﻿186 
  Bucher 
  — 
  Origin 
  of 
  Ripples, 
  and 
  

  

  They 
  must 
  owe 
  their 
  shape 
  to 
  a 
  secondary 
  transforma- 
  

   tion, 
  perhaps 
  connected 
  with 
  the 
  setting 
  of 
  the 
  sediment 
  47 
  

   after 
  the 
  wave 
  motion 
  has 
  ceased. 
  

  

  5. 
  Wave-length 
  and 
  amplitude. 
  — 
  A 
  number 
  of 
  meas- 
  

   urements 
  of 
  wave-length 
  and 
  amplitude 
  were 
  compiled 
  

   in 
  table 
  5. 
  

  

  The 
  following 
  observations 
  pertain 
  to 
  wave-length 
  and 
  

   amplitude 
  : 
  

  

  (a.) 
  When 
  first 
  appearing, 
  oscillation-ripples 
  show 
  a 
  

   wave 
  length 
  which 
  is 
  half 
  that 
  of 
  their 
  full 
  development. 
  

   (Darwin, 
  1884, 
  p. 
  23.) 
  

  

  (b.) 
  The 
  wave-length 
  increases 
  with 
  the 
  velocity 
  of 
  the 
  

   current, 
  that 
  is, 
  amplitude 
  over 
  period 
  of 
  the 
  oscillation. 
  

   De 
  Candolle's 
  and 
  Darwin's 
  experiments 
  have 
  shown 
  that 
  

   the 
  increment 
  of 
  wave-length 
  is 
  proportional 
  to 
  the 
  incre- 
  

   ment 
  of 
  velocity. 
  This 
  law, 
  of 
  course, 
  holds 
  good 
  only 
  

   between 
  two 
  critical 
  points 
  of 
  velocity, 
  between 
  which 
  

   oscillation-ripples 
  like 
  current-ripples 
  can 
  exist. 
  It 
  can 
  

   not 
  be 
  reversed; 
  that 
  is, 
  the 
  wave-length 
  does 
  not 
  

   decrease 
  with 
  the 
  velocity. 
  

  

  Darwin 
  noted 
  that 
  "when 
  once 
  a 
  fairly 
  regular 
  rip- 
  

   ple-mark 
  is 
  established, 
  a 
  wide 
  variability 
  of 
  amplitude 
  

   in 
  the 
  oscillation 
  is 
  consistent 
  with 
  its 
  maintenance 
  or 
  

   increase." 
  Forel 
  demonstrated 
  that 
  any 
  oscillation 
  

   weaker 
  than 
  that 
  which 
  produced 
  the 
  ripple 
  will 
  not 
  affect 
  

   its 
  orientation, 
  even 
  if 
  its 
  direction 
  diverges 
  from 
  the 
  

   original 
  up 
  to 
  45° 
  (1895, 
  p. 
  263). 
  This 
  explains 
  Forel 
  's 
  

   observation, 
  that 
  at 
  the 
  same 
  locality, 
  in 
  the 
  Bay 
  of 
  

   Morges, 
  near 
  the 
  center 
  of 
  the 
  north 
  shore 
  of 
  Lake 
  

   Geneva, 
  the 
  oscillation-ripples 
  never 
  changed 
  their 
  direc- 
  

   tion 
  during 
  three 
  months 
  of 
  observation, 
  although 
  waves 
  

   reach 
  the 
  Day 
  from 
  all 
  directions 
  between 
  east, 
  south 
  and 
  

   west. 
  Their 
  orientation 
  corresponded 
  to 
  waves 
  from 
  

   the 
  south, 
  the 
  direction 
  of 
  the 
  strongest 
  winds. 
  At 
  the 
  

   shore 
  they 
  swung 
  into 
  parallelism 
  with 
  the 
  shore-line 
  

   like 
  breaking 
  waves 
  (ib., 
  p. 
  270). 
  

  

  Since 
  the 
  amplitude 
  of 
  the 
  oscillation 
  at 
  the 
  bottom 
  of 
  

   the 
  water 
  body 
  is 
  a 
  function 
  of 
  the 
  height 
  of 
  the 
  water 
  

   wave 
  above, 
  this 
  must 
  bear 
  a 
  definite 
  relation 
  to 
  the 
  wave- 
  

   length 
  of 
  the 
  ripples. 
  It 
  is 
  not 
  impossible 
  that 
  this 
  

   relation 
  one 
  day 
  will 
  be 
  utilized 
  for 
  a 
  direct 
  determina- 
  

   tion 
  of 
  the 
  decrease 
  of 
  the 
  wave-amplitude 
  with 
  depth. 
  

  

  47 
  The 
  few 
  fossil 
  examples 
  of 
  this 
  type 
  seen 
  by 
  the 
  author 
  consisted 
  of 
  

   very 
  fine-grained 
  limestone, 
  originally 
  a 
  "mud. 
  ,; 
  

  

  