STUDIES FOR STUDENTS. 62 I 



the snow found itself at the close of the successive seasons of 

 melting. A small amount of dust descends from the atmosphere 

 with the snow when it falls. As the snow and ice melt, this is 

 set free, and, in its proper measure, swells the amount of dust 

 which gathers upon the surface in other ways. 



Surface melting has been greater at the end of a glacier 

 than at any point above. If it has not been washed away, there- 

 fore, the amount of dust which has passed from an englacial to 

 a superglacial position, as the result of surface melting, must be 

 greatest at the end of the glacier. Since the amount of wind- 

 borne superglacial dust which has had no englacial history is also 

 greatest here, it follows that the total amount of superglacial 

 dust which has come through the atmosphere, must be greatest 

 near the ends of glaciers, unless' conditions have prevented its 

 preservation. The dust is most likely to remain where the sur- 

 face of the ice is smoothest, and where there is little surface 

 drainage. Material blown upon the ice is much finer than most 

 of that which descends from the slopes above. 



2. PIEDMONT GLACIERS. 



Piedmont glaciers owe their origin to the fusion or coalescence 

 of several alpine glaciers. All the material which was on the 

 surface of the alpine glaciers which unite to make a piedmont 

 glacier, will be at the surface of the latter from the beginning. 

 All the englacial material which was carried by the contributing 

 alpine glaciers in their upper parts will become superglacial on 

 the piedmont glacier, so soon as surface melting has brought the 

 surface down to its horizon. Since the only piedmont glaciers 

 concerning which we have knowledge have little motion, surface 

 melting must greatly predominate over basal melting, and the 

 proportion of englacial drift which becomes superglacial must 

 therefore be great. On the Malaspina 1 glacier, which stands as 

 our representative of piedmont glaciers, superglacial drift is most 

 abundant near the eds^e, where surface ablation has been greatest. 



1 Russell, expedition to Mt. Saint Elias. National Geographical Magazine, vol. III. 

 pp. 53-204, also Journal of Geology, vol. I., No. 3, 1893. 



