﻿OF 
  THE 
  WESTERN 
  ISLES 
  OF 
  SCOTLAND. 
  219 
  

  

  felstone 
  and 
  masses 
  of 
  acid 
  breccias 
  and 
  tuffs, 
  as 
  laid 
  down 
  by 
  

   Prof. 
  Judd. 
  The 
  acid 
  rocks 
  were 
  confined 
  to 
  a 
  few 
  bosses 
  and 
  

   hundreds 
  of 
  dykes 
  and 
  veins, 
  and 
  instead 
  of 
  forming 
  the 
  oldest 
  

   masses 
  of 
  the 
  volcanic 
  series, 
  as, 
  trusting 
  to 
  the 
  map 
  of 
  1874, 
  he 
  

   had 
  believed 
  to 
  be 
  the 
  case, 
  they 
  were 
  actually 
  the 
  youngest, 
  and 
  

   could 
  be 
  seen 
  in 
  innumerable 
  localities, 
  sending 
  veins 
  into 
  them. 
  

   He 
  had 
  been 
  unable 
  to 
  discover 
  any 
  trace 
  of 
  felstones 
  which 
  had 
  

   reached 
  the 
  surface 
  before 
  the 
  outflow 
  of 
  the 
  basalts. 
  The 
  latter 
  

   he 
  had 
  everywhere, 
  through 
  Mull, 
  Hum, 
  Eigg, 
  and 
  Skye, 
  found 
  to 
  

   be 
  the 
  oldest 
  lavas. 
  Next 
  in 
  age 
  came 
  the 
  gabbros 
  which 
  had 
  been 
  

   injected 
  into 
  the 
  already 
  solidified 
  basalts, 
  andesites, 
  &c. 
  of 
  the 
  

   plateaux 
  ; 
  and 
  lastly 
  the 
  granophyres 
  and 
  other 
  acid 
  rocks 
  were 
  

   erupted 
  through 
  the 
  whole, 
  except 
  the 
  youngest 
  basic 
  dykes. 
  

  

  With 
  regard 
  to 
  the 
  criticism 
  which 
  had 
  been 
  offered 
  as 
  to 
  

   " 
  fissure-eruptions," 
  he 
  thought 
  that 
  some 
  misapprehension 
  existed. 
  

   He 
  did 
  not 
  suppose 
  that 
  the 
  lavas 
  flowed 
  out 
  directly 
  from 
  long 
  

   open 
  fissures, 
  but 
  that 
  vents 
  were 
  established 
  on 
  such 
  fissures, 
  

   sometimes 
  of 
  considerable 
  size, 
  with 
  the 
  usual 
  accompaniments 
  of 
  

   volcanic 
  eruptions. 
  He 
  contended 
  that 
  there 
  was 
  not 
  the 
  slightest 
  

   evidence 
  of 
  any 
  great 
  central 
  volcano 
  of 
  the 
  type 
  of 
  Vesuvius 
  or 
  

   Etna 
  in 
  any 
  part 
  of 
  the 
  Western 
  Islands, 
  but 
  that 
  the 
  vents 
  had 
  

   been 
  numerous, 
  widely 
  scattered, 
  and, 
  on 
  the 
  whole, 
  of 
  small 
  size. 
  

  

  It 
  would 
  be 
  impossible 
  to 
  discuss 
  all 
  the 
  details 
  of 
  Prof. 
  Judd's 
  

   paper, 
  and 
  if 
  he 
  had 
  not 
  replied 
  to 
  all 
  the 
  points 
  now 
  raised 
  it 
  was 
  

   not 
  from 
  inability 
  to 
  do 
  so. 
  He 
  entered 
  into 
  such 
  discussions 
  with 
  

   much 
  reluctance, 
  and 
  though 
  he 
  regretted 
  having 
  to 
  differ 
  so 
  greatly 
  

   from 
  Prof. 
  Judd, 
  he 
  felt 
  himself 
  entitled 
  to 
  make 
  known 
  the 
  con- 
  

   clusions 
  to 
  which 
  the 
  researches 
  of 
  so 
  long 
  a 
  series 
  of 
  years 
  had 
  

   finally 
  conducted 
  him. 
  

  

  The 
  Author 
  agreed 
  with 
  Dr. 
  Geikie 
  on 
  one 
  point, 
  namely, 
  

   reluctance 
  to 
  enter 
  upon 
  this 
  controversy, 
  which 
  had 
  been 
  forced 
  upon 
  

   him. 
  It 
  was 
  perfectly 
  true 
  that 
  Dr. 
  Geikie 
  had 
  published 
  many 
  

   papers 
  on 
  the 
  district 
  in 
  question 
  before 
  his 
  own 
  appeared 
  in 
  1874 
  ; 
  

   but 
  the 
  views 
  maintained 
  in 
  all 
  these 
  papers 
  were 
  utterly 
  irrecon- 
  

   cilable 
  with 
  those 
  which 
  were 
  enunciated 
  by 
  himself, 
  and 
  which 
  

   were 
  now 
  adopted 
  by 
  Dr. 
  Geikie. 
  The 
  key 
  to 
  his 
  own 
  explanation 
  

   of 
  the 
  structure 
  of 
  the 
  district 
  was 
  the 
  recognition 
  of 
  the 
  intimate 
  

   relations 
  between 
  the 
  gabbros 
  and 
  the 
  basalts 
  ; 
  while 
  Dr. 
  Geikie 
  

   had 
  always 
  held 
  that 
  the 
  former 
  were 
  of 
  metamorphic 
  origin 
  and 
  of 
  

   Laurentian 
  age, 
  and 
  the 
  latter 
  were 
  regarded 
  by 
  him 
  at 
  first 
  as 
  

   Jurassic, 
  and 
  afterwards 
  as 
  Tertiary 
  lavas. 
  

  

  The 
  sketch-map 
  of 
  Mull, 
  as 
  he 
  had 
  stated 
  when 
  he 
  published 
  it, 
  

   was 
  necessarily 
  diagrammatic, 
  inasmuch 
  as 
  the 
  district 
  was 
  one 
  of 
  

   great 
  complexity, 
  of 
  which 
  no 
  reliable 
  topographical 
  maps 
  were 
  at 
  

   the 
  time 
  in 
  existence. 
  But 
  he 
  maintained 
  its 
  general 
  accuracy 
  ; 
  

   the 
  contrasts 
  between 
  it 
  and 
  the 
  map 
  exhibited 
  by 
  Dr. 
  Geikie 
  were 
  

   largely 
  due 
  to 
  differences 
  in 
  the 
  system 
  of 
  rock-nomenclature 
  and 
  

   the 
  scheme 
  of 
  colouring 
  employed 
  in 
  the 
  two 
  cases. 
  

  

  