﻿Vol. 
  53.] 
  THE 
  PORTRAINE 
  1NLIER 
  (CO. 
  DUBLIN). 
  535 
  

  

  Portraine 
  to 
  show, 
  but 
  the 
  coarse 
  breccias 
  and 
  tuffs 
  of 
  Lambay 
  

   Island 
  seem 
  to 
  indicate 
  that 
  one 
  of 
  the 
  centres 
  of 
  vulcanicity 
  lay 
  to 
  

   the 
  east. 
  

  

  While 
  the 
  interest 
  attaching 
  to 
  these 
  Bala 
  beds 
  and 
  to 
  their 
  

   relation 
  to 
  English 
  and 
  Welsh 
  rocks 
  is 
  great, 
  the 
  importance 
  of 
  

   the 
  area 
  as 
  a 
  whole 
  is 
  enhanced 
  by 
  the 
  presence 
  of 
  rocks 
  of 
  a 
  

   conglomeratic 
  nature 
  formed 
  at 
  a 
  later 
  date. 
  

  

  In 
  a 
  paper 
  read 
  before 
  this 
  Society 
  in 
  1895 
  by 
  Messrs. 
  Lamplugh 
  

   & 
  W^atts 
  attention 
  was 
  drawn 
  to 
  crush-conglomerates 
  in 
  the 
  Isle 
  of 
  

   Man, 
  and 
  there 
  seem 
  to 
  be 
  many 
  points 
  of 
  resemblance 
  between 
  the 
  

   Portraine 
  and 
  the 
  Isle 
  of 
  Man 
  conglomerates. 
  In 
  both 
  cases 
  hard 
  

   beds 
  which 
  occur 
  among 
  beds 
  of 
  shale 
  have 
  been 
  cracked, 
  pulled 
  

   asunder, 
  and 
  converted 
  into 
  a 
  conglomeratic 
  deposit 
  ; 
  in 
  the 
  one 
  

   case 
  these 
  hard 
  beds 
  are 
  formed 
  of 
  limestone, 
  and 
  in 
  the 
  other 
  of 
  

   sandstone. 
  In 
  both 
  cases, 
  too, 
  shearing 
  has 
  taken 
  place, 
  and 
  along 
  

   the 
  thrust-planes 
  conglomerates 
  have 
  been 
  developed. 
  But 
  the 
  

   amount 
  of 
  actual 
  deformation 
  of 
  the 
  broken 
  pieces 
  of 
  the 
  hard 
  beds 
  

   at 
  Portraine 
  seems 
  to 
  have 
  been 
  quite 
  trifling 
  when 
  compared 
  with 
  

   that 
  which 
  has 
  occurred 
  in 
  the 
  Isle 
  of 
  Man, 
  and 
  this 
  appears 
  to 
  be 
  a 
  

   very 
  important 
  point. 
  The 
  amount 
  of 
  mineralogical 
  reconstruction 
  

   seems 
  also 
  very 
  small. 
  Either 
  the 
  nature 
  of 
  the 
  beds 
  at 
  Portraine 
  

   did 
  not 
  readily 
  lend 
  itself 
  to 
  alteration, 
  or 
  the 
  time 
  occupied 
  in 
  the 
  

   formation 
  of 
  the 
  conglomerate 
  was 
  long 
  ; 
  and 
  thus 
  the 
  heat 
  en- 
  

   gendered 
  had 
  time 
  to 
  be 
  conducted 
  away 
  before 
  the 
  rocks 
  had 
  arrived 
  

   at 
  a 
  sufficiently 
  high 
  temperature 
  for 
  mineralogical 
  alteration. 
  The 
  

   occasional 
  occurrence 
  of 
  sericite 
  is 
  the 
  only 
  evidence 
  of 
  mineralogical 
  

   reconstruction 
  due 
  to 
  the 
  crushing. 
  

  

  In 
  conclusion, 
  we 
  wish 
  to 
  express 
  our 
  sincere 
  thanks 
  to 
  Mr. 
  E. 
  

   E. 
  Cowper 
  Eeed, 
  E.G.S., 
  for 
  his 
  assistance 
  in 
  the 
  identification 
  of 
  our 
  

   fossils 
  and 
  for 
  writing 
  the 
  Appendix 
  to 
  this 
  paper. 
  At 
  the 
  same 
  

   time 
  we 
  would 
  thank 
  Miss 
  Elles 
  and 
  Miss 
  Wood 
  for 
  having 
  identified 
  

   our 
  graptolites 
  ; 
  Mr. 
  Alfred 
  Harker, 
  E.G.S., 
  for 
  looking 
  over 
  some 
  of 
  

   our 
  rock-sections 
  ; 
  Mr. 
  W. 
  W. 
  Watts, 
  F.G.S., 
  for 
  having 
  assisted 
  us 
  

   in 
  many 
  ways 
  ; 
  and 
  Mr. 
  H. 
  Preston, 
  F.G.S., 
  for 
  having 
  allowed 
  

   us 
  to 
  make 
  use 
  of 
  his 
  photographs 
  of 
  the 
  coast. 
  We 
  also 
  gratefully 
  

   acknowledge 
  the 
  kindness 
  of 
  the 
  authorities 
  of 
  the 
  Irish 
  Geological 
  

   Survey 
  in 
  giving 
  us 
  every 
  facility 
  for 
  examining 
  their 
  collection 
  of 
  

   fossils. 
  

  

  Appendix. 
  By 
  F. 
  R. 
  Cowper 
  Reed, 
  Esq., 
  M.A., 
  F.G.S. 
  

   (a) 
  Fossils 
  from 
  the 
  Limestone 
  at 
  point 
  C 
  in 
  the 
  Map. 
  

  

  Trilobita. 
  — 
  The 
  fauna 
  of 
  this 
  limestone 
  consists 
  principally 
  of 
  

   trilobites, 
  which 
  both 
  in 
  species 
  and 
  individuals 
  form 
  the 
  majority 
  

   of 
  the 
  fossils. 
  The 
  following 
  is 
  the 
  list 
  of 
  the 
  trilobites, 
  but 
  the 
  

   extremely 
  fragmentary 
  condition 
  of 
  most 
  of 
  the 
  specimens 
  rendered 
  

   their 
  identification 
  a 
  matter 
  of 
  much 
  difficultv 
  : 
  — 
  

  

  