﻿J. 
  W. 
  JUDD 
  ON 
  THE 
  SECONDARY 
  BOCKS 
  OF 
  SCOTLAND. 
  247 
  

  

  numerable 
  dykes. 
  Associated 
  with 
  the 
  agglomerates 
  are 
  numerous 
  

   ejected 
  blocks 
  ; 
  these 
  comprise 
  examples 
  of 
  nearly 
  all 
  the 
  rocks 
  

   found 
  beneath 
  the 
  lavas 
  of 
  Mull, 
  including 
  the 
  Lower 
  Silurian 
  gneiss, 
  

   quartzite, 
  mica-schist, 
  and 
  slate, 
  the 
  Newer 
  Palaeozoic 
  breccias, 
  con- 
  

   glomerates, 
  sandstones, 
  and 
  lavas, 
  the 
  Liassic 
  rocks, 
  and 
  the 
  Cre- 
  

   taceous 
  quartzose 
  conglomerates, 
  grits, 
  and 
  sandstones. 
  

  

  At 
  its 
  northern 
  end, 
  as 
  we 
  approach 
  the 
  summit, 
  the 
  whole 
  of 
  

   the 
  highly 
  siliceous 
  rocks 
  which 
  compose 
  the 
  mass 
  of 
  the 
  mountain, 
  

   granite, 
  felsite, 
  felstone 
  lavas, 
  and 
  felspathic 
  agglomerates, 
  are 
  seen 
  

   to 
  be 
  penetrated 
  indiscriminately 
  by 
  numerous 
  intrusive 
  sheets 
  or 
  

   dykes 
  on 
  the 
  grandest 
  scale, 
  composed 
  of 
  various 
  forms 
  of 
  gabbro, 
  

   passing 
  into 
  dolerite 
  and 
  basalt, 
  which 
  have 
  evidently 
  produced 
  a 
  

   greater 
  or 
  less 
  amount 
  of 
  alteration 
  at 
  the 
  planes 
  of 
  contact 
  in 
  the 
  

   rocks 
  which 
  they 
  traverse. 
  These 
  great 
  intrusive 
  sheets 
  and 
  d}dces 
  

   of 
  basic 
  igneous 
  rock 
  were, 
  from 
  their 
  position, 
  evidently 
  at 
  one 
  time 
  

   connected 
  with 
  the 
  great 
  masses 
  of 
  gabbro 
  forming 
  Beinn 
  Varnach 
  

   and 
  the 
  eastern 
  portion 
  of 
  Beinn 
  Tsalla, 
  from 
  which 
  they 
  are 
  now 
  

   separated 
  by 
  the 
  Forsa 
  Glen. 
  Owing 
  to 
  the 
  manner 
  in 
  which 
  these 
  

   gabbro 
  dykes 
  resist 
  denuding 
  influences 
  their 
  course 
  among 
  crumbling 
  

   rocks 
  of 
  the 
  acid 
  class 
  can 
  be 
  easily 
  traced 
  by 
  the 
  geological 
  observer. 
  

  

  The 
  last 
  point 
  to 
  be 
  noticed 
  with 
  regard 
  to 
  Craig 
  Craggen 
  is 
  that 
  

   the 
  spur 
  known 
  as 
  JN"id-a-shoag 
  (the 
  Hawk's 
  nest) 
  is 
  capped 
  by 
  an 
  

   isolated 
  patch 
  of 
  ordinary 
  basalt, 
  which, 
  from 
  its 
  amygdaloidal 
  

   character 
  is 
  recognized 
  as 
  a 
  portion 
  of 
  an 
  old 
  lava 
  sheet 
  ; 
  while, 
  

   overlapping 
  the 
  felstone 
  lavas, 
  towards 
  the 
  northern 
  foot 
  of 
  the 
  

   mountain 
  we 
  find 
  portions 
  of 
  the 
  great 
  series 
  of 
  basaltic 
  lavas, 
  which, 
  

   though 
  cut 
  off 
  abruptly 
  on 
  the 
  shores 
  of 
  the 
  Sound 
  of 
  Mull, 
  are 
  seen 
  

   to 
  be 
  continued 
  on 
  the 
  opposite 
  side 
  in 
  Morvern. 
  The 
  relations 
  of 
  the 
  

   several 
  masses 
  of 
  rock 
  of 
  the 
  basic 
  class 
  are 
  such 
  as 
  to 
  leave 
  no 
  room 
  

   for 
  doubt 
  that 
  the 
  comparatively 
  soft 
  sCoriaceous 
  masses 
  of 
  this 
  moun- 
  

   tain 
  owe 
  their 
  preservation 
  to 
  a 
  covering 
  of 
  basaltic 
  lavas, 
  of 
  which 
  

   the 
  outlier 
  of 
  Nid-a-shoag 
  constitutes 
  the 
  last 
  vestige 
  ; 
  and 
  it 
  seems 
  

   almost 
  equally 
  impossible 
  to 
  resist 
  the 
  inference 
  that 
  the 
  lavas 
  of 
  

   the 
  great 
  basaltic 
  sheets 
  were 
  once 
  actually 
  continuous 
  with 
  the 
  

   great 
  intrusive 
  gabbro 
  masses, 
  which 
  are 
  composed 
  of 
  identical 
  

   materials 
  with 
  them 
  though 
  in 
  a 
  different 
  state 
  of 
  aggregation. 
  

  

  d. 
  Beinn 
  More 
  (Section, 
  PI. 
  XXIII. 
  fig. 
  4). 
  — 
  To 
  complete 
  our 
  series 
  

   of 
  illustrations 
  of 
  the 
  relations 
  which 
  the 
  several 
  volcanic 
  products 
  

   of 
  the 
  island 
  of 
  Mull 
  bear 
  to 
  one 
  another, 
  we 
  cannot 
  do 
  better 
  than 
  

   notice 
  this, 
  the 
  highest 
  peak 
  in 
  the 
  island. 
  In 
  the 
  lower 
  parts 
  of 
  

   this 
  mountain 
  and 
  the 
  spurs 
  around 
  it 
  the 
  granites, 
  felsites, 
  felstone 
  

   lavas, 
  felspathic 
  agglomerates, 
  with 
  the 
  intersecting 
  dykes 
  of 
  gabbro, 
  

   dolerite, 
  and 
  basalt 
  may 
  be 
  observed 
  presenting 
  the 
  relations 
  to 
  one 
  

   another 
  which 
  have 
  been 
  already 
  described. 
  Resting 
  unconformably 
  

   upon 
  these 
  is 
  a 
  mass, 
  many 
  hundreds 
  of 
  feet 
  in 
  thickness 
  and 
  consti- 
  

   tuting 
  the 
  whole 
  of 
  the 
  higher 
  portions 
  of 
  the 
  mountain, 
  composed 
  of 
  

   basaltic 
  scoriae, 
  tuffs, 
  and 
  ashes, 
  alternating 
  with 
  lava 
  sheets 
  and 
  in- 
  

   tersected 
  by 
  a 
  plexus 
  of 
  dykes. 
  By 
  the 
  thinning-out 
  of 
  the 
  masse3 
  

   of 
  agglomerate 
  the 
  basaltic 
  lavas 
  come 
  together, 
  forming 
  the 
  great 
  

   peninsula 
  of 
  the 
  Bourg 
  or 
  Gribun, 
  which 
  is 
  made 
  up 
  of 
  lava 
  sheets 
  

  

  t2 
  

  

  