﻿H. 
  S. 
  Williams 
  — 
  Southern 
  Devonian 
  formations. 
  401 
  

  

  which 
  on 
  the 
  island 
  of 
  St. 
  Helena 
  a 
  small 
  patch 
  of 
  Helderberg 
  

   limestone 
  is 
  still 
  preserved, 
  and 
  still 
  further 
  on 
  to 
  connect 
  with 
  

   the 
  eastern 
  ocean 
  across 
  the 
  St. 
  Lawrence 
  Yalley. 
  

  

  Such 
  a 
  depression 
  is 
  also 
  the 
  natural 
  correlative 
  of 
  the 
  eleva- 
  

   tion 
  at 
  the 
  southwestern 
  corner 
  of 
  the 
  basin 
  which 
  the 
  various 
  

   facts 
  already 
  in 
  hand 
  seem 
  to 
  call 
  for. 
  It 
  is 
  not 
  difficult 
  to 
  

   imagine 
  an 
  event 
  similar 
  to 
  this 
  as 
  possible 
  at 
  the 
  present 
  

   epoch, 
  by 
  which 
  a 
  slight 
  depression, 
  taking 
  below 
  sea-level 
  the 
  

   snores 
  of 
  northern 
  Europe, 
  would 
  let 
  in 
  the 
  cold 
  waters 
  of 
  the 
  

   north 
  to 
  spread 
  over 
  the 
  plains 
  of 
  Russia, 
  into 
  the 
  Black 
  Sea 
  

   and 
  through 
  to 
  the 
  Mediterranean, 
  changing 
  its 
  fauna, 
  and, 
  if 
  

   the 
  current 
  were 
  strong 
  enough, 
  covering 
  the 
  bottom 
  with 
  the 
  

   wash 
  of 
  the 
  land, 
  and 
  with 
  a 
  rapidity, 
  and 
  in 
  quantities, 
  far 
  in 
  

   excess 
  of 
  the 
  sedimentation 
  ordinarily 
  occurring 
  there. 
  The 
  

   catastrophic 
  effects 
  would 
  be 
  coordinate 
  with 
  the 
  reaching 
  of 
  a 
  

   culmination 
  point 
  in 
  slowly 
  and 
  regularly 
  operating 
  move- 
  

   ments 
  of 
  the 
  crust. 
  The 
  crisis 
  would 
  occur 
  when 
  the 
  sea 
  level 
  

   was 
  reached 
  in 
  the 
  slow 
  depression 
  of 
  the 
  northern 
  continental 
  

   rim. 
  Such 
  an 
  event 
  is 
  supposed 
  to 
  have 
  occurred 
  at 
  the 
  time 
  of 
  

   the 
  incursion 
  of 
  the 
  great 
  mass 
  of 
  clastic 
  sediments 
  into 
  the 
  

   Lower 
  Helderberg 
  sea 
  with 
  a 
  new 
  fauna 
  which 
  marked 
  the 
  

   opening 
  of 
  the 
  Oriskany 
  epoch 
  in 
  North 
  America. 
  

  

  In 
  the 
  hypothesis 
  here 
  offered 
  to 
  explain 
  the 
  differences 
  in 
  

   stratigraphy 
  presented 
  by 
  the 
  formations 
  of 
  the 
  Devonian 
  in 
  

   various 
  points 
  of 
  the 
  intercontinental 
  basin 
  of 
  eastern 
  North 
  

   America, 
  a 
  few 
  fundamental 
  principles 
  are 
  introduced 
  which 
  

   have 
  heretofore 
  been 
  entirely 
  ignored, 
  or 
  given 
  a 
  very 
  insig- 
  

   nificant 
  place 
  in 
  the 
  solution 
  of 
  such 
  problems. 
  

  

  1st. 
  A 
  ttvo-fold 
  source 
  for 
  the 
  clastic 
  sediments 
  forming 
  the 
  

   material 
  of 
  the 
  strata 
  of 
  a 
  common 
  section. 
  — 
  In 
  the 
  present 
  

   case 
  the 
  black 
  shale 
  sediments 
  are 
  supposed 
  to 
  have 
  been 
  

   derived 
  from 
  the 
  decay 
  of 
  Lower 
  Silurian 
  rocks 
  protruding 
  

   more 
  or 
  less 
  above 
  sea-level 
  along 
  the 
  Cincinnati 
  plateau, 
  and 
  

   not 
  from 
  the 
  surfaces 
  of 
  the 
  Laurentia 
  or 
  Appalachia 
  lands, 
  

   from 
  which 
  the 
  sediments 
  making 
  up 
  the 
  bulk 
  of 
  the 
  strata 
  

   bordering 
  these 
  lands 
  seaward 
  were 
  derived. 
  

  

  2d. 
  The 
  agency 
  of 
  ocean 
  currents 
  in 
  determining 
  the 
  geo- 
  

   graphical 
  distribution 
  of 
  sediments 
  not 
  derived 
  from 
  the 
  imme- 
  

   diate 
  coasts 
  along 
  which 
  they 
  were 
  deposited. 
  — 
  In 
  the 
  cases 
  of 
  

   the 
  black 
  shale 
  and 
  of 
  the 
  Oriskany 
  sediments 
  this 
  agency 
  

   explains 
  conditions 
  of 
  distribution 
  which 
  have 
  not 
  been 
  

   accounted 
  for 
  by 
  any 
  cause 
  heretofore 
  suggested, 
  so 
  far 
  as 
  I 
  am 
  

   aware. 
  And 
  the 
  reconstruction 
  of 
  the 
  topographical 
  conditions 
  

   of 
  the 
  region 
  from 
  facts 
  already 
  known 
  is 
  not 
  inconsistent 
  with 
  

   the 
  assumption 
  that 
  the 
  required 
  currents 
  actually 
  existed 
  in 
  

   the 
  basin 
  during 
  the 
  time 
  when 
  the 
  distribution 
  of 
  the 
  sedi- 
  

   ments 
  took 
  place. 
  

  

  