﻿596 
  PROF. 
  C. 
  LAPWORTS 
  OX 
  THE 
  GIRVAX 
  SUCCESSION. 
  

  

  immediately 
  by 
  the 
  basal 
  division 
  of 
  the 
  great 
  overlying 
  Graptoli- 
  

   tiferous 
  series. 
  The 
  lowest 
  beds 
  of 
  this 
  division 
  are 
  well 
  exposed 
  

   in 
  several 
  natural 
  and 
  artificial 
  excavations 
  along 
  the 
  line 
  of 
  section, 
  

   in 
  a 
  magnificent 
  and 
  unbroken 
  cliff-section 
  between 
  the 
  farm 
  of 
  

   Ardwell 
  and 
  the 
  rocks 
  of 
  Kennedy's 
  Pass, 
  and 
  in 
  the 
  sides 
  of 
  the 
  

   narrow 
  gorge 
  dug 
  out 
  by 
  the 
  little 
  stream 
  of 
  Ardmillan 
  itself. 
  

  

  The 
  inferior 
  zones 
  of 
  this 
  lowest 
  division 
  of 
  the 
  Flagstone 
  group 
  

   may 
  be 
  seen 
  dipping 
  off 
  the 
  Balclatchie 
  Beds 
  in 
  the 
  gorge 
  of 
  

   Ardmillan 
  and 
  in 
  the 
  slopes 
  of 
  the 
  neighbouring 
  heights, 
  while 
  they 
  

   agree 
  everywhere 
  in 
  strike 
  and 
  inclination 
  with 
  the 
  underlying 
  

   group. 
  

  

  The 
  middle 
  beds 
  are 
  best 
  exposed 
  in 
  the 
  coast-section 
  south 
  of 
  

   Ardwell, 
  where 
  they 
  can 
  be 
  studied 
  foot 
  by 
  foot 
  in 
  the 
  continuous 
  

   exposures 
  washed 
  by 
  the 
  sea-waves. 
  The 
  lowest 
  beds 
  are 
  thin-bedded 
  

   shales, 
  of 
  a 
  dark 
  grey 
  colour, 
  with 
  a 
  few 
  seams 
  or 
  ribs 
  of 
  hard 
  grey 
  

   rock. 
  They 
  are 
  more 
  or 
  less 
  carbonaceous, 
  and 
  weather 
  with 
  a 
  

   rusty 
  exterior. 
  They 
  yield 
  a 
  few 
  Graptolithina, 
  chiefly 
  Diplograptus 
  

   foluiceus, 
  Murch., 
  D. 
  pristis, 
  His., 
  D. 
  rugosus, 
  Emm., 
  Climacograptus 
  

   bicornis, 
  Hall. 
  Higher 
  up, 
  the 
  rocks 
  become 
  rapidly 
  coarser 
  and 
  

   more 
  flag-like 
  in 
  their 
  character, 
  until 
  in 
  their 
  highest 
  zones 
  near 
  

   the 
  farm 
  of 
  Ardwell 
  they 
  may 
  be 
  described 
  as 
  a 
  series 
  of 
  dark-grey 
  

   flagstones 
  from 
  four 
  to 
  six 
  inches 
  in 
  individual 
  thickness, 
  separated 
  

   by 
  partings 
  of 
  dark 
  grey 
  shale. 
  The 
  same 
  fossils 
  are 
  here 
  met 
  with 
  

   as 
  in 
  the 
  lower 
  zones, 
  and, 
  in 
  addition, 
  Diwanograptus 
  ramosus, 
  

   Coryaoides 
  calycularis, 
  Ecculiomphalus 
  Bucklandi 
  and 
  an 
  occasional 
  

   Brachiopod. 
  The 
  highest 
  zone 
  is 
  formed 
  of 
  striped 
  shales 
  crowded 
  

   with 
  hosts 
  of 
  Climacograptus 
  caudatus 
  and 
  Diplograptus 
  rugosus. 
  

   The 
  exposure 
  of 
  these 
  beds 
  is 
  terminated 
  suddenly 
  by 
  the 
  sandy 
  bay 
  

   of 
  Ardwell; 
  and 
  the 
  rocks 
  which 
  next 
  make 
  their 
  appearance 
  are 
  the 
  

   lowest 
  zones 
  of 
  the 
  succeeding 
  group. 
  

  

  Although 
  the 
  oblique 
  section 
  of 
  Ihe 
  Ardwell 
  shales 
  and 
  flags 
  upon 
  

   the 
  coast 
  here 
  between 
  Kennedy's 
  Pass 
  and 
  the 
  farmland 
  of 
  Ardwell 
  

   exceeds 
  a 
  mile 
  in 
  length, 
  the 
  actual 
  transverse 
  breadth 
  of 
  the 
  zone 
  is 
  

   less 
  than 
  one 
  fourth 
  of 
  a 
  mile, 
  so 
  that 
  at 
  their 
  average 
  inclination 
  of 
  

   about 
  70° 
  or 
  80° 
  the 
  thickness 
  of 
  the 
  Ardwell 
  Beds 
  here 
  exposed 
  

   cannot 
  exceed 
  1000 
  feet. 
  It 
  is 
  more 
  than 
  doubtful, 
  however, 
  if 
  the 
  

   entire 
  thickness 
  of 
  the 
  Ardwell 
  Beds 
  is 
  here 
  developed, 
  as 
  the 
  

   hiatus 
  in 
  the 
  bay 
  probably 
  marks 
  the 
  position 
  of 
  a 
  line 
  of 
  fault 
  

   that 
  cuts 
  out 
  a 
  group 
  of 
  flaggy 
  sandstones 
  and 
  grits 
  (Cascade 
  Beds, 
  

   compare 
  p. 
  606), 
  which 
  appear 
  to 
  constitute 
  the 
  higher 
  parts 
  of 
  the 
  

   Ardwell 
  Beds 
  in 
  the 
  interior 
  of 
  the 
  country. 
  

  

  The 
  Ardwell 
  Beds, 
  as 
  seen 
  in 
  this 
  typical 
  locality, 
  are 
  much 
  more 
  

   intensely 
  hardened 
  than 
  is 
  generally 
  the 
  case 
  in 
  the 
  inland 
  sections, 
  

   and 
  fossils 
  are 
  rarer 
  and 
  more 
  difficult 
  of 
  extraction. 
  The 
  group 
  is 
  

   well 
  characterized, 
  however, 
  by 
  its 
  peculiar 
  penological 
  features. 
  

   Wherever 
  a 
  transverse 
  section 
  of 
  beds 
  is 
  laid 
  open, 
  the 
  strata 
  are 
  

   seen 
  to 
  be 
  normally 
  formed 
  of 
  thin 
  seams 
  of 
  alternate 
  grey 
  and 
  black 
  

   or 
  blue 
  laminae. 
  This 
  gives 
  to 
  the 
  beds 
  a 
  somewhat 
  striped 
  appear- 
  

   ance, 
  which 
  is 
  most 
  characteristic. 
  The 
  quantity 
  of 
  carbonaceous 
  

   matter 
  present 
  is 
  comparatively 
  large 
  ; 
  and 
  iron 
  is 
  sufficiently 
  

  

  