﻿PROF. 
  C. 
  LAPWORTH 
  ON 
  THE 
  GIRVAN 
  SUCCESSION. 
  663 
  

  

  i. 
  The 
  Girvan 
  succession 
  of 
  Lower 
  Palaeozoic 
  rocks 
  consists 
  of 
  a 
  

   generally 
  continuous 
  series 
  of 
  more 
  or 
  less 
  fossiliferous 
  strata 
  of 
  a 
  

   collective 
  thickness 
  of 
  7000 
  feet. 
  

  

  ii. 
  It 
  is 
  divisible 
  into 
  four 
  main 
  rock-formations, 
  each 
  of 
  which 
  is 
  

   individualized 
  by 
  special 
  petrological 
  and 
  palasontological 
  charac- 
  

   teristics. 
  

  

  iii. 
  Each 
  of 
  these 
  formations 
  is, 
  again, 
  made 
  up 
  of 
  several 
  subor- 
  

   dinate 
  members, 
  whose 
  relations 
  to 
  the 
  subformations 
  above 
  and 
  

   below 
  are 
  beyond 
  dispute, 
  and 
  which 
  retain 
  their 
  special 
  charac- 
  

   teristics 
  both 
  in 
  rocks 
  and 
  fossils 
  wherever 
  they 
  are 
  laid 
  open 
  for 
  

   investigation 
  within 
  the 
  district. 
  

  

  The 
  detailed 
  classification 
  of 
  these 
  Lower 
  Palaeozoic 
  strata 
  of 
  

   Girvan, 
  as 
  developed 
  in 
  the 
  preceding 
  pages, 
  is 
  given 
  in 
  the 
  Table, 
  

   fig. 
  31, 
  pp. 
  660, 
  661. 
  

  

  (5) 
  These 
  Girvan 
  rocks 
  appear 
  to 
  repose, 
  at 
  their 
  base, 
  upon 
  the 
  

   generally 
  older 
  igneous 
  and 
  altered 
  rocks 
  of 
  Ballantrae. 
  The 
  Bal- 
  

   lantrae 
  rocks 
  have, 
  as 
  yet, 
  been 
  too 
  imperfectly 
  studied 
  to 
  allow 
  us 
  

   to 
  hazard 
  any 
  conclusion 
  respecting 
  their 
  true 
  geological 
  age. 
  That 
  

   many 
  of 
  the 
  rocks 
  grouped 
  together 
  under 
  this 
  title 
  are 
  of 
  far 
  

   greater 
  antiquity 
  than 
  the 
  basement-beds 
  of 
  the 
  Girvan 
  succession 
  

   may 
  be 
  regarded 
  as 
  established 
  by 
  the 
  fact 
  that 
  fragments 
  of 
  the 
  

   Ballantrae 
  rocks 
  occur 
  in 
  the 
  Kirkland 
  or 
  Purple 
  Conglomerate 
  at 
  

   the 
  base 
  of 
  the 
  Girvan 
  sequence. 
  These 
  pre-Girvan 
  traps 
  and 
  ashes 
  

   must 
  either 
  represent 
  the 
  Arenig 
  and 
  Llandeilo 
  volcanic 
  rocks 
  of 
  

   "Wales 
  and 
  Cumberland 
  or 
  must 
  be 
  of 
  more 
  ancient 
  date. 
  On 
  the 
  

   other 
  hand, 
  rocks 
  which 
  are 
  unquestionably 
  of 
  true 
  Girvan 
  age 
  

   occur 
  at 
  many 
  localities 
  within 
  the 
  typical 
  Ballantrae 
  region 
  itself, 
  

   while 
  the 
  patches 
  of 
  altered 
  or 
  so-called 
  Ballantrae 
  rocks 
  found 
  

   outside 
  that 
  area, 
  as 
  at 
  Shalloch 
  Hill, 
  Laggan 
  Hill, 
  and 
  elsewhere, 
  

   almost 
  certainly 
  include 
  some 
  greatly 
  altered 
  Girvan 
  rocks. 
  

  

  (6) 
  The 
  sequence 
  among 
  the 
  Girvan 
  fossiliferous 
  rocks 
  is 
  broken 
  

   by 
  at 
  least 
  one 
  fairly 
  distinct 
  unconformability, 
  viz. 
  that 
  at 
  the 
  base 
  

   of 
  the 
  Craigskelly 
  conglomerate 
  ; 
  but 
  the 
  presence 
  of 
  boulder-beds 
  

   at 
  the 
  base 
  of 
  the 
  Mulloch-Hill 
  group, 
  at 
  the 
  base 
  of 
  the 
  Saugh- 
  

   Hill 
  Grits, 
  and 
  elsewhere, 
  renders 
  it 
  exceedingly 
  probable 
  that 
  

   other 
  local 
  stratigraphical 
  breaks 
  may 
  eventually 
  be 
  detected. 
  

  

  These 
  local 
  unconformities, 
  however, 
  can 
  be 
  of 
  no 
  great 
  syste- 
  

   matic 
  importance 
  ; 
  for 
  the 
  general 
  gradation, 
  both 
  in 
  sediments 
  and 
  

   fossils, 
  from 
  the 
  base 
  to 
  the 
  summit 
  of 
  the 
  Girvan 
  succession 
  is 
  

   practically 
  complete. 
  Each 
  distinct 
  petrological 
  formation 
  in 
  the 
  

   vertical 
  series 
  is 
  connected 
  with 
  its 
  neighbours, 
  both 
  above 
  and 
  

   below, 
  by 
  a 
  group 
  of 
  beds 
  intermediate 
  both 
  in 
  physical 
  and 
  in 
  

   zoological 
  features. 
  Thus 
  the 
  very 
  distinct 
  formations 
  of 
  the 
  Stinchar 
  

   Limestone 
  and 
  the 
  Benan 
  Conglomerate 
  graduate 
  into 
  each 
  other 
  

   through 
  the 
  transitional 
  zone 
  of 
  the 
  Didymofjraj)tus-heds 
  (Ab 
  l 
  ), 
  the 
  

   Benan 
  and 
  Ardwell 
  series 
  through 
  the 
  transitional 
  Balclatchie 
  group, 
  

   the 
  Ardwell 
  and 
  Whitehouse 
  beds 
  through 
  the 
  intermediary 
  Cascade 
  

   beds, 
  and 
  so 
  on. 
  Even 
  the 
  two 
  grand 
  divisions 
  of 
  the 
  succession, 
  

   the 
  Upper 
  and 
  Lower 
  divisions 
  of 
  the 
  Girvan 
  rocks, 
  are 
  united 
  by 
  

   the 
  intermediary 
  formation 
  of 
  the 
  Mulloch-Hill 
  beds. 
  

  

  