﻿400 
  H. 
  8. 
  Williams 
  — 
  Southern 
  Devonian 
  formations. 
  

  

  plateau, 
  and 
  also 
  along 
  the 
  southern 
  shores 
  of 
  the 
  Missouri 
  

   island, 
  is 
  further 
  in 
  harmony 
  with 
  the 
  hypothesis 
  of 
  current- 
  

   scour 
  and 
  transportation. 
  Since 
  the 
  black 
  shale 
  conditions 
  fol- 
  

   lowed 
  soon 
  after 
  the 
  first 
  appearance 
  of 
  the 
  Oriskany 
  sediments 
  

   and 
  fauna 
  in 
  the 
  basin, 
  this 
  event 
  requires 
  consideration. 
  

  

  The 
  more 
  conspicuous 
  facts 
  regarding 
  the 
  Oriskany 
  crisis 
  are 
  

   the 
  following: 
  In 
  a 
  great 
  interior 
  continental 
  basin, 
  closed 
  all 
  

   around 
  its 
  north, 
  east 
  and 
  part 
  of 
  its 
  southern 
  border 
  (see 
  the 
  

   chart), 
  the 
  closing 
  epoch 
  of 
  the 
  Silurian 
  era 
  was 
  marked 
  by 
  a 
  

   widely 
  distributed 
  limestone 
  accumulation 
  which 
  appears 
  to 
  

   have 
  its 
  purer 
  and 
  more 
  characteristic 
  center 
  in 
  the 
  extreme 
  

   northeastern 
  part 
  of 
  the 
  basin. 
  Here 
  depression 
  was 
  taking 
  

   place 
  so 
  that 
  in 
  eastern 
  New 
  York 
  the 
  formation 
  is 
  markedly 
  

   thicker 
  than 
  in 
  its 
  western 
  part. 
  Suddenly 
  there 
  was 
  an 
  irrup- 
  

   tion 
  of 
  coarse 
  sand 
  with 
  a 
  sharply 
  differentiated 
  fauna, 
  which 
  

   from 
  Oriskany 
  Falls, 
  N. 
  Y., 
  extends 
  in 
  diminishing 
  thickness 
  

   across 
  to 
  Ontario, 
  Canada. 
  On 
  the 
  eastern 
  shore, 
  however, 
  

   along 
  the 
  edge 
  of 
  Appalachia, 
  as 
  far 
  as 
  Georgia, 
  the 
  fauna 
  at 
  

   its 
  base 
  appears 
  to 
  be 
  more 
  or 
  less 
  blended 
  with 
  the 
  Helder- 
  

   berg 
  species 
  which 
  continue 
  upward 
  in 
  the 
  sections. 
  In 
  the 
  

   extreme 
  southward 
  extension 
  only 
  a 
  few 
  of 
  the 
  Oriskany 
  

   species 
  reach 
  the 
  region 
  and 
  the 
  Helderberg 
  fauna 
  does 
  not 
  

   appear 
  to 
  cease 
  till 
  after 
  the 
  Oriskany 
  conditions 
  of 
  sedimenta- 
  

   tion 
  had 
  closed. 
  In 
  eastern 
  Pennsylvania, 
  the 
  coarser 
  Oriskany 
  

   sediments 
  are 
  not 
  found 
  on 
  the 
  extreme 
  eastern 
  side 
  but 
  as 
  

   far 
  west 
  as 
  the 
  Lehigh 
  Water 
  Gap, 
  where, 
  too, 
  they 
  are 
  thicker, 
  

   by 
  four 
  times, 
  than 
  at 
  the 
  Delaware 
  Water 
  Gap, 
  some 
  thirty 
  

   miles 
  further 
  east, 
  and 
  the 
  more 
  eastern 
  sections 
  are 
  limestones 
  

   and 
  lime 
  shales, 
  while 
  to 
  the 
  westward 
  sandstones 
  and 
  conglom- 
  

   erates 
  appear 
  in 
  heavy 
  sections.* 
  

  

  Furthermore, 
  when 
  we 
  examine 
  the 
  distribution 
  of 
  the 
  

   fauna 
  we 
  discover 
  that, 
  while 
  it 
  constitutes 
  the 
  principal 
  De- 
  

   vonian 
  marine 
  fauna 
  in 
  the 
  troughs 
  entering 
  from 
  the 
  east 
  into 
  

   the 
  Acadian 
  and 
  New 
  England 
  region, 
  both 
  the 
  sedimentation 
  

   and 
  fauna 
  of 
  the 
  Oriskany 
  of 
  the 
  interior 
  continental 
  basin 
  are 
  

   confined 
  to 
  the 
  shores 
  of 
  Lauren 
  tia 
  and 
  Appalacha 
  east 
  of 
  

   the 
  Cincinnati 
  plateau, 
  and 
  to 
  the 
  eastern 
  shore 
  of 
  the 
  Cincin- 
  

   nati 
  plateau. 
  In 
  its 
  purity 
  the 
  fauna 
  is 
  confined 
  to 
  the 
  north- 
  

   east 
  bay 
  of 
  this 
  interior 
  continental 
  sea. 
  To 
  explain 
  all 
  these 
  

   peculiar 
  conditions 
  one 
  event 
  seems 
  to 
  be 
  fully 
  sufficient. 
  If 
  

   we 
  suppose 
  that 
  the 
  sinking 
  of 
  the 
  area, 
  including 
  the 
  north- 
  

   eastern 
  rim 
  of 
  this 
  basin, 
  continued 
  till 
  sea 
  level 
  was 
  reached* 
  

   we 
  then 
  have 
  a 
  sufficient 
  cause 
  for 
  the 
  incursion 
  of 
  the 
  vast 
  

   amount 
  of 
  coarse 
  sands, 
  and 
  with 
  them 
  the 
  new 
  fauna, 
  which 
  

   suddenly 
  appeared 
  first 
  in 
  the 
  extreme 
  northeast 
  corner 
  of 
  this 
  

   inland 
  sea. 
  There 
  is 
  sufficient 
  reason 
  for 
  the 
  belief 
  that 
  such 
  

   a 
  sinking 
  was 
  going 
  on 
  during 
  Helderberg 
  time, 
  and 
  that 
  it 
  

   extends 
  along 
  the 
  Champlain 
  valley 
  as 
  far 
  as 
  Montreal, 
  near 
  

  

  * 
  See 
  Perm. 
  Geol. 
  Surv. 
  Summary, 
  final 
  report, 
  vol. 
  ii, 
  p. 
  1042. 
  

  

  