﻿0E 
  THE 
  WESTERN 
  ISLES 
  OE 
  SCOTLAND. 
  195 
  

  

  presence 
  between 
  the 
  successive 
  lava-flows 
  of 
  burnt 
  soils 
  (" 
  laterites 
  " 
  

   of 
  some 
  authors) 
  ; 
  of 
  beds 
  of 
  lignite, 
  with 
  the 
  remains 
  of 
  terrestrial 
  

   vegetation 
  ; 
  of 
  sheets 
  of 
  volcanic 
  mud 
  ; 
  of 
  river-gravels 
  ; 
  and 
  of 
  cha- 
  

   racteristic 
  lacustrine 
  deposits 
  — 
  including 
  beds 
  of 
  iron-ore 
  analogous 
  

   to 
  the 
  well-known 
  " 
  lake-ores 
  " 
  of 
  Sweden. 
  

  

  (2) 
  While 
  some 
  of 
  the 
  igneous 
  rock-masses 
  are 
  of 
  strikingly 
  

   fresh 
  appearance 
  and 
  unaltered 
  character, 
  others 
  exhibit 
  the 
  most 
  

   unmistakable 
  evidence 
  of 
  having 
  undergone 
  remarkable 
  changes, 
  so 
  

   that 
  they 
  have 
  come 
  to 
  resemble 
  the 
  igneous 
  products 
  of 
  far 
  older 
  

   geological 
  periods. 
  There 
  is 
  the 
  clearest 
  evidence, 
  however, 
  that 
  

   the 
  whole 
  of 
  the 
  igneous 
  rocks, 
  gabbros, 
  and 
  granites, 
  equally 
  with 
  

   basalts 
  and 
  " 
  felstones," 
  are 
  of 
  'Tertiary 
  age. 
  

  

  (1) 
  The 
  conclusion 
  as 
  to 
  the 
  subaerial 
  origin 
  of 
  the 
  volcanic 
  rocks 
  

   of 
  the 
  Western 
  Isles 
  is 
  fully 
  borne 
  out 
  by 
  the 
  detailed 
  memoir 
  just 
  

   published 
  (see 
  T. 
  E. 
  S. 
  E. 
  1888, 
  pp. 
  87-89). 
  This 
  confirmation 
  is 
  

   particularly 
  important 
  at 
  the 
  present 
  time. 
  

  

  My 
  friend 
  Dr. 
  E. 
  Beyer, 
  in 
  his 
  recently 
  published 
  very 
  valuable 
  

   ' 
  Theoretische 
  Geologie,' 
  has 
  argued 
  that 
  the 
  highly 
  crystalline 
  cha- 
  

   racter 
  of 
  the 
  gabbro- 
  and 
  granite-masses 
  of 
  the 
  Western 
  Isles 
  of 
  

   Scotland 
  must 
  be 
  the 
  result 
  of 
  " 
  hydrostatic 
  pressure," 
  and 
  that 
  the 
  

   weight 
  of 
  overlying 
  and 
  permeable 
  rocks 
  could 
  not 
  possibly 
  account 
  

   for 
  the 
  production 
  of 
  the 
  granitic 
  texture. 
  He 
  therefore 
  insists 
  

   that 
  the 
  more 
  highly 
  crystalline 
  portions 
  of 
  the 
  Hebridean 
  eruptions 
  

   must 
  have 
  been 
  of 
  submarine 
  origin, 
  and 
  contemporaneous 
  with 
  the 
  

   marine 
  Mesozoic 
  strata 
  among 
  which 
  they 
  lie 
  *. 
  

  

  On 
  the 
  other 
  hand, 
  M. 
  Loewinson-Lessing, 
  adopting 
  a 
  view 
  very 
  

   generally 
  held 
  in 
  Germany 
  that 
  the 
  ophitic 
  structure 
  — 
  which 
  I 
  have 
  

   shown 
  to 
  be 
  so 
  characteristically 
  exhibited 
  by 
  the 
  basaltic 
  lavas 
  of 
  

   Western 
  Scotland 
  — 
  is 
  distinctive 
  of 
  the 
  diabases, 
  has 
  argued 
  that 
  

   this 
  structure 
  is 
  the 
  result 
  of 
  the 
  outflow 
  of 
  lavas 
  of 
  basic 
  compo- 
  

   sition 
  under 
  a 
  considerable 
  pressure 
  of 
  sea-water 
  f 
  . 
  

  

  That 
  the 
  ophitic, 
  or 
  " 
  diabasic 
  " 
  structure, 
  as 
  some 
  authors 
  prefer 
  

   to 
  call 
  it, 
  is 
  found 
  both 
  in 
  Iceland 
  and 
  in 
  Scotland 
  in 
  rocks 
  which 
  

   were 
  extruded 
  in 
  Tertiary 
  times 
  and 
  under 
  subaerial 
  conditions 
  has 
  

   been 
  maintained 
  both 
  by 
  M. 
  Breon 
  and 
  by 
  myself, 
  and 
  I 
  am 
  happy 
  

   now 
  to 
  be 
  able 
  to 
  fortify 
  my 
  own 
  position 
  by 
  the 
  testimony 
  of 
  the 
  

   officers 
  of 
  the 
  Geological 
  Survey. 
  

  

  (2) 
  With 
  respect 
  to 
  the 
  Tertiary 
  age 
  of 
  the 
  gabbros 
  and 
  granites, 
  

   as 
  well 
  as 
  of 
  the 
  basalts 
  and 
  " 
  ielstones," 
  the 
  evidence 
  brought 
  for- 
  

   ward 
  in 
  the 
  recently 
  published 
  memoir 
  is 
  equally 
  conclusive 
  (T. 
  B. 
  

   S. 
  E. 
  1888, 
  pp. 
  84, 
  182). 
  

  

  It 
  is 
  impossible, 
  in 
  view 
  of 
  discussions 
  which 
  have 
  taken 
  place 
  

   upon 
  the 
  subject, 
  to 
  overestimate 
  the 
  importance 
  of 
  the 
  admissions 
  

   now 
  made. 
  

  

  Dr. 
  Sterry 
  Hunt 
  and 
  others 
  have 
  frequently 
  quoted 
  the 
  case 
  of 
  

   the 
  so-called 
  " 
  Norites 
  " 
  of 
  the 
  Western 
  Isles 
  as 
  supplying 
  evidence 
  

  

  * 
  Theoretische 
  Geologie 
  von 
  Dr. 
  E. 
  Beyer 
  (Stuttgart, 
  1888), 
  p. 
  371. 
  

   t 
  Bull, 
  de 
  la 
  Soc. 
  Beige 
  de 
  Geol. 
  &c, 
  tome 
  ii. 
  (1888), 
  pp. 
  84-87. 
  

  

  