﻿V°1- 
  53'^ 
  THE 
  P0RTRA1NE 
  INLIER 
  (CO. 
  DUBLIN). 
  525 
  

  

  two 
  points 
  on 
  the 
  coast 
  south-east; 
  of 
  the 
  martello 
  tower 
  men- 
  

   tioned 
  above, 
  and, 
  for 
  reasons 
  which 
  we 
  give, 
  we 
  consider 
  it 
  to 
  

   be 
  due 
  to 
  earth-movements. 
  It 
  was 
  natural, 
  therefore, 
  that 
  the 
  idea 
  

   should 
  suggest 
  itself 
  that 
  this 
  conglomerate 
  north 
  of 
  the 
  martello 
  

   tower, 
  which 
  we 
  have 
  just 
  described, 
  should 
  be 
  due 
  to 
  similar 
  

   causes. 
  But 
  the 
  observations 
  which 
  we 
  made 
  in 
  the 
  field 
  and 
  

   under 
  the 
  microscope 
  forbade 
  us 
  maintaining 
  that 
  idea. 
  

  

  In 
  the 
  first 
  place, 
  there 
  occur 
  in 
  the 
  conglomerate 
  the 
  two 
  bands 
  of 
  

   limestone 
  and 
  accompanying 
  shale 
  which 
  we 
  have 
  mentioned. 
  Now, 
  

   if 
  the 
  conglomerate 
  owed 
  its 
  existence 
  to 
  earth-movements, 
  it 
  is 
  

   difficult 
  to 
  see 
  how 
  these 
  thin 
  bands 
  of 
  limestone 
  and 
  shale 
  would 
  

   have 
  preserved 
  their 
  continuity 
  and 
  have 
  shown 
  such 
  slight 
  signs 
  

   of 
  being 
  greatly 
  squeezed 
  and 
  fractured, 
  while 
  hard 
  igneous 
  rocks 
  

   and 
  compact 
  ash 
  -beds 
  were 
  broken 
  up 
  into 
  fragments. 
  

  

  The 
  very 
  definite 
  nature 
  of 
  the 
  blocks 
  forming 
  the 
  conglomerate 
  at 
  

   different 
  points 
  is 
  another 
  objection 
  to 
  the 
  idea. 
  We 
  have 
  men- 
  

   tioned 
  that 
  the 
  blocks 
  are 
  at 
  first 
  chiefly 
  of 
  the 
  nature 
  of 
  ashes 
  and 
  

   limestones, 
  while 
  at 
  the 
  top 
  of 
  the 
  conglomerate 
  they 
  are 
  largely 
  of 
  

   the 
  nature 
  of 
  porphyrites 
  and 
  andesites. 
  The 
  bed 
  on 
  which 
  the 
  

   conglomerate 
  rests 
  is 
  an 
  andesite, 
  yet 
  very 
  few 
  blocks 
  of 
  andesite 
  

   are 
  found 
  in 
  the 
  lower 
  parts 
  of 
  the 
  conglomerate. 
  No 
  squeezing 
  or 
  

   drawing 
  out 
  of 
  the 
  blocks 
  is 
  to 
  be 
  seen 
  in 
  the 
  main 
  mass 
  of 
  the 
  rock. 
  

   Microscopic 
  investigation 
  points 
  in 
  the 
  same 
  direction. 
  No 
  minera- 
  

   logical 
  alteration 
  is 
  apparent, 
  though 
  this 
  is 
  not 
  a 
  point 
  on 
  which 
  

   much 
  stress 
  can 
  be 
  laid, 
  considering 
  the 
  very 
  slight 
  traces 
  of 
  

   such 
  alteration 
  that 
  can 
  be 
  observed 
  in 
  the 
  undoubted 
  thrust- 
  

   conglomerates 
  along 
  the 
  coast. 
  But 
  the 
  microscope 
  does 
  not 
  reveal 
  

   either 
  any 
  such 
  crushing 
  or 
  drawing 
  out 
  of 
  the 
  materials 
  of 
  which 
  

   the 
  groundmass 
  is 
  made 
  as 
  might 
  be 
  expected 
  if 
  this 
  were 
  a 
  thrust- 
  

   conglomerate. 
  The 
  groundmass 
  is 
  seen 
  to 
  be 
  of 
  the 
  nature 
  of 
  an 
  

   ash, 
  beaig 
  formed 
  of 
  angular 
  fragments 
  of 
  lavas. 
  

  

  It 
  is 
  true 
  that 
  near 
  the 
  martello 
  tower 
  disturbance 
  does 
  begin 
  to 
  

   be 
  visible, 
  and 
  the 
  finer 
  beds 
  overlying 
  the 
  conglomerate 
  show 
  signs 
  

   of 
  bending, 
  but 
  this 
  phenomenon 
  appears 
  to 
  be 
  very 
  local 
  and 
  to 
  be 
  

   connected 
  with 
  the 
  movement 
  which 
  brought 
  the 
  limestone-and- 
  

   shale 
  series 
  under 
  the 
  martello 
  tower 
  into 
  its 
  present 
  position. 
  

  

  If 
  the 
  conglomerate 
  were 
  due 
  to 
  earth-movements, 
  it 
  is 
  difficult 
  

   to 
  see 
  why 
  the 
  overlying 
  bands 
  of 
  limestone 
  and 
  ash 
  were 
  not 
  bent 
  

   and 
  fractured, 
  so 
  that 
  a 
  passage 
  between 
  the 
  two 
  beds 
  could 
  be 
  

   observed. 
  

  

  These 
  are 
  the 
  most 
  important 
  reasons 
  that 
  led 
  us 
  to 
  conclude 
  that 
  

   this 
  conglomerate 
  is 
  not 
  one 
  due 
  to 
  earth 
  -movements, 
  but 
  is 
  a 
  

   sedimentary 
  conglomerate, 
  with 
  a 
  matrix 
  largely 
  made 
  up 
  of 
  angular 
  

   fragments 
  of 
  lava. 
  

  

  IV. 
  The 
  Igneous 
  Rocks 
  at 
  the 
  Southern 
  End 
  of 
  the 
  Inliek. 
  

  

  (a) 
  Those 
  exposed 
  along 
  the 
  Shore. 
  

  

  At 
  the 
  southern 
  end 
  of 
  the 
  area, 
  near 
  the 
  southern 
  martello 
  tower, 
  

   igneous 
  rocks 
  are 
  again 
  exposed 
  on 
  the 
  foreshore. 
  These 
  rocks 
  are 
  

  

  