102 WAVES OF SAND AND SNOW 



the sand-waves and their motion was much more 

 rapid. The weather faces were being rapidly 

 scoured away, whilst the lee cliffs were built out 

 by the arrival of snow from two directions, some 

 pouring over the edge of the cliff from the wind- 

 ward, some being swept back to it along the 

 surface from the leeward. Their advance was 

 sufficiently rapid to be easily visible, and the effect 

 of the silent, stealthy creep of the whole series of 

 waves across the field was extremely weird. The 

 snow thus travelling in waves was only a part 

 of what the wind was drifting, for much was per- 

 manently in suspension, whirling along at a great 

 rate in the air as a thin haze extending high above 

 my head. The waves were in isolated ridges with 

 hard snow between. They had an average wave- 

 length of 15 feet 104 inches, and an average 

 height of 4" 9 i^iches, so that their length was 3 8' 8 6 

 times their height, or in other words, they were 

 only half as steep as the aeolian sand-waves. The 

 profile of passive waves in granular material simply 

 shows the form of the wind eddy. A ridge of the 

 loose snow, which is less resistant than a ridge of 

 sand, cannot withstand as strong a pressure. If 

 the ridges were built artificially to greater steep- 

 ness, the horizontal thrust of the wind would plough 

 off the upper layers. 



