﻿558 
  PROP. 
  C. 
  IAPWOPvTH 
  ON 
  THE 
  GIRVAN 
  SUCCESSION. 
  

  

  Jinis 
  and 
  Strophomena; 
  and 
  the 
  sandstone 
  group 
  is 
  best 
  regarded 
  as 
  

   the 
  zone 
  of 
  transition 
  between 
  the 
  Orthis 
  confinis-ftagstones 
  and 
  the 
  

   deep-seated 
  purple 
  conglomerate 
  we 
  shall 
  next 
  consider. 
  

  

  Purple 
  Conglomerate. 
  — 
  Immediately 
  below 
  the 
  basal 
  beds 
  of 
  these 
  

   O.-conjmis 
  sandstones 
  a 
  massive 
  conglomerate 
  suddenly 
  sets 
  in 
  of 
  most 
  

   extraordinary 
  petrological 
  characters 
  (Aa 
  1 
  ). 
  In 
  the 
  present 
  locality 
  

   the 
  contrast 
  between 
  this 
  older 
  conglomerate 
  and 
  the 
  great 
  boulder- 
  

   conglomerate 
  of 
  the 
  summit 
  of 
  Benan 
  Hill 
  is 
  most 
  striking. 
  The 
  

   Benan-Hill 
  rock 
  is 
  of 
  a 
  dull 
  greenish 
  or 
  greyish 
  colour 
  where 
  freshly 
  

   fractured, 
  becoming 
  more 
  or 
  less 
  yellow 
  upon 
  its 
  weathered 
  surface. 
  

   Its 
  matrix 
  is 
  of 
  a 
  sandy, 
  or 
  ashy, 
  and 
  more 
  or 
  less 
  open 
  texture, 
  and 
  

   offers 
  not 
  the 
  slightest 
  indication 
  of 
  the 
  presence 
  of 
  calcareous 
  matter. 
  

   In 
  the 
  much 
  older 
  conglomerate 
  under 
  description, 
  which 
  supports 
  the 
  

   O.-conjmis 
  sandstones, 
  we 
  see 
  a 
  rock 
  of 
  a 
  wholly 
  different 
  character 
  ; 
  

   its 
  matrix 
  is 
  of 
  a 
  bright 
  purple 
  colour, 
  and 
  it 
  is 
  so 
  highly 
  calcareous 
  

   that 
  the 
  mass 
  is 
  filled 
  with 
  patches 
  of 
  lime 
  and 
  veins 
  of 
  white 
  calcareous 
  

   spar. 
  The 
  included 
  pebbles 
  are 
  of 
  all 
  sizes 
  and 
  all 
  colours 
  ; 
  green 
  and 
  

   grey 
  porphyrites 
  predominate, 
  but 
  granites, 
  metamorphic 
  rocks, 
  lime- 
  

   stones, 
  and 
  unaltered 
  sandstones 
  are 
  all 
  present 
  and 
  in 
  no 
  small 
  abun- 
  

   dance. 
  The 
  whole 
  mass 
  is 
  intensely 
  hardened 
  and 
  compaetedtogether, 
  

   so 
  that 
  it 
  is 
  next 
  to 
  impossible 
  to 
  detach 
  a 
  pebble 
  from 
  the 
  general 
  

   mass, 
  the 
  plane 
  of 
  fracture 
  of 
  the 
  indurated 
  rock 
  traversing 
  the 
  

   pebbles 
  and 
  vitreous 
  matrix 
  alike. 
  The 
  brilliantly 
  purple 
  matrix 
  

   of 
  this 
  conglomerate, 
  veined 
  with 
  innumerable 
  streaks 
  of 
  milk- 
  

   white 
  spar, 
  forms 
  a 
  most 
  exquisite 
  contrast 
  to 
  the 
  included 
  masses 
  

   of 
  foreign 
  material, 
  green, 
  grey, 
  brown, 
  and 
  white, 
  with 
  which 
  it 
  is 
  

   tilled. 
  The 
  beautiful 
  sight 
  presented 
  by 
  a 
  sheet 
  of 
  this 
  rock, 
  when 
  

   seen 
  at 
  its 
  best 
  in 
  the 
  wetted 
  cliffs 
  of 
  the 
  many 
  waterfalls 
  that 
  dash 
  

   over 
  it, 
  lingers 
  long 
  in 
  the 
  memory 
  of 
  the 
  investigator. 
  

  

  Of 
  this 
  purple 
  conglomerate 
  no 
  great 
  thickness 
  is 
  visible 
  in 
  the 
  

   burn 
  itself, 
  but 
  its 
  beds 
  may 
  be 
  followed 
  by 
  the 
  eye 
  in 
  the 
  rugged 
  

   slopes 
  of 
  Craigbickarae 
  a 
  few 
  yards 
  to 
  the 
  west, 
  coming 
  out 
  steadily 
  

   from 
  below 
  the 
  Orthis-confinis 
  sandstones, 
  and 
  continued 
  in 
  unbroken 
  

   mass 
  downwards 
  into 
  the 
  wooded 
  slopes 
  below, 
  for 
  a 
  thickness 
  of 
  at 
  

   least 
  150 
  feet. 
  

  

  This 
  purple 
  conglomerate 
  forms 
  the 
  basal 
  member 
  of 
  the 
  Girvan 
  

   succession 
  as 
  exposed 
  in 
  this 
  locality. 
  Its 
  lowest 
  beds 
  are 
  lost 
  in 
  

   the 
  alluvial 
  fiats 
  of 
  the 
  Stinchar 
  below 
  the 
  base 
  of 
  Craigbickarae, 
  

   and 
  no 
  further 
  rock- 
  exposure 
  is 
  visible 
  for 
  more 
  than 
  a 
  mile 
  to 
  the 
  

   southward. 
  

  

  Summary. 
  — 
  In 
  this 
  locality, 
  therefore, 
  we 
  have 
  evidence 
  that 
  the 
  

   great 
  green 
  Benan 
  conglomerate 
  is 
  conformably 
  underlain 
  by 
  a 
  series 
  

   of 
  older 
  strata 
  of 
  very 
  distinct 
  petrological 
  characters, 
  namely 
  : 
  — 
  

  

  (1) 
  A 
  calcareous 
  group, 
  about 
  100 
  feet 
  in 
  thickness, 
  composed 
  of 
  

   three 
  members 
  — 
  («) 
  a 
  set 
  of 
  nodular 
  shales 
  with 
  Graptolites 
  and 
  

   Lingulida3, 
  (b) 
  a 
  set 
  of 
  comparatively 
  pure 
  and 
  compact 
  flaggy 
  lime- 
  

   stones, 
  and 
  (c) 
  a 
  set 
  of 
  impure 
  calcareous 
  flags. 
  

  

  (2) 
  A 
  purple 
  conglomerate 
  of 
  great 
  thickness 
  and 
  remarkable 
  

   aspect, 
  which 
  graduates 
  downwards 
  from 
  the 
  foregoing 
  group 
  through 
  

   a 
  transitional 
  zone 
  of 
  pebbly 
  sandstones. 
  

  

  