﻿224 
  J. 
  W. 
  JTJDD 
  0ST 
  THE 
  SECONDARY 
  ROCKS 
  OE 
  SCOTLAND. 
  

  

  cations 
  of 
  the 
  volcanic 
  character 
  of 
  the 
  mountain 
  of 
  Beinn 
  More, 
  in 
  

   the 
  same 
  island, 
  afforded 
  by 
  the 
  highly 
  scoriaceous 
  character 
  of 
  its 
  

   materials*. 
  

  

  Although 
  many 
  very 
  valuable 
  geological 
  observations 
  have 
  been 
  

   placed 
  on 
  record 
  by 
  Dr. 
  Jameson, 
  Boue, 
  Dr. 
  Macculloch, 
  Principal 
  

   J. 
  D. 
  Forbes, 
  and 
  Prof. 
  A. 
  Geikie, 
  but 
  little 
  has 
  been 
  hitherto 
  done 
  

   in 
  the 
  systematic 
  examination 
  of 
  the 
  relations 
  of 
  these 
  old 
  volcanic 
  

   rocks. 
  The 
  characters 
  of 
  the 
  minerals 
  and 
  rocks 
  themselves, 
  have, 
  

   however, 
  been 
  much 
  more 
  successfully 
  investigated 
  by 
  several 
  of 
  

   these 
  authors. 
  Dr. 
  Macculloch's 
  mineralogical 
  knowledge 
  was 
  so 
  

   large 
  and 
  accurate 
  that 
  the 
  lapse 
  of 
  more 
  than 
  fifty 
  years 
  has 
  failed 
  

   to 
  deprive 
  his 
  descriptions 
  of 
  the 
  rocks 
  of 
  this 
  district 
  of 
  their 
  

   interest 
  and 
  value 
  ; 
  and 
  very 
  recently 
  one 
  of 
  the 
  greatest 
  masters 
  of 
  

   the 
  methods 
  of 
  penological 
  research, 
  Prof. 
  Zirkel 
  of 
  Leipsic, 
  has 
  

   supplemented 
  these 
  early 
  observations 
  by 
  a 
  series 
  of 
  careful 
  re- 
  

   examinations 
  of 
  the 
  same 
  rocks, 
  to 
  the 
  results 
  of 
  which 
  I 
  shall 
  

   have 
  occasion 
  to 
  refer 
  more 
  particularly 
  hereafter. 
  

  

  2. 
  Volcanic 
  Origin 
  of 
  the 
  rocks 
  constituting 
  the 
  great 
  plateaux 
  of 
  

   the 
  Hebrides 
  and 
  the 
  North 
  of 
  Ireland. 
  — 
  The 
  rocks 
  which 
  constitute 
  

   such 
  extensive 
  plateaux, 
  both 
  in 
  Ulster 
  and 
  the 
  Hebrides, 
  have 
  

   long 
  excited 
  attention 
  and 
  interest 
  in 
  consequence 
  of 
  the 
  remarkably 
  

   picturesque 
  forms 
  which 
  are 
  assumed 
  by 
  them 
  at 
  certain 
  points 
  

   where 
  the 
  columnar 
  structure 
  is 
  finely 
  developed 
  ; 
  this 
  is 
  especially 
  

   the 
  case 
  with 
  those 
  justly 
  celebrated 
  localities 
  the 
  Giant's 
  Cause- 
  

   way 
  and 
  the 
  isle 
  of 
  Staffa. 
  That 
  the 
  rocks 
  which 
  present 
  these 
  

   remarkable 
  characters 
  are 
  of 
  volcanic 
  origin, 
  and 
  indeed 
  constitute 
  

   the 
  remains 
  of 
  great 
  lava-streams, 
  is 
  a 
  fact 
  which 
  was 
  clearly 
  re- 
  

   cognized 
  by 
  some 
  even 
  of 
  the 
  earliest 
  geological 
  observers 
  f 
  ; 
  and 
  

   the 
  more 
  minutely 
  and 
  carefully 
  the 
  phenomena 
  presented 
  by 
  the 
  

   rocks 
  connected 
  with 
  active 
  or 
  recently 
  extinct 
  volcanoes 
  have 
  been 
  

   examined, 
  the 
  more 
  strikingly 
  has 
  the 
  soundness 
  of 
  this 
  conclusion 
  

   been 
  made 
  apparent. 
  

  

  At 
  the 
  present 
  day 
  the 
  volcanic 
  origin 
  of 
  these 
  rocks 
  may 
  be 
  

   regarded 
  as 
  so 
  far 
  an 
  established 
  portion 
  of 
  geological 
  science 
  as 
  to 
  

   render 
  quite 
  superfluous 
  on 
  this 
  occasion 
  any 
  details 
  of 
  the 
  grounds 
  

   on 
  which 
  it 
  rests. 
  Whether 
  we 
  regard 
  the 
  chemical 
  composition 
  of 
  

   the 
  different 
  varieties 
  of 
  rock, 
  or 
  their 
  mineralogical 
  constitution 
  

   (especially 
  as 
  this 
  is 
  revealed 
  to 
  us 
  by 
  the 
  microscope), 
  or 
  the 
  pecu- 
  

   liarities 
  of 
  their 
  petrographic 
  structure, 
  such 
  as 
  the 
  remarkable 
  

   vesicular 
  and 
  columnar 
  features 
  which 
  they 
  exhibit, 
  — 
  we 
  are 
  alike 
  

   struck 
  by 
  the 
  perfect 
  identity 
  of 
  characters 
  between 
  them 
  and 
  the 
  

   materials 
  of 
  recent 
  lava-streams. 
  Innumerable 
  minor 
  features 
  serve 
  

   to 
  confirm 
  this 
  conclusion 
  — 
  such 
  as, 
  among 
  others, 
  the 
  highly 
  vesi- 
  

   cular 
  or 
  scoriaceous 
  character 
  of 
  the 
  upper 
  and 
  under 
  surfaces 
  of 
  

   the 
  great 
  masses, 
  the 
  inclusion 
  between 
  them 
  of 
  layers 
  of 
  scoria?, 
  

  

  * 
  Brit. 
  Assoc. 
  Report 
  (1867), 
  Trans, 
  of 
  Sections, 
  p. 
  55, 
  and 
  Address 
  to 
  Geol. 
  

   Soc. 
  1873, 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xxix. 
  p. 
  lxxv. 
  

  

  t 
  Vide 
  Sir 
  Joseph 
  Banks, 
  in 
  Pennant's 
  ' 
  Voyage 
  to 
  the 
  Hebrides,' 
  p. 
  267 
  ; 
  

   A. 
  Mills, 
  in 
  Phil. 
  Trans, 
  for 
  1790, 
  pp. 
  73-100; 
  Macculloch, 
  Syst. 
  of 
  Geol. 
  

   (1831), 
  vol. 
  ii. 
  p. 
  114, 
  &c. 
  

  

  