SNOW- WAVES AND SNOW-RIPPLES 105 



The snow-waves advanced 6 feet 6 inches in 

 forty minutes, or at the rate of 2 inches per 

 minute, which is about two hundred times as fast 

 as the rate of advance which I observed in aeolian 

 sand-waves in a wind of rather less strength. The 

 speed of the sand-waves was, however, measured 

 by the advance made during forty-eight hours, and 

 the wind dropped during the nights. If the 

 measurements of the waves of sand and snow had 

 been made under precisely similar conditions, the 

 rate of advance of the latter would have been, 

 perhaps, fifty times as great as that of the former. 



The snow-waves were not rippled upon the sur- 

 face. The reason of this is, no doubt, that the 

 friable snowflakes provided no obstructions to take 

 the place of the coarser sand-grains which, 

 travelling only on the surface and forming an eddy- 

 making barrier where they accumulate, produce the 

 rippled surface of the sand-waves in the manner 

 which I have already explained. 



On the flat and more open prairie near Winni- 

 peg snow-waves are formed in larger groups than 

 in the fields round Montreal. On the i8th of 

 February, the temperature being zero Fahrenheit 

 and a strong wind blowing, I went out from the 

 city of Winnipeg on to the open prairie. Five 

 inches of fresh, dry snow had fallen in calm weather 



