﻿568 
  PROF. 
  C. 
  LAPWORTH 
  ON 
  THE 
  GTRVAN 
  SUCCESSION. 
  

  

  in 
  abundance 
  in 
  the 
  conglomerate 
  itself. 
  But 
  the 
  line 
  of 
  contact 
  is 
  

   clearly 
  a 
  fault, 
  while 
  the 
  patches 
  of 
  lime 
  in 
  the 
  conglomerate 
  lie 
  in 
  

   regular 
  seams, 
  and 
  have 
  the 
  appearance 
  of 
  being 
  merely 
  nodular 
  

   concretions, 
  as 
  if 
  the 
  conditions 
  favourable 
  to 
  the 
  deposition 
  of 
  

   calcareous 
  matter, 
  which 
  marked 
  the 
  epoch 
  of 
  the 
  formation 
  of 
  the 
  

   limestone 
  series, 
  were 
  continued 
  into 
  the 
  earlier 
  stages 
  of 
  the 
  

   period 
  in 
  which 
  the 
  Benan 
  Conglomerate 
  was 
  laid 
  down. 
  

  

  That 
  this 
  is 
  the 
  correct 
  interpretation 
  is 
  placed 
  beyond 
  question 
  

   by 
  a 
  careful 
  comparison 
  of 
  the 
  phenomena 
  presented 
  by 
  the 
  suc- 
  

   ceeding 
  quarries 
  to 
  the 
  north-west 
  of 
  this 
  locality. 
  In 
  some 
  of 
  these 
  

   the 
  Didymograptus-shales 
  (Ab 
  4 
  ) 
  are 
  lost 
  through 
  faulting 
  ; 
  in 
  others 
  

   they 
  are 
  well 
  displayed, 
  and 
  are 
  found 
  to 
  possess 
  all 
  their 
  usual 
  

   characters, 
  lithological 
  and 
  palaeontological. 
  Sections 
  of 
  the 
  two 
  

   most 
  important 
  of 
  these 
  exposures 
  are 
  given 
  on 
  the 
  opposite 
  page. 
  

  

  In 
  the 
  first 
  of 
  these 
  (fig. 
  6) 
  the 
  Didymograptus-shales 
  (Ab 
  4 
  ) 
  are 
  

   formed 
  of 
  a 
  group 
  of 
  greenish 
  shales 
  and 
  impure 
  nodular 
  limestones, 
  

   and 
  lie, 
  precisely 
  as 
  in 
  the 
  Stinchar 
  valley, 
  between 
  the 
  Compact 
  

   Limestones 
  and 
  the 
  Benan 
  Conglomerates. 
  The 
  basal 
  beds 
  of 
  the 
  

   latter 
  are 
  filled 
  with 
  limestone 
  nodules, 
  arranged 
  generally 
  along 
  the 
  

   lines 
  of 
  stratification, 
  and 
  weather 
  to 
  a 
  light 
  yellow 
  or 
  orange-colour. 
  

  

  In 
  the 
  second 
  (fig. 
  7) 
  the 
  Didymograptus-zone 
  is 
  most 
  effectively 
  

   displayed, 
  and 
  is 
  seen 
  to 
  be 
  composed, 
  as 
  usual, 
  of 
  bands 
  of 
  grey 
  and 
  

   green 
  shales, 
  which 
  graduate 
  from 
  the 
  Compact 
  Limestones 
  below, 
  

   through 
  a 
  series 
  of 
  nodular 
  beds, 
  into 
  the 
  Benan 
  Conglomerate 
  above, 
  

   the 
  basal 
  zones 
  of 
  the 
  latter 
  being 
  filled 
  with 
  seams 
  and 
  patches 
  

   of 
  calcareous 
  nodules, 
  and 
  weathering 
  of 
  the 
  usual 
  buff 
  or 
  orange 
  

   tint. 
  

  

  The 
  Didymograptus-shales 
  themselves 
  yield 
  the 
  characteristic 
  

   fossils 
  Didymograptus 
  super 
  stes, 
  Climacograptus 
  nanus, 
  Acrotreta 
  

   Nichohoni, 
  &e. 
  

  

  Summary. 
  — 
  Our 
  study 
  of 
  this 
  portion 
  of 
  the 
  Dupin-Brockloch 
  

   band 
  has 
  taught 
  us 
  that 
  along 
  this 
  line 
  there 
  is 
  no 
  line 
  of 
  irregular 
  

   erosion 
  at 
  the 
  base 
  of 
  the 
  Benan 
  Conglomerate. 
  In 
  Dupin, 
  mid- 
  

   way 
  along 
  its 
  course, 
  the 
  Didymograptus-hedLS 
  (Ab 
  4 
  ) 
  are 
  present 
  in 
  

   force, 
  and 
  with 
  their 
  typical 
  aspect 
  as 
  exhibited 
  in 
  the 
  Minuntion 
  

   and 
  Stinchar 
  area. 
  As 
  we 
  pass 
  eastward 
  along 
  the 
  deserted 
  quarries 
  

   of 
  Brockloch 
  and 
  Craigwells, 
  their 
  place 
  is 
  distinctly 
  occupied 
  by 
  

   a 
  thin 
  group 
  of 
  nodular 
  limestones 
  and 
  Graptolitic 
  shales, 
  sur- 
  

   mounted 
  by 
  conglomerates 
  full 
  of 
  seams 
  and 
  balls 
  of 
  calcareous 
  

   matter. 
  These 
  overlying 
  beds, 
  though 
  they 
  appear 
  to 
  be 
  derived 
  

   partially 
  from 
  the 
  reconstructed 
  debris 
  of 
  the 
  calcareous 
  series, 
  are 
  

   rather 
  interpretable 
  as 
  evidence 
  that 
  the 
  era 
  between 
  the 
  period 
  

   of 
  deposition 
  of 
  the 
  Stinchar 
  calcareous 
  series 
  and 
  that 
  of 
  the 
  Benan 
  

   Conglomerate 
  was 
  a 
  period 
  of 
  oscillation, 
  and 
  that 
  the 
  lime-pro- 
  

   ducing 
  conditions 
  which 
  prevailed 
  during 
  the 
  time 
  of 
  deposition 
  of 
  

   the 
  Stinchar 
  calcareous 
  series 
  were 
  prolonged 
  into 
  the 
  earlier 
  stages 
  

   of 
  the 
  epoch 
  in 
  which 
  the 
  tumultuous 
  Benan 
  Conglomerate 
  was 
  

   formed. 
  

  

  To 
  the 
  north 
  of 
  that 
  portion 
  of 
  the 
  Dupin-Craigwells 
  limestone 
  

  

  