﻿Related 
  Sedimentary 
  Surface 
  Forms. 
  189 
  

  

  This 
  calls 
  attention 
  to 
  a 
  factor 
  which 
  is 
  of 
  some 
  impor- 
  

   tance 
  in 
  connection 
  with 
  the 
  interpretation 
  of 
  fossil 
  rip- 
  

   ples. 
  The 
  waves 
  which 
  produced 
  a 
  velocity 
  sufficient 
  to 
  

   form 
  ripples 
  of 
  4-5 
  inches 
  wave-length 
  at 
  a 
  depth 
  of 
  20 
  

   ft., 
  had, 
  of 
  course, 
  a 
  higher 
  orbital 
  velocity 
  at 
  the 
  depth 
  

   of 
  2 
  feet. 
  This- 
  velocity 
  ought 
  to 
  have 
  produced 
  ripples 
  

   of 
  larger 
  wave-length, 
  since 
  5 
  inches 
  (12-7 
  cm.) 
  probably 
  

   was 
  not 
  the 
  greatest 
  wave-length 
  possible 
  on 
  the 
  sedi- 
  

   ment 
  in 
  question. 
  According 
  to 
  Forel's 
  observations, 
  

   such 
  large 
  ripples, 
  if 
  ever 
  formed, 
  would 
  persist. 
  Their 
  

   general 
  absence 
  is 
  good 
  evidence 
  that 
  they 
  never 
  formed. 
  

   We 
  are, 
  therefore, 
  led 
  to 
  the 
  conclusion 
  that 
  above 
  a 
  cer- 
  

   tain 
  minimum 
  depth 
  a 
  given 
  bottom 
  oscillation 
  of 
  a 
  water 
  

   wave 
  tvill 
  not 
  produce 
  ripples. 
  This 
  is 
  probably 
  due 
  to 
  

   the 
  abnormal 
  conditions 
  of 
  flow 
  resulting 
  from 
  the 
  

   "breaking" 
  of 
  the 
  wave. 
  In 
  shallower 
  water, 
  therefore, 
  

   only 
  smaller 
  waves 
  will 
  produce 
  ripples, 
  of 
  course 
  of 
  

   smaller 
  wave-length. 
  Consequently 
  along 
  a 
  gently 
  slop- 
  

   ing 
  shore 
  we 
  should 
  theoretically 
  expect 
  to 
  find 
  at 
  first 
  

   a 
  rather 
  rapid 
  increase 
  of 
  the 
  wave-length 
  of 
  the 
  persist- 
  

   ing 
  ripples 
  to 
  a 
  certain 
  depth 
  and 
  then 
  a 
  very 
  gradual 
  

   decrease 
  down 
  to 
  very 
  small 
  size. 
  

  

  (d.) 
  The 
  experiments 
  of 
  De 
  Candolle, 
  Darwin 
  and 
  

   Forel 
  show 
  that 
  the 
  wave-length 
  increases 
  with 
  increasing 
  

   size 
  of 
  the 
  grain. 
  According 
  to 
  Forel, 
  in 
  mixtures, 
  the 
  

   largest 
  grains, 
  if 
  present 
  in 
  sufficient 
  numbers, 
  determine 
  

   the 
  wave-length. 
  

  

  (e.) 
  Forel 
  makes 
  the 
  statement 
  that 
  the 
  wave-length 
  

   of 
  oscillation-ripples 
  is 
  inversely 
  proportional 
  to 
  the 
  

   density 
  of 
  the 
  grains. 
  This 
  is, 
  however, 
  not 
  based 
  on 
  

   experimental 
  evidence 
  and 
  seems 
  quite 
  improbable 
  in 
  

   face 
  of 
  Hahmann's 
  experiments 
  with 
  current-ripples. 
  

   (Seep. 
  159.) 
  

  

  (/.) 
  Darwin 
  found 
  that 
  ripples 
  formed 
  on 
  a 
  very 
  thin 
  

   layer 
  of 
  sand 
  were 
  smaller 
  than 
  such 
  formed 
  under 
  equal 
  

   conditions 
  on 
  a 
  thick 
  layer 
  of 
  sand. 
  His 
  explanation 
  of 
  

   this 
  phenomenon 
  is 
  that 
  "the 
  maximum 
  velocity 
  of 
  the 
  

   water 
  relatively 
  to 
  the 
  bottom 
  must 
  depend 
  upon 
  the 
  

   intensity 
  of 
  the 
  vortices, 
  and 
  this 
  depends 
  upon 
  the 
  height 
  

   of 
  the 
  ripple-mark. 
  ' 
  ' 
  If 
  this 
  can 
  not 
  develop, 
  the 
  former 
  

   must 
  remain 
  lower, 
  thus 
  reducing 
  the 
  wave-length 
  of 
  the 
  

   ripple. 
  

  

  (g.) 
  No 
  data 
  exist 
  concerning 
  the 
  influence 
  of 
  the 
  

   shape 
  of 
  the 
  grains. 
  

  

  