﻿264 
  

  

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

  

  Seat, 
  the 
  volcanic 
  origin 
  of 
  which 
  has 
  been 
  so 
  admirably 
  illustrated 
  

   by 
  Charles 
  Maclaren, 
  Edward 
  Forbes, 
  and 
  Archibald 
  Geikie, 
  the 
  

   similarity 
  of 
  the 
  phenomena 
  presented 
  by 
  Beinn 
  Shiant 
  will 
  be 
  suf- 
  

   ficiently 
  striking- 
  ; 
  nor 
  will 
  he 
  fail 
  to 
  recognize 
  that 
  in 
  either 
  case 
  

   we 
  have 
  a 
  much- 
  denuded 
  and 
  ruined 
  volcanic 
  cone 
  submitted 
  to 
  our 
  

   study. 
  The 
  volcano 
  of 
  Beinn 
  Shiant, 
  however, 
  was 
  of 
  far 
  larger 
  

   dimensions 
  than 
  that 
  of 
  which 
  the 
  ruins 
  constitute 
  Arthur's 
  Seat. 
  

  

  Although 
  the 
  lava 
  streams 
  of 
  Beinn 
  Shiant 
  are 
  now, 
  by 
  denuda- 
  

   tion, 
  reduced 
  to 
  more 
  or 
  less 
  isolated 
  fragments, 
  yet 
  such 
  is 
  their 
  di- 
  

   stinctive 
  character 
  that 
  I 
  believe 
  there 
  will 
  be 
  little 
  difficulty, 
  when 
  

   the 
  country 
  is 
  accurately 
  mapped, 
  in 
  restoring 
  the 
  main 
  features 
  of 
  

   this 
  volcanic 
  cone 
  and 
  of 
  the 
  lava 
  streams 
  which 
  issued 
  from 
  it. 
  Of 
  

   the 
  posteriority 
  in 
  date 
  of 
  this 
  volcanic 
  pile 
  to 
  both 
  the 
  felspathic 
  

   and 
  basaltic 
  lavas 
  of 
  the 
  great 
  central 
  volcanoes, 
  we 
  have 
  the 
  

   clearest 
  evidence 
  ; 
  for 
  not 
  only 
  do 
  its 
  products 
  overlie 
  the 
  sheets 
  

   forming 
  the 
  great 
  plateaux, 
  but 
  the 
  fragments 
  of 
  the 
  latter 
  are 
  in- 
  

   cluded 
  in 
  great 
  numbers 
  in 
  the 
  agglomerates 
  which 
  compose 
  it. 
  

   Further, 
  it 
  is 
  clear 
  that 
  these 
  earlier 
  lavas 
  had 
  undergone 
  a 
  vast 
  

   amount 
  of 
  denudation 
  before 
  the 
  outflow 
  of 
  those 
  from 
  Beinn 
  Shiant; 
  

   for 
  the 
  latter 
  overlap 
  the 
  older 
  basalts, 
  and 
  in 
  places, 
  where 
  these 
  

   have 
  been 
  wholly 
  removed 
  by 
  erosion, 
  rest 
  directly 
  upon 
  the 
  bared 
  

   surfaces 
  of 
  Lower 
  Silurian 
  gneiss. 
  

  

  If 
  in 
  the 
  case 
  of 
  Beinn 
  Shiant 
  we 
  are 
  unable 
  to 
  trace 
  the 
  igneous 
  

   masses 
  of 
  this 
  volcanic 
  cone 
  penetrating 
  the 
  older 
  lavas 
  and 
  gneiss, 
  

   this 
  is 
  solely 
  due, 
  as 
  in 
  the 
  case 
  of 
  recent 
  volcanoes, 
  to 
  the 
  covering 
  

   of 
  ejected 
  materials 
  wholly 
  concealing 
  the 
  relations 
  of 
  the 
  rocks 
  

   which 
  lie 
  below 
  them. 
  Fortunately, 
  however, 
  many 
  examples 
  of 
  

   analogous 
  later 
  eruptions 
  which 
  have 
  taken 
  place 
  within 
  this 
  district 
  

   occur, 
  wherein, 
  as 
  a 
  result 
  of 
  the 
  removal 
  by 
  denudation 
  of 
  the 
  

   materials 
  of 
  the 
  volcanic 
  pile, 
  the 
  relations 
  between 
  the 
  older 
  lavas 
  

   and 
  the 
  newer 
  intrusive 
  masses 
  are 
  very 
  clearly 
  exhibited. 
  One 
  of 
  

   the 
  most 
  interesting 
  of 
  these 
  we 
  shall 
  now 
  proceed 
  to 
  describe. 
  

  

  At 
  a 
  distance 
  of 
  three 
  miles 
  to 
  the 
  south-west 
  of 
  the 
  village 
  of 
  

   Tobermory 
  in 
  the 
  island 
  of 
  Mull 
  there 
  rises, 
  in 
  the 
  midst 
  of 
  the 
  

   great 
  plateau 
  of 
  basaltic 
  lavas, 
  a 
  hill 
  presenting 
  somewhat 
  striking 
  

   features, 
  known 
  as 
  Sarsta 
  Beinn 
  (see 
  woodcut, 
  fig. 
  4). 
  Its 
  height 
  

  

  Fig. 
  4. 
  — 
  View 
  of 
  Sarsta 
  Beinn 
  from 
  Stot 
  Hill. 
  

  

  above 
  the 
  sea-level 
  is 
  apparently 
  about 
  800 
  or 
  900 
  feet 
  ; 
  but 
  the 
  

   peculiarity 
  of 
  the 
  mode 
  of 
  weathering 
  of 
  the 
  rock 
  masses 
  which 
  

   compose 
  it, 
  as 
  compared 
  with 
  the 
  surrounding 
  tabular 
  basalts, 
  

  

  