﻿150 
  Bucher 
  — 
  Origin 
  of 
  Ripples, 
  and 
  

  

  4. 
  Data 
  concerning 
  current 
  ripples. 
  

  

  5. 
  The 
  formation 
  of 
  current 
  ripples. 
  

  

  6. 
  Linguoid 
  ripples. 
  

  

  II. 
  Sand-waves 
  and 
  related 
  surface 
  forms. 
  

  

  1. 
  The 
  second 
  critical 
  point 
  of 
  current 
  velocity. 
  

   2A. 
  Eegressive 
  sand-waves. 
  

  

  1. 
  The 
  third 
  critical 
  point. 
  

  

  2. 
  The 
  first 
  appearance 
  of 
  regressive 
  sand- 
  waves. 
  

  

  3. 
  Data 
  concerning 
  regressive 
  sand- 
  waves. 
  

  

  B. 
  Sand-waves 
  in 
  rivers. 
  

  

  1. 
  Definition. 
  

  

  2. 
  The 
  first 
  appearance 
  of 
  " 
  sand-waves. 
  ' 
  ' 
  

  

  3. 
  Data 
  concerning 
  large 
  sand-waves 
  in 
  rivers. 
  

  

  C. 
  Large 
  ripples 
  exposed 
  after 
  high 
  water 
  along 
  rivers 
  and 
  

  

  on 
  tidal 
  flats. 
  

  

  1. 
  Along 
  rivers. 
  

  

  2. 
  On 
  tidal 
  flats. 
  

  

  3. 
  Formation 
  of 
  sand-waves. 
  

  

  III. 
  Oscillation-ripples. 
  

  

  1. 
  The 
  first 
  appearance 
  of 
  oscillation 
  ripples. 
  

  

  2. 
  Data 
  concerning 
  oscillation 
  ripples. 
  

  

  3. 
  The 
  formation 
  of 
  oscillation 
  ripples. 
  

  

  IV. 
  Compound 
  ripple 
  patterns. 
  

  

  1. 
  Transformation 
  of 
  one 
  type 
  into 
  another. 
  

  

  2. 
  Oscillation 
  cross-ripples. 
  

  

  3. 
  Current 
  cross-ripples. 
  

  

  4. 
  Compound 
  ripples. 
  

  

  V. 
  Eolian 
  ripples 
  and 
  dunes. 
  

  

  1. 
  Eolian 
  current 
  ripples. 
  

  

  2. 
  Eolian 
  dunes. 
  

  

  VI. 
  General 
  conclusions. 
  

   VII. 
  Eemarks 
  on 
  nomenclature. 
  

   Bibliography. 
  

  

  I. 
  Subaqueous 
  Current-ripples. 
  

   1. 
  The 
  first 
  critical 
  point 
  of 
  current 
  velocity. 
  

  

  Below 
  a 
  certain 
  velocity 
  a 
  current 
  is 
  unable 
  to 
  move 
  

   the 
  debris 
  forming 
  its 
  bed. 
  The 
  point 
  at 
  which, 
  with 
  

   increasing 
  velocity, 
  motion 
  is 
  started, 
  in 
  the 
  following 
  

   discussion 
  is 
  called 
  the 
  " 
  first 
  critical 
  point." 
  1 
  

  

  In 
  Table 
  1 
  are 
  given 
  the 
  results 
  of 
  three 
  series 
  of 
  deter- 
  

   minations 
  of 
  the 
  first 
  critical 
  point, 
  which, 
  though 
  not 
  

   giving 
  absolute 
  measurements 
  of 
  the 
  critical 
  velocity 
  

   proper, 
  at 
  least 
  indicate 
  its 
  order 
  of 
  magnitude. 
  2 
  

  

  Umpfenbach 
  measured 
  the 
  surface 
  velocities 
  of 
  natural 
  

   water 
  courses 
  at 
  times 
  of 
  flood 
  and 
  noted 
  the 
  size 
  of 
  

  

  1 
  It 
  corresponds 
  to 
  the 
  lower 
  critical 
  velocity 
  of 
  Lechalas 
  and 
  to 
  the 
  

   velocity 
  competent 
  for 
  traction 
  of 
  Gilbert's 
  nomenclature. 
  Gilbert, 
  1914, 
  

   p. 
  194. 
  In 
  this 
  and 
  similar 
  cases 
  in 
  the 
  text, 
  see 
  the 
  Bibliography 
  at 
  the 
  

   end 
  of 
  this 
  paper. 
  

  

  2 
  Date 
  obtained 
  from 
  artificial 
  channels 
  with 
  rigid 
  bed 
  cannot 
  be 
  used 
  

   directly; 
  cf. 
  Gilbert, 
  1914, 
  p. 
  218. 
  

  

  