﻿196 
  Bucher 
  — 
  Origin 
  of 
  Ripples, 
  and 
  

  

  what 
  extent 
  the 
  principles 
  established 
  for 
  subaqueous 
  

   ripples 
  are 
  applicable 
  to 
  eolian 
  ripples. 
  An 
  adequate 
  

   treatment, 
  especially 
  of 
  the 
  surprising* 
  variety 
  of 
  forms 
  

   of 
  dunes 
  and 
  of 
  the 
  great 
  diversity 
  of 
  factors 
  entering 
  

   into 
  their 
  formation, 
  would 
  lead 
  too 
  far. 
  

  

  1. 
  Eolian 
  current-ripples. 
  

  

  The 
  general 
  characteristics 
  and 
  the 
  origin 
  of 
  sub-aerial 
  

   current-ripples 
  are 
  the 
  same 
  as 
  those 
  of 
  sub-aqueous 
  rip- 
  

   ples. 
  They 
  form 
  and 
  exist 
  between 
  two 
  limits 
  of 
  wind 
  

   velocity, 
  corresponding 
  to 
  our 
  first 
  and 
  second 
  critical 
  

   points. 
  (Hahmann, 
  1912.) 
  

  

  Their 
  formation 
  on 
  a 
  smooth 
  sand 
  surface 
  begins 
  with 
  

   the 
  appearance 
  of 
  small 
  pits 
  (King, 
  1916, 
  p. 
  197), 
  which 
  

   gradually 
  coalesce 
  to 
  form 
  ripples 
  and 
  increase 
  consid- 
  

   erably 
  in 
  size 
  till 
  they 
  reach 
  the 
  maximum 
  development 
  

   for 
  the 
  given 
  wind 
  velocity. 
  This 
  process 
  is 
  exactly 
  the 
  

   same 
  as 
  already 
  described 
  for 
  water 
  ripples, 
  but 
  owing 
  

   to 
  the 
  much 
  smaller 
  density 
  of 
  air, 
  it 
  meets 
  with 
  greater 
  

   difficulties. 
  Perfect 
  uniformity 
  (Cornish, 
  1889; 
  Hah- 
  

   mann, 
  1912) 
  as 
  well 
  as 
  too 
  great 
  a 
  disproportion 
  (King, 
  

   1916, 
  p. 
  204) 
  in 
  the 
  size 
  of 
  the 
  grains 
  prevents 
  the 
  forma- 
  

   tion 
  of 
  ripples. 
  In 
  the 
  former 
  case 
  to 
  move 
  one 
  grain 
  

   means 
  to 
  move 
  all, 
  while 
  very 
  large 
  grains 
  among 
  much 
  

   smaller 
  ones 
  will 
  not 
  move, 
  when-necessary, 
  with 
  sufficient 
  

   readiness, 
  thus 
  effectively 
  preventing 
  the 
  small 
  eddies 
  to 
  

   coalesce. 
  

  

  As 
  to 
  shape 
  and 
  structure, 
  wind-formed 
  current-ripples 
  

   in 
  general 
  resemble 
  those 
  formed 
  under 
  water. 
  Of 
  the 
  

   characteristics 
  that 
  have 
  been 
  suggested 
  by 
  different 
  

   authors 
  as 
  a 
  means 
  for 
  the 
  distinction 
  of 
  eolian 
  and 
  sub- 
  

   aqueous 
  ripples, 
  only 
  one 
  seems 
  sufficiently 
  established, 
  

   to 
  warrant 
  its 
  application 
  in 
  the 
  interpretation 
  of 
  fossil 
  

   ripples. 
  From 
  a 
  great 
  number 
  of 
  individual 
  measure- 
  

   ments 
  of 
  both 
  eolian 
  and 
  subaqueous 
  ripples, 
  Cornish 
  

   drew 
  the 
  conclusion 
  that 
  the 
  ratio 
  of 
  wave-length 
  to 
  

   amplitude, 
  that 
  is, 
  the 
  vertical 
  form 
  index, 
  is 
  consider- 
  

   ably 
  greater 
  in 
  the 
  former. 
  The 
  average 
  for 
  subaqueous 
  

   ripples 
  is 
  12: 
  for 
  eolian 
  18. 
  57 
  These 
  ratios 
  are 
  of 
  value 
  

   primarily 
  as 
  averages. 
  They 
  seem, 
  however, 
  to 
  apply 
  

   fairly 
  well 
  to 
  m< 
  aes. 
  From 
  the 
  data 
  in 
  my 
  tables 
  it 
  

  

  seems 
  that 
  the 
  ratio 
  is 
  even 
  more 
  likely 
  to 
  be 
  larger 
  in 
  

  

  aiah, 
  V. 
  On 
  Snow 
  Waves 
  and 
  Snow-drifts 
  in 
  Canada, 
  Geosrr. 
  Journal, 
  

   vol, 
  20, 
  p. 
  151, 
  1902. 
  

  

  