138 WAVES OF SAND AND SNOW 



tions of loose sand would have their steep face 

 turned away from the wind, pits excavated in 

 cohering sand would have their steep side facing 

 the wind. 



The last erosion form in snow to which I need 

 refer was an uncommon one of crescentic shape, 

 of which I give a drawing for the purpose of com- 

 parison with the form of the crescentic waves, or 

 barchans, in loose snow (Fig. 1 1). The cliff faces 

 the wind instead of being turned away from it, 

 and the gently sloping side is concave, instead of 

 convex, towards the sky. 



Note on the Longitudinal Sand-dunes of the 

 Great Indian Desert. 



I deal in this book almost entirely with what 

 I have myself observed in the field, but the 

 following paragraph relates to sand-dunes which 

 I have not seen but which have been elaborately 

 mapped and mineralogically examined. 



The prevailing winds in the region of the Great 

 Indian Desert are south-west and north-east, of 

 which the south-west is the stronger. Far inland 

 the dunes are transverse to this common direction 

 and face north-east. Near the sea they consist of 

 very long ridges with equally steep slopes on either 

 side and trend from south-west to north-east. At 



