join the main Cowlitz river some distance outside 

 the National Park. The term "Muddy Fork" might, with equal ap- 

 propriateness, be applied to all those streams issuing from glaciers in 

 this region, as each of them is heavily laden with the debris and rock 

 "flour" brought down by the ice from the mountain above. 



The volcanic material of which this mountain is formed is very 

 easy of erosion, and it is for that reason that these glaciers have been 

 able to excavate such enormous canyons as those in which they now 

 flow. The work of a glacier is performed principally by grinding the 

 rocks of its bed and side-walls. This grinding is due primarily to the 

 weight of the ice upon the stones frozen into its lower surface. It pro- 

 duces a very finely divided rock flour which, because of its fineness, is 

 carried in suspension by streams for a long distance. Where the rocks 

 are of a light color this powder imparts to the water a peculiar milky 

 appearance. At Mt. Rainier, on the other hand, most of the rock flour 

 is derived from dark-colored rocks and the result is that the streams 

 have a chocolate-brown color. 



All of these rivers which are fed from the glaciers of the mountain 

 are liable to a peculiar fluctuation in level. It would, of course, be ex- 

 pected that, since their water supply depends upon the melting of the 

 ice, these streams would vary largely with the season and be very low 

 in the winter and correspondingly high in the summer. This is true, 

 but it is also accompanied by a lesser, though more striking variation of 

 daily occurrence. In the early morning, most of these streams appear 

 to be but small mountain brooks flowing through beds of boulders, but 

 in the mid-afternoon, when the sun's rays have heated to the maximum, 

 the ice from which the streams originate, they become greatly swollen 

 and are able then to move these same boulders. Such a daily varia- 

 tion can be noted in almost all the streams in Rainier Park and in many 

 cases, where it is necessary to ford such streams, it is important to time 

 the arrival at the crossing at an hour when the stream is at its low 

 level. 



The Cowlitz Glacier would have been a very suitable subject for 

 making a panoramic group, but because of the inaccessibility of its 

 lower portion, it was necessary to abandon the idea of working at this 



