﻿J. 
  W. 
  JT/DD 
  OjST 
  THE 
  SECONDARY 
  ROCKS 
  OE 
  SCOTLAND. 
  223 
  

  

  In 
  this 
  manner 
  we 
  are 
  led 
  to 
  many 
  very 
  interesting 
  conclusions 
  

   with 
  regard 
  to 
  the 
  chronology 
  of 
  the 
  various 
  rocks 
  of 
  the 
  Scottish 
  

   Highlands. 
  

  

  Moreover, 
  as 
  I 
  hope 
  to 
  be 
  able 
  to 
  show, 
  the 
  prosecution 
  of 
  this 
  

   research 
  concerning 
  the 
  relations 
  between 
  these 
  sedimentary 
  and 
  

   eruptive 
  rocks, 
  is 
  calculated 
  to 
  throw 
  new 
  light 
  upon 
  some 
  of 
  the 
  

   obscurest 
  problems 
  of 
  physical 
  geology. 
  

  

  Under 
  these 
  circumstances, 
  I 
  have 
  considered 
  it 
  advisable 
  to 
  con- 
  

   fine 
  myself 
  in 
  the 
  present 
  communication 
  to 
  this 
  question 
  of 
  the 
  

   mutual 
  relations 
  between 
  the 
  Secondary 
  and 
  Volcanic 
  rocks 
  of 
  the 
  

   west 
  coast 
  of 
  Scotland 
  — 
  a 
  question 
  of 
  much 
  complication 
  but 
  at 
  the 
  

   same 
  time 
  of 
  the 
  highest 
  interest 
  — 
  reserving 
  for 
  a 
  future 
  occasion 
  

   the 
  details 
  of 
  the 
  history 
  of 
  the 
  Mesozoic 
  periods 
  in 
  the 
  district, 
  as 
  

   deduced 
  from 
  the 
  palseontological 
  and 
  physical 
  evidence. 
  

  

  1. 
  History 
  of 
  Previous 
  Opinion 
  on 
  the 
  subject. 
  — 
  The 
  very 
  inti- 
  

   mate 
  manner 
  in 
  which 
  the 
  Secondary 
  and 
  Volcanic 
  rocks 
  of 
  the 
  

   Hebrides 
  are 
  associated 
  with 
  one 
  another 
  not 
  unnaturally 
  led 
  the 
  

   earlier 
  geological 
  observers 
  to 
  regard 
  them 
  as 
  being 
  of 
  contempora- 
  

   neous 
  age. 
  This 
  opinion 
  received 
  its 
  first 
  shock 
  in 
  1851, 
  through 
  

   the 
  discovery 
  by 
  the 
  Duke 
  of 
  Argyll 
  of 
  the 
  leaf-beds 
  of 
  Ardtun, 
  and 
  

   the 
  determination 
  by 
  Professor 
  Edward 
  Forbes 
  of 
  the 
  Miocene 
  age 
  

   of 
  the 
  fossil 
  plants 
  contained 
  in 
  these 
  deposits*. 
  It 
  then 
  became 
  

   evident 
  that 
  a 
  part 
  at 
  least 
  of 
  the 
  Volcanic 
  rocks 
  of 
  the 
  Hebrides 
  

   belongs 
  to 
  the 
  Tertiary 
  period. 
  In 
  1865 
  Professor 
  A. 
  Geikie 
  had 
  

   arrived 
  at 
  the 
  important 
  conclusion 
  that 
  the 
  vast 
  sheets 
  of 
  igneous 
  

   rock 
  lying 
  between 
  the 
  Secondary 
  strata 
  in 
  the 
  Hebrides 
  are 
  in 
  

   every 
  case 
  intrusive, 
  and 
  therefore 
  not 
  contemporaneous 
  with 
  those 
  

   rocks 
  ; 
  and 
  on 
  a 
  review 
  of 
  all 
  the. 
  facts 
  of 
  the 
  case, 
  he 
  was 
  led 
  to 
  an- 
  

   nounce 
  his 
  conviction 
  that 
  the 
  whole 
  of 
  the 
  volcanic 
  rocks 
  under 
  

   consideration 
  belong 
  to 
  the 
  Tertiary 
  period 
  f 
  . 
  This 
  conclusion 
  I 
  have 
  

   been 
  able 
  to 
  confirm 
  by 
  showing 
  that 
  the 
  volcanic 
  rocks 
  in 
  question 
  

   unconformably 
  overlie 
  even 
  the 
  youngest 
  members 
  of 
  the 
  Chalk. 
  

  

  The 
  unmistakably 
  volcanic 
  origin 
  of 
  the 
  so-called 
  " 
  trap 
  rocks 
  " 
  of 
  

   the 
  Western 
  Isles 
  had 
  been 
  noticed 
  by 
  many 
  observers 
  ; 
  and 
  some 
  of 
  

   these, 
  especially 
  Dr. 
  Macculloch 
  J 
  and 
  Professor 
  Geikie 
  §, 
  have 
  dwelt 
  

   upon 
  the 
  evidently 
  close 
  relations 
  between 
  these 
  and 
  the 
  Plutonic 
  

   rocks 
  of 
  the 
  district. 
  The 
  Duke 
  of 
  Argyll 
  has 
  remarked 
  on 
  the 
  

   manner 
  in 
  which 
  the 
  two 
  classes 
  of 
  igneous 
  rock, 
  as 
  seen 
  in 
  a 
  section 
  

   in 
  Midi, 
  appear 
  to 
  graduate 
  into 
  one 
  another 
  — 
  and 
  also 
  on 
  the 
  indi- 
  

  

  * 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  vii. 
  pp. 
  89, 
  103. 
  

  

  t 
  Proe. 
  Roy. 
  Soc. 
  Edinb. 
  vol. 
  vi. 
  (1866-67), 
  p. 
  72, 
  and 
  Quart. 
  Journ. 
  Geol. 
  

   Soc. 
  (1869), 
  vol. 
  xxvii. 
  p. 
  283. 
  I 
  gladly 
  take 
  the 
  present 
  opportunity 
  of 
  bearing 
  

   ■witness 
  to 
  the 
  great 
  value 
  of 
  Professor 
  Geikie's 
  researches 
  among 
  the 
  volcanic 
  

   rocks 
  of 
  Scotland. 
  Although 
  the 
  conclusions 
  at 
  which 
  I 
  have 
  arrived 
  are, 
  in 
  

   many 
  cases, 
  very 
  different 
  from 
  the 
  opinions 
  which 
  he 
  has 
  expressed 
  on 
  some 
  of 
  

   the 
  phenomena 
  of 
  this 
  interesting 
  district, 
  I 
  think 
  that 
  in 
  almost 
  every 
  case 
  it 
  will 
  

   be 
  found 
  that 
  the 
  points 
  in 
  which 
  he 
  differs 
  from 
  myself 
  are 
  those 
  in 
  which 
  he 
  

   has 
  put 
  forward 
  useful 
  suggestions 
  of 
  a 
  tentative 
  character 
  rather 
  than 
  the 
  

   results 
  of 
  direct 
  observation. 
  In 
  almost 
  every 
  case 
  of 
  the 
  latter 
  kind, 
  I 
  am 
  

   happy 
  to 
  be 
  able 
  to 
  confirm 
  his 
  great 
  accuracy 
  and 
  acumen.. 
  

  

  £ 
  'A 
  Description 
  of 
  the 
  Western 
  Isles 
  of 
  Scotland,' 
  1819. 
  

  

  § 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xxvii. 
  p. 
  282. 
  

  

  