﻿*2±-2 
  Bucher 
  — 
  Origin 
  of 
  Ripples, 
  and 
  

  

  Introduction. 
  

  

  The 
  question, 
  why 
  one 
  or 
  the 
  other 
  type 
  of 
  ripples 
  is 
  

   not 
  found 
  in 
  a 
  certain 
  sediment, 
  recurs 
  frequently 
  in 
  the 
  

   following 
  discussions. 
  The 
  answer 
  is 
  always 
  : 
  Either 
  it 
  

   was 
  not 
  formed 
  or 
  not 
  preserved. 
  While 
  the 
  conditions 
  

   necessary 
  for 
  their 
  formation 
  are 
  different 
  for 
  the 
  vari- 
  

   ous 
  types 
  of 
  ripples, 
  those 
  favoring 
  their 
  preservation 
  

   are 
  the 
  same 
  for 
  all. 
  They 
  must 
  all, 
  soon 
  after 
  their 
  

   formation, 
  be 
  sufficiently 
  covered 
  with 
  sediment 
  settling 
  

   on 
  them 
  from 
  above 
  1 
  (see 
  pp. 
  156 
  and 
  185). 
  

  

  1. 
  In 
  the 
  sea, 
  in 
  rivers 
  and 
  in 
  air, 
  most 
  of 
  this 
  sedi- 
  

   ment 
  is 
  supplied 
  by 
  a 
  local 
  stirring 
  of 
  the 
  bottom 
  through 
  

   storms 
  and 
  currents, 
  throwing 
  some 
  sediment 
  into 
  sus- 
  

   pension 
  which, 
  when 
  carried 
  by 
  upper 
  currents, 
  settles 
  

   into 
  quieter 
  layers 
  below. 
  In 
  a 
  sediment 
  too 
  coarse 
  to 
  be 
  

   carried 
  any 
  distance 
  in 
  suspension, 
  when 
  stirred, 
  this 
  pro- 
  

   cess 
  becomes 
  ineffective. 
  

  

  2. 
  The 
  sediment 
  thus 
  thrown 
  into 
  suspension 
  in 
  the 
  

   air, 
  may 
  settle 
  in 
  the 
  water 
  of 
  the 
  sea, 
  lakes 
  or 
  of 
  rivers. 
  

  

  3. 
  The 
  load 
  carried 
  by 
  rivers 
  and 
  streams 
  into 
  seas 
  

   and 
  lakes, 
  reaches 
  the 
  bottom 
  in 
  an 
  unceasing 
  rain 
  of 
  par- 
  

   ticles. 
  

  

  4. 
  Also, 
  in 
  both 
  water 
  and 
  air, 
  the 
  volcanic 
  sands 
  and 
  

   dust, 
  ejected 
  during 
  an 
  eruption, 
  locally 
  play 
  a 
  role. 
  

  

  Thus, 
  if 
  covered 
  soon 
  enough, 
  even 
  the 
  most 
  transient 
  

   features 
  may 
  be 
  preserved, 
  like 
  the 
  tracks 
  of 
  flitting 
  crus- 
  

   taceans, 
  the 
  marks 
  left 
  by 
  the 
  trailing 
  arms 
  of 
  a 
  jelly-fish, 
  

   oscillation-ripples 
  formed 
  during 
  still-water 
  between 
  the 
  

   tides, 
  or 
  current-ripples 
  produced 
  by 
  an 
  exceptional 
  

   wind-drift 
  on 
  sediments 
  not 
  ordinarily 
  reached 
  by 
  cur- 
  

   rents. 
  The 
  shorter 
  the 
  time 
  during 
  which 
  the 
  formation 
  

   of 
  any 
  of 
  these 
  surface 
  marks 
  is 
  possible, 
  and 
  the 
  rarer 
  

   the 
  recurrence 
  of 
  conditions 
  favorable 
  for 
  it, 
  the 
  smaller 
  

   is 
  the 
  probability 
  that 
  they 
  will 
  be 
  preserved. 
  

  

  I. 
  Oscillation-ripples. 
  

   1. 
  Description. 
  

  

  Fossil 
  oscillation-ripples 
  cover 
  the 
  same 
  range 
  of 
  sizes 
  

   and 
  forms 
  as 
  those 
  found 
  in 
  present 
  waters. 
  2 
  The 
  sharp 
  

  

  1 
  Page 
  references 
  in 
  the 
  text 
  refer 
  to 
  Part 
  I 
  in 
  the 
  March 
  number. 
  In 
  

   cases 
  where 
  references 
  to 
  authors 
  are 
  given, 
  see 
  the 
  Bibliography 
  on 
  pp. 
  

   209, 
  210. 
  

  

  2 
  Giant 
  ripples, 
  such 
  as 
  suggested 
  by 
  Gilbert 
  (Ripple-marks 
  and 
  cross 
  

   bedding, 
  Bull. 
  Geol. 
  Soc. 
  Amer., 
  vol. 
  10, 
  p. 
  135-139, 
  1899), 
  can 
  not 
  be 
  

   formed 
  directly 
  by 
  wave 
  action. 
  Gilbert's 
  interpretation 
  was 
  refuted 
  on 
  

   other 
  grounds 
  by 
  Fairchild, 
  (Beach 
  Structure 
  in 
  the 
  Medina 
  Sandstone, 
  

   Amer. 
  Geologist, 
  vol. 
  28, 
  pp. 
  9-13, 
  1901). 
  

  

  