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SMITHSONIAN MISCELLANEOUS COLLECTIONS 



[vol. 47 



the ice getting a purchase upon the thin covering of ground moraine 

 and by a series of minor advances and retreats pushing it up into 

 concentric ridges and detached knolls. Later a more general advance 

 permitted the ice to override the structures, but so lightly that they 

 were simply smoothed and rounded without being completely de- 

 stroyed, and the surface dressing of sand and gravel was applied 



Fig. 85. — A suggestion of Wisconsin-morainic topography ; in front of 

 Wapta glacier. 



as the ice finally retreated. Tn miniature, with their smooth contours 

 and undrained basins, they strongly remind one of the morainic 

 topography left by the latest ice sheet in America and Europe. 



6. Glacial Granules. — In both the Wapta and Illecillewaet glaciers, 

 on account of their size, unusually good material is to be obtained 

 for the study of the granules, of which the glacier from its neve to 

 its nose is known to be composed. About the lower end of the 

 Wapta these granules range from 5 to 70 mm. in maximum diameter 

 and seem to average between 20 and 30 mm., becoming gradually 

 smaller towards the neve. These granules are irregular polyhedrons 

 with their faces so firmly pressed together in general that no inter- 

 spaces occur and the ice appears homogeneous and of uniform color. 



