﻿644 
  PROF. 
  C. 
  LAPWORTH 
  ON 
  THE 
  GTRVAN 
  SUCCESSION. 
  

  

  It 
  is 
  interesting 
  to 
  notice 
  also 
  that 
  this 
  special 
  stratigraphical 
  break 
  

   occurs 
  at 
  precisely 
  the 
  same 
  palaeontological 
  horizon 
  as 
  that 
  which 
  

   divides 
  the 
  so-called 
  Lower 
  and 
  Upper 
  Silurian 
  of 
  Southern 
  Britain. 
  

  

  If 
  these 
  conclusions 
  are 
  accepted, 
  we 
  have 
  in 
  the 
  strata 
  belonging 
  

   to 
  the 
  same 
  general 
  group 
  as 
  the 
  Xewlands 
  and 
  Glenshalloch 
  beds 
  

   of 
  the 
  northern 
  inlier 
  the 
  following 
  zones 
  south 
  of 
  the 
  datum-line 
  of 
  

   the 
  Camregan 
  limestone 
  : 
  — 
  

  

  Cbc. 
  Mono 
  g 
  rap- 
  ( 
  2. 
  Thick 
  zone 
  of 
  Graptolitic 
  shales, 
  aluminiferous 
  and 
  con- 
  

   tus 
  Sedgwickii 
  \ 
  cretionary, 
  with 
  Monograptus 
  Sedgwickii. 
  

  

  beds. 
  100 
  feet. 
  [ 
  1. 
  Grey 
  and 
  green, 
  non-ibssilif'erous 
  shales 
  and 
  mudstones. 
  

  

  Cbb. 
  Sangh-Hill 
  I 
  J 
  Coarse 
  yellow 
  sandstones, 
  flags 
  and 
  grits 
  with 
  pebbles. 
  

   C 
  rita 
  and 
  yellow 
  grits 
  and 
  nags, 
  with 
  a 
  zone 
  ot 
  impure 
  ealca- 
  

  

  Shales. 
  200ft.], 
  n 
  reo 
  f 
  rock 
  ; 
  . 
  , 
  .. 
  

  

  { 
  1. 
  Quartz 
  conglomerate 
  and 
  grits. 
  

  

  (4. 
  Green, 
  non-fossiliferous 
  shales. 
  

   3. 
  Black 
  and 
  striped 
  Graptolitic 
  shales. 
  

   2. 
  Woodland 
  or 
  Lower 
  Pentamerus-limeatcme. 
  

   1. 
  Craigskelly 
  conglomerate. 
  

  

  (E) 
  Strata 
  North 
  of 
  the 
  Camregan 
  Limestone. 
  

   (a) 
  The 
  Camregan 
  Limestone 
  and 
  its 
  associated 
  Strata. 
  

  

  Having 
  completed 
  our 
  examination 
  of 
  the 
  shattered 
  and 
  more 
  or 
  

   less 
  incomplete 
  sections 
  of 
  the 
  wide 
  band 
  of 
  Saugh-Hill 
  rocks, 
  we 
  

   now 
  enter 
  upon 
  the 
  study 
  of 
  those 
  found 
  in 
  the 
  area 
  lying 
  imme- 
  

   diately 
  to 
  the 
  northward. 
  This 
  new 
  area 
  is, 
  by 
  contrast, 
  one 
  of 
  

   great 
  geological 
  simplicity, 
  where, 
  as 
  a 
  consequence, 
  our 
  task 
  of 
  

   determining 
  the 
  order 
  of 
  succession 
  is 
  comparativelv 
  easy 
  and 
  satis- 
  

   factory 
  (Plate 
  XXV. 
  1). 
  

  

  It 
  is 
  formed 
  of 
  a 
  narrow 
  belt 
  of 
  Lower 
  Palaeozoic 
  strata, 
  about 
  12 
  

   miles 
  in 
  length, 
  lying 
  between 
  the 
  band 
  of 
  dark 
  mudstone 
  with 
  

   Monograptus 
  Sedgwickii, 
  which 
  forms 
  the 
  terminal 
  member 
  of 
  the 
  

   Saugh-Hill 
  Group, 
  and 
  a 
  line 
  drawn 
  parallel 
  with 
  this 
  zone 
  about 
  half 
  

   a 
  mile 
  to 
  the 
  northward. 
  The 
  belt 
  of 
  country 
  thus 
  defined, 
  as 
  we 
  

   have 
  more 
  than 
  once 
  pointed 
  out, 
  is 
  occupied 
  by 
  several 
  parallel 
  

   zones 
  of 
  rock, 
  individualized 
  by 
  well-marked 
  petrographical 
  and 
  

   palaeontological 
  peculiarities, 
  and 
  traceable 
  longitudinally 
  through 
  

   the 
  area 
  from 
  the 
  Braehill 
  fault 
  on 
  the 
  west 
  to 
  the 
  Old 
  Red 
  Sand- 
  

   stone 
  of 
  the 
  Hadyard 
  Hills 
  on 
  the 
  east. 
  

  

  In 
  the 
  complete 
  transverse 
  section 
  of 
  these 
  strata 
  afforded 
  by 
  the 
  

   gorge 
  of 
  Pen 
  wh 
  apple 
  to 
  the 
  south 
  of 
  the 
  old 
  castle 
  of 
  Penkill 
  (fig. 
  28) 
  

   we 
  find 
  the 
  beds 
  of 
  the 
  soft 
  crumpled 
  mudstones 
  of 
  the 
  M. 
  -Sedgwickii 
  

   zone 
  crushed 
  suddenly 
  against 
  a 
  group 
  of 
  massive 
  gritstones 
  and 
  

   flags 
  to 
  the 
  north. 
  The 
  first 
  beds 
  of 
  this 
  new 
  group 
  weather 
  of 
  

   a 
  yellow 
  tinge, 
  and 
  vary 
  from 
  2 
  to 
  4 
  feet 
  in 
  thickness. 
  In- 
  

   teriorly 
  they 
  are 
  of 
  a 
  pale 
  bluish 
  -white 
  colour, 
  agreeing 
  in 
  this 
  

   respect 
  precisely 
  with 
  the 
  thick-bedded 
  gritstones 
  of 
  Saugh 
  Hill. 
  

   The 
  massive 
  grits 
  immediately 
  above 
  the 
  M 
  .-Sedgwickii 
  zone 
  

   are 
  almost 
  perpendicular, 
  and 
  the 
  line 
  of 
  contact, 
  in 
  which 
  the 
  

   crushed 
  and 
  contorted 
  mudstones 
  and 
  shales 
  of 
  the 
  latter 
  are 
  sud- 
  

  

  

  

  