VIII] 



SAND DUNES 



125 



as this formation of ridges depends upon constancy 

 of direction of the wind, it is only occasionally 

 apparent on our own coasts, and the ridges themselves 

 are only of small dimensions ; for here the variable 



Fig. 20. Showing a stone, and a bunch of dead grass as seen on the 

 beach after a high wind. Each has a long streamer of sand 

 collected under its lee. In the close foreground are wind-ripples. 



direction of the wind is liable soon to destroy such 

 constancy of form as a gale of some days may have 

 produced. 



There has been some controversy as to the method 



