﻿652 
  PE0P. 
  C. 
  LAPWOETH 
  ON 
  THE 
  GIEYAN 
  SUCCESSION. 
  

  

  thickness,, 
  the 
  purple 
  strata 
  distinctly 
  predominating, 
  occasionally 
  

   passing 
  on 
  the 
  one 
  hand 
  into 
  soft 
  mndstones 
  almost 
  destitute 
  of 
  

   definite 
  lamination, 
  and 
  on 
  the 
  other 
  into 
  flagstones 
  of 
  great 
  thick- 
  

   ness. 
  They 
  continue 
  down 
  the 
  stream 
  from 
  the 
  line 
  of 
  Pentamerus- 
  

   gritstone 
  to 
  the 
  final 
  crook 
  of 
  the 
  burn 
  below 
  the 
  farmhouse 
  of 
  

   Penkill, 
  where 
  they 
  are 
  succeeded 
  by 
  a 
  very 
  distinct 
  group 
  of 
  pale 
  

   grey 
  flagstones. 
  

  

  The 
  strata 
  lying 
  between 
  these 
  limits 
  must 
  be 
  assigned 
  on 
  petro- 
  

   logical 
  grounds 
  to 
  one 
  and 
  the 
  same 
  group 
  or 
  subordinate 
  forma- 
  

   ation, 
  and 
  will 
  be 
  referred 
  to 
  as 
  the 
  Penkill 
  Beds. 
  The 
  section 
  of 
  

   these 
  beds 
  here 
  displayed 
  appears 
  to 
  be 
  continuous. 
  It 
  is 
  about 
  

   500 
  yards 
  in 
  length, 
  and 
  the 
  total 
  thickness 
  of 
  the 
  strata 
  exposed 
  

   may 
  be 
  estimated 
  at 
  about 
  1000 
  feet. 
  

  

  (Da 
  1 
  ) 
  Grossopodia 
  Beds 
  or 
  Purple 
  Shales. 
  — 
  For 
  the 
  first 
  150 
  yards 
  

   the 
  strata 
  of 
  the 
  Penkill 
  Beds 
  consist 
  of 
  finely 
  laminated 
  shales 
  of 
  a 
  

   deep 
  purple 
  colour, 
  only 
  occasionally 
  interrupted 
  by 
  narrow 
  seams 
  

   of 
  green 
  or 
  grey. 
  On 
  a 
  few 
  horizons, 
  however, 
  the 
  purple 
  and 
  green 
  

   shales 
  are 
  arranged 
  in 
  alternating 
  bands 
  of 
  colour 
  of 
  an 
  inch 
  or 
  two 
  

   in 
  thickness, 
  forming 
  a 
  peculiar 
  striped 
  rock 
  of 
  remarkable 
  appear- 
  

   ance. 
  These 
  purple 
  shales 
  are 
  magnificently 
  exposed 
  at 
  this 
  locality, 
  

   and 
  not 
  only 
  in 
  the 
  bed 
  of 
  the 
  stream 
  itself, 
  but 
  in 
  the 
  steep 
  wooded 
  

   cliffs 
  on 
  both 
  sides 
  of 
  the 
  gorge 
  ; 
  and 
  there 
  is 
  little 
  appearance 
  of 
  

   contortion 
  or 
  repetition 
  among 
  them. 
  

  

  They 
  are 
  crowded 
  along 
  many 
  horizons 
  with 
  multitudes 
  of 
  worm- 
  

   tracks 
  and 
  so-called 
  Annelid-trails 
  : 
  in 
  some 
  spots 
  near 
  the 
  

   southern 
  end 
  of 
  the 
  exposure 
  every 
  lamina 
  is 
  a 
  perfect 
  maze 
  of 
  these 
  

   imperfectly 
  studied 
  markings. 
  The 
  commonest 
  and 
  most 
  charac- 
  

   teristic 
  is 
  M'Coy's 
  Crossopodia 
  scotica 
  ; 
  and 
  the 
  less 
  conspicuous 
  

   species 
  are 
  : 
  — 
  

  

  Nernertites 
  tenuis, 
  M'Coy. 
  Nereites 
  cambrensis, 
  M'Coy. 
  

  

  Nereites 
  Sedgwickii, 
  M 
  Coy. 
  

  

  Graptolites 
  occur 
  also 
  in 
  the 
  greatest 
  variety 
  in 
  a 
  few 
  seams 
  of 
  

   slightly 
  carbonaceous 
  shales, 
  discernible 
  with 
  difficulty 
  on 
  several 
  

   horizons 
  in 
  the 
  succession 
  ; 
  they 
  are 
  mere 
  laminae, 
  and 
  the 
  Grap- 
  

   tolites 
  themselves 
  are 
  poorly 
  preserved. 
  The 
  forms 
  collected 
  by 
  

   myself 
  include 
  : 
  — 
  

  

  Monograptus 
  exiguus, 
  Kick. 
  

  

  Beckii, 
  Barr. 
  

  

  galaensis, 
  Lapw. 
  

  

  Rastrites 
  distans, 
  Lapw. 
  

   Diplograptus, 
  sp. 
  

   Retiolites 
  obesus, 
  Lapw. 
  

  

  (Da 
  2 
  ) 
  Protovirgularia 
  Flags 
  and 
  Grits. 
  — 
  These 
  purple 
  shales 
  are 
  

   succeeded 
  in 
  the 
  section 
  by 
  an 
  equal 
  thickness 
  of 
  flaggy 
  beds 
  of 
  a 
  

   greyish-green 
  colour, 
  about 
  two 
  inches 
  in 
  thickness, 
  which 
  alternate 
  

   with 
  green 
  and 
  purple 
  shales, 
  identical 
  with 
  those 
  of 
  the 
  preceding 
  

   subgroup, 
  and 
  forming 
  a 
  well-marked 
  division 
  of 
  this 
  formation, 
  

   exactly 
  intermediate 
  in 
  petrological 
  features 
  and 
  geographical 
  position 
  

   between 
  the 
  purple 
  shales 
  below 
  and 
  the 
  division 
  next 
  to 
  be 
  described. 
  

   They 
  contain 
  a 
  few 
  of 
  the 
  usual 
  Annelids, 
  together 
  with 
  rare 
  ex- 
  

   amples 
  of 
  the 
  characteristic 
  Monograptus 
  exiguus, 
  jNlch., 
  found 
  in 
  a 
  

   small 
  stream 
  near 
  the 
  northern 
  extremity 
  of 
  the 
  section 
  of 
  these 
  beds, 
  

  

  