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  J. 
  W. 
  JUDD 
  ON 
  THE 
  SECONDARY 
  ROCKS 
  OF 
  SCOTLAND. 
  

  

  tains 
  form 
  to 
  the 
  western. 
  The 
  recent 
  soundings 
  of 
  H.M.S. 
  ' 
  Chal- 
  

   lenger 
  ' 
  have 
  not 
  only 
  confirmed 
  these 
  conclusions, 
  but 
  have 
  shown 
  

   that 
  the 
  elevation 
  of 
  this 
  old 
  Andes 
  of 
  the 
  eastern 
  continent 
  was 
  not 
  

   inferior 
  to 
  that 
  of 
  its 
  existing 
  homologue 
  in 
  the 
  western, 
  and 
  that 
  

   some 
  of 
  the 
  peaks 
  rose 
  to 
  the 
  height 
  of 
  at 
  least 
  25000 
  feet 
  above 
  the 
  

   surrounding 
  plains. 
  

  

  16. 
  General 
  Conclusions 
  from 
  the 
  relations 
  between 
  the 
  Volcanic 
  and 
  

   Plutonic 
  roclcs 
  of 
  the 
  Tertiary 
  period. 
  — 
  The 
  study 
  of 
  the 
  rocks 
  of 
  

   the 
  Inner 
  Hebrides 
  has 
  clearly 
  demonstrated 
  a 
  fact 
  which 
  had 
  been 
  

   already 
  strongly 
  suspected 
  by 
  Dr. 
  Macculloch, 
  Prof. 
  Geikie, 
  and 
  other 
  

   geologists, 
  that 
  the 
  granitic 
  rocks 
  of 
  that 
  area 
  had 
  a 
  close 
  connexion 
  

   and 
  were 
  of 
  contemporaneous 
  age 
  with 
  the 
  old 
  lava 
  streams 
  so 
  ex- 
  

   tensively 
  developed 
  in 
  their 
  neighbourhood. 
  

  

  We 
  have 
  shown 
  how, 
  by 
  the 
  more 
  or 
  less 
  complete 
  removal 
  of 
  its 
  

   upper 
  portions 
  and 
  the 
  consequent 
  exposure 
  of 
  its 
  deeply 
  seated 
  

   rocks 
  through 
  denudation, 
  a 
  volcano 
  may 
  present 
  many 
  different 
  as- 
  

   pects 
  — 
  from 
  examples 
  such 
  as 
  that 
  of 
  Mull, 
  in 
  which 
  the 
  relations 
  of 
  

   the 
  various 
  volcanic 
  products 
  can 
  still 
  be 
  easily 
  traced, 
  to 
  others, 
  like 
  

   that 
  of 
  Skye, 
  in 
  which 
  these 
  relations 
  are 
  by 
  no 
  means 
  so 
  clear 
  at 
  

   first 
  sight. 
  It 
  will 
  be 
  easy 
  to 
  conceive 
  a 
  still 
  further 
  stage 
  of 
  ruin 
  

   in 
  a 
  volcano 
  in 
  which, 
  all 
  the 
  surrounding 
  lavas 
  and 
  other 
  erupted 
  

   materials 
  being 
  removed, 
  we 
  should 
  have 
  left 
  only 
  the 
  central 
  core 
  

   of 
  granite 
  or 
  gabbro 
  (the 
  latter 
  perhaps 
  altered 
  into 
  various 
  serpen- 
  

   tinous 
  rocks) 
  rising 
  in 
  the 
  midst 
  of 
  a 
  series 
  of 
  stratified 
  rocks 
  ; 
  and 
  

   in 
  such 
  cases 
  there 
  would 
  be 
  nothing 
  to 
  connect 
  such 
  eruptive 
  masses 
  

   with 
  the 
  ordinary 
  subaerial 
  phenomena 
  of 
  volcanic 
  activity. 
  

  

  When 
  we 
  reflect 
  on 
  the 
  striking 
  similarity 
  of 
  the 
  products 
  of 
  this 
  

   series 
  of 
  Tertiary 
  volcanoes, 
  we 
  can 
  scarcely 
  doubt 
  of 
  their 
  connexion, 
  

   or 
  of 
  their 
  materials 
  having 
  been 
  derived 
  from 
  a 
  common 
  reservoir. 
  

   It 
  is, 
  under 
  these 
  circumstances, 
  easy 
  to 
  imagine 
  that, 
  by 
  the 
  total 
  

   removal 
  of 
  the 
  superincumbent 
  rocks, 
  the 
  consolidated 
  contents 
  of 
  

   this 
  old 
  reservoir 
  may 
  be 
  exposed. 
  In 
  such 
  cases 
  we 
  might 
  reasonably 
  

   expect 
  to 
  find 
  at 
  the 
  surface 
  a 
  tract 
  of 
  granite 
  of 
  wide 
  extent, 
  like 
  

   that 
  of 
  Leinster. 
  

  

  Fortunately 
  the 
  same 
  district 
  which 
  we 
  are 
  now 
  studying 
  affords 
  

   us, 
  in 
  a 
  series 
  of 
  igneous 
  rocks 
  of 
  older 
  date 
  than 
  those 
  already 
  de- 
  

   scribed, 
  a 
  number 
  of 
  beautiful 
  illustrations 
  and 
  convincing 
  proofs 
  of 
  

   the 
  truth 
  of 
  these 
  views 
  concerning 
  the 
  relations 
  between 
  the 
  Volcanic 
  

   and 
  the 
  Plutonic 
  rocks. 
  These 
  we 
  now 
  proceed 
  to 
  describe. 
  

  

  III. 
  The 
  Newer 
  Palaeozoic 
  Volcanoes. 
  

  

  That 
  there 
  is 
  evidence 
  in 
  the 
  Highlands 
  of 
  Scotland 
  of 
  a 
  great 
  

   period 
  of 
  volcanic 
  activity 
  which 
  preceded 
  the 
  deposition 
  of 
  the 
  Se- 
  

   condary 
  strata 
  of 
  the 
  district 
  has 
  been 
  already 
  pointed 
  out. 
  I 
  shall 
  

   proceed 
  to 
  show 
  that 
  the 
  eruptions 
  of 
  this 
  earlier 
  period 
  were 
  on 
  a 
  

   scale 
  of 
  at 
  least 
  equal 
  magnitude 
  with 
  those 
  of 
  the 
  Tertiary 
  epoch 
  

   just 
  described, 
  that 
  like 
  these 
  latter 
  they 
  gave 
  rise 
  to 
  the 
  formation 
  

   of 
  vast 
  plateaux 
  composed 
  of 
  lava 
  streams 
  surrounding 
  on 
  all 
  sides 
  

   great 
  volcanic 
  mountains, 
  and 
  that 
  under 
  the 
  action 
  of 
  denuding 
  

  

  