﻿Related 
  Sedimentary 
  Surface 
  Forms. 
  255 
  

  

  tion 
  has 
  been 
  called 
  to 
  this 
  matter, 
  current-ripples 
  will 
  

   be 
  reported 
  from 
  numerous 
  marine 
  formations. 
  

  

  They 
  are 
  rather 
  common 
  on 
  the 
  surfaces 
  of 
  very 
  fine- 
  

   grained, 
  bluish 
  limestone 
  layers 
  of 
  the 
  Eden 
  and 
  Rich- 
  

   mond 
  Groups 
  of 
  Kentucky 
  and 
  Ohio, 
  in 
  the 
  former 
  

   especially 
  in 
  the 
  fine-grained 
  sandy 
  limestones 
  of 
  the 
  

   4 
  ' 
  Garrard 
  Sandstone 
  ' 
  ' 
  of 
  Kentucky. 
  

  

  Such 
  current-ripples 
  may 
  be 
  formed 
  by 
  the 
  wave 
  of 
  

   translation 
  on 
  the 
  strand, 
  or 
  by 
  wind-drift 
  or 
  tidal 
  cur- 
  

   rents 
  down 
  to 
  considerable 
  depths. 
  That 
  no 
  information 
  

   can 
  be 
  expected 
  from 
  marine 
  current-ripples 
  concerning 
  

   any 
  systems 
  of 
  currents, 
  is 
  made 
  obvious 
  by 
  an 
  inspec- 
  

   tion 
  of 
  the 
  results 
  of 
  modern 
  marine 
  current 
  measure- 
  

   ments, 
  especially 
  those 
  made 
  on 
  the 
  cruises 
  of 
  the 
  

   "Michael 
  Sars" 
  during 
  the 
  last 
  fifteen 
  years. 
  37 
  These 
  

   investigations 
  have 
  shown 
  that 
  the 
  system 
  of 
  currents 
  in 
  

   such 
  seas 
  as 
  the 
  Norwegian 
  and 
  the 
  North 
  Sea 
  is 
  vastly 
  

   more 
  complex 
  than 
  was 
  anticipated. 
  By 
  interference 
  of 
  

   wind-drifts 
  and 
  tidal 
  currents, 
  of 
  these 
  again 
  with 
  

   reflected 
  tidal 
  waves, 
  along 
  the 
  shore 
  with 
  shore-drift, 
  

   undertow 
  and 
  freshwater 
  surface 
  currents 
  and 
  their 
  

   counter 
  currents, 
  a 
  great 
  variety 
  of 
  conditions 
  are 
  pro- 
  

   duced. 
  These 
  are 
  further 
  complicated 
  by 
  the 
  existence 
  

   of 
  vortical 
  movements 
  with 
  vertical 
  axes, 
  in 
  the 
  open 
  

   ocean 
  as 
  well 
  as 
  in 
  coastal 
  waters, 
  and 
  by 
  the 
  fact 
  that 
  

   in 
  the 
  great 
  majority 
  of 
  cases 
  the 
  bottom 
  currents 
  follow 
  

   their 
  own 
  laws. 
  In 
  the 
  Skagerack, 
  for 
  instance, 
  "the 
  

   tidal 
  currents 
  are 
  scarcely 
  noticeable 
  in 
  the 
  upper 
  water 
  

   layers, 
  whereas 
  they 
  have 
  been 
  met 
  with 
  there 
  down 
  at 
  

   the 
  very 
  bottom 
  at 
  such 
  great 
  depths 
  as 
  200 
  m." 
  3S 
  

  

  This 
  raises 
  the 
  question 
  of 
  the 
  maximum 
  depth 
  at 
  which 
  

   such 
  current-ripples 
  as 
  are 
  found, 
  for 
  instance, 
  in 
  certain 
  

   marine 
  limestones, 
  might 
  have 
  originated. 
  It 
  can 
  be 
  

   answered 
  best 
  by 
  a 
  reference 
  to 
  one 
  of 
  the 
  most 
  interest- 
  

   ing 
  measurements 
  made 
  on 
  the 
  "Michael 
  Sars." 
  On 
  

   the 
  edge 
  of 
  the 
  continental 
  slope, 
  about 
  SO 
  km. 
  northwest 
  

   of 
  Aalesund 
  on 
  the 
  Norwegian 
  coast, 
  39 
  in 
  the 
  open 
  ocean, 
  

   not 
  in 
  any 
  channel, 
  the 
  Atlantic 
  current 
  was 
  found 
  run- 
  

   ning, 
  on 
  the 
  average, 
  parallel 
  with 
  the 
  continental 
  slope, 
  

  

  37 
  See 
  especially 
  Helland-Hansen, 
  Current 
  Measurements 
  in 
  Norwegian 
  

   Fiords, 
  the 
  Norwegian 
  Sea 
  and 
  the 
  North 
  Sea, 
  in 
  1906, 
  Bergen's 
  Museums 
  

   Aarbog. 
  1907, 
  No. 
  15; 
  and 
  Helland-Hansen, 
  and 
  Nansen, 
  The 
  Norwegian 
  

   Sea, 
  Eept. 
  Norweg. 
  Fishery 
  and 
  Marine 
  Investigations, 
  vol. 
  2, 
  No. 
  2, 
  1909. 
  

  

  ss 
  Report 
  Norweg. 
  Fishery 
  and 
  Marine 
  Investigations, 
  vol. 
  2, 
  No. 
  1, 
  p. 
  79, 
  

   1909. 
  

  

  39 
  62°50' 
  N. 
  Lat.; 
  4°47' 
  E. 
  Long. 
  

  

  