﻿270 
  MR. 
  F. 
  R. 
  COWPER 
  REED 
  ON 
  THE 
  RED 
  ROCKS 
  [May 
  1 
  89 
  7, 
  

  

  groups 
  of 
  these 
  beds 
  ' 
  clearly 
  interstratified 
  with 
  the 
  Lower 
  Silurian 
  ' 
  

   rocks 
  and 
  folded 
  with 
  them. 
  

  

  Mr. 
  Kinahan, 
  1 
  however, 
  in 
  1878, 
  pointed 
  out 
  that 
  they 
  lay 
  

   un 
  conform 
  ably 
  on 
  the 
  ' 
  Cambro-Silurian 
  ' 
  rocks, 
  and 
  ascribed 
  them 
  

   with 
  some 
  hesitation 
  to 
  the 
  ' 
  Lower 
  Carboniferous 
  ' 
  ( 
  = 
  Old 
  Red 
  

   Sandstone). 
  

  

  The 
  same 
  writer 
  in 
  1887 
  2 
  speaks 
  of 
  these 
  red 
  beds 
  as 
  lying 
  on 
  

   or 
  partly 
  in 
  the 
  Ordovician, 
  and 
  says 
  that 
  they 
  ' 
  must 
  be 
  either 
  of 
  

   Silurian 
  or 
  Devonian 
  age, 
  probably 
  the 
  latter 
  — 
  that 
  is, 
  small 
  

   outliers 
  of 
  the 
  Comeragh 
  conglomerates.' 
  In 
  1889 
  he 
  writes 
  3 
  of 
  

   the 
  Knockmahon 
  conglomerate 
  lying 
  unconformably 
  on 
  the 
  Ordo- 
  

   vician, 
  but 
  observes 
  that 
  farther 
  west 
  the 
  red 
  beds 
  appear 
  as 
  isolated 
  

   masses 
  in 
  the 
  Ordovician. 
  

  

  Sir 
  Archibald 
  Geikie, 
  in 
  his 
  Presidential 
  Address 
  to 
  the 
  Geological 
  

   Society 
  4 
  in 
  1891, 
  hesitated 
  to 
  express 
  a 
  decided 
  opinion, 
  but 
  seemed 
  

   to 
  incline 
  to 
  the 
  view 
  that 
  they 
  were 
  not 
  of 
  Lower 
  Silurian 
  age. 
  

  

  II. 
  General 
  Structure 
  oe 
  the 
  District. 
  

  

  If 
  we 
  first 
  glance 
  at 
  the 
  characters 
  and 
  distribution 
  of 
  the 
  

   undoubted 
  Lower 
  Silurian 
  and 
  Old 
  Eed 
  Sandstone 
  rocks, 
  and 
  at 
  the 
  

   general 
  structure 
  of 
  the 
  district, 
  we 
  shall 
  be 
  in 
  a 
  better 
  position 
  to 
  

   attack 
  the 
  problem. 
  

  

  The 
  Lower 
  Silurian 
  (Ordovician) 
  is 
  represented 
  in 
  this 
  part 
  of 
  

   Ireland 
  by 
  a 
  great 
  assemblage 
  of 
  igneous 
  rocks, 
  together 
  with 
  

   sedimentary 
  beds 
  comprising 
  black, 
  grey, 
  greenish, 
  and 
  buff 
  slates 
  

   and 
  mudstones, 
  and 
  a 
  few 
  thin 
  limestones. 
  The 
  igneous 
  rocks 
  

   largely 
  preponderate, 
  and 
  consist 
  of 
  contemporaneous 
  lavas, 
  ashes, 
  

   and 
  agglomerates 
  pierced 
  by 
  intrusive 
  sheets, 
  dykes, 
  and 
  irregular 
  

   masses, 
  and 
  occasionally 
  by 
  breccia-filled 
  'pipes/ 
  belonging 
  to 
  

   several 
  more 
  or 
  less 
  distinct 
  periods 
  of 
  irruption. 
  

  

  The 
  sedimentary 
  members 
  of 
  this 
  system 
  nowhere 
  assume 
  in 
  this 
  

   district 
  the 
  character 
  of 
  red 
  sandstones, 
  etc., 
  if 
  we 
  except 
  for 
  the 
  

   moment 
  these 
  disputed 
  patches 
  on 
  the 
  coast. 
  Prima 
  facie, 
  therefore, 
  

   we 
  might 
  well 
  hesitate 
  to 
  include 
  these 
  isolated 
  masses 
  in 
  the 
  

   Ordovician. 
  If 
  they 
  be 
  really 
  interbedded 
  with 
  the 
  Ordovician 
  Series, 
  

   we 
  might 
  reasonably 
  expect 
  that 
  deposits 
  possessing 
  such 
  well-marked 
  

   and 
  distinctive 
  characters 
  and 
  so 
  great 
  a 
  thickness 
  would 
  give 
  

   indications 
  of 
  their 
  presence 
  elsewhere, 
  especially 
  as 
  the 
  Ordovician 
  

   strata 
  of 
  the 
  district 
  seem 
  to 
  be 
  repeated 
  by 
  a 
  series 
  of 
  folds 
  ; 
  but 
  

   such 
  is 
  not 
  the 
  case, 
  for 
  nowhere 
  else 
  in 
  the 
  county 
  do 
  we 
  

   meet 
  with 
  red 
  rocks 
  which 
  can 
  be 
  ascribed 
  by 
  anyone 
  to 
  any 
  for- 
  

   mation 
  but 
  the 
  Old 
  Eed 
  Sandstone. 
  

  

  The 
  Old 
  Eed 
  Sandstone 
  of 
  the 
  county 
  itself 
  rests 
  everywhere 
  

  

  1 
  ' 
  Geology 
  of 
  Ireland,' 
  1878, 
  p. 
  28. 
  

  

  2 
  Sci. 
  Proc. 
  Eoy. 
  Dubl. 
  Soc. 
  vol. 
  v. 
  (1887) 
  p. 
  611. 
  

  

  3 
  Ibid. 
  vol. 
  vi. 
  (1889) 
  p. 
  283. 
  

  

  4 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xlvii. 
  (1891) 
  Proc. 
  p. 
  158. 
  

  

  5 
  Eed 
  conglomerates 
  of 
  a 
  similar 
  character 
  are 
  said 
  to 
  appear 
  in 
  the 
  Lower 
  

   Silurian 
  (Ordovician) 
  slates 
  of 
  Tagoat, 
  Co. 
  Wexford, 
  but 
  their 
  relations 
  have 
  

   not 
  been 
  clearly 
  described, 
  and 
  I 
  have 
  been 
  unable 
  to 
  visit 
  the 
  spot. 
  

  

  