16 CONTENTS 



CHAPTER II 



PAGE 



AEOLIAN SAND-RIPPLES ..... 



All aeolian sand-waves have a rippled surface — 75 

 Description of the formation of aeolian sand-ripples 

 in level deposits of loose sand blown from the beach — 

 Measurements of height and length — The ripples grow 

 without change of shape — Ratio of length to height 

 the same as in the larger sand-waves — Rate of advance 

 — Winnowing of fine from coarse sand-grains observed 

 during growth of aeolian ripples — " Erosion ripples " 

 formed where the level of the sand is being lowered — 

 The formation of a protecting cover of " lag gravel " 

 on the crests — Experiments by means of an artificial 

 blast — No rippling of assorted sand-grains of uniform 

 large size, although travelling freely — Immediate 

 rippling when small sand-grains mixed with them — 

 Explanation offered, that eddy in lee of larger grains 

 tosses away the smaller, hence the existence of ripples 

 upon the larger waves — Ripples in shell-sand showing 

 lines of notches in the wave-fronts where the troughs 

 are deeper. 



PART II 



SNOW- WAVES AND SNOWDRIFTS 

 CHAPTER III 



SNOW-WAVES AND SNOW-RIPPLES . . -93 



Ripples in Moist Snow. 



Damp snow and dry snow — Ripples in moist snow 

 during snowfall observed in Hyde Park — They face up- 



