108 WAVES OF SAND AND SNOW 



underwent a transformation, for ridges facing to 

 windward were formed by erosion of the compact 

 snow. The snow of the drifted waves (which face 

 to leeward) had, moreover, set hard during the 

 still nights, and remained immobile. Thus the 

 snow exhibited two kinds of ridges — one with their 

 faces towards the wind, the other facing to lee- 

 ward : the former with a surface grooved and 

 scarped, the latter with a surface generally 

 smoother and more rounded. The appearance to 

 the novice is a mere confusion of forms, but when 

 I had learnt the secret of the two kinds of waved 

 surface produced in loose and compact snow 

 respectively I could always recognize the two sets 

 of forrns, and detect order where all at first had 

 seemed chaotic. 



I have now described two occasions upon which 

 the formation of travelling waves occurred when 

 wind was removing a level deposit of loose snow. 

 On another day I saw the formation of such waves 

 during the covering of the ground by a fresh snow- 

 fall accompanied by wind. The surface was hard 

 and glazed, being that of old snow which had 

 thawed and been afterwards frozen. The snowfall 

 began at 10.30 a.m., at about the time I arrived 

 upon the ground, and continued throughout the 

 day, accompanied by a light to moderate breeze. 



