﻿554 
  PKOE. 
  C. 
  LAPWOETH 
  ON 
  THE 
  GIRT 
  AN 
  SUCCESSION. 
  

  

  subsequently 
  they 
  detected 
  proofs 
  of 
  a 
  possible 
  unconformability 
  at 
  

   the 
  base 
  of 
  the 
  Caradoc 
  beds 
  of 
  the 
  Uplands, 
  this 
  Benan 
  unconforma- 
  

   bility 
  seemed 
  to 
  be 
  very 
  naturally 
  accounted 
  for, 
  and 
  its 
  theoretical 
  

   age 
  was 
  altered 
  to 
  the 
  epoch 
  of 
  the 
  Lower 
  Bala. 
  

  

  Now, 
  to 
  a 
  geologist 
  who 
  studies 
  the 
  strata 
  in 
  a 
  general 
  way, 
  

   the 
  foregoing 
  conclusions 
  are 
  inevitable: 
  and 
  upon 
  this 
  ground 
  

   the 
  officers 
  of 
  the 
  Survey 
  were 
  amply 
  justified 
  in 
  their 
  deductions. 
  

   But 
  when 
  these 
  enigmatical 
  calcareous 
  zones 
  are 
  studied 
  foot 
  by 
  

   foot, 
  and 
  each 
  exposure 
  is 
  compared 
  minutely 
  with 
  its 
  neighbours, 
  

   very 
  different 
  conclusions 
  are 
  arrived 
  at, 
  and 
  the 
  stratigraphist 
  is 
  

   soon 
  delighted 
  to 
  discover 
  incontrovertible 
  proofs 
  of 
  an 
  orderly 
  

   sequence, 
  explanatory 
  of 
  the 
  visible 
  phenomena 
  in 
  every 
  locality, 
  

   and 
  exhibiting 
  the 
  most 
  perfect 
  harmony 
  in 
  all 
  its 
  parts. 
  

  

  Tn 
  the 
  steep 
  slopes 
  of 
  the 
  hills 
  of 
  Benan 
  and 
  Auchensoul, 
  which 
  

   overhang 
  the 
  north 
  bank 
  of 
  the 
  valley 
  of 
  the 
  Stinchar, 
  a 
  line 
  of 
  

   ancient 
  lime- 
  quarries 
  is 
  visible. 
  These 
  mark 
  the 
  place 
  of 
  a 
  thick 
  

   band 
  of 
  limestone, 
  which 
  ranges 
  uninterruptedly 
  from 
  the 
  farmstead 
  

   of 
  Minuntion 
  to 
  that 
  of 
  Auchensoul, 
  a 
  distance 
  of 
  about 
  three 
  

   miles. 
  Throughout 
  this 
  extent, 
  the 
  limestone, 
  beyond 
  occasional 
  

   and 
  insignificant 
  local 
  slips, 
  is 
  unbroken 
  by 
  dislocations, 
  and 
  is 
  

   fully 
  exposed 
  to 
  the 
  investigator 
  in 
  numerous 
  artificial 
  excavations, 
  

   and 
  in 
  the 
  beds 
  and 
  banks 
  of 
  the 
  many 
  little 
  brooklets 
  that 
  drain 
  

   the 
  grassy 
  summits 
  of 
  the 
  Benan 
  Hills. 
  From 
  end 
  to 
  end 
  of 
  this 
  

   line, 
  the 
  limestone 
  plunges 
  into 
  the 
  hill-side 
  at 
  an 
  angle 
  of 
  about 
  

   forty 
  -five 
  degrees, 
  below 
  the 
  wide-spreading 
  and 
  continuous 
  mass 
  of 
  

   coarse 
  Boulder-conglomerate 
  already 
  noticed, 
  of 
  which 
  the 
  higher 
  

   points 
  of 
  Benan 
  Hill 
  and 
  the 
  neighbouring 
  heights 
  are 
  composed. 
  

  

  1. 
  Benan 
  Burn. 
  — 
  About 
  midway 
  along 
  its 
  course 
  the 
  limestone 
  

   and 
  its 
  associated 
  beds 
  are 
  admirably 
  exposed 
  in 
  the 
  banks 
  of 
  the 
  little 
  

   stream 
  of 
  the 
  Benan 
  Burn, 
  where 
  the 
  highly 
  instructive 
  section 
  is 
  

   displayed 
  which 
  is 
  generalized 
  in 
  the 
  accompanying 
  figure 
  (fig. 
  1). 
  

  

  The 
  coarse 
  green 
  boulder-conglomerate 
  of 
  the 
  region, 
  which 
  

   occupies 
  the 
  high 
  ground 
  of 
  the 
  ridge 
  above, 
  forms 
  here 
  a 
  semicircle 
  

   of 
  steep 
  slopes, 
  partly 
  enclosing 
  a 
  cirque-like 
  area 
  in 
  the 
  hill-side, 
  

   where 
  four 
  little 
  streams 
  take 
  origin 
  that 
  unite 
  to 
  form 
  the 
  Benan 
  

   Burn. 
  These 
  steep 
  grass-clad 
  slopes 
  show 
  miniature 
  cliffs 
  of 
  naked 
  

   rock, 
  composed 
  of 
  well-bedded 
  masses 
  of 
  the 
  great 
  Benan 
  conglo- 
  

   merate, 
  showing 
  all 
  its 
  characteristic 
  features 
  and 
  dipping 
  steadily 
  

   into 
  the 
  hill-face 
  at 
  an 
  angle 
  of 
  from 
  forty 
  to 
  fifty 
  degrees. 
  The 
  

   four 
  rills 
  unite 
  in 
  the 
  centre 
  of 
  this 
  cirque-like 
  area 
  ; 
  and 
  a 
  few 
  

   yards 
  above 
  their 
  point 
  of 
  confluence 
  the 
  coarse 
  conglomerate 
  

   suddenly 
  ceases, 
  and 
  the 
  naked 
  banks 
  of 
  the 
  most 
  westerly 
  rill 
  show 
  

   that 
  we 
  have 
  here 
  reached 
  its 
  basal 
  beds, 
  and 
  that 
  they 
  repose 
  upon 
  

   a 
  set 
  of 
  greenish 
  concretionary 
  shales 
  and 
  mudstones 
  having 
  the 
  

   same 
  trend 
  and 
  inclination 
  as 
  the 
  conglomerate 
  itself. 
  

  

  Didymograptus-shales. 
  — 
  These 
  shales 
  (Ab 
  4 
  ) 
  have 
  a 
  collective 
  thick- 
  

   ness 
  of 
  about 
  30 
  feet. 
  They 
  are 
  of 
  a 
  greenish-blue 
  colour, 
  hard, 
  

   nodular, 
  and 
  more 
  or 
  less 
  concretionary 
  in 
  structure, 
  but 
  of 
  a 
  fine 
  

   texture 
  and 
  distinctly 
  laminated. 
  Under 
  the 
  hammer 
  they 
  break 
  

   up 
  into 
  well-rounded 
  nodules 
  and 
  irregularly 
  concentric 
  flakes. 
  They 
  

  

  

  