﻿PROF. 
  C. 
  LAP 
  WORTH 
  ON 
  THE 
  GIRVAN 
  SUCCESSION. 
  591 
  

  

  Bridge, 
  having 
  the 
  same 
  concretionary 
  structure, 
  and 
  being 
  equally 
  

   difficult 
  of 
  disintegration 
  under 
  the 
  hammer. 
  The 
  fossils, 
  too, 
  are 
  

   preserved 
  precisely 
  in 
  the 
  same 
  manner 
  ; 
  the 
  majority 
  are 
  found 
  in 
  

   perfect 
  relief, 
  the 
  chitinous 
  forms 
  with 
  highly 
  polished 
  surfaces, 
  and 
  

   the 
  Testacea 
  with 
  their 
  shells 
  often 
  beautifully 
  preserved. 
  

  

  The 
  commonest 
  forms 
  that 
  meet 
  the 
  eye 
  of 
  the 
  collector 
  in 
  these 
  

   shales 
  are 
  identical 
  with 
  those 
  of 
  the 
  green 
  mudstones 
  of 
  Balclatchie, 
  

   The 
  following 
  are 
  especially 
  numerous 
  : 
  — 
  

  

  Theea 
  reversa. 
  Salt. 
  

   Bellerophon 
  acutus. 
  

   Mocliolopsis, 
  sp. 
  

   Leptsena 
  tenuicincta. 
  

   sericea. 
  

  

  Strophoraena, 
  sp. 
  

   Rhaphistoma, 
  sp. 
  

   Dicranograptus 
  tarrliusculus. 
  

   Didymograptus 
  moffatensis. 
  

   Cyclonema 
  crebristria. 
  

  

  The 
  Graptolitic 
  flagstones 
  of 
  Penwhapple 
  are 
  not 
  exposed 
  at 
  this 
  

   locality, 
  with 
  the 
  exception 
  of 
  the 
  basal 
  calcareous 
  and 
  carbonaceous 
  

   band, 
  which 
  yields 
  its 
  usual 
  Lasiograptidae 
  in 
  good 
  preservation. 
  

  

  The 
  relation 
  of 
  the 
  fossiliferous 
  Balclatchie 
  Sandstones 
  to 
  the 
  

   Benan 
  Conglomerate 
  at 
  this 
  locality 
  is 
  presumptive 
  of 
  a 
  dislocation 
  

   between 
  the 
  two 
  : 
  and 
  if 
  the 
  natural 
  sequence 
  contains 
  the 
  same 
  

   members 
  here 
  as 
  at 
  Balclatchie, 
  the 
  beds 
  here 
  in 
  contact 
  with 
  the 
  

   conglomerate 
  must 
  be 
  the 
  highest 
  beds 
  — 
  the 
  fossiliferous 
  mudstones 
  

   being 
  the 
  lowest 
  strata 
  of 
  the 
  transitional 
  groups 
  here 
  exposed, 
  and 
  

   owing 
  their 
  great 
  thickness 
  to 
  their 
  being 
  arranged 
  in 
  anticlinal 
  

   form. 
  The 
  hiatus 
  in 
  the 
  succession 
  would 
  naturally 
  be 
  filled 
  by 
  the 
  

   (xraptolitiferous 
  mudstones, 
  over 
  which 
  follow 
  the 
  shell-bearing 
  grit- 
  

   stones 
  in 
  their 
  proper 
  sequence. 
  

  

  If 
  this 
  be 
  the 
  true 
  interpretation 
  of 
  the 
  •visible 
  phenomena, 
  it 
  

   follows 
  that 
  the 
  shell-bearing 
  gritstones 
  should 
  be 
  repeated 
  between 
  

   these 
  quarries 
  and 
  the 
  Graptolitic 
  flagstones 
  visible 
  in 
  the 
  roadway, 
  

   or 
  must 
  be 
  again 
  cut 
  out 
  by 
  a 
  fault. 
  That 
  ^he 
  latter 
  supposition 
  is 
  

   in 
  all 
  probability 
  the 
  correct 
  one 
  is 
  evident 
  from 
  the 
  fact 
  that 
  where 
  

   the 
  sequence 
  is 
  unbroken, 
  a 
  quarter 
  of 
  a 
  mile 
  to 
  the 
  westward, 
  it 
  is 
  

   identical 
  with 
  that 
  at 
  Balclatchie, 
  as 
  is 
  also 
  the 
  case 
  in 
  Ardmillan 
  

   Burn 
  about 
  half 
  a 
  mile 
  further 
  to 
  the 
  east. 
  

  

  4. 
  Ardmillan 
  Burn. 
  — 
  In 
  the 
  steep 
  and 
  narrow 
  gorge 
  excavated 
  

   by 
  the 
  little 
  burn 
  of 
  Ardmillan 
  a 
  continuous 
  section 
  is 
  laid 
  bare 
  

   from 
  the 
  Benan 
  Conglomerate 
  into 
  the 
  heart 
  of 
  the 
  Graptolitic 
  flag- 
  

   stones. 
  The 
  Balclatchie 
  beds 
  themselves 
  yield 
  many 
  of 
  the 
  same 
  

   fossils 
  as 
  those 
  found 
  at 
  Ardmillan 
  Braes 
  ; 
  but 
  the 
  phenomena 
  they 
  

   present 
  afford 
  us 
  little 
  worthy 
  of 
  notice 
  as 
  respects 
  the 
  stratigraphy 
  

   of 
  the 
  group. 
  

  

  5. 
  Lagg'an 
  Gill. 
  — 
  In 
  the 
  narrow 
  glen 
  which 
  separates 
  the 
  two 
  

   masses 
  of 
  Benan 
  Conglomerate 
  that 
  cap 
  the 
  points 
  of 
  Laggan 
  Hill 
  

   and 
  Glendrissoch, 
  the 
  Balclatchie 
  Beds 
  are 
  displayed 
  in 
  the 
  banks 
  of 
  

   the 
  small 
  streamlet 
  which 
  passes 
  the 
  old 
  hamlet 
  of 
  Laggan. 
  

  

  The 
  section 
  here 
  is, 
  in 
  many 
  respects, 
  a 
  most 
  remarkable 
  one. 
  

   The 
  structure 
  will 
  be 
  understood 
  from 
  t'ie 
  accompanying 
  section 
  

   (fig. 
  15). 
  The 
  Balclatchie 
  shales 
  and 
  gritstones 
  are 
  seen 
  in 
  in- 
  

   verted 
  position 
  in 
  the 
  cliffs 
  to 
  the 
  west 
  of 
  the 
  little 
  gorge, 
  and 
  

   yield 
  a 
  few 
  of 
  the 
  usual 
  fossils, 
  which, 
  however, 
  are 
  procurable 
  with 
  

  

  