﻿J. 
  W. 
  JUDD 
  ON 
  THE 
  SECONDARY 
  ROCKS 
  OF 
  SCOTLAND. 
  289 
  

  

  through 
  the 
  whole 
  of 
  the 
  Newer 
  Palaeozoic 
  periods 
  was 
  brought 
  to 
  

   a 
  close. 
  

  

  8. 
  The 
  Eruptive 
  Masses 
  of 
  the 
  Grampian 
  Mountains. 
  — 
  From 
  Peter- 
  

   head, 
  on 
  the 
  north-east, 
  to 
  the 
  Ross 
  of 
  Mull, 
  on 
  the 
  south-west, 
  there 
  

   occur, 
  along 
  the 
  whole 
  course 
  of 
  the 
  Grampian 
  Mountains, 
  as 
  is 
  

   well 
  known 
  to 
  all 
  geologists, 
  a 
  series 
  of 
  masses 
  of 
  crystalline 
  and 
  

   igneous 
  rocks 
  which 
  have 
  evidently 
  been 
  protruded 
  through 
  the 
  con- 
  

   torted 
  and 
  metamorphosed 
  strata 
  of 
  the 
  Lower 
  Silurian. 
  At 
  an 
  early 
  

   period 
  in 
  the 
  history 
  of 
  geology 
  these 
  rocks 
  excited 
  much 
  attention, 
  

   from 
  their 
  bearing 
  upon 
  the 
  controversies 
  then 
  raging 
  between 
  the 
  

   supporters 
  of 
  the 
  Neptunian 
  and 
  Plutonic 
  theories 
  respectively. 
  Many 
  

   of 
  the 
  phenomena 
  were 
  most 
  carefully 
  studied, 
  especially 
  in 
  Glen 
  

   Tilt, 
  where 
  Hutton 
  found 
  the 
  most 
  beautiful 
  illustration 
  of 
  his 
  theory 
  

   of 
  the 
  igneous 
  origin 
  of 
  the 
  granites, 
  and 
  where 
  Playfair, 
  Webb 
  Sey- 
  

   mour, 
  and 
  Macculloch 
  by 
  a 
  series 
  of 
  patient 
  observations 
  contributed 
  

   so 
  much 
  towards 
  the 
  establishment 
  of 
  the 
  truth 
  of 
  that 
  theory. 
  

  

  The 
  largest 
  and 
  most 
  important 
  of 
  the 
  igneous 
  masses 
  of 
  the 
  

   Grampians 
  are 
  the 
  great 
  granitic 
  bosses, 
  which 
  give 
  rise 
  to 
  so 
  many 
  

   varieties 
  of 
  physical 
  feature 
  — 
  from 
  the 
  lofty 
  mountains 
  of 
  the 
  Cairn- 
  

   gorm, 
  Beinn 
  Nevis, 
  and 
  Beinn 
  Cruachan 
  groups, 
  to 
  the 
  low, 
  undu- 
  

   lating, 
  and 
  sometimes 
  almost 
  level 
  tracts 
  of 
  the 
  Ross 
  of 
  Mull, 
  the 
  Moor 
  

   of 
  Rannoch, 
  and 
  many 
  districts 
  in 
  Aberdeenshire. 
  Where, 
  through 
  

   extensive 
  denudation, 
  the 
  lower 
  and 
  deeper 
  portions 
  of 
  these 
  masses 
  

   are 
  exposed, 
  they 
  are 
  found 
  to 
  be 
  composed 
  of 
  an 
  almost 
  uniform 
  mass 
  

   of 
  typical 
  granite, 
  such 
  as 
  is 
  so 
  well 
  seen 
  in 
  the 
  Ross 
  of 
  Mull 
  ; 
  but 
  

   where, 
  on 
  the 
  other 
  hand, 
  they 
  rise 
  into 
  lofty 
  peaks, 
  the 
  granite 
  is 
  

   found 
  to 
  become 
  more 
  and 
  more 
  hornblendic, 
  and 
  then 
  to 
  graduate 
  

   through 
  euritic 
  varieties 
  into 
  afelsite, 
  usually 
  more 
  or 
  less 
  porphyri- 
  

   tic 
  in 
  structure 
  (porphyry 
  of 
  authors). 
  The 
  same 
  changes 
  are 
  often 
  

   found 
  to 
  take 
  place 
  in 
  the 
  characters 
  of 
  the 
  rocks 
  composing 
  these 
  

   great 
  eruptive 
  masses 
  when 
  we 
  trace 
  them 
  from 
  their 
  central 
  portions 
  

   towards 
  their 
  outer 
  margins. 
  

  

  The 
  relations 
  which 
  exist 
  between 
  the 
  great 
  granitic 
  masses 
  and 
  

   the 
  stratified 
  rocks 
  among 
  which 
  they 
  lie 
  have 
  been 
  clearly 
  described 
  

   by 
  many 
  observers. 
  Whenever 
  we 
  approach 
  such 
  intrusions 
  the 
  

   prevalent 
  strike 
  and 
  dip 
  of 
  the 
  beds 
  in 
  their 
  neighbourhood 
  appear 
  

   to 
  be 
  more 
  or 
  less 
  interfered 
  with, 
  and 
  the 
  strata 
  are 
  seen 
  to 
  be 
  

   frequently 
  affected 
  by 
  sudden 
  disturbance 
  and 
  contortion. 
  Moreover 
  

   the 
  uniformly 
  metamorphosed 
  Lower 
  Silurian 
  rocks 
  are 
  found 
  in 
  the 
  

   neighbourhood 
  of 
  all 
  these 
  masses 
  to 
  have 
  undergone 
  further 
  and 
  

   striking 
  changes, 
  which 
  are 
  of 
  a 
  comparatively 
  local 
  character. 
  

  

  It 
  is 
  evident 
  that 
  these 
  great 
  masses 
  of 
  granitic 
  rock 
  have 
  been 
  

   forced 
  in 
  a 
  fluid 
  or 
  semifluid 
  condition 
  through 
  the 
  strata 
  among 
  

   which 
  they 
  lie, 
  and 
  which, 
  in 
  their 
  passage, 
  they 
  have 
  disturbed 
  and 
  

   altered. 
  This 
  is 
  confirmed 
  by 
  the 
  fact 
  that 
  when 
  we 
  examine 
  the 
  

   j 
  unction 
  of 
  the 
  granite 
  and 
  stratified 
  rocks 
  ; 
  we 
  find 
  the 
  former 
  sending 
  

   off 
  numerous 
  veins 
  into 
  the 
  latter, 
  which 
  veins 
  often 
  include 
  angular 
  

   fragments 
  of 
  the 
  traversed 
  rock, 
  that 
  have 
  been 
  caught 
  up 
  and 
  

   enclosed 
  in 
  their 
  substance. 
  Moreover 
  similar 
  fragments, 
  often 
  of 
  

   large 
  size, 
  but 
  more 
  or 
  less 
  altered 
  on 
  their 
  surfaces 
  and 
  frequently 
  

  

  