396 



EARTH FEATURES AND THEIR MEANING 



entirely close the basin with water ice and produce the familiar 

 glacier star (Fig. 424 c). 



If the dirt upon the glacier surface, instead of being scattered, 

 is so disposed as to make a patch completely covering the ice to 



G I e- 1 s 



FIG. 424. Effects of differential melting and subsequent refreezing upon the 

 glacier surface, a, dust wells ; 6, glacier tub produced by melting about a group of 

 scattered dust particles ; c, glacier star produced when the inclosed water of the 

 glacier well has frozen in successive nights; d, "bath tub." 



the thickness of an inch or more, the effect is altogether different. 

 Protecting as it now does the ice below, a local ice hillock rises 

 upon its site as the surrounding surface is lowered, and as this 



FIG. 425. Dirt cone and one with its casing in part removed. Victoria glacier 



(after Sherzer). 



grows in height its declivities increase and a portion of the dirt 

 slides down the side. The final product of this shaping. is an 

 almost perfectly conical ice hill encased in dirt and known as a 



