﻿J. 
  W. 
  JDDD 
  ON 
  THE 
  SECONDARY 
  ROCKS 
  OF 
  SCOTLAND. 
  291 
  

  

  often 
  wholly 
  made 
  up 
  of 
  fragments 
  of 
  Silurian 
  strata. 
  This 
  absence, 
  

   is 
  very 
  striking 
  when, 
  as 
  sometimes 
  occurs, 
  masses 
  of 
  granite 
  

   are 
  now 
  exposed 
  in 
  the 
  immediate 
  neighbourhood 
  of 
  the 
  conglome- 
  

   rates 
  ; 
  and 
  it 
  affords 
  a 
  strong 
  confirmation 
  of 
  the 
  age 
  which 
  we 
  have 
  

   assigned 
  to 
  the 
  granites, 
  by 
  showing 
  that 
  at 
  the 
  time 
  when 
  the 
  Old 
  

   Red 
  conglomerates 
  were 
  formed, 
  the 
  granites 
  were 
  not 
  exposed 
  at 
  

   the 
  surface. 
  

  

  Now, 
  in 
  the 
  whole 
  of 
  the 
  phenomena 
  presented 
  by 
  the 
  igneous 
  

   masses 
  of 
  the 
  Grampian 
  Mountains, 
  we 
  have 
  an 
  exact 
  counterpart 
  of 
  

   those 
  which 
  we 
  have 
  seen 
  are 
  displayed, 
  as 
  the 
  result 
  of 
  subterranean 
  

   action, 
  in 
  the 
  case 
  of 
  the 
  great 
  Tertiary 
  volcanoes 
  of 
  the 
  Hebrides. 
  

   In 
  both 
  cases 
  we 
  find 
  great 
  intrusive 
  masses 
  of 
  granite, 
  passing 
  by 
  

   insensible 
  gradations 
  into 
  syenite-granite 
  and 
  felsite 
  ; 
  and 
  these, 
  in 
  

   rising 
  through 
  the 
  surrounding 
  strata, 
  violently 
  disturb 
  and 
  greatly 
  

   metamorphose 
  them. 
  With 
  the 
  great 
  bosses 
  of 
  igneous 
  rock 
  are 
  

   evidently 
  connected, 
  in 
  both 
  cases, 
  those 
  smaller 
  masses 
  and 
  dykes 
  

   of 
  similar 
  materials, 
  which 
  traverse 
  the 
  surrounding 
  rocks, 
  producing 
  

   in 
  them 
  degrees 
  of 
  disturbance 
  and 
  metamorphism 
  proportional 
  to 
  

   their 
  bulk. 
  

  

  "We 
  have 
  already 
  seen 
  that 
  both 
  north 
  and 
  south 
  of 
  the 
  Grampian 
  

   Mountains 
  we 
  have 
  proofs 
  of 
  the 
  former 
  existence 
  of 
  extensive 
  

   plateaux 
  composed 
  of 
  lavas, 
  for 
  the 
  most 
  part 
  of 
  a 
  felspathic 
  charac- 
  

   ter. 
  Unmistakable 
  evidence, 
  both 
  stratigraphical 
  and 
  palseonto- 
  

   logical, 
  and 
  of 
  totally 
  independent 
  character 
  in 
  either 
  case, 
  has 
  led 
  

   us 
  to 
  the 
  conclusion 
  that 
  the 
  subaerial 
  felstone 
  and 
  porphyrite 
  lavas 
  

   of 
  Lorn, 
  the 
  similar 
  subaqueous 
  lavas 
  of 
  Central 
  Scotland, 
  and 
  the 
  

   intrusive 
  masses 
  of 
  identical 
  ultimate 
  chemical 
  composition 
  in 
  the 
  

   Grampians, 
  were 
  all 
  formed 
  during 
  the 
  same 
  geological 
  periods, 
  those 
  

   constituting 
  the 
  latter 
  part 
  of 
  the 
  Palaeozoic 
  epoch. 
  From 
  the 
  rela- 
  

   tions 
  shown 
  to 
  exist 
  between 
  the 
  granitic 
  rocks 
  and 
  lavas 
  of 
  Tertiary 
  

   age 
  already 
  described, 
  we 
  are 
  thus 
  led 
  to 
  see 
  that 
  there 
  are 
  strong 
  

   grounds 
  for 
  the 
  presumption 
  that 
  a 
  connexion 
  between 
  these 
  different 
  

   igneous 
  rock 
  masses 
  once 
  existed, 
  and 
  that 
  they 
  all 
  form 
  fragments, 
  

   now 
  isolated 
  from 
  one 
  another 
  by 
  extensive 
  denudation, 
  of 
  the 
  same 
  

   great 
  series 
  of 
  volcanic 
  outbursts. 
  I 
  shall 
  now 
  proceed 
  to 
  adduce 
  

   evidence 
  which 
  is, 
  I 
  think, 
  sufficient 
  to 
  convert 
  this 
  strong 
  presump- 
  

   tion 
  into 
  almost 
  absolute 
  certainty. 
  

  

  9. 
  Relations 
  of 
  the 
  Igneous 
  RocTcs 
  of 
  Beinn 
  Nevis 
  and 
  Glencoe. 
  — 
  

   In 
  spite 
  of 
  the 
  arguments 
  already 
  brought 
  forward 
  in 
  support 
  of 
  the 
  

   view 
  that 
  the 
  subaqueous 
  lavas 
  of 
  Central 
  Scotland 
  and 
  the 
  subaerial 
  

   lavas 
  of 
  Lorn 
  originally 
  formed 
  parts 
  of 
  one 
  series 
  of 
  wide-spread 
  

   plateaux, 
  and 
  that 
  the 
  great 
  igneous 
  masses 
  of 
  the 
  Grampians 
  are 
  

   the 
  relics 
  of 
  great 
  centres 
  of 
  eruption 
  during 
  the 
  same 
  period, 
  some 
  

   may 
  be 
  inclined 
  to 
  regard 
  it 
  rather 
  as 
  a 
  bold 
  speculation 
  than 
  as 
  an 
  

   established 
  scientific 
  conclusion. 
  It 
  is 
  a 
  fortunate 
  circumstance, 
  

   therefore, 
  that 
  we 
  are 
  able 
  to 
  point 
  to 
  more 
  than 
  one 
  relic 
  of 
  these 
  

   volcanoes 
  of 
  the 
  Newer 
  Palaeozoic 
  period, 
  the 
  study 
  of 
  which 
  is 
  suffi- 
  

   cient, 
  I 
  believe, 
  to 
  convince 
  the 
  most 
  sceptical 
  upon 
  the 
  subject. 
  

  

  Amid 
  that 
  broad 
  belt 
  of 
  elevated 
  ground 
  constituting 
  the 
  Gram- 
  

   pians, 
  the 
  peak 
  which 
  rises 
  superior 
  to 
  all 
  the 
  rest 
  is 
  — 
  that 
  monarch 
  

  

  