﻿154 
  Bucher 
  — 
  Origin 
  of 
  Ripples, 
  and 
  

  

  pattern 
  which 
  Forel 
  6 
  aptly 
  compared 
  to 
  that 
  formed 
  by 
  

   the 
  grooves 
  of 
  the 
  palm 
  of 
  the 
  human 
  hand. 
  "Where 
  con- 
  

   fined 
  to 
  a 
  narrow 
  channel, 
  the 
  current-ripples 
  are 
  more 
  

   or 
  less 
  crescent-shaped, 
  the 
  convex 
  side 
  directed 
  down 
  

   stream, 
  often 
  not 
  extending 
  across 
  the 
  whole 
  channel. 
  

   Where 
  the 
  current 
  lacks 
  uniformity, 
  the 
  shape 
  and 
  

   arrangement 
  of 
  the 
  ripples 
  tends 
  to 
  be 
  irregular. 
  Irreg- 
  

   ularities 
  of 
  the 
  stream 
  bed, 
  of 
  vortices 
  within 
  the 
  current 
  

   may 
  give 
  rise 
  to 
  a 
  rather 
  complicated 
  arrangement 
  

   (Berthololy, 
  1900, 
  p. 
  94). 
  Vortices 
  forming 
  along 
  the 
  

   bank 
  of 
  a 
  stream 
  may 
  even 
  produce 
  ripples 
  trending 
  par- 
  

   allel 
  to 
  the 
  main 
  current. 
  Several 
  such 
  cases 
  were 
  

   observed 
  by 
  the 
  author 
  along 
  the 
  shores 
  of 
  creeks 
  in 
  the 
  

   vicinity 
  of 
  Cincinnati 
  after 
  floods, 
  7 
  and 
  Berthololy 
  (1. 
  c.) 
  

   reports 
  similar 
  occurrences. 
  

  

  2. 
  Profile. 
  — 
  The 
  profile 
  of 
  a 
  typical 
  current-ripple 
  is 
  

   that 
  of 
  a 
  miniature 
  dune 
  with 
  a 
  gentle 
  stoss-side 
  and 
  a 
  

   steep 
  lee-side. 
  The 
  degree 
  of 
  asymmetry 
  may 
  be 
  

   expressed 
  by 
  the 
  ratio 
  of 
  the 
  horizontal 
  length 
  of 
  the 
  

   lee-side 
  to 
  that 
  of 
  the 
  stoss-side. 
  This 
  will 
  be 
  called 
  the 
  

  

  "horizontal 
  form 
  index," 
  in 
  contrast 
  to 
  ^r- 
  ~ 
  — 
  

  

  amplitude 
  

  

  the 
  ''vertical 
  form 
  index." 
  In 
  the 
  few 
  cases 
  recorded 
  

   on 
  table 
  3, 
  the 
  horizontal 
  form 
  index 
  ranges 
  approx- 
  

   imately 
  from 
  2 
  to 
  4. 
  

  

  3. 
  Lines 
  of 
  flow. 
  — 
  The 
  lines 
  of 
  flow, 
  as 
  represented 
  in 
  

   fig. 
  9A, 
  were 
  first 
  recognized 
  and 
  figured 
  by 
  Darwin 
  

   (1884, 
  p. 
  23), 
  who 
  demonstrated 
  the 
  existence 
  of 
  a 
  vortex 
  

   on 
  the 
  lee-side 
  by 
  placing 
  a 
  drop 
  of 
  ink 
  in 
  the 
  trough 
  

   between 
  two 
  ripples. 
  The 
  action 
  of 
  this 
  vortex 
  causes 
  

   small 
  particles 
  to 
  creep 
  up-stream 
  on 
  the 
  lee-side 
  of 
  a 
  

   ripple. 
  This 
  was 
  repeatedly 
  seen 
  by 
  the 
  author 
  as 
  well 
  

   as 
  by 
  other 
  observers. 
  8 
  

  

  4. 
  Traveling. 
  — 
  Current-ripples 
  travel 
  down 
  stream 
  as 
  

   the 
  grains 
  are 
  rolled 
  up 
  the 
  gentle 
  slope 
  and 
  dropped 
  into 
  

   the 
  vortex 
  of 
  the 
  lee-side, 
  to 
  be 
  deposited 
  there. 
  9 
  It 
  

   should 
  be 
  noted 
  especially 
  that 
  the 
  ripple 
  as 
  such 
  is 
  abso- 
  

   lutely 
  rigid, 
  while 
  just 
  the 
  grains 
  of 
  the 
  top 
  layer 
  roll 
  

   along 
  the 
  surface, 
  no 
  grains 
  being 
  carried 
  in 
  suspension. 
  

   The 
  structure 
  of 
  a 
  current-ripple 
  should, 
  therefore, 
  in 
  the 
  

  

  6 
  1895, 
  p. 
  250 
  (speaking 
  of 
  wave-formed 
  ripples). 
  

  

  7 
  Cf. 
  No. 
  1 
  of 
  tabic 
  2. 
  

  

  8 
  Darwin, 
  1884, 
  p. 
  22; 
  Berthololy, 
  1900, 
  p. 
  86. 
  

  

  "Forel 
  calls 
  the 
  stoss-side 
  "face 
  d 
  'erosion," 
  the 
  lee-side, 
  "face 
  d 
  'al- 
  

   luvion." 
  

  

  