﻿PliOF. 
  C. 
  LAPWORTtt 
  ON 
  TRE 
  filRVAN 
  SUCCESSION. 
  587 
  

  

  lying 
  sandstone, 
  consisting 
  of 
  rounded 
  fragments 
  of 
  felstone 
  and 
  

   quartz 
  imbedded 
  in 
  a 
  greenish 
  dust. 
  But 
  it 
  is, 
  in 
  addition, 
  Highly 
  

   calcareous 
  along 
  certain 
  laminae, 
  and 
  presents 
  that 
  peculiar 
  mode 
  of 
  

   weathering 
  into 
  concentric 
  Hakes 
  so 
  common 
  among 
  basaltic 
  dykes. 
  

   The 
  included 
  pebbles 
  are 
  of 
  quartz 
  and 
  several 
  varieties 
  of 
  volcanic 
  

   rocks, 
  and 
  are 
  collectively 
  of 
  the 
  same 
  general 
  type 
  as 
  those 
  of 
  the 
  

   underlying 
  Benan 
  Conglomerate. 
  

  

  Lying 
  buried 
  in 
  the 
  sandier 
  part 
  of 
  the 
  matrix, 
  and 
  often 
  scattered 
  

   through 
  the 
  coarsest 
  part 
  of 
  the 
  conglomerate 
  itself, 
  occur 
  many 
  

   poorly 
  preserved 
  fossils. 
  The 
  most 
  frequent 
  are 
  corals 
  and 
  those 
  

   Brachiopoda 
  whose 
  shells 
  are 
  composed 
  of 
  carbonate 
  of 
  lime, 
  both 
  

   of 
  which 
  groups 
  are 
  practically 
  wanting 
  in 
  the 
  hard 
  Balclatchie 
  

   mudstones 
  below. 
  The 
  commonest 
  forms 
  are 
  : 
  — 
  

  

  Lindstroemia, 
  several 
  species. 
  I 
  Leptaeua 
  sericea, 
  Sow. 
  

  

  Fistulipora 
  favosa, 
  N 
  df 
  L. 
  I 
  transversalia, 
  Wahl. 
  

  

  Strophomena 
  corrugatella, 
  Dav. 
  Bellerophon, 
  &c. 
  

   Leptaena 
  quinquecostata. 
  

  

  The 
  conglomerate 
  passes 
  upwards 
  into 
  a 
  series 
  of 
  dark 
  green 
  ashy 
  

   sandstones 
  (d 
  2 
  '"), 
  identical 
  in 
  petrological 
  character 
  with 
  those 
  below, 
  

   but 
  generally 
  thicker-bedded, 
  and 
  having 
  about 
  twice 
  their 
  vertical 
  

   extent. 
  They 
  contain 
  a 
  few 
  fossils 
  of 
  the 
  same 
  type 
  as 
  those 
  of 
  the 
  

   underlying 
  conglomerate. 
  

  

  These 
  green 
  gritstones 
  are 
  well 
  shown 
  in 
  the 
  bed 
  of 
  the 
  burn, 
  

   lying 
  at 
  a 
  medium 
  angle 
  upon 
  the 
  ashy 
  conglomerate, 
  where 
  an 
  old 
  

   hill-road 
  fords 
  the 
  stream. 
  Immediately 
  beyond, 
  they 
  are 
  succeeded 
  

   by 
  the 
  thick 
  masses 
  of 
  dark 
  flaggy 
  shales 
  and 
  mudstones 
  which 
  form 
  

   the 
  bed 
  and 
  bounding 
  walls 
  of 
  the 
  gorge 
  for 
  a 
  long 
  distance 
  below 
  

   this 
  locality, 
  and 
  which 
  compose 
  the 
  first 
  member 
  of 
  the 
  overlying 
  

   Ardmillan 
  Graptoliiic 
  series 
  (Ba), 
  which 
  falls 
  to 
  be 
  described 
  in 
  the 
  

   following 
  section 
  of 
  this 
  memoir. 
  At 
  the 
  junction 
  of 
  ihe 
  two 
  groups, 
  

   however, 
  occurs 
  a 
  peculiar 
  transitional 
  band 
  which 
  must 
  here 
  be 
  

   noticed. 
  It 
  consists 
  of 
  a 
  few 
  feet 
  of 
  iron 
  -stained 
  shales, 
  with 
  seams 
  

   of 
  hard 
  calcareous 
  and 
  concretionary 
  rock. 
  The 
  shales 
  contain 
  

   abundant 
  Graptolites 
  of 
  the 
  species 
  

  

  Cryptograptus 
  tricornis, 
  Curr. 
  I 
  Diplograptus 
  foliaceus, 
  Murch., 
  &c. 
  ; 
  

   Lasiograptus 
  Harknessi, 
  Nick. 
  \ 
  

  

  while 
  the 
  calcareous 
  band 
  yields 
  a 
  few 
  examples 
  of 
  Brachiopoda, 
  

   chiefly 
  

  

  Leptajna 
  corrugatella, 
  | 
  Orthis 
  calligramma, 
  &c. 
  

  

  We 
  learn, 
  therefore, 
  that 
  in 
  this 
  special 
  locality 
  the 
  Benan 
  Con- 
  

   glomerate 
  becomes 
  interstratified 
  with 
  fossiliferous 
  mudstones 
  at 
  its 
  

   summit 
  ; 
  and 
  what 
  may 
  be 
  regarded 
  as 
  its 
  final 
  member, 
  from 
  a 
  

   physical 
  point 
  of 
  view, 
  is 
  a 
  thin 
  series 
  of 
  green 
  gritstones, 
  which 
  

   are 
  divided 
  from 
  the 
  typical 
  boulder-beds 
  of 
  the 
  great 
  conglo- 
  

   merate 
  below 
  by 
  a 
  group 
  of 
  fossiliferous 
  shales. 
  The 
  general 
  

   identity 
  of 
  the 
  matrix 
  and 
  enclosures 
  of 
  the 
  gritstones 
  with 
  those 
  

   of 
  the 
  Benan 
  Conglomerate 
  is 
  suggestive 
  of 
  the 
  natural 
  union 
  of 
  

   the 
  gritstone 
  group 
  with 
  the 
  Barr 
  or 
  Stinchar 
  series, 
  rather 
  than 
  

   with 
  the 
  succeeding 
  Graptolitic 
  flagstones 
  of 
  the 
  Penwhapple. 
  The 
  

  

  2k 
  2 
  

  

  