﻿J. 
  W. 
  JT/I)D 
  ON 
  JHE 
  SECONDARY 
  ROCKS 
  OF 
  SCOTLAXD. 
  231 
  

  

  covered 
  many 
  thousands 
  of 
  square 
  miles*-— 
  that, 
  moreover, 
  these 
  

   fragments 
  which 
  remain 
  still 
  constitute 
  mountains 
  nearly 
  2000 
  feet 
  

   in 
  height, 
  entirely 
  made 
  up 
  of 
  almost 
  horizontal 
  lava 
  sheets, 
  — 
  must 
  

   we 
  not 
  conclude 
  that 
  the 
  volcanoes 
  from 
  which 
  these 
  wide-spreading 
  

   and 
  thickly 
  piled 
  masses 
  of 
  lava 
  were 
  ejected 
  could 
  have 
  been 
  of 
  no 
  

   mean 
  dimensions 
  or 
  insignificant 
  character? 
  

  

  At 
  what 
  points, 
  then, 
  were 
  these 
  great 
  volcanoes 
  situated 
  ? 
  Where 
  

   are 
  the 
  relics 
  of 
  their 
  vast 
  masses, 
  the 
  indications 
  of 
  their 
  violent 
  

   action 
  ? 
  Can 
  it 
  be 
  that 
  all 
  traces 
  of 
  such 
  great 
  mountain-piles, 
  

   belonging 
  as 
  they 
  do 
  to 
  one 
  of 
  the 
  most 
  recent 
  of 
  the 
  geological 
  

   periods, 
  have 
  altogether 
  disappeared 
  ? 
  Or 
  are 
  we 
  rather 
  to 
  con- 
  

   clude 
  that 
  denudation 
  and 
  other 
  causes 
  have 
  so 
  modified 
  and 
  dis- 
  

   guised 
  their 
  characters, 
  that 
  their 
  true 
  Dature 
  is 
  not 
  now 
  at 
  first 
  

   sight 
  recognizable 
  ? 
  These 
  are 
  the 
  questions 
  that 
  everywhere 
  pre- 
  

   sent 
  themselves 
  to 
  the 
  geologist 
  in 
  the 
  Western 
  Highlands, 
  and 
  press 
  

   for 
  a 
  solution. 
  

  

  In 
  support 
  of 
  the 
  opinion 
  that, 
  even 
  within 
  a 
  comparatively 
  recent 
  

   geological 
  period, 
  such 
  vast 
  volcanoes 
  may 
  have 
  entirely 
  disappeared, 
  

   while 
  extensive 
  fragments 
  of 
  the 
  lava 
  streams 
  which 
  flowed 
  from 
  them 
  

   so 
  conspicuously 
  remain, 
  it 
  may 
  be 
  pointed 
  out, 
  first, 
  that 
  the 
  former 
  

   would 
  be 
  composed 
  mainly 
  of 
  loose 
  and 
  fragmentary 
  materials, 
  which 
  

   are 
  much 
  more 
  easily 
  acted 
  upon 
  by 
  degrading 
  forces 
  than 
  the 
  solid 
  

   rocks 
  of 
  the 
  latter 
  ; 
  secondly, 
  that 
  their 
  greater 
  elevation 
  would 
  faci- 
  

   litate 
  their 
  destruction; 
  and, 
  thirdly, 
  that 
  the 
  evidence 
  of 
  denudation, 
  

   even 
  on 
  the 
  most 
  stupendous 
  scale, 
  having 
  taken 
  place 
  in 
  the 
  district 
  

   since 
  the 
  period 
  of 
  the 
  formation 
  of 
  these 
  volcanoes, 
  geologically 
  re- 
  

   cent 
  though 
  they 
  are, 
  is 
  of 
  the 
  most 
  unmistakable 
  character. 
  

  

  Hut 
  on 
  the 
  other 
  hand 
  it 
  must 
  be 
  remembered 
  that 
  the 
  remains 
  

   of 
  the 
  great 
  volumes 
  of 
  fluid 
  materials 
  which 
  ascended 
  through 
  the 
  

   volcanic 
  piles, 
  and, 
  sending 
  off 
  ramifications 
  in 
  all 
  directions, 
  served 
  

   to 
  bind 
  together 
  the 
  masses 
  of 
  fragmentary 
  matter, 
  must 
  not 
  only 
  

   in 
  themselves 
  have 
  constituted 
  rocks 
  of 
  great 
  solidity 
  and 
  permaur- 
  

   ence, 
  but, 
  by 
  affording 
  coherence 
  to 
  the 
  volcanoes 
  have 
  retarded 
  

   their 
  denudation. 
  Of 
  these 
  solidified 
  igneous 
  springs, 
  which 
  con-r 
  

   gtituted 
  the 
  connexions 
  between 
  the 
  great 
  rivers 
  of 
  lava 
  and 
  the 
  sub- 
  

   terranean 
  reservoirs 
  of 
  liquefied 
  rock, 
  it 
  is 
  hard, 
  nay, 
  impossible, 
  to 
  

   conceive 
  the 
  remains 
  to 
  have 
  been 
  wholly 
  removed 
  while 
  any 
  

   portion 
  of 
  the 
  older 
  rocks 
  which 
  they 
  penetrated 
  remained 
  ; 
  though 
  

   in 
  many 
  cases 
  we 
  can 
  readily 
  understand 
  the 
  effects 
  of 
  denudation 
  

   to 
  be 
  such 
  as 
  to 
  render 
  obscure 
  the 
  connexion 
  between 
  these 
  solidi- 
  

  

  * 
  It 
  is 
  perhans 
  not 
  possible 
  to 
  adduce 
  any 
  more 
  striking 
  illustration 
  of 
  the 
  

   vast 
  changes 
  which 
  have 
  taken 
  place 
  in 
  the 
  relative 
  position 
  of 
  rock-ni 
  asses, 
  

   .and 
  the 
  extent 
  to 
  which 
  tiny 
  have 
  been 
  subjected 
  to 
  denuding 
  agencies 
  since 
  a 
  

   period 
  so 
  geologically 
  recent 
  as 
  the 
  Miocene, 
  than 
  that 
  which 
  is 
  afforded 
  to 
  us 
  

   in 
  the 
  great 
  fault, 
  at 
  Morvern. 
  Heiewe 
  find 
  a 
  mass 
  of 
  strata 
  composed 
  of 
  

   Lias 
  unconformab'y 
  overlain 
  by 
  Upper 
  Cretaceous, 
  and 
  this 
  in 
  turn 
  by 
  Miocene 
  

   basalts, 
  let 
  down 
  by 
  a 
  fault, 
  which 
  must 
  have 
  a 
  throw 
  of 
  nearly 
  20U0feet, 
  against 
  

   the 
  contorted 
  gneissic 
  rocks 
  of 
  the 
  Lower 
  Silurian. 
  Nothing 
  can 
  present 
  a 
  

   greater 
  contrast 
  than 
  the 
  green 
  terraced 
  hills 
  of 
  the 
  former, 
  rising 
  in 
  Glashven 
  

   to 
  the 
  height 
  of 
  1516 
  feet, 
  and 
  the 
  barren 
  and 
  rugged 
  mountains 
  of 
  the 
  latter 
  

   culminating 
  in 
  Garbh-shlios 
  (1638 
  feet). 
  The 
  abrupt 
  junction 
  of 
  these 
  rocks 
  

   can 
  ba 
  traced 
  in 
  the 
  wild 
  ravine 
  of 
  Innimore. 
  

  

  s2 
  

  

  