﻿292 
  

  

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

  

  among 
  British 
  mountains 
  — 
  Beinn 
  Nevis. 
  The 
  superior 
  elevation 
  of 
  

   this 
  peak 
  has 
  resulted 
  in 
  the 
  preservation 
  of 
  rocks 
  elsewhere 
  wholly- 
  

   removed 
  by 
  denudation 
  ; 
  and 
  the 
  mountain 
  group 
  of 
  which 
  it 
  forms 
  

   a 
  part 
  is 
  as 
  conspicuous 
  for 
  the 
  value 
  of 
  the 
  evidence 
  which 
  it 
  affords 
  

   to 
  the 
  geologist, 
  as 
  it 
  is 
  for 
  its 
  great 
  elevation 
  and 
  its 
  strikingly 
  

   picturesque 
  features. 
  Let 
  us 
  therefore 
  ascend 
  this 
  mountain 
  and 
  

   study 
  its 
  structure. 
  

  

  Beinn 
  Nevis 
  consists 
  of 
  a 
  well-marked 
  and, 
  to 
  a 
  great 
  extent, 
  

   isolated 
  group 
  of 
  mountains, 
  having 
  a 
  circumference 
  of 
  about 
  20 
  miles 
  

  

  Fig. 
  11. 
  — 
  Diagrammatic 
  Section 
  illustrating 
  the 
  Relations 
  of 
  the 
  

   Rocks 
  forming 
  Beinn 
  Nevis. 
  

  

  Corrie. 
  Cairn. 
  Lake. 
  

  

  a. 
  Lower 
  Silurian 
  rocks, 
  greatly 
  contorted 
  and 
  metamorphosed 
  at 
  their 
  junction 
  

  

  with 
  the 
  granite. 
  

  

  b. 
  Coarse-grained 
  porphyritic 
  granite, 
  with 
  many 
  "contemporaneous 
  veins" 
  

  

  graduating 
  into 
  c. 
  

  

  c. 
  Fine-grained 
  granite 
  graduating 
  into 
  felsite. 
  

  

  d. 
  Felsite 
  sending 
  off 
  reins 
  into 
  c. 
  

  

  e. 
  Felstone 
  lavas 
  and 
  volcanic 
  agglomerates 
  alternating 
  with 
  one 
  another. 
  

  

  and 
  culminating 
  in 
  a 
  peak 
  4406 
  feet 
  above 
  the 
  level 
  of 
  the 
  sea 
  

   (woodcut, 
  fig. 
  11). 
  

  

  The 
  outskirts 
  of 
  this 
  mountain 
  group 
  are 
  composed 
  of 
  the 
  gneiss, 
  

   schist, 
  quartzite 
  and 
  limestones 
  of 
  the 
  Lower 
  Silurian, 
  the 
  highly 
  

   inclined 
  strata 
  of 
  which 
  are 
  seen 
  striking 
  N.E. 
  and 
  S.W., 
  on 
  either 
  

   side 
  of 
  the. 
  great 
  intrusive 
  mass 
  of 
  granite 
  which 
  cuts 
  across 
  them 
  

   abruptly. 
  From 
  the 
  great 
  central 
  granitic 
  mass 
  there 
  proceed 
  nume- 
  

   rous 
  offshoots, 
  sheets, 
  veins 
  and 
  dykes, 
  composed 
  of 
  granite, 
  syenite- 
  

   granite, 
  felsite, 
  &c, 
  which 
  traverse 
  the 
  stratified 
  rocks 
  in 
  all 
  direc- 
  

   tions, 
  penetrating 
  between 
  or 
  cutting 
  across 
  their 
  beds. 
  

  

  As 
  we 
  approach 
  the 
  central 
  mass 
  of 
  igneous 
  rocks, 
  the 
  regular 
  

   dip 
  and 
  strike 
  of 
  the 
  stratified 
  rocks 
  is 
  found 
  to 
  be 
  greatly 
  interfered 
  

   with, 
  considerable 
  disturbance 
  and 
  contortion 
  being 
  manifested 
  among 
  

   them. 
  Further, 
  in 
  proximity 
  to 
  the 
  intrusive 
  igneous 
  mass, 
  the 
  

   already 
  metamorphosed 
  Lower 
  Silurian 
  rocks 
  are 
  found 
  to 
  have 
  under- 
  

   gone 
  still 
  greater 
  alteration 
  ; 
  the 
  uniform 
  flaggy 
  masses 
  pass 
  into 
  

   highly 
  micaceous, 
  chloritic, 
  talcose,hornblendic 
  and 
  actinolitic 
  schists, 
  

   while 
  the 
  associated 
  limestones 
  become 
  more 
  highly 
  crystalline 
  and 
  

   intermingled 
  with 
  serpentine. 
  

  

  The 
  great 
  mass 
  of 
  the 
  central 
  mountain-group 
  of 
  Beinn 
  Nevis 
  is 
  

  

  