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YEARBOOK, PUBLIC MUSEUM, MILWAUKEE 



[Vol. 11. 



is composed of ice and is covered with a thin coating of dust. Such 

 irregularities, shown in figure 39, are called "dust cones." 



In sharp contrast to this action are other places where small 

 accumulations of dust cause the concentration of the sun's heat and 

 they are gradually lowered into the surface of the glacier until they 

 reach a point where the side of the opening shelters the dust particles 



Fig. 39. — A dust cone on the surface of Nisqually Glacier. 



from the rays of the stm. These little pits are called "dust wells" and 

 are very abundant on the surfaces of some of the glaciers. 



The many crevasses which cross the glacier are also of great 

 interest and never fail to excite the imagination of a visitor on account 

 of their great variety of form and color. In many of the crevasses 

 the ice is rather clear in the upper layers, being whitish and looking like 

 hard-packed snow. Farther down in the ice mass the tint changes to 



