﻿208 
  

  

  Bucher 
  — 
  Origin 
  of 
  Ripples, 
  and 
  

  

  Classification 
  of 
  Sedimentary 
  Ripples. 
  

  

  Current 
  of 
  uniform 
  direction 
  Current 
  oscillating 
  

   Subaqueous 
  Eolian 
  

  

  I. 
  Eipples 
  forming 
  at 
  low 
  veloc- 
  Current-ripples 
  

   ities, 
  (below 
  the 
  second 
  critical 
  a. 
  normal 
  

   point), 
  with 
  no 
  sediment 
  in 
  sus- 
  b. 
  rhomboid 
  

   pension. 
  A 
  part 
  of 
  the 
  fluid 
  mov- 
  c. 
  linguoid 
  

   ing 
  in 
  horizontal 
  vortices 
  set 
  up 
  as 
  

   grains 
  shift 
  on 
  the 
  surface 
  of 
  the 
  

   sediment 
  otherwise 
  at 
  rest. 
  

  

  Current-ripples 
  Oscillation-ripples 
  

  

  II. 
  Eipples 
  forming 
  at 
  high 
  veloc- 
  

   ities, 
  (above 
  the 
  second 
  critical 
  

   point), 
  with 
  more 
  or 
  less 
  sediment 
  

   in 
  suspension. 
  

  

  1. 
  ■ 
  A 
  part 
  of 
  the 
  fluid 
  moving 
  

   in 
  horizontal 
  vortices 
  set 
  up 
  by 
  a 
  

   preexisting 
  obstacle 
  of 
  relatively 
  

   large 
  size, 
  with 
  the 
  bulk 
  of 
  the 
  

   sediment 
  at 
  rest. 
  

  

  Transverse 
  dunes 
  

  

  2. 
  No 
  horizontal 
  vortices, 
  the 
  

   fluid 
  moving 
  everywhere 
  in 
  the 
  Sand-waves 
  

   same 
  direction 
  at 
  contact 
  with 
  the 
  

   sediment, 
  which 
  itself 
  is 
  in 
  motion 
  ; 
  a. 
  progressive 
  

   the 
  ripples 
  destroyed 
  or 
  trans- 
  b. 
  regressive 
  

   formed 
  when 
  motion 
  ceases. 
  

  

  (impossible) 
  

  

  III. 
  Eesulting 
  from 
  a 
  transforma- 
  

   tion 
  of 
  sand-waves, 
  when 
  the 
  veloc- 
  a. 
  Meta-ripples 
  

   ity 
  of 
  the 
  current 
  fails: 
  b. 
  Para-ripples 
  8 
  

  

  IV. 
  Eesulting 
  from 
  the 
  interference 
  of 
  two 
  sets 
  of 
  ripples. 
  

  

  1. 
  One 
  set 
  forming 
  after 
  the 
  completion 
  of 
  the 
  other. 
  

  

  a. 
  The 
  second 
  set 
  consisting 
  of 
  oscillation-ripples: 
  Oscillation 
  cross-ripples. 
  

  

  b. 
  The 
  second 
  set 
  consisting 
  of 
  current-ripples: 
  Current 
  cross-ripples. 
  

  

  2. 
  The 
  two 
  sets 
  forming 
  simultaneously: 
  Compound 
  ripples. 
  

  

  M 
  See 
  Part 
  II, 
  in 
  a 
  later 
  number. 
  

  

  