32 WAVES OF SAND AND SNOW 



pyramids of Sakhara. I had to land upon an 

 extensive stretch of loose sand uncovered by the 

 subsidence of the river, which was then at a 

 low stage. The river-borne sand is very different 

 from the somewhat coarse, rounded, quartz sand 

 of the desert, being composed of minute 

 particles of many different minerals, including 

 flakes of light -coloured mica and splinters of 

 dark -coloured minerals derived from eruptive 

 rocks. Many of the splinters stuck in a wire 

 sieve with a mesh of y^-inch diameter, but many 

 slipped through a mesh of g-J^ of an inch. The 

 sand that lay even a little above the present level 

 of the river was thoroughly dried by the action 

 of the sun and of the desiccating desert wind. 

 A brisk wind was blowing of about the force which 

 sailors describe as a " moderate breeze," which has 

 a velocity of 1 5 miles an hour. The light sand 

 drifted freely before it, not only close to the 

 surface but also in considerable quantity for a 

 height of several feet above. The appearance of 

 the sand -bank was very remarkable, for the 

 surface was in regular ridges and furrows, or 

 waves, transverse to the wind. They were on an 

 average i foot 8 inches in height with a wave- 

 length from crest to crest of 30 feet 9 inches. 

 They were desk -shaped, having a long slope on 



