﻿J. 
  W. 
  JUDD 
  ON 
  THE 
  SECONDARY 
  ROCKS 
  OF 
  SCOTLAND. 
  2S7 
  

  

  and 
  larger 
  part 
  of 
  the 
  Lorn 
  series 
  the 
  volcanic 
  forces 
  appear 
  to 
  have 
  

   been 
  almost 
  the 
  sole 
  agency 
  concerned 
  in 
  the 
  accumulation 
  of 
  the 
  

   rocks 
  ; 
  for 
  these 
  consist 
  of 
  subaerial 
  lavas 
  alternating 
  with 
  unstrati- 
  

   fied 
  tuffs. 
  

  

  6. 
  Age 
  of 
  the 
  Volcanic 
  series 
  of 
  Lorn. 
  — 
  In 
  the 
  entire 
  absence 
  of 
  

   palaeontological 
  evidence, 
  this 
  question 
  must 
  be 
  admitted 
  to 
  be 
  still 
  

   to 
  a 
  certain 
  extent 
  an 
  open 
  one. 
  In 
  forming 
  a 
  judgment 
  concern- 
  

   ing 
  it, 
  however, 
  we 
  have 
  the 
  following 
  facts 
  to 
  guide 
  us 
  : 
  — 
  

  

  (1) 
  The 
  very 
  marked 
  unconformity 
  between 
  these 
  rocks 
  and 
  the 
  

   strata 
  of 
  Lower 
  Silurian 
  age 
  on 
  which 
  they 
  He. 
  The 
  latter 
  were 
  

   evidently 
  not 
  oiily 
  deposited, 
  but 
  bent 
  into 
  great 
  contortions 
  and 
  

   folds, 
  and 
  brought 
  to 
  their 
  present 
  metamorphosed 
  condition, 
  before 
  

   the 
  period 
  of 
  the 
  formation 
  of 
  the 
  former. 
  

  

  (2) 
  The 
  fact 
  that 
  the 
  Mesozoic 
  strata 
  appear 
  to 
  rest 
  upon 
  them, 
  

   and, 
  in 
  some 
  instances 
  at 
  least, 
  quite 
  unconformabry. 
  

  

  (3) 
  The 
  resemblance 
  which 
  the 
  lava 
  streams, 
  of 
  which 
  they 
  are 
  

   so 
  largely 
  composed, 
  present 
  in 
  their 
  petrological 
  characters 
  to 
  

   others 
  on 
  the 
  south 
  of 
  the 
  Grampians, 
  which 
  sometimes 
  alternate 
  

   with 
  strata 
  containing 
  fishes 
  of 
  Old-Hed-Sandstone 
  species. 
  

  

  With 
  these 
  points 
  of 
  evidence 
  before 
  us, 
  we 
  can 
  scarcely 
  hesitate 
  

   to 
  regard 
  the 
  volcanic 
  and 
  associated 
  rocks 
  of 
  Lorn 
  as 
  belonging 
  to 
  

   some 
  part 
  of 
  the 
  Newer 
  Palaeozoic 
  periods 
  ; 
  but 
  to 
  hazard 
  any 
  closer 
  

   approximation 
  to 
  their 
  age 
  would 
  probably 
  be 
  unsafe. 
  

  

  7. 
  The 
  Newer 
  Pcdceozoic 
  Lavas 
  of 
  the 
  Lowlands 
  of 
  Scotland. 
  — 
  

   South 
  of 
  the 
  Grampian 
  Mountains 
  very 
  large 
  areas 
  of 
  Scotland 
  are 
  

   occupied 
  by 
  series 
  of 
  old 
  lavas, 
  which, 
  so 
  far 
  as 
  mineral 
  characters 
  

   go, 
  present 
  very 
  striking 
  resemblances 
  to 
  those 
  of 
  Lorn 
  which 
  we 
  

   have 
  been 
  describing. 
  These 
  rocks 
  have 
  been 
  more 
  or 
  less 
  fully 
  

   described 
  by 
  many 
  authors, 
  and 
  the 
  evidences 
  of 
  their 
  volcanic 
  origin 
  

   and 
  of 
  the 
  conditions 
  under 
  which 
  they 
  were 
  accumulated 
  very 
  ably 
  

   discussed 
  by 
  Maclaren 
  and 
  Prof. 
  A. 
  Geikie. 
  Moreover 
  the 
  districts 
  

   where 
  they 
  are 
  developed 
  are 
  now 
  being 
  mapped 
  by 
  the 
  Geological 
  

   Survey, 
  and 
  the 
  relations 
  and 
  characters 
  of 
  these 
  old 
  lavas 
  are 
  being 
  

   very 
  admirably 
  illustrated 
  by 
  the 
  maps, 
  sections, 
  and 
  memoirs 
  issued 
  

   by 
  that 
  department. 
  Under 
  these 
  circumstances 
  it 
  will 
  only 
  be 
  

   necessary 
  for 
  the 
  purpose 
  of 
  the 
  present 
  argument 
  to 
  refer 
  briefly 
  to 
  

   the 
  general 
  characters 
  presented 
  by 
  these 
  interesting 
  rocks. 
  

  

  Nearly 
  tbe 
  whole 
  of 
  the 
  hill-ranges 
  of 
  Central 
  Scotland, 
  such 
  as 
  

   the 
  Ochils, 
  Sidlaws, 
  Pentland 
  and 
  Braid 
  Hills, 
  Campsie 
  Pells, 
  Kil- 
  

   patrick 
  Hills 
  &c, 
  are 
  composed 
  of 
  these 
  volcanic 
  rocks. 
  The 
  pre- 
  

   servation 
  and 
  present 
  positions 
  of 
  the 
  masses 
  of 
  these 
  rocks 
  which 
  

   still 
  remain, 
  appear 
  to 
  have 
  been 
  determined 
  by 
  the 
  great 
  N.E. 
  and 
  

   S.W. 
  faults 
  which 
  traverse 
  the 
  country. 
  The 
  exact 
  positions 
  and 
  

   effects 
  of 
  these 
  lines 
  of 
  fracture 
  are 
  very 
  admirably 
  shown 
  on 
  the 
  

   detailed 
  maps 
  of 
  the 
  Survey, 
  so 
  far 
  as 
  it 
  has 
  gone. 
  

  

  The 
  lavas 
  composing 
  these 
  great 
  ranges 
  of 
  hills, 
  which 
  are 
  in 
  

   some 
  cases 
  over 
  2000 
  feet 
  in 
  height, 
  consist 
  for 
  the 
  most 
  part 
  of 
  

   rocks 
  of 
  a 
  more 
  or 
  less 
  felspathic 
  character, 
  though 
  not 
  usually 
  so 
  

   highly 
  siliceous 
  as 
  those 
  of 
  the 
  earliest 
  Tertiary 
  period. 
  Like 
  those 
  

   of 
  Lorn 
  they 
  commonly 
  display 
  in 
  a 
  very 
  marked 
  manner 
  the 
  

  

  