﻿PROF. 
  C. 
  LAPWORTH 
  ON 
  THE 
  GIRVAN 
  SUCCESSION. 
  633 
  

  

  In 
  the 
  grey 
  shales 
  themselves 
  Graptolites 
  are 
  remarkably 
  rare. 
  

   The 
  only 
  forms 
  collected 
  by 
  myself 
  are 
  Diplograptus 
  modestus, 
  Lapw., 
  

   and 
  Dvplograptus, 
  sp. 
  

  

  (Cbb.) 
  Greg 
  Flags 
  and 
  Grits. 
  — 
  The 
  grey 
  shales 
  are 
  followed 
  by 
  a 
  

   similar 
  thickness 
  of 
  hard 
  grey 
  gritstones 
  (Cbb). 
  Many 
  of 
  the 
  beds 
  

   are 
  three 
  or 
  four 
  feet 
  in 
  thickness, 
  and 
  are 
  filled 
  with 
  small 
  quartz 
  

   pebbles 
  about 
  the 
  size 
  of 
  a 
  pea. 
  They 
  are 
  associated 
  with 
  more 
  

   thinly 
  bedded 
  flagstones 
  without 
  quartz 
  pebbles. 
  The 
  beds 
  are 
  usu- 
  

   ally 
  of 
  a 
  pale 
  grey 
  interiorly, 
  and 
  the 
  majority 
  weather 
  exteriorly 
  

   in 
  the 
  stream-course 
  to 
  an 
  orange-yellow 
  tinge. 
  They 
  are 
  greatly 
  

   twisted 
  and 
  broken 
  ; 
  and 
  no 
  reliable 
  estimate 
  can 
  be 
  formed 
  of 
  their 
  

   thickness. 
  No 
  fossils 
  are 
  known 
  from 
  this 
  group. 
  

  

  This 
  grit 
  series 
  is 
  succeeded 
  by 
  a 
  second 
  zone 
  of 
  the 
  grey 
  shales 
  so 
  

   characteristic 
  of 
  the 
  group. 
  These 
  are 
  very 
  similar 
  to 
  those 
  of 
  the 
  

   first 
  zone, 
  but 
  are 
  more 
  micaceous 
  and 
  iron-stained 
  : 
  but, 
  to 
  judge 
  

   from 
  the 
  general 
  disposition 
  of 
  the 
  strata 
  (see 
  fig. 
  24), 
  they 
  are 
  merely 
  

   a 
  repetition 
  of 
  the 
  same 
  beds. 
  They 
  contain 
  no 
  visible 
  fossils 
  in 
  

   this 
  locality. 
  

  

  A 
  second 
  grit 
  band 
  follows, 
  resembling 
  the 
  first 
  band 
  in 
  all 
  essen- 
  

   tials, 
  but 
  containing 
  more 
  of 
  the 
  thick-bedded 
  pea-grits, 
  some 
  bands 
  

   of 
  which 
  are 
  at 
  least 
  six 
  feet 
  in 
  thickness. 
  

  

  (Cbc.) 
  Monograptus-Sedgwickii 
  Mudstones. 
  — 
  Above 
  follows 
  the 
  

   third 
  and 
  final 
  shaly 
  zone 
  of 
  the 
  series. 
  This 
  is 
  composed 
  of 
  a 
  most 
  

   conspicuous 
  group 
  of 
  grey 
  and 
  black 
  shales, 
  apparently 
  more 
  than 
  

   a 
  hundred 
  feet 
  in 
  thickness. 
  The 
  lower 
  or 
  southern 
  half 
  of 
  the 
  

   band 
  is 
  formed 
  of 
  greyish-green 
  shales 
  identical 
  with 
  those 
  of 
  the 
  

   previous 
  shaly 
  zone, 
  and 
  like 
  them 
  wholly 
  devoid 
  of 
  organic 
  remains. 
  

   The 
  upper 
  or 
  northern 
  half, 
  however, 
  is 
  most 
  unique 
  in 
  its 
  litho- 
  

   logical 
  features. 
  

  

  It 
  consists 
  essentially 
  of 
  soft 
  shaly 
  mudstones, 
  containing 
  a 
  large 
  

   proportion 
  of 
  carbonaceous 
  matter 
  ; 
  and 
  impregnated 
  with 
  sulphate 
  

   of 
  iron. 
  The 
  entire 
  group 
  is 
  stained 
  of 
  a 
  deep 
  iron-shot 
  colour, 
  and 
  

   is 
  so 
  excessively 
  crushed 
  and 
  contorted 
  that 
  the 
  bedding 
  can 
  only 
  

   be 
  made 
  out 
  with 
  the 
  utmost 
  difficulty. 
  Calcareous 
  matter 
  is 
  

   occasionally 
  present 
  in 
  notable 
  quantity 
  ; 
  and 
  large 
  nodular 
  con- 
  

   cretions 
  are 
  abundant 
  in 
  the 
  steep 
  cliffs 
  of 
  the 
  rock 
  which 
  overhang 
  

   the 
  right 
  bank 
  of 
  the 
  stream. 
  

  

  Graptolites 
  are 
  abundant, 
  but 
  are 
  most 
  difficult 
  of 
  extraction, 
  in 
  

   consequence 
  of 
  the 
  crushing 
  to 
  which 
  these 
  beds 
  have 
  been 
  sub- 
  

   jected; 
  while 
  fragments 
  of 
  Crustacea 
  and 
  Orthoceratites 
  are 
  occasion- 
  

   ally 
  seen. 
  

  

  The 
  Graptolites 
  as 
  a 
  whole 
  are 
  very 
  distinct 
  from 
  those 
  of 
  the 
  

   black 
  shale 
  near 
  the 
  Saugh-Hill 
  fault 
  at 
  the 
  base 
  of 
  our 
  section. 
  

   A 
  few 
  of 
  the 
  forms 
  there 
  obtainable 
  are 
  still 
  present, 
  viz. 
  : 
  — 
  

  

  Diplograptus 
  tamariscus, 
  Nick. 
  • 
  I 
  Climacograptus 
  normalis, 
  Lapw. 
  

   Monograptus 
  tenuis, 
  Portl. 
  Monograptus 
  attenuatus, 
  Hopk. 
  

  

  But 
  they 
  are 
  accompanied 
  by 
  a 
  host 
  of 
  other 
  forms 
  unknown 
  in 
  the 
  

   basal 
  beds, 
  chiefly 
  the 
  familiar 
  species 
  : 
  — 
  

  

  Q. 
  J. 
  G. 
  S. 
  No. 
  152. 
  2 
  u 
  

  

  