﻿J. 
  W. 
  JUDD 
  ON 
  THE 
  SECONDARY 
  ROCKS 
  OF 
  SCOTLAND. 
  277 
  

  

  forces 
  these 
  plateaux 
  have 
  been 
  broken 
  up 
  into 
  more 
  or 
  less 
  isolated 
  

   fragments, 
  while 
  the 
  central 
  volcanic 
  cones 
  have 
  been 
  so 
  worn 
  away 
  

   as 
  to 
  have 
  lost 
  many 
  of 
  their 
  distinctive 
  features. 
  From 
  the 
  facts 
  to 
  

   be 
  adduced 
  it 
  will 
  clearly 
  appear 
  that, 
  prior 
  to 
  the 
  Mesozoic 
  epoch, 
  

   the 
  greater 
  part 
  of 
  the 
  southern 
  and 
  central 
  districts 
  of 
  Scotland, 
  both 
  

   northand 
  south 
  of 
  the 
  Grampians, 
  was 
  covered 
  to 
  the 
  depth 
  of 
  thousands 
  

   of 
  feet 
  by 
  the 
  products 
  of 
  igneous 
  activity 
  and 
  the 
  strata 
  enclosed 
  

   between 
  them. 
  But, 
  as 
  might 
  be 
  anticipated 
  from 
  their 
  far 
  greater 
  

   antiquity, 
  the 
  lava 
  plateaux 
  of 
  this 
  earlier 
  period 
  are 
  in 
  a 
  more 
  

   fragmentary 
  condition, 
  and 
  its 
  volcanic 
  cones 
  in 
  a 
  far 
  more 
  ruined 
  state 
  

   than 
  those 
  of 
  the 
  Tertiary 
  period. 
  Aided, 
  however, 
  by 
  the 
  analogies 
  

   of 
  the 
  latter, 
  I 
  hope 
  to 
  be 
  able 
  to 
  demonstrate 
  what 
  were 
  the 
  prin- 
  

   cipal 
  characters 
  of 
  this 
  earlier 
  volcanic 
  period, 
  to 
  trace 
  the 
  history 
  

   of 
  the 
  succession 
  of 
  events 
  which 
  took 
  place 
  during 
  its 
  continuance 
  ; 
  

   but 
  more 
  especially, 
  as 
  bearing 
  upon 
  the 
  objects 
  of 
  the 
  present 
  in- 
  

   quiry, 
  my 
  endeavours 
  will 
  be 
  directed 
  to 
  the 
  reconstruction 
  of 
  those 
  

   ancient 
  physical 
  features 
  which 
  resulted 
  from 
  these 
  volcanic 
  out- 
  

   bursts, 
  and 
  which 
  to 
  so 
  great 
  an 
  extent 
  determined 
  the 
  conditions 
  

   under 
  which 
  the 
  Mesozoic 
  strata 
  were 
  deposited. 
  

  

  1. 
  Lavas 
  of 
  Lorn 
  and 
  the 
  adjacent 
  islands. 
  — 
  In 
  the 
  same 
  district 
  of 
  

   the 
  Western 
  Highlands 
  with 
  the 
  Tertiary 
  lavas 
  already 
  described, 
  and 
  

   in 
  close 
  proximity 
  to 
  them, 
  we 
  find 
  another 
  series 
  of 
  volcanic 
  rocks 
  

   belonging 
  to 
  a 
  very 
  different 
  geological 
  period. 
  They 
  occupy 
  a 
  large 
  

   portion 
  of 
  the 
  district 
  of 
  Lorn, 
  and 
  are 
  also 
  extensively 
  developed 
  in 
  

   the 
  south-eastern 
  part 
  of 
  Mull, 
  in 
  Kerrera, 
  Seil, 
  and 
  the 
  smaller 
  is- 
  

   lands 
  in 
  their 
  vicinity. 
  By 
  Loch 
  Etive 
  this 
  volcanic 
  tract, 
  which 
  

   extends 
  about 
  22 
  miles 
  from 
  north 
  to 
  south 
  and 
  18 
  miles 
  from 
  east 
  

   to 
  west, 
  is 
  divided 
  into 
  two 
  very 
  unequal 
  portions 
  — 
  the 
  smaller 
  and 
  

   northern 
  portion 
  extending 
  through 
  Benediraloch 
  towards 
  Loch 
  Cre- 
  

   ran, 
  and 
  the 
  larger 
  and 
  southern 
  portion 
  to 
  the 
  neighbourhood 
  of 
  

   Loch 
  Awe 
  and 
  Loch 
  Melfort. 
  An 
  examination 
  of 
  the 
  boundaries 
  

   and 
  relations 
  of 
  this 
  volcanic 
  tract 
  shows 
  that 
  it 
  must 
  be 
  regarded 
  as 
  

   a 
  fragmentary 
  patch 
  of 
  a 
  series 
  of 
  deposits 
  once 
  widely 
  spread, 
  which 
  

   has 
  been 
  preserved 
  from 
  denudation, 
  like 
  so 
  many 
  other 
  masses 
  of 
  

   rock 
  of 
  various 
  ages 
  in 
  the 
  Highlands 
  of 
  Scotland, 
  through 
  being 
  let 
  

   down 
  between 
  great 
  faults 
  or 
  within 
  vast 
  synclinal 
  folds. 
  This 
  con- 
  

   clusion 
  is 
  fully 
  borne 
  out, 
  as 
  we 
  shall 
  hereafter 
  see, 
  by 
  the 
  existence 
  

   of 
  small 
  and 
  distant 
  isolated 
  patches 
  (outliers) 
  of 
  the 
  same 
  formation. 
  

  

  Until 
  very 
  recently 
  the 
  " 
  trap-rocks 
  " 
  of 
  Lorn 
  were 
  confounded 
  

   with 
  those 
  of 
  Tertiary 
  age 
  which 
  are 
  developed 
  in 
  their 
  immediate 
  

   neighbourhood. 
  Macculloch 
  appears 
  to 
  have 
  considered 
  that 
  the 
  

   sandstones 
  and 
  conglomerates 
  which 
  occur 
  at 
  their 
  base 
  were 
  part 
  of 
  

   the 
  Secondary 
  series 
  of 
  the 
  Highlands, 
  while 
  Prof. 
  Nicol 
  suggested 
  

   that 
  they 
  might 
  represent 
  the 
  Trias. 
  In 
  the 
  map 
  of 
  Scotland 
  pub- 
  

   lished 
  in 
  1861 
  by 
  Sir 
  B. 
  Murchison 
  and 
  Prof. 
  Geikie 
  the 
  " 
  traps 
  " 
  of 
  

   Lorn 
  are 
  indicated 
  as 
  being 
  of 
  Old 
  Bed 
  Sandstone 
  age. 
  

  

  The 
  general 
  features 
  of 
  the 
  district 
  occupied 
  by 
  these 
  rocks, 
  and 
  the 
  

   scenery 
  to 
  which 
  they 
  give 
  rise 
  are 
  those 
  which 
  usually 
  characterize 
  

   tracts 
  of 
  rocks 
  of 
  volcanic 
  origin. 
  These 
  are 
  well 
  illustrated 
  by 
  the 
  

   annexed 
  outline 
  sketch 
  of 
  the 
  mountain 
  which 
  rises 
  at 
  the 
  eastern 
  end 
  

  

  Q.J.G.S. 
  No. 
  119. 
  x 
  

  

  