﻿J. 
  W. 
  JUDD 
  ON 
  THE 
  SECONDARY 
  ROCKS 
  OF 
  SCOTLAND. 
  265 
  

  

  makes 
  it 
  a 
  rather 
  conspicuous 
  object. 
  Its 
  summit 
  is 
  occupied 
  by 
  a 
  

   small 
  loch, 
  or 
  mountain-tarn, 
  which 
  is 
  said 
  to 
  be 
  of 
  great 
  depth. 
  

  

  When 
  we 
  examine 
  this 
  rocky 
  mass 
  standing 
  up 
  so 
  abruptly 
  in 
  

   the 
  midst 
  of 
  the 
  basaltic 
  plateau, 
  we 
  find 
  it 
  to 
  be 
  composed 
  of 
  a 
  

   dolerite 
  of 
  the 
  coarsest 
  grain, 
  passing 
  in 
  its 
  lower 
  portions 
  into 
  gabbro. 
  

   The 
  rugged, 
  rnsty-brown 
  surfaces 
  of 
  these 
  rocks, 
  which 
  resist 
  denu- 
  

   dation 
  and 
  the 
  growth 
  of 
  vegetation, 
  form 
  a 
  striking 
  contrast 
  with 
  the 
  

   grassy 
  tabular 
  masses 
  of 
  the 
  basaltic 
  lavas 
  in 
  the 
  midst 
  of 
  which 
  

   they 
  rise. 
  

  

  The 
  identity 
  in 
  character 
  between 
  this 
  rock 
  mass 
  and 
  others 
  of 
  

   eruptive 
  origin 
  which 
  we 
  have 
  before 
  described 
  is 
  sufficiently 
  obvious. 
  

   That 
  it 
  was 
  actually 
  upheaved 
  through 
  the 
  older 
  basaltic 
  lava 
  sheets, 
  

   we 
  have 
  the 
  clearest 
  and 
  most 
  unmistakable 
  evidence. 
  As 
  shown 
  in 
  

   the 
  plan 
  and 
  section 
  (woodcuts, 
  figs. 
  5 
  and 
  6), 
  the 
  contact 
  between 
  

  

  Fig. 
  5. 
  — 
  Plan 
  of 
  the 
  Hill 
  of 
  Sarsta 
  Beinn. 
  

  

  a. 
  Ordinary 
  basalts 
  covered 
  by 
  boggy 
  ground. 
  

  

  b. 
  Basalts 
  altered 
  by 
  contact 
  with 
  the 
  intrusive 
  mas?. 
  

  

  c. 
  Great 
  mass 
  of 
  coarse 
  dolerite 
  graduating 
  into 
  gabbro. 
  

  

  Fig. 
  6. 
  — 
  Section 
  of 
  Sarsta 
  Beinn. 
  

  

  /z 
  

  

  loch 
  /yi}" 
  

  

  a. 
  Basalts 
  of 
  the 
  great 
  plateaux. 
  

  

  b. 
  Basalts 
  altered 
  by 
  contact 
  with 
  the 
  intrusive 
  mass 
  c. 
  

  

  c. 
  Intrusive 
  mass, 
  composed 
  of 
  dolerite 
  in 
  places 
  graduating 
  into 
  gabbro. 
  

  

  these 
  highly 
  crystalline 
  rocks 
  and 
  the 
  basalts 
  in 
  the 
  midst 
  of 
  which 
  

   they 
  lie 
  is 
  marked 
  by 
  a 
  belt 
  of 
  metamorphosed 
  rock. 
  The 
  basalts 
  

   near 
  their 
  junction 
  with 
  the 
  intrusive 
  dolerites 
  and 
  gabbro 
  have 
  

   acquired 
  a 
  harder 
  texture, 
  a 
  splintery 
  fracture, 
  and 
  a 
  peculiar 
  platy 
  

   mode 
  of 
  weathering, 
  often 
  in 
  concentrically 
  curved 
  planes. 
  In 
  con- 
  

  

  