122 WAVES OF SAND AND SNOW 



size of fine sand — but these particles were too 

 friable to maintain themselves intact as projections 

 upon the surface. 



The almost icy crust formed during the night 

 upon the surface of the snow-waves would, I think, 

 when broken up form snow-sand capable of 

 rippling, and I have explained how this might 

 perhaps be produced without melting and re- 

 freezing. 



On the afternoon of January 25th on the prairie 

 near Winnipeg much of the snow-sand was drift- 

 ing low over the hard, unlevel surface of the old 

 snow, never rising more than a few inches above 

 the ground. The temperature was about zero 

 Fahrenheit, and the wind had a velocity of 27 miles 

 an hour— /.^., that of a strong breeze. The 

 low sun, casting shadows from the steeper lee 

 faces, threw the ripples into relief. The drift- 

 ing snow-sand accumulated in the shallow de- 

 pressions in the surface of the old, hardened 

 snow. These deposits quickly fell into ripples. 

 The increase of their wave-length was more 

 rapid than that of aeolian sand-ripples, and 

 their motion was also more rapid. In one of these 

 patches of snow-sand, ripples having a wave-length 

 of 9 inches advanced that distance in i minute 

 50 seconds — i.e., at the rate of 49 inches per 



