SNOW-WAVES AND SNOW-RIPPLES 199 



ponents. Where change of their relative velocity 

 occurs there is a change in the proportion of the 

 three grades of material deposited. i 



On " Banner Clouds " and on Sandbanks to Lee- 

 ward of Promontories. 



The following remarks are in continuation of 

 what has been said of structures taking the form 

 of tails or streamers to leeward of a narrow 

 obstruction. 



When wind blows over a peak on a mountain 

 ridge the eddy on the lee side brings up air which 

 is in a different condition as to temperature and 

 moisture from that which comes over the ridge ; 

 and when the two bodies of air mingle with one 

 another the chilling of the warmer part frequently 

 results in the formation of a cloud — the " banner 

 cloud," which is so often seen as a stationary 

 streamer stretching to leeward of a mountain peak, 

 revealing the long eddying wake left in the wind 

 by this projection. Although the cloud is 

 stationary in position, a whirling movement can 

 often be seen in its substance. 



On the coasts of England are several sandbanks 



^ See " Waves of the Sea and other Water Waves " and 

 Journal of the Royal Society of Arts, November 8, 1912, Cantor 

 Lecture by the author on " Ocean Waves, Sea-beaches, and 

 Sandbanks." 



