DESERT SAND-DUNES 



65 



a ridge was growing with a steep lee cliff to the 

 west and the original east cliff for its weather side. 

 Thus each of the four large sand-dunes presented 

 the appearance of a wave with its crest curled back 

 (Fig. 2). It was evident that if the present wind 

 persisted long enough these sand-dunes would be 

 completely reversed, for the eastern faces were, 

 no doubt, being flattened. 



Fig. 3. 



I saw the ridge of one great sand-dune with 

 four peaks and three intermediate saddles (Fig. 3). 

 The sand being so much coarser than that of the 

 Helwan sandbank, the ridges can, however, grow 

 to a large size before the sand in a saddle is 

 ploughed off, making vertical sinuosities inevitable. 

 In some cases there were very prominent peaks 

 with a great mound of sand piled against their 



