﻿H. 
  S. 
  Williams 
  — 
  Silurian-Devonian 
  boundary. 
  203 
  

  

  Art. 
  XXII. 
  — 
  The 
  Silurian- 
  Devonian 
  boundary 
  in 
  North 
  

   America. 
  I. 
  The 
  Chapman 
  Sandstone 
  fauna 
  / 
  by 
  Henry 
  

  

  S. 
  Williams. 
  

  

  The 
  identification 
  of 
  the 
  Chapman 
  sandstone 
  fauna 
  of 
  Aroos- 
  

   took 
  County, 
  Maine, 
  with 
  the 
  typical 
  Ludlow 
  "Tilestone" 
  

   fauna 
  of 
  Murchison, 
  furnishes 
  important 
  new 
  evideuce 
  bear- 
  

   ing 
  upon 
  the 
  question 
  of 
  the 
  exact 
  boundary 
  between 
  the 
  

   Silurian 
  and 
  Devonian 
  systems 
  in 
  North 
  America, 
  Before 
  the 
  

   identity 
  was 
  recognized 
  by 
  the 
  author, 
  the 
  general 
  position 
  of 
  

   the 
  fauna, 
  in 
  relation 
  to 
  the 
  change 
  in 
  sedimentation 
  from 
  

   limestone 
  to 
  the 
  sandstones 
  of 
  the 
  Gaspe 
  peninsula, 
  was 
  seen 
  

   to 
  give 
  probability 
  of 
  the 
  presence 
  of 
  an 
  uppermost 
  Silurian 
  

   fauna 
  in 
  this 
  part 
  of 
  the 
  continent. 
  A 
  discussion 
  of 
  this 
  sub- 
  

   ject 
  was 
  arranged 
  to 
  take 
  place 
  at 
  the 
  summer 
  meeting 
  of 
  the 
  

   Geological 
  Society 
  in 
  1899, 
  when 
  Mr. 
  Schuchert 
  proposed 
  to 
  

   present 
  arguments 
  for 
  inclusion 
  of 
  Lower 
  Helderberg 
  faunas 
  

   in 
  the 
  Devonian. 
  The 
  absence 
  of 
  Mr. 
  Schuchert 
  led 
  to 
  the 
  

   postponement 
  of 
  the 
  discussion 
  to 
  the 
  winter 
  meeting 
  in 
  

   December, 
  1899. 
  At 
  that 
  meeting, 
  I 
  briefly 
  referred 
  to 
  the 
  

   facts 
  here 
  given, 
  but 
  did 
  not 
  discuss 
  the 
  paleontological 
  evi- 
  

   dence 
  upon 
  which 
  the 
  identification 
  was 
  based. 
  In 
  the 
  present 
  

   article 
  it 
  is 
  proposed 
  to 
  state 
  briefly 
  the 
  paleontological 
  reasons 
  

   for 
  believing 
  the 
  Chapman 
  sandstone 
  fauna 
  to 
  be 
  the 
  American 
  

   equivalent 
  of 
  the 
  " 
  Tilestone 
  " 
  fauna 
  of 
  Wales, 
  leaving 
  the 
  full 
  

   description 
  and 
  illustration 
  of 
  the 
  fauna 
  for 
  a 
  future 
  work. 
  

  

  The 
  accurate 
  determination 
  of 
  boundary 
  planes 
  between 
  

   geological 
  systems 
  on 
  different 
  continents 
  is 
  of 
  greater 
  import- 
  

   ance 
  than 
  local 
  geologists 
  are 
  wont 
  to 
  appreciate. 
  As 
  in 
  the 
  

   case 
  of 
  current 
  money, 
  the 
  crucial 
  test 
  of 
  a 
  geological 
  classifi- 
  

   cation 
  is 
  most 
  deeply 
  felt 
  when 
  attempt 
  is 
  made 
  to 
  pass 
  it 
  in 
  a 
  

   foreign 
  country. 
  All 
  the 
  geological 
  system 
  boundary-planes 
  

   were 
  first 
  determined 
  outside 
  America; 
  and, 
  following 
  the 
  

   rule 
  of 
  historical 
  precedent, 
  such 
  standard 
  planes 
  must 
  form 
  

   the 
  basis 
  of 
  comparison 
  for 
  all 
  local 
  standards 
  set 
  up 
  in 
  

   America. 
  For 
  our 
  own 
  uses 
  alone 
  it 
  is 
  not 
  important 
  that 
  our 
  

   systems 
  should 
  accurately 
  correspond 
  at 
  their 
  limits 
  with 
  the 
  

   same 
  systems 
  of 
  Britain 
  and 
  Europe. 
  They 
  differ 
  more 
  or 
  

   less 
  in 
  their 
  fossil 
  contents 
  ; 
  and 
  a 
  general 
  agreement 
  in 
  

   boundaries, 
  adjusting 
  them 
  to 
  the 
  peculiarities 
  of 
  our 
  forma- 
  

   tions, 
  is 
  sufficient 
  for 
  the 
  mapping 
  and 
  discussion 
  of 
  our 
  local 
  

   geological 
  problems. 
  

  

  When, 
  however, 
  the 
  history 
  of 
  organisms 
  is 
  under 
  discus- 
  

   sion, 
  it 
  becomes 
  essential 
  to 
  correlate 
  with 
  accuracy 
  the 
  chief 
  

   time 
  boundaries 
  for 
  all 
  continents 
  ; 
  and 
  for 
  this 
  purpose 
  a 
  few 
  

  

  