﻿241 
  Bucher 
  — 
  Origin 
  of 
  Ripples, 
  and 
  

  

  the 
  tide 
  is 
  sufficiently 
  low 
  or 
  lacking 
  entirely. 
  We 
  are, 
  

   therefore, 
  justified 
  in 
  concluding 
  that 
  the 
  body 
  of 
  water 
  

   in 
  which, 
  for 
  instance, 
  the 
  Bedf 
  ord-Berea 
  sediments 
  were 
  

   laid 
  down, 
  was 
  not 
  in 
  free 
  communication 
  with 
  the 
  sea. 
  

   That 
  the 
  Mississippian 
  embayment, 
  farther 
  west, 
  had 
  

   tides 
  is 
  proved 
  by 
  the 
  presence 
  of 
  very 
  large 
  current- 
  

   ripples, 
  measuring 
  about 
  180 
  cm. 
  from 
  crest 
  to 
  crest, 
  in 
  

   the 
  lower 
  part 
  of 
  the 
  Burlington 
  in 
  southeastern 
  Louisa 
  

   County, 
  Iowa. 
  7 
  Since 
  sedimentation 
  was 
  probably 
  con- 
  

   tinuous 
  in 
  this 
  region, 
  the 
  difference 
  in 
  time 
  between 
  the 
  

   two 
  deposits 
  can 
  not 
  form 
  a 
  serious 
  objection. 
  

  

  b. 
  Occurrence 
  of 
  oscillation 
  and 
  current-ripples 
  in 
  the 
  

   same 
  formation, 
  on 
  the 
  other 
  hand, 
  indicates 
  deposition 
  

   alternatingly 
  in 
  quiet 
  water 
  and 
  under 
  the 
  influence 
  of 
  

   currents 
  (of 
  water 
  or 
  of 
  air). 
  Favorable 
  conditions 
  for 
  

   such 
  a 
  combination 
  of 
  processes 
  exist 
  : 
  

  

  (1) 
  In 
  shallow 
  seas 
  with 
  tidal 
  currents 
  and 
  wind- 
  

   drifts 
  8 
  alternating 
  with 
  periods 
  of 
  quiet. 
  

  

  (2) 
  On 
  tidal 
  flats, 
  especially 
  on 
  irregular 
  shores 
  with 
  

   lagoons 
  and 
  pools. 
  9 
  

  

  (3) 
  On 
  alluvial 
  plains 
  where 
  floods 
  leave 
  stagnant 
  

   lakes, 
  and 
  dust 
  and 
  sand 
  are 
  blown 
  about 
  by 
  the 
  wind, 
  

   especially 
  in 
  arid 
  regions, 
  where 
  the 
  rivers 
  end 
  in 
  shift- 
  

   ing, 
  shallow 
  lakes 
  surrounded 
  by 
  dunes 
  (e. 
  g. 
  Lob-Nur 
  in 
  

   the 
  Tarim 
  Basin). 
  

  

  In 
  general, 
  the 
  last 
  case 
  offers 
  by 
  far 
  the 
  best 
  chances 
  

   for 
  the 
  preservation 
  of 
  both 
  types 
  of 
  ripples, 
  especially 
  

   the 
  large 
  flood 
  plains 
  of 
  semi-arid 
  regions, 
  where 
  the 
  

   wind, 
  at 
  the 
  approach 
  of 
  the 
  dry 
  season, 
  buries 
  the 
  rip- 
  

   ples 
  in 
  stagnant 
  lakes 
  and 
  along 
  the 
  water 
  courses 
  under 
  

   clouds 
  of 
  silt 
  and 
  sand. 
  

  

  There 
  are 
  practically 
  no 
  data 
  on 
  hand 
  for 
  a 
  comparison 
  

   of 
  the 
  relative 
  frequency 
  of 
  the 
  two 
  types 
  of 
  ripples 
  in 
  

   different 
  formations. 
  In 
  a 
  quarry 
  of 
  red 
  Triassic 
  

   "Buntsandstein" 
  in 
  the 
  German 
  Palatinate, 
  15 
  of 
  23 
  

   slabs 
  show 
  symmetrical, 
  the 
  others 
  asymmetrical 
  ripples. 
  

   (Berthology 
  1900, 
  p. 
  181.) 
  A 
  terrestrial 
  origin 
  of 
  this 
  

   part 
  of 
  the 
  Buntsandstein 
  is 
  almost 
  universally 
  assumed. 
  

  

  7 
  J. 
  A. 
  Udden, 
  Jour. 
  Geo!., 
  vol. 
  24, 
  pp. 
  123 
  ff., 
  1916. 
  

  

  8 
  For 
  a 
  discussion 
  of 
  the 
  effect 
  of 
  -wind 
  drifts 
  on 
  tidal 
  currents 
  see 
  

   W. 
  H. 
  Bucher, 
  Proc. 
  Nat. 
  Acad. 
  Sci., 
  vol. 
  3, 
  p. 
  288, 
  1917 
  and 
  Chapter 
  III 
  

   of 
  this 
  paper. 
  

  

  Oscillation 
  -ripples 
  formed 
  on 
  shores 
  where 
  the 
  tides 
  are 
  high 
  and 
  tidal 
  

   currents 
  strong, 
  were, 
  for 
  instance, 
  described 
  by 
  Brown, 
  1911 
  (Coast 
  of 
  

   Labrador), 
  and 
  Cornish, 
  1901 
  (English 
  Coast). 
  

  

  