SNOW-WAVES AND SNOW-RIPPLES 113 



saw subsequently on frozen lakes I concluded that 

 the increased friction upon the surface of these rem- 

 nants rendered possible the complete covering of the 

 ice when the snowfall was accompanied by wind. 



It was with peculiar interest that I found, not 

 only that more regular and extensive series of 

 travelling snow-waves were formed upon the flat 

 and open prairie than in undulating and enclosed 

 country, but that the waves formed also on per- 

 fectly level and smooth ice of a large frozen lake. 

 The latter observation afforded a remarkable con- 

 firmation of the view I had already advanced, that 

 waves in granular material do not require for their 

 formation the existence of an eddy-making obstruc- 

 tion, as was formerly held, but inevitably originate 

 upon an unobstructed surface from the silting and 

 scouring action which is exercised when the wind 

 (blowing as it always does with variable velocity) 

 has a speed, even in the lulls, sufficient to pick 

 up the particles, which must be themselves of such 

 a density and size that they do not follow the lines 

 of flow of the air, but subside at an appreciable 

 rate. 



Crescentic Snow -waves or Snow -bar chans. 



When there is only a small amount of loose, dry 

 snow drifting over a hard surface it does not accu- 



