﻿J. 
  W. 
  JUDD 
  ON 
  IHE 
  SECONDARY 
  ROCKS 
  OF 
  SCOTLAND. 
  271 
  

  

  varying 
  in 
  dimensions 
  from 
  great 
  mountain-groups 
  down 
  to 
  the 
  

   minutest 
  veins 
  and 
  strings, 
  exhibiting 
  innumerable 
  distinctions 
  of 
  

   miner 
  alogical 
  constitution, 
  and 
  belonging 
  to 
  three 
  successive 
  geolo- 
  

   gical 
  periods. 
  Nor 
  is 
  it 
  easy 
  to 
  imagine 
  a 
  more 
  striking 
  series 
  of 
  me- 
  

   chanical 
  and 
  chemical 
  changes 
  than 
  those 
  which 
  in 
  the 
  surrounding 
  

   strata 
  have 
  attended 
  the 
  eruption 
  of 
  these 
  masses, 
  resulting 
  in 
  the 
  

   most 
  extraordinary 
  contortions 
  and 
  the 
  extremest 
  metamorphism. 
  

  

  Such 
  features 
  are 
  admirably 
  exhibited 
  alike 
  in 
  the 
  district 
  of 
  

   Strath 
  in 
  Skye, 
  on 
  the 
  southern 
  coast 
  of 
  Mull, 
  and 
  at 
  various 
  points 
  

   around 
  Pum, 
  but 
  in 
  none 
  in 
  so 
  striking 
  a 
  manner 
  as 
  in 
  the 
  penin- 
  

   sula 
  of 
  Ardnamurchan. 
  Here 
  the 
  scalpel 
  of 
  denudation 
  has 
  revealed 
  

   the 
  intricate 
  and 
  curious 
  relations 
  of 
  the 
  several 
  varieties 
  of 
  igneous 
  

   rocks 
  with 
  one 
  another 
  and 
  with 
  the 
  Primary 
  and 
  Secondary 
  strata. 
  

   To 
  represent 
  these, 
  however 
  imperfectly, 
  would 
  require 
  a 
  series 
  of 
  

   maps 
  and 
  sections 
  on 
  the 
  very 
  grandest 
  scale 
  ; 
  in 
  many 
  cases, 
  indeed, 
  

   adequate 
  conceptions 
  of 
  the 
  relations 
  of 
  such 
  very 
  intricate 
  rock 
  

   structures 
  could 
  only 
  be 
  conveyed 
  by 
  means 
  of 
  models. 
  It 
  is, 
  how- 
  

   ever, 
  to 
  the 
  rocks 
  themselves 
  that 
  the 
  student 
  must 
  be 
  referred 
  ; 
  

   and 
  he 
  will 
  find 
  in 
  them 
  illustrations 
  of 
  the 
  characters 
  and 
  action 
  of 
  

   igneous 
  intrusions 
  which 
  will 
  amply 
  repay 
  him 
  for 
  the 
  time 
  and 
  

   labour 
  expended 
  in 
  their 
  investigation 
  *. 
  

  

  14. 
  Ages 
  of 
  the 
  several 
  Volcanic 
  Outbursts 
  already 
  described. 
  — 
  That 
  

   the 
  events 
  of 
  which 
  we 
  have 
  been 
  discussing 
  the 
  evidence, 
  stupen- 
  

   dous 
  as 
  they 
  are 
  in 
  scale 
  and 
  complicated 
  as 
  they 
  are 
  in 
  succession, 
  

   all 
  took 
  place 
  subsequently 
  to 
  the 
  Mesozoic 
  epoch, 
  we 
  have 
  the 
  most 
  

   ample 
  proof: 
  — 
  

  

  First, 
  in 
  the 
  fact 
  of 
  the 
  entire 
  absence 
  of 
  contemporary 
  volcanic 
  

   deposits 
  among 
  the 
  Secondary 
  strata. 
  I 
  have 
  already 
  alluded 
  to 
  the 
  

   earlier 
  misapprehensions 
  which 
  prevailed 
  upon 
  this 
  subject, 
  and 
  on 
  

   the 
  manner 
  in 
  which 
  these 
  were 
  removed 
  by 
  the 
  observations 
  of 
  

   Prof. 
  Geikie 
  in 
  1865. 
  

  

  Secondly, 
  in 
  the 
  circumstance 
  that 
  the 
  volcanic 
  masses 
  are 
  thrust 
  

   through 
  and 
  among 
  the 
  representatives 
  of 
  the 
  whole 
  series 
  of 
  Secon- 
  

   dary 
  strata, 
  up 
  to 
  and 
  including 
  the 
  Upper 
  Chalk; 
  and 
  that 
  the 
  

   volcanic 
  products 
  unconformably 
  overlie 
  and 
  include 
  numerous 
  

   fragments 
  of 
  the 
  whole 
  of 
  the 
  Secondary 
  rocks 
  — 
  these 
  fragments 
  

   having 
  acquired 
  their 
  present 
  positions 
  either 
  through 
  being 
  

   ejected 
  from 
  volcanic 
  vents 
  (as 
  in 
  the 
  case 
  of 
  the 
  breccias 
  of 
  Mull, 
  

   Pum, 
  &c), 
  or 
  by 
  the 
  agency 
  of 
  ordinary 
  denuding 
  agencies 
  opera- 
  

  

  * 
  Below 
  Mingary 
  Castle, 
  near 
  Kilchoan 
  in 
  Ardnamurchan, 
  a 
  section 
  may 
  be 
  

   observed 
  which 
  is 
  interesting 
  as 
  throwing 
  light 
  on 
  the 
  probable 
  mode 
  of 
  for- 
  

   mation 
  of 
  the 
  celebrated 
  Puy 
  Chopine 
  in 
  Auvergne, 
  the 
  peculiar 
  and 
  appa- 
  

   rently, 
  at 
  first 
  sight, 
  anomalous 
  characters 
  of 
  which 
  have 
  been 
  frequently 
  re- 
  

   marked 
  upon 
  (see 
  Scrope's 
  ' 
  Geology 
  and 
  Extinct 
  Volcanos 
  of 
  Central 
  France,' 
  

   pp. 
  72-76). 
  At 
  Mingary 
  a 
  mass 
  of 
  quartziferous 
  porphyry 
  has 
  been 
  forced 
  

   between 
  beds 
  of 
  Lower 
  Lias 
  shale, 
  while 
  a 
  later-formed 
  sheet 
  of 
  basalt 
  has 
  

   evidently 
  taken 
  advantage 
  of 
  the 
  plane 
  of 
  weakness, 
  constituted 
  by 
  their 
  junc- 
  

   tion, 
  to 
  force 
  itself 
  between 
  them. 
  In 
  the 
  Puy 
  Chopine 
  a 
  mass 
  of 
  the 
  older 
  

   rocks 
  ( 
  in 
  this 
  case 
  composed 
  of 
  granite) 
  has 
  been 
  forced 
  upwards 
  by 
  an 
  extru- 
  

   sion 
  of 
  domite, 
  while 
  a 
  sheet 
  of 
  basalt 
  has 
  similarly 
  inserted 
  itself 
  along 
  their 
  

   line 
  of 
  junction. 
  

  

  