﻿PROF. 
  C. 
  LAPWORTH 
  ON 
  THE 
  GIRVAN 
  SUCCESSION. 
  658 
  

  

  These 
  flaggy 
  or 
  ribbed 
  shales 
  are 
  followed 
  to 
  the 
  northward 
  by 
  a 
  

   mass 
  of 
  well-bedded 
  greywackes, 
  which 
  are 
  seen 
  to 
  perfection 
  at 
  

   the 
  foot 
  of 
  Penkill 
  Burn, 
  below 
  the 
  old 
  castle. 
  Their 
  most 
  southerly 
  

   beds 
  consist 
  of 
  greywackes 
  from 
  two 
  to 
  three 
  feet 
  in 
  thickness. 
  All 
  

   the 
  middle 
  and 
  main 
  mass 
  of 
  the 
  zone 
  are 
  flagstones 
  or 
  flaggy 
  

   greywackes, 
  frequently 
  less 
  than 
  a 
  foot 
  in 
  thickness, 
  with 
  an 
  occa- 
  

   sional 
  seam 
  of 
  shale. 
  The 
  final 
  band 
  is 
  a 
  pale 
  grey 
  calcareous 
  grey- 
  

   wacke, 
  forming 
  a 
  solid 
  mass 
  several 
  feet 
  in 
  thickness. 
  Fossils 
  are 
  

   rare. 
  Those 
  known 
  are 
  of 
  the 
  same 
  species 
  of 
  Graptolites 
  as 
  those 
  

   enumerated 
  from 
  the 
  preceding 
  division 
  ; 
  they 
  occur 
  in 
  an 
  insignifi- 
  

   cant, 
  highly 
  carbonaceous 
  seam 
  overlying 
  the 
  highest 
  greywacke 
  bed. 
  

  

  (Da 
  3 
  ) 
  Cyrtograptus-Grayi 
  Mudstones. 
  — 
  The 
  fourth 
  and 
  final 
  divi- 
  

   sion 
  of 
  the 
  Penkill 
  Beds 
  is 
  a 
  mass 
  of 
  soft 
  purple 
  and 
  green 
  mudstones. 
  

   They 
  are 
  very 
  imperfectly 
  seen 
  in 
  their 
  more 
  southerly 
  beds, 
  between 
  

   the 
  foot 
  of 
  Penkill 
  Burn 
  and 
  the 
  crook 
  of 
  Penwhapple 
  ; 
  but 
  their 
  

   terminal 
  zone 
  is 
  well 
  exhibited 
  at 
  the 
  latter 
  locality. 
  The 
  purple 
  

   mudstones 
  are 
  here 
  capped 
  by 
  thin 
  seams 
  of 
  graptolitic 
  and 
  more 
  or 
  

   less 
  calcareous 
  shales, 
  which 
  are 
  easily 
  studied 
  in 
  the 
  south 
  bank, 
  at 
  

   the 
  right 
  angle 
  of 
  the 
  burn 
  at 
  this 
  spot, 
  and 
  in 
  the 
  bed 
  of 
  the 
  stream 
  

   itself 
  at 
  the 
  western 
  angle. 
  The 
  fossils 
  they 
  afford 
  occur 
  in 
  a 
  most 
  

   exquisite 
  state 
  of 
  preservation, 
  the 
  Graptolites 
  being 
  frequently 
  pre- 
  

   served 
  with 
  their 
  full 
  relief. 
  Here 
  occur 
  

  

  Retiolites 
  Geinitzianus, 
  Barr. 
  

   Monograptus 
  priodon, 
  Bronn. 
  

   var. 
  Flemingii, 
  Salt. 
  

  

  Cyrtograptus 
  Grayi, 
  Lapw. 
  

   Cardiola 
  fibrosa, 
  Sow. 
  

   Acidaspis 
  Brightii, 
  &c, 
  Murch. 
  

  

  together 
  with 
  a 
  few 
  examples 
  of 
  Brachiopoda 
  and 
  Crustacea. 
  

  

  The 
  remaining 
  rocks 
  of 
  this 
  locality 
  belong 
  to 
  the 
  distinct 
  Bar- 
  

   gany 
  beds, 
  and 
  will 
  be 
  noticed 
  in 
  detail 
  when 
  we 
  come 
  to 
  speak 
  of 
  

   the 
  strata 
  to 
  the 
  eastward. 
  

  

  This 
  completes 
  the 
  description 
  of 
  the 
  Purple-shale 
  and 
  Flagstone 
  

   group 
  as 
  seen 
  in 
  Penwhapple 
  Glen. 
  The 
  section 
  here 
  must 
  be 
  

   regarded 
  as 
  typical. 
  The 
  old 
  castle 
  of 
  Penkill, 
  the 
  seat 
  of 
  the 
  Boyd 
  

   family, 
  is 
  built 
  upon 
  these 
  rocks, 
  above 
  the 
  cliffs 
  of 
  Penwhapple, 
  about 
  

   the 
  centre 
  of 
  the 
  group. 
  It 
  is 
  therefore 
  entitled 
  the 
  Penkill 
  group, 
  

   and 
  is 
  regarded 
  as 
  being 
  composed 
  of 
  the 
  following 
  divisions 
  : 
  — 
  

  

  p 
  , 
  .-,, 
  j 
  (4) 
  Penkill 
  mudstones 
  or 
  Priodon 
  (67ray?')-beds. 
  

   (CroZpodia-) 
  ] 
  [S 
  S 
  g^ywaflkes. 
  j 
  ProtovirffU 
  i 
  aHa 
  . 
  hedSm 
  

   roup. 
  [(l) 
  Penkill 
  or 
  Purple 
  shales 
  (Crossopodia-beds). 
  

  

  Geographical 
  Extension 
  of 
  the 
  Penkill 
  Beds. 
  — 
  The 
  broad 
  band 
  of 
  

   purple 
  and 
  grey 
  strata 
  formed 
  by 
  the 
  beds 
  of 
  the 
  Penkill 
  group 
  is 
  

   traceable 
  for 
  some 
  distance 
  both 
  east 
  and 
  west 
  of 
  the 
  typical 
  section 
  

   in 
  Penwhapple 
  Glen. 
  A 
  tolerably 
  continuous 
  section 
  across 
  many 
  

   of 
  the 
  beds 
  of 
  the 
  group 
  is 
  seen 
  in 
  the 
  course 
  of 
  the 
  small 
  burns 
  

   which 
  descend 
  the 
  northern 
  slope 
  of 
  Camregan 
  Hill, 
  immediately 
  

   west 
  of 
  the 
  plantation, 
  while 
  scattered 
  exposures 
  are 
  seen 
  in 
  occa- 
  

   sional 
  quarries 
  in 
  the 
  wood 
  itself. 
  In 
  all 
  these 
  localities 
  we 
  find 
  an 
  

   abundance 
  of 
  the 
  characteristic 
  Annelid-trails 
  &c. 
  

  

  