﻿646 
  PEOE. 
  C. 
  LAPWOETH 
  ON 
  THE 
  GIEVAN 
  SUCCESSION. 
  

  

  denly 
  succeeded 
  by 
  the 
  gritstones, 
  has 
  all 
  the 
  appearance 
  of 
  a 
  fault. 
  

   The 
  gritstone 
  zone 
  extends 
  down 
  the 
  burn 
  for 
  a 
  distance 
  of 
  about 
  

   60 
  or 
  70 
  yards. 
  Its 
  beds 
  are 
  all 
  much 
  convulsed 
  and 
  disturbed, 
  so 
  

   that 
  no 
  reliable 
  estimate 
  can 
  be 
  formed 
  of 
  their 
  thickness. 
  They 
  

   are 
  quite 
  barren 
  in 
  their 
  central 
  portions 
  ; 
  but 
  in 
  their 
  lower 
  beds, 
  in 
  

   the 
  neighbourhood 
  of 
  the 
  M.-SedgwicHi 
  band, 
  their 
  weathered 
  edges 
  

   are 
  crowded 
  with 
  casts 
  of 
  Rhynchonetta, 
  associated 
  with 
  rarer 
  ex- 
  

   amples 
  of 
  OrtJiis 
  and 
  Strophomena. 
  

  

  These 
  thick-bedded 
  yellow 
  Rhi/nchonella-grits 
  are 
  followed 
  by 
  a 
  

   group 
  of 
  calcareous 
  flagstones 
  which 
  have 
  an 
  apparent 
  thickness 
  of 
  

   about 
  50 
  feet. 
  Their 
  more 
  southerly 
  beds 
  are 
  much 
  shattered, 
  but 
  

   the 
  terminal 
  zones 
  dip 
  steadily 
  to 
  the 
  southward 
  at 
  an 
  angle 
  of 
  from 
  

   60° 
  to 
  70°. 
  A 
  beautifully 
  complete 
  section 
  of 
  these 
  beds 
  is 
  afforded 
  

   by 
  the 
  cliffs 
  on 
  the 
  right 
  side 
  of 
  the 
  gorge. 
  

  

  The 
  lower 
  or 
  southerly 
  beds 
  are 
  nodular, 
  but 
  they 
  contain 
  no 
  

   fossils 
  ; 
  but 
  the 
  upper 
  beds, 
  which 
  are 
  so 
  highly 
  calcareous 
  that 
  they 
  

   may 
  be 
  regarded 
  as 
  impure 
  limestones, 
  are 
  many 
  of 
  them 
  a 
  mass 
  of 
  

   corals 
  and 
  shells. 
  

  

  The 
  genus 
  Lindstrcemia 
  or 
  Petraia 
  occurs 
  in 
  myriads, 
  in 
  asso- 
  

   ciation 
  with 
  Pentamerus, 
  Atrypa, 
  and 
  Strophomena, 
  buried 
  in 
  a 
  

   rock 
  of 
  extraordinary 
  toughness 
  and 
  compactness 
  under 
  the 
  hammer. 
  

  

  The 
  terminal 
  scams 
  arc 
  blue 
  shales, 
  strongly 
  calcareous, 
  the 
  irre- 
  

   gular 
  laminae 
  of 
  which 
  are 
  covered 
  with 
  trails 
  and 
  markings 
  of 
  

   Annelida. 
  In 
  these 
  shales 
  fossils 
  are 
  less 
  plentiful 
  than 
  in 
  the 
  

   limestone 
  flags, 
  but 
  they 
  are 
  more 
  easily 
  extracted 
  and 
  more 
  com- 
  

   pletely 
  preserved. 
  

  

  Here 
  we 
  find 
  the 
  usual 
  Upper 
  (xirvan 
  fossils 
  : 
  — 
  

  

  Encrinurus 
  punctatus. 
  

  

  variolar] 
  s. 
  

  

  Bronteus 
  Brongniarti. 
  

   Illa?nus 
  Thoiuscmi, 
  &e. 
  

  

  Halysites 
  catenulatus. 
  

   Atrypa 
  hemispha;rica. 
  

  

  reticularis. 
  

  

  Pen 
  tamer 
  us 
  oblon^us. 
  

  

  This 
  highly 
  fossiliferous 
  zone 
  I 
  denominate 
  the 
  Penkill 
  or 
  Cam- 
  

   regan 
  limestone, 
  after 
  the 
  localities 
  where 
  its 
  fossils 
  have 
  been 
  most 
  

   carefully 
  studied, 
  and 
  which 
  will 
  be 
  presently 
  noticed 
  more 
  parti- 
  

   cularly. 
  

  

  In 
  this 
  typical 
  locality 
  in 
  Penwh 
  apple 
  Glen, 
  this 
  Camregan 
  lime- 
  

   stone 
  is 
  succeeded 
  to 
  the 
  northward 
  by 
  a 
  zone 
  of 
  purple 
  and 
  green 
  

   mudstones 
  of 
  about 
  the 
  same 
  thickness 
  as 
  the 
  limestone 
  zone 
  below 
  

   it. 
  These 
  mudstones 
  contain 
  merely 
  a 
  few 
  Annelid-markings 
  

   throughout 
  their 
  entire 
  vertical 
  extent, 
  except 
  in 
  one 
  thin 
  seam 
  of 
  

   dark 
  carbonaceous 
  shales 
  near 
  their 
  centre, 
  about 
  a 
  foot 
  and 
  a 
  half 
  in 
  

   total 
  thickness. 
  

  

  This 
  carbonaceous 
  seam 
  may 
  be 
  followed 
  by 
  the 
  eye 
  across 
  the 
  

   stream 
  from 
  the 
  east 
  to 
  the 
  west 
  bank 
  of 
  the 
  gorge, 
  and 
  thence 
  up 
  

   the 
  course 
  of 
  a 
  small 
  runnel 
  descending 
  the 
  steep 
  slope 
  to 
  the 
  left, 
  

   where 
  its 
  laminae 
  are 
  laid 
  open 
  and 
  may 
  be 
  studied 
  in 
  situ. 
  It 
  here 
  

   contains 
  an 
  abundance 
  of 
  fairly 
  preserved 
  Graptolithina, 
  together 
  

   with 
  occasional 
  examples 
  of 
  Phyllopodous 
  Crustacea. 
  From 
  these 
  

   beds 
  I 
  have 
  collected, 
  among 
  other 
  forms 
  : 
  — 
  

  

  

  