﻿152 
  Bucher 
  — 
  Origin 
  of 
  Ripples, 
  and 
  

  

  Berthololy 
  (1900, 
  p. 
  84), 
  who 
  studied 
  the 
  formation 
  of 
  

   current-ripples 
  on 
  the 
  bottom 
  of 
  shallow 
  creeks, 
  describes 
  

   their 
  first 
  appearance 
  as 
  being 
  similar 
  to 
  that 
  of 
  wind- 
  

   formed 
  ripples, 
  as 
  one 
  can 
  observe 
  it 
  on 
  any 
  surface 
  of 
  

   dry 
  sand 
  exposed 
  to 
  the 
  wind. 
  3 
  After 
  having 
  smoothed 
  

   the 
  sand 
  by 
  means 
  of 
  a 
  board, 
  he 
  observed 
  that 
  the 
  first 
  

   minute 
  accumulations 
  of 
  sand 
  seemed 
  to 
  form 
  about 
  some 
  

   of 
  the 
  larger 
  grains 
  lying 
  scattered 
  over 
  the 
  surface 
  with- 
  

   out 
  any 
  definite 
  arrangement. 
  They 
  soon 
  began 
  to 
  travel 
  

   downstream 
  and 
  to 
  lengthen 
  in 
  the 
  direction 
  at 
  right- 
  

   angles 
  to 
  the 
  current, 
  and 
  finally 
  united 
  laterally 
  to 
  form 
  

   normal 
  current-ripples. 
  If 
  the 
  surface 
  of 
  the 
  sand 
  was 
  

   perfectly 
  smooth, 
  the 
  first 
  minute 
  accumulations 
  of 
  sand 
  

   did 
  not 
  appear 
  until 
  after 
  some 
  time 
  ; 
  as 
  soon, 
  however, 
  

   as 
  they 
  had 
  reached 
  a 
  certain 
  size, 
  they 
  grew 
  rapidly 
  

   until 
  they 
  had 
  reached 
  their 
  full 
  development. 
  

  

  For 
  the 
  interpretation 
  of 
  the 
  mechanical 
  processes 
  

   involved, 
  the 
  statement 
  is 
  of 
  great 
  importance, 
  that 
  the 
  

   obstacle 
  which 
  forms 
  the 
  nucleus 
  for 
  the 
  growing 
  current- 
  

   ripple 
  must 
  be 
  very 
  small. 
  Otherwise, 
  a 
  vortex 
  form- 
  

   ing 
  in 
  front 
  of 
  the 
  obstacle 
  will 
  prevent 
  deposition 
  there 
  

   and 
  even 
  undermine 
  it. 
  This 
  occurred 
  in 
  front 
  of 
  a 
  ruler, 
  

   one 
  centimeter 
  thick, 
  placed 
  on 
  the 
  sand 
  at 
  right 
  angles 
  

   of 
  the 
  current, 
  while 
  an 
  ordinary 
  current-ripple 
  was 
  built 
  

   over 
  it, 
  when 
  only 
  its 
  uppermost 
  edge 
  was 
  permitted 
  to 
  

   extend 
  beyond 
  the 
  surface 
  of 
  the 
  sand. 
  

  

  Berthololy 
  's 
  observations 
  and 
  the 
  experiments 
  per- 
  

   formed 
  more 
  recently 
  by 
  Blasius, 
  Hahmann, 
  Gilbert 
  and 
  

   others, 
  prove 
  beyond 
  doubt 
  that 
  current-ripples 
  may 
  be 
  

   formed 
  by 
  a 
  uniform 
  current, 
  a 
  fact 
  that 
  had 
  been 
  doubted 
  

   by 
  Darwin 
  (1893, 
  p. 
  34), 
  and 
  that 
  they 
  originate 
  simul- 
  

   taneously 
  over 
  the 
  whole 
  bed, 
  not 
  successively 
  as 
  Forel 
  

   (1895, 
  p. 
  253) 
  had 
  thought. 
  

  

  Gilbert 
  (1914, 
  pp. 
  242, 
  243) 
  states 
  that 
  in 
  his 
  experi- 
  

   mental 
  work 
  on 
  stream 
  traction 
  he 
  found 
  "positive 
  

   evidence 
  that 
  the 
  dune 
  interval 
  was 
  determined 
  by 
  a 
  pre- 
  

   ( 
  s 
  x 
  i 
  stent 
  water 
  rhythm. 
  ' 
  ' 
  " 
  In 
  certain 
  experiments 
  a 
  slow 
  

   current 
  moving 
  over 
  a 
  bed 
  of 
  debris 
  artificially 
  smoothed 
  

   and 
  leveled, 
  was 
  gradually 
  quickened 
  until 
  transporta- 
  

   tion 
  began. 
  ^ 
  The 
  movement 
  of 
  particles 
  did 
  not 
  begin 
  at 
  

   the 
  same 
  time 
  all 
  along 
  the 
  bed 
  but 
  was 
  initiated 
  in 
  a 
  

   series 
  of 
  spots 
  separated 
  by 
  uniform 
  intervals, 
  and 
  the 
  

   first 
  result 
  of 
  the 
  transportation 
  was 
  the 
  creation 
  of 
  a 
  

  

  8 
  Cf., 
  e.g., 
  Oh. 
  Lyell, 
  Principles 
  of 
  Geology, 
  1892, 
  11th 
  edit, 
  p. 
  342. 
  

  

  