﻿Related 
  Sedimentary 
  Surface 
  Forms. 
  183 
  

  

  and 
  the 
  rocking 
  begins, 
  the 
  sand 
  dances 
  backwards 
  and 
  

   forwards 
  on 
  the 
  bottom, 
  the 
  grains 
  rolling 
  as 
  they 
  go. 
  

   Very 
  shortly 
  the 
  sand 
  begins 
  to 
  aggregate 
  into 
  irregular 
  

   little 
  flocculent 
  masses, 
  the 
  appearance 
  being 
  something 
  

   like 
  that 
  of 
  curdling 
  milk. 
  The 
  position 
  of 
  the 
  masses 
  

   is, 
  I 
  believe, 
  solely 
  determined 
  by 
  the 
  friction 
  of 
  the 
  sand 
  

   on 
  the 
  bottom, 
  and 
  as 
  soon 
  as 
  a 
  grain 
  sticks, 
  it 
  thereby 
  

   increases 
  the 
  friction 
  at. 
  that 
  place. 
  The 
  aggregations 
  

   gradually 
  become 
  elongated 
  and 
  rearrange 
  themselves. 
  

   . 
  . 
  . 
  Some 
  of 
  the 
  elongated 
  patches 
  disappear, 
  and 
  others 
  

   fuse 
  together 
  and 
  form 
  ridges, 
  the 
  ridges 
  become 
  

   straighter, 
  and 
  finally 
  a 
  regular 
  ripple 
  mark 
  is 
  formed' 
  ' 
  

   (1884, 
  p. 
  23). 
  

  

  It 
  should 
  be 
  noted 
  that 
  in 
  this 
  as 
  in 
  other 
  experiments 
  

   in 
  which 
  stationary 
  waves 
  were 
  formed, 
  the 
  ridges 
  and 
  

   furrows 
  do 
  not 
  correspond 
  to 
  the 
  nodes 
  and 
  antinodes 
  

   of 
  the 
  stationary 
  waves, 
  each 
  one 
  giving 
  rise 
  to 
  a 
  number 
  

   of 
  ripples. 
  Their 
  formation, 
  therefore, 
  is 
  independent 
  

   of 
  the 
  stationary 
  nature 
  of 
  the 
  wave 
  in 
  such 
  experiments. 
  

   They 
  form 
  equally 
  well 
  in 
  oscillating 
  currents 
  produced 
  

   in 
  a 
  vessel 
  rotated 
  alternately 
  in 
  opposite 
  directions, 
  

   where 
  there 
  is 
  no 
  evidence 
  of 
  stationary 
  waves, 
  or 
  at 
  the 
  

   bottom 
  of 
  water 
  bodies 
  agitated 
  by 
  waves 
  where 
  the 
  same 
  

   reversal 
  of 
  current 
  takes 
  place. 
  

  

  2. 
  Data 
  concerning 
  oscillation 
  ripples. 
  

  

  1. 
  Groundplan 
  37 
  — 
  In 
  groundplan 
  the 
  pattern 
  of 
  oscil- 
  

   lation 
  ripples 
  is 
  the 
  same 
  as 
  that 
  of 
  current-ripples, 
  but 
  of 
  

   striking 
  regularity, 
  the 
  ridges 
  usually 
  being 
  practically 
  

   equidistant 
  and 
  parallel. 
  Between 
  rocks 
  and 
  other 
  

   irregularities 
  of 
  the 
  surface, 
  however, 
  their 
  arrangement 
  

   may 
  be 
  very 
  irregular 
  and 
  complex, 
  as 
  can 
  be 
  seen 
  on 
  

   every 
  shore. 
  379, 
  

  

  2. 
  Profile. 
  — 
  The 
  profile 
  of 
  current-ripples 
  is 
  strictly 
  

   symmetrical, 
  with 
  sharp 
  crests 
  and 
  broad 
  round 
  hol- 
  

   lows. 
  38 
  The 
  contrast 
  between 
  the 
  original 
  and 
  the 
  cast 
  

   is 
  therefore 
  marked 
  and 
  offers 
  to 
  the 
  geologist 
  a 
  means 
  

   to 
  distinguish 
  the 
  upper 
  and 
  lower 
  surface 
  of 
  strata 
  in 
  

   regions 
  of 
  complicated 
  structure. 
  A 
  good 
  illustration 
  

  

  3T 
  For 
  good 
  illustrations 
  see 
  Brown, 
  1911, 
  pi. 
  41 
  ; 
  Kindle, 
  1917, 
  pis. 
  20, 
  21. 
  

  

  87 
  aCf. 
  e. 
  g. 
  Forel, 
  1895, 
  vol. 
  2, 
  fig. 
  98. 
  De 
  Candolle 
  noted 
  that 
  in 
  his 
  

   experiments 
  the 
  ripples 
  were 
  less 
  regular 
  if 
  produced 
  on 
  an 
  inclined 
  surface 
  ; 
  

   1883, 
  p. 
  252. 
  

  

  38 
  For 
  excellent 
  illustrations 
  see 
  Daly, 
  Geology 
  North 
  American 
  Cordillera, 
  

   Canada 
  Dept. 
  of 
  Mines, 
  Memoir 
  38, 
  pi. 
  17. 
  

  

  