﻿254 
  J. 
  W. 
  JTTDD 
  ON 
  THE 
  SECONDAKY 
  ROCKS 
  OE 
  SCOTLAND. 
  

  

  Bloodstone 
  Hill, 
  these 
  rocks 
  present 
  some 
  features 
  of 
  interest 
  to 
  

   the 
  mineralogist, 
  owing 
  to 
  the 
  beautiful 
  specimens 
  of 
  heliotrope 
  and 
  

   other 
  minerals 
  which 
  are 
  found 
  in 
  their 
  amygdaloidal 
  cavities. 
  

  

  But 
  to 
  the 
  geologist 
  the 
  fact 
  of 
  greatest 
  interest 
  in 
  connexion 
  with 
  

   these 
  basaltic 
  lavas 
  is 
  that 
  they 
  rest 
  directly 
  upon 
  the 
  granite 
  and 
  

   the 
  Cambrian 
  sandstone, 
  thus 
  affording 
  a 
  most 
  striking 
  proof 
  of 
  the 
  

   unconformity 
  which 
  exists 
  between 
  the 
  products 
  of 
  the 
  two 
  great 
  

   periods 
  of 
  volcanic 
  eruption, 
  and 
  an 
  indication 
  that 
  a 
  vast 
  interval 
  

   must 
  have 
  elapsed 
  between 
  them. 
  This 
  is 
  plain 
  from 
  the 
  fact, 
  of 
  

   which 
  we 
  have 
  clear 
  evidence, 
  that 
  rocks 
  of 
  the 
  acid 
  class 
  were 
  

   much 
  wasted 
  by 
  denudation 
  before 
  being 
  covered 
  up 
  by 
  the 
  ejection 
  

   of 
  basaltic 
  materials. 
  

  

  It 
  is 
  unnecessary 
  for 
  me 
  to 
  remark 
  on 
  the 
  striking 
  manner 
  in 
  

   which 
  the 
  peculiar 
  features 
  and 
  relations 
  of 
  the 
  rocks 
  of 
  Mull 
  and 
  

   Ardnamurchan 
  are, 
  in 
  every 
  essential 
  detail, 
  repeated 
  in 
  those 
  of 
  

   Bum 
  ; 
  nor 
  is 
  it 
  necessary 
  to 
  insist 
  upon 
  the 
  conclusion 
  that, 
  like 
  the 
  

   examples 
  before 
  described, 
  these 
  rocks 
  must 
  be 
  regarded 
  as 
  the 
  

   relics 
  of 
  a 
  great 
  volcanic 
  pile, 
  and 
  the 
  products 
  of 
  a 
  similar 
  succession 
  

   of 
  eruptions. 
  

  

  8. 
  The 
  Volcano 
  of 
  Shje.— 
  It 
  is 
  doubtless 
  a 
  misfortune 
  that 
  the 
  

   attempts 
  to 
  unravel 
  the 
  somewhat 
  complicated 
  phenomena 
  presented 
  

   by 
  the. 
  igneous 
  rocks 
  of 
  the 
  Hebrides 
  have 
  hitherto, 
  for 
  the 
  most 
  

   part, 
  been 
  made 
  in 
  the 
  most 
  frequently 
  visited 
  island 
  of 
  the 
  group, 
  

   Skye. 
  For, 
  although 
  the 
  relations 
  of 
  the 
  rocks 
  of 
  this 
  island 
  are 
  suffi- 
  

   ciently 
  clear 
  j 
  when 
  viewed 
  in 
  connexion 
  with 
  the 
  analogies 
  presented 
  

   by 
  the 
  other 
  islands 
  ; 
  yet, 
  considered 
  alone, 
  they 
  are 
  by 
  no 
  means 
  

   obvious. 
  It 
  is 
  not 
  surprising 
  therefore 
  that 
  observers, 
  unacquainted 
  ' 
  

   with 
  the 
  clearer 
  sections 
  of 
  Mull, 
  Ardnamurchan, 
  and 
  Bum, 
  should 
  

   have 
  been 
  sometimes 
  led 
  to 
  conflicting 
  conclusions 
  upon 
  the 
  subject. 
  

  

  I 
  will 
  in 
  the 
  first 
  instance 
  point 
  out 
  briefly 
  in 
  how 
  exact 
  a 
  

   manner 
  all 
  the 
  essential 
  and 
  distinctive 
  features 
  of 
  the 
  old 
  volcanoes 
  

   already 
  described 
  are 
  repeated 
  in 
  that 
  portion 
  of 
  the 
  island 
  of 
  Skye 
  

   which 
  is 
  included 
  between 
  Loch 
  Sligachan 
  and 
  Broadford 
  Bay 
  on 
  

   the 
  north, 
  and 
  Lochs 
  Brettle 
  and 
  Eichart 
  on 
  the 
  south. 
  

  

  Nearly 
  the 
  whole 
  of 
  this 
  district 
  is 
  composed 
  of 
  intrusive 
  rocks 
  

   which 
  have 
  burst 
  through 
  strata 
  of 
  Pakeozoic 
  ( 
  Cambrian 
  and 
  Lower 
  

   Silurian) 
  and 
  Mesozoic 
  (Liassic 
  and 
  Oolitic) 
  age 
  : 
  these 
  are 
  seen 
  at 
  

   a 
  number 
  of 
  points 
  lying 
  in 
  a 
  greatly 
  disturbed 
  and 
  hightly 
  meta- 
  

   morphosed 
  condition 
  upon 
  the 
  flanks 
  of 
  the 
  igneous 
  masses. 
  

  

  These 
  igneous 
  intrusive 
  masses 
  consist 
  of 
  two 
  different 
  kinds 
  of 
  

   crystalline 
  rocks, 
  granite 
  and 
  gabbro 
  ; 
  and 
  the 
  contrasts 
  between 
  

   their 
  modes 
  of 
  weathering 
  are 
  exhibited 
  in 
  their 
  most 
  exaggerated 
  

   form 
  in 
  the 
  island 
  of 
  Skye. 
  The 
  granitic 
  masses 
  of 
  the 
  Bed 
  

   Mountains, 
  culminating 
  in 
  Beinn 
  Glamaig 
  (2670 
  feet) 
  and 
  Beinn-na- 
  

   Cailleach 
  (2385 
  feet), 
  are 
  as 
  remarkable 
  for 
  their 
  strikingly 
  smooth 
  

   pyramidal 
  forms 
  as 
  the 
  gabbro 
  masses 
  of 
  the 
  Cuchullin 
  Hills 
  and 
  

   Beinn 
  Blabheinn 
  (both 
  exceeding 
  3000 
  feet 
  in 
  height) 
  are 
  un- 
  

   rivalled 
  for 
  their 
  wild, 
  jagged, 
  and 
  fantastic 
  outlines*. 
  The 
  granites 
  

   of 
  the 
  Bed 
  Mountains 
  graduate 
  into 
  many 
  varieties 
  of 
  felsitic 
  rocks, 
  

   * 
  Vide 
  G-eikie, 
  ' 
  Scenery 
  of 
  Scotland,' 
  pis. 
  2 
  & 
  4. 
  

  

  