176 WAVES OF SAND AND SNOW 



roofed over the cover would have the shape of 

 a sole, plaice, or other flat-fish lying head up- 

 stream. 



In the case of both snow-barchans and sand- 

 barchans there is sometimes a longitudinal ridge 

 projecting to leeward from the middle of the cliff 

 (Fig. 27). -When the barchan possesses this 

 adjunct it is more easy to realize its structural 

 similarity to the swirl left when an oar leaves the 



Fig. 27 



Longitudinal growth on lee sids of a» 

 travelling snow'drift. 



water at the end of its stroke. The surface of 

 the water shows an eddying disturbance travelling 

 astern with a boundary convex to the direction of 

 its motion and on the bow side, or side towards 

 the oar, a right-handed and a left-handed spiral 

 or vortex in which the water revolves round a 

 vertical axis. A current is visible flowing astern 

 and entering the whirlpool between the right and 

 left-handed spirals, supplying water to replace that 



