﻿Related 
  Sedimentary 
  Surface 
  Forms. 
  178 
  

  

  2. 
  Profile 
  and 
  structure. 
  — 
  The 
  contrast 
  in 
  the 
  slopes 
  

   of 
  the 
  up 
  and 
  down-stream 
  sides 
  is 
  striking. 
  Ockerson 
  

   states^ 
  "the 
  bluff 
  part 
  of 
  the 
  wave 
  .... 
  is 
  frequently 
  

   nearly 
  vertical, 
  the 
  slope 
  of 
  the 
  up-stream 
  side 
  is 
  gener- 
  

   ally 
  very 
  gentle." 
  Partiot 
  gives 
  45° 
  as 
  the 
  angle 
  of 
  the 
  

   lee-side 
  in 
  one 
  case 
  (p. 
  270). 
  In 
  the 
  cases 
  observed 
  by 
  

   me, 
  the 
  horizontal 
  form 
  index 
  ranged 
  from 
  7 
  to 
  10. 
  

  

  It 
  is 
  this 
  typical 
  dune 
  shape 
  which 
  distinguishes 
  the 
  

   large 
  ripples 
  exposed 
  after 
  high 
  water 
  from 
  the 
  sand- 
  

   waves 
  in 
  the 
  deeper 
  parts 
  of 
  the 
  same 
  river. 
  

  

  The 
  observations 
  made 
  by 
  Hider, 
  however, 
  leave 
  no 
  

   doubt 
  that 
  these 
  ripples 
  have 
  the 
  same 
  origin 
  as 
  the 
  

   sand 
  waves 
  and 
  owe 
  their 
  dune-like 
  profile 
  to 
  a 
  trans- 
  

   formation 
  resulting 
  from 
  the 
  decrease 
  of 
  the 
  velocity 
  

   and 
  the 
  depth 
  of 
  the 
  water. 
  Hider, 
  in 
  speaking 
  of 
  the 
  

   large 
  sand- 
  waves 
  in 
  the 
  Mississippi 
  River, 
  says 
  their 
  size 
  

   decreases 
  "as 
  the 
  water 
  becomes 
  of 
  less 
  depth, 
  until, 
  in 
  

   shallow 
  water 
  and 
  removed 
  from 
  the 
  main 
  current, 
  they 
  

  

  Fig. 
  4. 
  

  

  .:^|!fj^^ 
  :■■*•: 
  *v 
  i 
  -:->: 
  * 
  i 
  »?.^v,^v.-v 
  

  

  Fig. 
  4. 
  Cross-section 
  of 
  meta-ripples 
  observed 
  on 
  a 
  sand-bank 
  in 
  Little 
  

   Miami 
  Eiver 
  after 
  a 
  flood; 
  m 
  — 
  mud; 
  s 
  = 
  sand; 
  g 
  = 
  coarse 
  sand 
  full 
  of 
  

   small 
  pebbles. 
  

  

  resolve 
  themselves 
  into 
  waves 
  or 
  ridges 
  transverse 
  to 
  the 
  

   direction 
  of 
  the 
  current, 
  varying 
  from 
  20 
  to 
  100 
  feet 
  

   apart, 
  and 
  from 
  a 
  few 
  inches 
  to 
  one 
  or 
  two 
  feet 
  in 
  height" 
  

   (p. 
  2196). 
  

  

  The 
  structure 
  of 
  large 
  ripples 
  observed 
  on 
  sand-banks 
  

   of 
  the 
  Little 
  Miami 
  River 
  near 
  its 
  mouth 
  offer 
  good 
  evi- 
  

   dence 
  of 
  this 
  process 
  of 
  transformation 
  (cf. 
  fig. 
  4). 
  

   Paving 
  the 
  bottom 
  of 
  the 
  hollows 
  and 
  the 
  adjoining 
  

   slopes 
  for 
  a 
  short 
  distance 
  was 
  a 
  layer 
  of 
  sticky 
  mud, 
  

   about 
  three 
  to 
  five 
  mm. 
  thick; 
  the 
  adjoining 
  part 
  of 
  the 
  

   gentle 
  slope 
  was 
  covered 
  with 
  fine 
  sand, 
  underneath 
  which 
  

   appeared 
  a 
  very 
  coarse 
  sand 
  full 
  of 
  small 
  pebbles 
  which 
  

   formed 
  the 
  bulk 
  of 
  the 
  sand-wave, 
  while 
  the 
  crest 
  proper 
  

   consisted 
  of 
  sand 
  without 
  any 
  pebbles. 
  The 
  core, 
  con- 
  

   sisting 
  of 
  the 
  coarser 
  materials, 
  was 
  nearly 
  symmetrical 
  

   when 
  it 
  became 
  stationary, 
  but 
  the 
  sand 
  and 
  mud 
  dropped 
  

   by 
  the 
  slackening 
  current 
  was 
  deposited 
  over 
  this 
  solid- 
  

   fied 
  "wave" 
  giving 
  it 
  its 
  "dune" 
  shape. 
  In 
  deeper 
  

  

  