﻿Belated 
  Sedimentary 
  Surface 
  Forms. 
  163 
  

  

  and 
  13-94 
  cm. 
  in 
  Hahmann's 
  experiments. 
  The 
  range 
  

   observed 
  in 
  nature, 
  on 
  the 
  other 
  hand, 
  extends 
  from 
  1-5 
  

   to 
  SO 
  cm! 
  This 
  discrepancy 
  seems 
  to 
  indicate 
  that 
  

   another 
  factor 
  enters 
  into 
  the 
  equilibrium 
  of 
  forces 
  which 
  

   determines 
  the 
  spacing, 
  that 
  is, 
  the 
  wave-length, 
  of 
  cur- 
  

   rent-ripples. 
  

  

  I 
  suggest 
  that 
  the 
  vertical 
  distribution 
  of 
  velocities 
  

   above 
  the 
  vortical 
  layer 
  exerts 
  a 
  strong 
  influence 
  on 
  that 
  

   within 
  it. 
  In 
  Hahmann's 
  experiments, 
  made 
  with 
  a 
  sand- 
  

  

  Fig. 
  2. 
  

  

  Fig. 
  2. 
  Outline 
  of 
  actual 
  shape 
  of 
  linguoid 
  ripples 
  formed 
  in 
  experiment 
  

   trough 
  (ground-plan). 
  (Eedrawn 
  after 
  H. 
  Blasius, 
  1910, 
  pi. 
  50, 
  fig. 
  11.) 
  

  

  covered 
  semicircular 
  disc 
  rotated 
  under 
  water, 
  the 
  distri- 
  

   bution 
  of 
  velocities 
  was 
  determined 
  solely 
  by 
  the 
  internal 
  

   friction 
  of 
  the 
  liquid. 
  The 
  depth 
  of 
  the 
  water 
  was 
  small 
  

   and 
  the 
  velocities 
  changed 
  rapidly 
  from 
  a 
  minimum 
  in 
  

   contact 
  with 
  the 
  bed 
  to 
  the 
  maximum 
  at 
  the 
  surface. 
  In 
  

   nature, 
  the 
  vertical 
  distribution 
  of 
  velocities 
  varies 
  

   greatly 
  according 
  to 
  slope 
  of 
  bed, 
  depth 
  of 
  water 
  and 
  

   other 
  conditions, 
  as 
  a 
  glance 
  at 
  the 
  latest 
  curves 
  published 
  

   l>y 
  Gilbert 
  (1914, 
  pp. 
  244-246) 
  will 
  show. 
  This 
  difference 
  

   may 
  account 
  for 
  the 
  different 
  results. 
  

  

  