﻿552 
  PROF. 
  C. 
  LAPWORTH 
  ON 
  THE 
  GIRVAN 
  SUCCESSION. 
  

  

  feature 
  in 
  the 
  ascending 
  sequence 
  ; 
  and, 
  to 
  be 
  completely 
  satisfac- 
  

   tory 
  for 
  our 
  special 
  purpose, 
  it 
  should 
  be 
  of 
  wide 
  horizontal 
  extent, 
  

   so 
  that 
  it 
  may 
  afford 
  a 
  large 
  number 
  of 
  points 
  of 
  reference 
  upon 
  the 
  

   ground 
  itself, 
  that 
  there 
  may 
  be 
  no 
  possibility 
  of 
  doubt 
  or 
  ambiguity 
  

   as 
  respects 
  its 
  true 
  relationship 
  to 
  the 
  remaining 
  members 
  of 
  the 
  

   succession. 
  

  

  It 
  is, 
  in 
  truth, 
  most 
  fortunate 
  for 
  the 
  student 
  of 
  the 
  stratigraphy 
  

   of 
  the 
  Girvan 
  rocks 
  that 
  all 
  these 
  desiderata 
  are 
  afforded 
  him 
  by 
  

   what 
  is 
  actually 
  the 
  most 
  remarkable 
  formation 
  in 
  the 
  Girvan 
  

   region 
  — 
  the 
  great 
  Boulder-conglomerate 
  of 
  Benan 
  Hill 
  ; 
  its 
  extra- 
  

   ordinary 
  petrol 
  ogical 
  character, 
  composed, 
  as 
  it 
  is, 
  of 
  masses 
  of 
  

   rounded 
  boulders 
  heaped 
  tumultuously 
  together 
  in 
  a 
  faintly 
  stratified 
  

   sandy 
  matrix, 
  renders 
  it 
  identifiable 
  at 
  a 
  glance 
  in 
  the 
  field 
  : 
  its 
  great 
  

   thickness, 
  as 
  displayed 
  in 
  Milljoan 
  and 
  Pinjerroch, 
  where 
  its 
  almost 
  

   horizontal 
  beds 
  are 
  apparently 
  piled 
  one 
  above 
  the 
  other 
  to 
  more 
  than 
  

   1000 
  feet 
  in 
  height, 
  makes 
  it, 
  geologically, 
  one 
  of 
  the 
  most 
  important 
  

   members 
  of 
  the 
  Girvan 
  succession 
  ; 
  lastly, 
  in 
  its 
  geographical 
  ex- 
  

   tension 
  it 
  excels 
  all 
  its 
  sister 
  formations, 
  stretching 
  in 
  one 
  vast 
  

   and 
  almost 
  continuous 
  band 
  more 
  than 
  a 
  mile 
  in 
  width 
  from 
  end 
  to 
  

   end 
  of 
  the 
  entire 
  region. 
  

  

  Selecting, 
  therefore, 
  this 
  great 
  Boulder-conglomerate 
  as 
  our 
  

   general 
  horizon 
  of 
  reference, 
  we 
  commence 
  the 
  description 
  of 
  the 
  

   Girvan 
  succession 
  by 
  an 
  account 
  of 
  the 
  stratigraphy 
  of 
  those 
  subareas 
  

   where 
  its 
  true 
  relationships 
  are 
  most 
  effectively 
  displayed. 
  

  

  (a) 
  Description 
  of 
  the 
  Typical 
  Sections 
  of 
  the 
  Valley 
  of 
  the 
  

   Stinchar. 
  

  

  The 
  subarea 
  which 
  most 
  satisfactorily 
  exhibits 
  the 
  development 
  

   and 
  interrelationships 
  of 
  the 
  great 
  Boulder- 
  con 
  glomerate 
  and 
  its 
  

   associated 
  strata 
  within 
  the 
  Girvan 
  region 
  is 
  the 
  mound-like 
  ridge 
  

   lying 
  to 
  the 
  north-west 
  of 
  the 
  little 
  village 
  of 
  Barr 
  and 
  its 
  bounding 
  

   valleys 
  of 
  the 
  Assel 
  and 
  Stinchar. 
  The 
  general 
  contour 
  of 
  this 
  area 
  

   rises 
  in 
  successive 
  steps 
  from 
  the 
  average 
  level 
  of 
  these 
  valleys 
  in 
  the 
  

   west, 
  to 
  a 
  height 
  of 
  nearly 
  1200 
  feet 
  in 
  the 
  east, 
  where 
  it 
  merges 
  

   into 
  the 
  elevated 
  Old 
  Red 
  Sandstone 
  terrace 
  of 
  Garlefnn. 
  Its 
  three 
  

   rounded 
  summits 
  of 
  Benan 
  Hill, 
  Pinjerroch, 
  and 
  the 
  Mull 
  of 
  Mill- 
  

   joan 
  rise 
  in 
  succession 
  abruptly 
  from 
  the 
  southern 
  edge 
  of 
  the 
  long 
  

   straight 
  valley 
  of 
  the 
  Stinchar 
  to 
  the 
  respective 
  heights 
  of 
  900, 
  

   1000, 
  and 
  1100 
  feet, 
  forming 
  between 
  them 
  a 
  broadly 
  rounded 
  

   ridge, 
  which 
  occupies 
  a 
  superficial 
  area 
  of 
  at 
  least 
  15 
  square 
  miles. 
  

  

  The 
  whole 
  of 
  this 
  ridge, 
  together 
  with 
  its 
  outlying 
  dependencies 
  of 
  

   Barr 
  and 
  Balclatchie, 
  from 
  the 
  low-lying 
  river-valleys 
  that 
  bound 
  it 
  

   to 
  the 
  summit 
  of 
  its 
  highest 
  point, 
  is 
  composed 
  almost 
  entirely 
  of 
  

   one 
  continuous 
  sheet 
  of 
  the 
  coarse 
  Boulder-conglomerate. 
  It 
  is 
  

   here 
  made 
  up 
  of 
  rounded 
  masses 
  of 
  stone 
  of 
  all 
  dimensions, 
  from 
  

   blocks 
  several 
  feet 
  in 
  cubical 
  extent 
  to 
  chips 
  the 
  size 
  of 
  a 
  marble. 
  

   These 
  blocks 
  are 
  generally 
  of 
  igneous 
  origin, 
  consisting 
  of 
  granites, 
  

   porphyries, 
  serpentines, 
  and 
  various 
  felsites 
  ; 
  they 
  are 
  occasionally 
  

   intermixed 
  with 
  pieces 
  f 
  white 
  and 
  red 
  quartz, 
  and 
  with 
  rarer 
  

  

  

  