98 WAVES OF SAND AND SNOW 



inequalities did not long survive when the wind had 

 cut down to lower layers of snow which had become 

 compact owing to the pressure to which they had 

 been subjected by the superincumbent layers. 



The density of snowfall varies from' minute to 

 minute, and the result is to produce an incipient 

 stratification. Pressure develops this, so that the 

 deeper layers when uncovered have a strongly 

 marked horizontal stratification, the beds being 

 usually a fraction of an inch in thickness. The 

 result of this is that at first the wind here forms 

 long transverse cliffs of minute height facing up- 

 wind, but the hard particles eroded therefrom' do 

 not adhere to the smooth surfaces, but, on the 

 contrary, erode after the manner of a sand-blast. 

 Thus, wherever a notch or re-entrant angle is 

 formed in a cliff it is rapidly increased, and soon 

 the transverse ridges are cut quite through. The 

 last structures to survive are longitudinal ridges 

 with a cliff, or sometimes an overhanging cornice, 

 facing the wind. These are, I believe, the 

 structures often referred to in narratives of polar 

 travels as sastragi. 



These observations of the change from trans- 

 verse to longitudinal structure during erosion of 

 compact snow were confirmed and extended during 

 the following winter, which I spent in Canada. 



