﻿608 
  PROF. 
  C. 
  LAPWORTH 
  ON 
  THE 
  GIRVAN 
  SUCCESSION. 
  

  

  restricted 
  coast-section, 
  the 
  first 
  division 
  of 
  this 
  group 
  consists 
  (Be 
  1) 
  

   mainly 
  of 
  green 
  mudstones, 
  with 
  distant 
  ribs 
  of 
  flagstone. 
  This 
  

   division 
  is 
  most 
  conspicuous 
  in 
  the 
  floor 
  of 
  the 
  glen 
  between 
  the 
  line 
  

   of 
  the 
  variegated 
  mudstones 
  and 
  the 
  foot 
  of 
  Laigh 
  Assel 
  Burn. 
  The 
  

   stream 
  has 
  worn 
  away 
  the 
  soft 
  shaly 
  mudstones 
  into 
  deep 
  hollows, 
  

   between 
  which 
  rise 
  the 
  hard 
  and 
  conspicuous 
  intercalary 
  ribs. 
  In 
  

   one 
  or 
  two 
  spots 
  these 
  mudstones 
  are 
  crowded 
  with 
  their 
  charac- 
  

   teristic 
  organism, 
  Nematolites 
  Grayii, 
  Lapw., 
  of 
  the 
  corresponding 
  

   beds 
  of 
  Shalloch 
  Mill. 
  

  

  Continuing 
  our 
  progress 
  down 
  the 
  stream, 
  beyond 
  the 
  terminal 
  

   strata 
  of 
  this 
  essentially 
  shaly 
  division 
  we 
  encounter 
  bed 
  after 
  bed 
  

   of 
  rock 
  of 
  the 
  same 
  general 
  type, 
  but 
  in 
  which 
  the 
  sandstone 
  and 
  

   flaggy 
  ribs 
  become 
  rapidly 
  more 
  numerous 
  and 
  of 
  greater 
  thickness 
  

   (Be 
  2). 
  These 
  all 
  dip 
  invariably 
  to 
  the 
  southward, 
  as 
  if 
  passing 
  below 
  

   the 
  Whitehouse 
  Beds 
  of 
  the 
  higher 
  parts 
  of 
  the 
  burn 
  ; 
  but 
  the 
  rapid 
  

   variation 
  in 
  strike 
  and 
  dip, 
  and 
  the 
  frequent 
  faults, 
  show 
  that 
  it 
  is 
  

   impossible 
  to 
  suppose 
  that 
  we 
  have 
  here 
  a 
  true 
  ascending 
  section, 
  

   but 
  that, 
  as 
  in 
  the 
  former 
  case, 
  we 
  are 
  dealing 
  with 
  a 
  rapid 
  succes- 
  

   sion 
  of 
  inverted 
  folds. 
  Excellent 
  sections 
  of 
  the 
  beds 
  are 
  seen 
  until 
  

   Ave 
  reach 
  the 
  termination 
  of 
  the 
  group, 
  a 
  quarter 
  of 
  a 
  mile 
  to 
  the 
  

   north 
  of 
  Penwhapple 
  bridge, 
  where 
  it 
  is 
  abruptly 
  faulted 
  against 
  a 
  

   series 
  of 
  black 
  Graptolitic 
  shales 
  of 
  the 
  much 
  newer 
  Pentamerus- 
  

   group 
  of 
  Saugh 
  Hill. 
  

  

  Some 
  hard 
  grey 
  gritty 
  flags, 
  with 
  interbedded 
  subcalcareous 
  shales, 
  

   visible 
  in 
  the 
  broken 
  sections 
  near 
  the 
  northern 
  termination 
  of 
  these 
  

   beds, 
  are 
  different 
  from 
  any 
  of 
  the 
  strata 
  of 
  this 
  group 
  recognizable 
  

   upon 
  the 
  shore, 
  and 
  are 
  probably 
  higher 
  in 
  the 
  series 
  than 
  any 
  strata 
  

   there 
  displayed. 
  They 
  are, 
  however, 
  most 
  distinctly 
  to 
  be 
  placed 
  

   in 
  the 
  same 
  sub 
  formation 
  of 
  the 
  Barren 
  Flagstones, 
  with 
  which 
  they 
  

   agree 
  in 
  all 
  essential 
  particulars, 
  and 
  of 
  which 
  they 
  undoubtedly 
  

   form 
  an 
  integral 
  portion 
  in 
  this 
  locality, 
  and 
  a 
  few 
  others 
  yet 
  to 
  be 
  

   described. 
  

  

  They 
  contain 
  a 
  few 
  fragmentary 
  Graptolites 
  in 
  the 
  greyish 
  brown 
  

   shales 
  seen 
  in 
  the 
  land-slips 
  near 
  the 
  great 
  fault. 
  The 
  only 
  form 
  

   clearly 
  recognizable 
  is 
  Diplograptus 
  truncatus, 
  Lapw. 
  

  

  Thus 
  in 
  this 
  section 
  in 
  Penwhapple 
  Glen 
  we 
  recognize, 
  lying 
  

   between 
  the 
  Benan 
  Conglomerate 
  and 
  the 
  Great 
  Fault, 
  a 
  series 
  of 
  

   strata 
  whose 
  members 
  are 
  identical 
  in 
  geographical 
  succession, 
  in 
  

   mineralogical 
  characters, 
  and 
  in 
  fossils, 
  with 
  those 
  developed 
  in 
  our 
  

   typical 
  area 
  of 
  Ardmillan. 
  This 
  sequence, 
  though 
  repeatedly 
  broken 
  

   by 
  numerous 
  and 
  important 
  dislocations, 
  bears 
  evidence 
  of 
  having 
  

   been 
  originally 
  identical 
  with 
  that 
  of 
  Ardmillan 
  in 
  every 
  particular, 
  

   many 
  of 
  the 
  most 
  characteristic 
  petrological 
  zones 
  there 
  exhibited 
  

   being 
  developed 
  here 
  in 
  positions 
  precisely 
  correspondent. 
  The 
  

   apparent 
  dip 
  of 
  the 
  beds 
  through 
  a 
  great 
  part 
  of 
  the 
  section 
  is, 
  it 
  

   is 
  true, 
  different 
  from 
  that 
  seen 
  upon 
  the 
  shore-line 
  ; 
  but, 
  as 
  we 
  

   have 
  shown, 
  it 
  may 
  be 
  regarded 
  as 
  certain 
  that 
  these 
  inharmoni- 
  

   ously-dipping 
  beds 
  are 
  actually 
  arranged 
  in 
  rapid 
  and 
  inverted 
  

   folds. 
  

  

  