﻿286 
  J. 
  W. 
  JTJDD 
  ON 
  THE 
  SECONDARY 
  ROCKS 
  OF 
  SCOTLAND. 
  

  

  that 
  series 
  consists 
  of 
  stream 
  after 
  stream 
  of 
  lava 
  piled 
  one 
  upon 
  

   the 
  other 
  in 
  almost 
  endless 
  succession 
  ; 
  and 
  so 
  far 
  as 
  I 
  have 
  ob- 
  

   served, 
  these 
  include 
  between 
  them 
  no 
  stratified 
  deposits. 
  The 
  mode 
  

   of 
  weathering 
  peculiar 
  to 
  " 
  trap 
  " 
  rocks, 
  while 
  it 
  often 
  exhibits 
  large 
  

   faces 
  of 
  the 
  different 
  lava 
  currents, 
  causes 
  their 
  junction 
  to 
  be 
  

   usually 
  buried 
  beneath 
  a 
  talus 
  of 
  fallen 
  fragments. 
  Nevertheless 
  

   we 
  are 
  able 
  to 
  observe 
  at 
  many 
  points, 
  as 
  near 
  Loch 
  Feochan, 
  Loch 
  

   Nell, 
  and 
  Glen 
  Lonnan, 
  that 
  between 
  the 
  old 
  lava 
  streams 
  there 
  

   occur 
  masses 
  of 
  a 
  peculiar 
  rock, 
  usually 
  of 
  a 
  bright 
  red 
  colour. 
  At 
  

   first 
  sight 
  these 
  red 
  rocks 
  present 
  but 
  little 
  resemblance 
  to 
  " 
  trap- 
  

   tuffs," 
  being 
  often 
  extremely 
  hard 
  and 
  compact 
  in 
  texture, 
  through 
  

   the 
  infilling 
  of 
  their 
  pores 
  with 
  crystalline 
  materials. 
  Fresh 
  frac- 
  

   tured 
  surfaces, 
  however, 
  show 
  that 
  the 
  rock 
  is 
  made 
  up 
  of 
  angular 
  

   fragments 
  of 
  lava, 
  <fec. 
  Qajpilli), 
  quite 
  unstratified 
  ; 
  and 
  here, 
  again, 
  

   weathering 
  processes 
  come 
  to 
  the 
  aid 
  of 
  the 
  geologist, 
  and, 
  by 
  re- 
  

   moving 
  to 
  some 
  extent 
  the 
  crystallized 
  materials 
  from 
  the 
  interstices 
  

   of 
  the 
  rock, 
  reveal 
  its 
  true 
  tufaceous 
  structure. 
  Occasionally 
  too 
  

   we 
  find 
  in 
  the 
  beds 
  unmistakable 
  fragments, 
  and 
  more 
  rarely 
  

   entire 
  examples, 
  of 
  volcanic 
  bombs 
  ; 
  but 
  these 
  it 
  is 
  seldom 
  possible 
  

   to 
  extract 
  entire, 
  owing 
  to 
  the 
  jointed 
  structure 
  which 
  they 
  have 
  

   acquired 
  since 
  being 
  imbedded 
  in 
  the 
  rock 
  wherein 
  they 
  lie. 
  

  

  5. 
  Conditions 
  under 
  which 
  the 
  Volcanic 
  series 
  of 
  Lorn 
  was 
  de- 
  

   posited. 
  — 
  The 
  highly 
  irregular 
  surface 
  of 
  the 
  old 
  slate 
  rocks, 
  with 
  

   its 
  hollows 
  filled 
  by 
  breccias 
  composed 
  of 
  their 
  angular 
  frag- 
  

   ments, 
  points 
  to 
  the 
  existence 
  of 
  an 
  old 
  land-surface. 
  F/pon 
  

   this, 
  as 
  we 
  have 
  seen, 
  the 
  accumulation 
  of 
  lava 
  sheets 
  and 
  great 
  

   masses 
  of 
  conglomerate 
  and 
  sandstone 
  appears 
  to 
  have 
  gone 
  on 
  

   simultaneously 
  for 
  a 
  very 
  considerable 
  period. 
  The 
  stratified 
  rocks 
  

   associated 
  with 
  the 
  lower 
  lava 
  sheets 
  of 
  the 
  Lorn 
  series 
  are 
  of 
  such 
  

   an 
  extremely 
  local 
  and 
  irregular 
  character, 
  that 
  they 
  do 
  not 
  by 
  any 
  

   means 
  necessarily 
  imply 
  a 
  subsidence 
  of 
  the 
  old 
  land-surface 
  beneath 
  

   the 
  sea-level. 
  On 
  the 
  contrary, 
  the 
  accumulation 
  of 
  large 
  blocks 
  

   of 
  the 
  local 
  rocks, 
  with 
  alternating 
  seams 
  of 
  sand 
  of 
  various 
  

   degrees 
  of 
  fineness, 
  would 
  seem 
  rather 
  to 
  indicate 
  the 
  action 
  of 
  

   mountain-streams 
  subject 
  to 
  violent 
  floods. 
  The 
  causes 
  so 
  clearly 
  

   described 
  by 
  Mr. 
  Drew* 
  as 
  having 
  given 
  rise 
  to 
  the 
  formation 
  of 
  the 
  

   great 
  fan-shaped 
  masses 
  of 
  alluvium 
  in 
  India 
  (the 
  nature 
  and 
  dis- 
  

   position 
  of 
  the 
  materials 
  of 
  which 
  would 
  seem 
  to 
  be 
  strikingly 
  simi- 
  

   lar 
  to 
  those 
  of 
  the 
  beds 
  we 
  are 
  describing) 
  appear 
  to 
  me 
  to 
  be 
  fully 
  

   competent 
  to 
  the 
  production 
  of 
  the 
  peculiar 
  deposits 
  of 
  Lorn. 
  

  

  It 
  therefore 
  appears 
  that 
  the 
  remarkable 
  series 
  of 
  rocks 
  in 
  Lorn 
  

   was 
  accumulated 
  along 
  the 
  flanks 
  of 
  a 
  range 
  of 
  lofty 
  volcanoes, 
  the 
  

   heaping 
  up 
  of 
  conglomerates 
  by 
  monntain-torrents 
  and 
  the 
  out- 
  

   pouring 
  of 
  lava 
  streams, 
  under 
  which 
  these 
  were 
  buried 
  and 
  pre- 
  

   served, 
  going 
  on 
  side 
  by 
  sidef. 
  During 
  the 
  formation 
  of 
  the 
  upper 
  

  

  * 
  Quart. 
  Journ. 
  Geol. 
  Soe. 
  vol. 
  xxix. 
  p. 
  441. 
  

  

  t 
  Mr. 
  Scrope 
  has 
  clearly 
  described 
  the 
  important 
  part 
  which 
  is 
  played 
  by 
  

   violent 
  floods 
  (resulting 
  either 
  from 
  the 
  sudden 
  melting 
  of 
  snows 
  on 
  volcanic 
  

   cones 
  during 
  their 
  eruptions, 
  or 
  from 
  the 
  condensation 
  of 
  the 
  enormous 
  quan- 
  

   tities 
  of 
  vapour 
  to 
  which 
  they 
  give 
  origin) 
  in 
  distributing 
  and 
  rearranging 
  the 
  

   materials 
  thrown 
  out 
  from 
  volcanic 
  vents. 
  

  

  