﻿Belated 
  Sedimentary 
  Surface 
  Forms. 
  185 
  

  

  action 
  of 
  these 
  vortices, 
  the 
  particles 
  near 
  the 
  crest 
  swing 
  

   from 
  one 
  side 
  to 
  the 
  other, 
  while 
  those 
  in 
  the 
  trough 
  

   oscillate 
  to 
  and 
  fro, 
  with 
  smaller 
  amplitude, 
  as 
  can 
  easily 
  

   he 
  observed 
  in 
  artificial 
  and 
  natural 
  ripples. 
  The 
  phase 
  

   of 
  the 
  later 
  is 
  the 
  same 
  as 
  that 
  of 
  the 
  former 
  in 
  the 
  case 
  

   of 
  strong 
  oscillation, 
  but 
  opposite 
  if 
  the 
  oscillation 
  is 
  

   weak. 
  

  

  4. 
  Traveling. 
  — 
  Oscillation- 
  ripples 
  are 
  stationary. 
  

   They 
  can 
  not 
  advance 
  in 
  either 
  direction, 
  owing 
  to 
  the 
  

   formation 
  of 
  vortices 
  alternately 
  on 
  either 
  side 
  of 
  the 
  

   ripple 
  as 
  the 
  current 
  is 
  reversed. 
  

  

  The 
  preservation 
  of 
  typical 
  oscillation-ripples 
  under 
  a 
  

   thick 
  layer 
  of 
  rather 
  coarse 
  sand, 
  as 
  it 
  is 
  frequently 
  seen 
  

   in 
  many 
  sandstone 
  formations, 
  offers 
  the 
  same 
  problem 
  

   as 
  that 
  of 
  current-ripples, 
  but 
  more 
  surprising 
  yet. 
  The 
  

   very 
  existence 
  of 
  oscillation-ripples 
  excludes 
  any, 
  even 
  

   the 
  slightest 
  current 
  action 
  in 
  the 
  vicinity 
  of 
  the 
  sedimen- 
  

   tary 
  surface. 
  Since 
  we 
  can 
  not 
  assume 
  that 
  the 
  sharp 
  

   crested 
  ripples 
  had 
  hardened 
  sufficiently 
  to 
  resist 
  modi- 
  

   fication 
  through 
  the 
  current, 
  which 
  carried 
  the 
  additional 
  

   sediment, 
  the 
  latter 
  must 
  have 
  existed 
  a 
  sufficient 
  dis- 
  

   tance 
  above 
  the 
  bottom, 
  so 
  as 
  not 
  to 
  reach 
  it, 
  but 
  drop 
  its 
  

   load 
  unto 
  it. 
  The 
  necessary 
  conditions 
  are 
  the 
  same 
  as 
  

   those 
  outined 
  for 
  current-ripples 
  on 
  page 
  156. 
  It 
  should 
  

   be 
  noted 
  especially 
  that 
  a 
  storm 
  may 
  throw 
  a 
  great 
  

   quantity 
  of 
  sediment 
  into 
  suspension 
  at 
  one 
  locality, 
  

   while 
  at 
  another, 
  perhaps 
  not 
  far 
  distant, 
  its 
  only 
  effect 
  

   on 
  the 
  sea-bottom 
  is 
  the 
  production 
  of 
  oscillation-ripples. 
  

   The 
  wind-drift 
  set 
  up 
  by 
  the 
  storm 
  may 
  carry 
  such 
  sedi- 
  

   ment 
  from 
  the 
  former 
  to 
  the 
  latter 
  locality 
  in 
  the 
  upper 
  

   levels 
  of 
  the 
  water. 
  The 
  much-quoted 
  observations 
  of 
  

   sand 
  left 
  on 
  deck 
  by 
  breaking 
  waves 
  over 
  a 
  depth 
  of 
  75 
  

   feet 
  on 
  the 
  banks 
  of 
  Newfoundland, 
  may 
  serve 
  to 
  illus- 
  

   trate 
  to 
  what 
  extent 
  sand 
  may 
  be 
  thrown 
  into 
  suspension 
  

   by 
  storm 
  waves. 
  

  

  The 
  action 
  of 
  the 
  vortices, 
  no 
  matter 
  how 
  weak, 
  will 
  

   always 
  tend 
  to 
  keep 
  the 
  crest 
  of 
  the 
  ripple 
  sharp, 
  never, 
  

   however, 
  to 
  round 
  it 
  off. 
  Mere 
  decrease 
  of 
  wave 
  action 
  44 
  

   can, 
  therefore, 
  not 
  account 
  for 
  the 
  small 
  ripples 
  with 
  

   symmetrical 
  round 
  crests 
  and 
  hollows, 
  that 
  are 
  some- 
  

   times 
  found 
  both 
  in 
  modern 
  45 
  and 
  in 
  fossil 
  sediments. 
  46 
  

  

  44 
  As 
  suggested 
  by 
  Gilbert, 
  1899, 
  p. 
  136. 
  

  

  45 
  See 
  e. 
  g., 
  Kindle, 
  1917, 
  pi. 
  21, 
  figs. 
  A 
  and 
  B. 
  

  

  4 
  ®E. 
  g. 
  one 
  specimen 
  in 
  Ordovician 
  limestone 
  in 
  the 
  collection 
  of 
  the 
  geo- 
  

   logical 
  department 
  of 
  the 
  University 
  of 
  Cincinnati. 
  

  

  