﻿5S6 
  PROF. 
  C. 
  LAPWORTH 
  ON 
  THE 
  GIRVAN 
  SUCCESSION. 
  

  

  of 
  passage-beds, 
  in 
  which 
  the 
  characteristic 
  Balclatchie 
  fossils 
  may 
  

   be 
  collected 
  from 
  the 
  shale 
  bands 
  lying 
  below 
  the 
  terminal 
  pebble- 
  

   beds 
  that 
  mark 
  the 
  final 
  disappearance 
  of 
  the 
  peculiar 
  physical 
  con- 
  

   ditions 
  which 
  gave 
  origin 
  to 
  the 
  Benan 
  conglomerate. 
  

  

  Balclatchie 
  Shales, 
  Ad 
  1 
  . 
  — 
  The 
  lowest 
  division 
  of 
  this 
  overlying 
  

   fossiliferous 
  group 
  is 
  composed 
  of 
  about 
  40 
  feet 
  of 
  concretionary 
  mud- 
  

   stones 
  of 
  a 
  dark 
  bluish-green 
  colour, 
  and 
  excessively 
  jointed. 
  They 
  

   are 
  somewhat 
  calcareous, 
  usually 
  effervescing 
  upon 
  the 
  application 
  

   of 
  an 
  acid, 
  and 
  weather 
  down 
  into 
  shivery 
  fragments, 
  the 
  joints 
  of 
  

   which 
  are 
  coated 
  by 
  the 
  yellow 
  oxide 
  of 
  iron. 
  They 
  are 
  well 
  ex- 
  

   posed 
  upon 
  the 
  roadside 
  ; 
  but 
  they 
  are 
  even 
  better 
  displayed 
  in 
  a 
  

   small 
  cliff 
  on 
  the 
  opposite 
  side 
  of 
  the 
  stream-course, 
  a 
  few 
  yards 
  

   distant. 
  In 
  the 
  cliff, 
  however, 
  and 
  in 
  the 
  floor 
  of 
  the 
  stream 
  at 
  its 
  

   foot, 
  they 
  are 
  but 
  slightly 
  weathered, 
  and 
  they 
  compose 
  a 
  tough 
  

   homogeneous 
  mass, 
  which 
  flics 
  into 
  rough 
  conchoidal 
  fragments 
  

   only 
  after 
  repeated 
  blows 
  of 
  the 
  hammer. 
  These 
  green 
  mudstones 
  

   (which 
  resemble 
  the 
  greenish 
  Did]/mor/raptus-jnudstonea 
  at 
  the 
  base 
  

   of 
  the 
  Benan 
  Conglomerate 
  in 
  all 
  their 
  petrographical 
  characters), 
  

   contain 
  a 
  profusion 
  of 
  organic 
  remains, 
  generally 
  fragmentary, 
  but 
  

   always 
  in 
  an 
  excellent 
  state 
  of 
  preservation. 
  This 
  spot 
  has 
  long 
  

   been 
  known 
  to 
  paleontologists 
  for 
  the 
  abundance 
  and 
  beauty 
  of 
  its 
  

   fossils 
  ; 
  and 
  the 
  fauna 
  of 
  these 
  green 
  shales 
  has 
  been 
  more 
  com- 
  

   pletely 
  worked 
  out 
  than 
  that 
  of 
  any 
  other 
  single 
  horizon 
  (with 
  the 
  

   exception 
  perhaps 
  of 
  the 
  Craighead 
  Limestone) 
  in 
  the 
  Girvan 
  region. 
  

  

  The 
  more 
  characteristic 
  fossils 
  obtainable 
  here 
  are 
  : 
  — 
  

  

  Dieranograptus 
  tardiusculus, 
  Lapic. 
  

   Dicellograptus 
  lnotfatcnsis, 
  Carr. 
  

   Gk'ssugraptus 
  Hineksii, 
  Hojpk. 
  

   Asaphas 
  gigas. 
  De 
  Kay. 
  

   Remopleurides 
  Barrandii, 
  Ether. 
  

   Tkeca 
  simplex, 
  Salt. 
  

  

  Lasiograptus 
  Harknessi, 
  Nick. 
  

   Climacograptus 
  Sckarenbergi, 
  Lapw. 
  

   Lingula 
  attenuata, 
  Sow. 
  

   Acrutreta 
  Nicbolsoni, 
  Dav. 
  

   Leptsena 
  corrugateila, 
  Dav. 
  

  

  Balclatchie 
  Grits 
  and 
  Conglomerates, 
  Ad". 
  — 
  The 
  small 
  group 
  of 
  

   fossiliferous 
  shales 
  is 
  succeeded 
  immediately 
  by 
  a 
  thicker 
  set 
  of 
  

   sandstones 
  and 
  conglomerates 
  of 
  a 
  most 
  distinctive 
  lithological 
  

   character. 
  

  

  The 
  matrix 
  of 
  these 
  overlying 
  sandstones 
  is 
  of 
  a 
  dark 
  green 
  tint, 
  

   passing 
  into 
  a 
  blackish-blue 
  colour 
  upon 
  the 
  weathered 
  faces. 
  Their 
  

   lowest 
  strata 
  are 
  flagstones 
  (d' 
  2 
  '), 
  each 
  a 
  few 
  inches 
  in 
  thickness, 
  

   and 
  partly 
  rormed 
  of 
  coarse 
  irregular 
  grains 
  of 
  felspar 
  &c, 
  as 
  if 
  de- 
  

   rived 
  from 
  the 
  washings 
  of 
  a 
  greenish 
  porphyry 
  or 
  voleanio 
  ash. 
  

  

  Here 
  and 
  there 
  the 
  beds 
  are 
  finer 
  ; 
  but 
  nowhere 
  are 
  the 
  component 
  

   grains 
  of 
  sufficient 
  fineness 
  to 
  reduce 
  the 
  rock 
  to 
  the 
  nature 
  or 
  a 
  

   shale. 
  It 
  is, 
  throughout, 
  a 
  coarse 
  roughly 
  bedded 
  sandstone, 
  breaking 
  

   up 
  into 
  flake-like 
  plates 
  an 
  inch 
  or 
  so 
  in 
  thickness, 
  having 
  the 
  

   irregularly 
  wrinkled 
  or 
  undulated 
  bedding-faces 
  characteristic 
  of 
  

   laminated 
  dykes 
  and 
  volcanic 
  gritstones. 
  

  

  These 
  flaggy 
  sandstones, 
  which 
  yield 
  an 
  occasional 
  badly 
  preserved 
  

   Brachiopod 
  or 
  coral, 
  pass 
  up 
  into 
  several 
  feet 
  of 
  a 
  coarse 
  green 
  con- 
  

   glomerate 
  (d 
  2 
  "), 
  which 
  is 
  excellently 
  exposed 
  in 
  a 
  small 
  cliff 
  on 
  the 
  

   left 
  bank 
  of 
  the 
  stream. 
  

  

  The 
  matrix 
  of 
  this 
  conglomerate 
  is 
  similar 
  to 
  that 
  of 
  the 
  under- 
  

  

  