﻿Related 
  Sedimentary 
  Surface 
  Forms. 
  243 
  

  

  crests 
  in 
  contrast 
  to 
  the 
  broad, 
  rounded 
  troughs, 
  often 
  

   with 
  a 
  minor 
  ridge 
  in 
  their 
  center, 
  which, 
  of 
  course, 
  never 
  

   appears 
  on 
  the 
  crests, 
  render 
  these 
  ripples 
  especially 
  

   valuable 
  for 
  the 
  distinction 
  betwen 
  the 
  upper 
  and 
  lower 
  

   surfaces 
  of 
  strata 
  in 
  structural 
  work. 
  — 
  (Cf. 
  p. 
  184.) 
  

  

  2. 
  Interpretation. 
  

  

  The 
  following 
  points 
  bear 
  on 
  the 
  paleogeographical 
  

   interpretation 
  of 
  oscillation 
  ripples: 
  

  

  1. 
  The 
  presence 
  of 
  oscillation-ripples 
  in 
  a 
  sediment 
  

   implies 
  complete 
  absence 
  of 
  horizontal 
  currents 
  at 
  the 
  

   time 
  of 
  their 
  formation. 
  

  

  a. 
  Water 
  bodies, 
  in 
  which 
  sediments 
  showing 
  no 
  

   other 
  but 
  symmetrical 
  ripples 
  were 
  laid 
  down, 
  must 
  have 
  

   been 
  practically 
  free 
  from 
  currents 
  of 
  any 
  kind. 
  The 
  two 
  

   types 
  of 
  currents 
  which 
  alone 
  would 
  produce 
  on 
  a 
  larger 
  

   scale 
  ripples 
  in 
  standing 
  bodies 
  of 
  water, 
  are 
  tides 
  and 
  

   wind-drifts. 
  The 
  effect 
  of 
  the 
  latter 
  decreases 
  rapidly 
  

   with 
  depth 
  ; 
  it 
  is 
  probably 
  limited 
  to 
  the 
  upper 
  50 
  m. 
  of 
  

   the 
  neritique 
  zone 
  of 
  the 
  sea. 
  3 
  The 
  insignificance 
  of 
  the 
  

   tides 
  in 
  enclosed 
  parts 
  of 
  the 
  sea 
  as 
  well 
  as 
  in 
  lakes 
  is 
  

   well 
  known. 
  The 
  Baltic, 
  the 
  Black 
  Sea, 
  the 
  largest 
  part 
  

   of 
  the 
  European 
  and 
  American 
  Mediterraneans 
  have 
  tides 
  

   negligible 
  for 
  our 
  purposes; 
  4 
  some, 
  like 
  the 
  Black 
  Sea, 
  

   none 
  at 
  all. 
  5 
  Ripples 
  cannot, 
  therefore, 
  be 
  used 
  to 
  dis- 
  

   tinguish 
  marine 
  and 
  lacustrine 
  sediments. 
  

  

  A 
  sediment 
  like 
  the 
  Berea 
  Sandstone, 
  which 
  consists 
  

   largely 
  of 
  fine-grained, 
  almost 
  pure 
  quartz 
  sand 
  and 
  

   abounds 
  in 
  oscillation-ripples 
  without 
  a 
  trace 
  of 
  current- 
  

   ripples, 
  6 
  may 
  therefore 
  have 
  originated 
  either 
  in 
  a 
  lake 
  

   or 
  in 
  a 
  sea 
  free 
  from 
  tidal 
  currents. 
  

  

  A 
  study 
  of 
  map 
  No. 
  20 
  of 
  Bo^haus' 
  " 
  Atlas 
  der 
  Hydro- 
  

   graphie" 
  shows 
  that, 
  so 
  far 
  as. 
  recorded, 
  all 
  epiconti- 
  

   nental 
  seas 
  which 
  are 
  in 
  open 
  connection 
  with 
  the 
  ocean 
  

   have 
  rather 
  great 
  tidal 
  ranges 
  and 
  therefore 
  are 
  agitated 
  

   by 
  tidal 
  currents. 
  In 
  open 
  bays 
  the 
  range 
  is 
  invariably 
  

   increased. 
  It 
  is 
  only 
  in 
  landlocked 
  bodies 
  of 
  water 
  that 
  

  

  3 
  ' 
  'District 
  littoral" 
  of 
  Pruvot 
  (cf. 
  E. 
  Haug, 
  Traite 
  de 
  Geologie, 
  1911, 
  

   p. 
  87) 
  ; 
  ''littoral 
  region" 
  of 
  Schuchert 
  (Historical 
  Geology, 
  1915, 
  p. 
  490). 
  

  

  4 
  Cf 
  . 
  Kruemmel, 
  Handbuch 
  d. 
  Ozeanographie, 
  vol. 
  2, 
  pp. 
  304 
  ff 
  ., 
  1911. 
  

  

  5 
  Kindle, 
  in 
  making 
  the 
  generalization 
  that 
  oscillation-ripples 
  are 
  generally 
  

   found 
  on 
  lake 
  bottoms 
  and 
  current-ripples 
  on 
  sea 
  bottoms 
  (1917, 
  p. 
  49; 
  

   see 
  Bibliography, 
  Part 
  I) 
  , 
  overlooked 
  the 
  fact 
  that 
  the 
  coast 
  of 
  Nova 
  Scotia 
  

   with 
  its 
  strong 
  tides 
  offers 
  by 
  no 
  means 
  typical 
  or 
  average 
  conditions 
  for 
  

   all 
  marine 
  shores 
  or 
  the 
  sea 
  bottom 
  at 
  large. 
  

  

  6 
  J. 
  E. 
  Hyde, 
  Jour. 
  Geology, 
  vol. 
  19, 
  pp. 
  258-269. 
  

  

  