﻿Vol. 
  53.] 
  THE 
  POIiTKAIKE 
  IXLIEB. 
  (CO. 
  DUJBLIx). 
  539 
  

  

  genal 
  angles, 
  the 
  pits 
  are 
  arranged 
  as 
  in 
  the 
  type-form, 
  but 
  the 
  pits 
  

   in 
  the 
  two 
  outer 
  concentric 
  rows 
  lie 
  in 
  short, 
  regular, 
  radiating 
  

   grooves 
  with 
  intervening 
  ridges, 
  thus 
  resembling 
  Tr. 
  fimbriatus, 
  but 
  

   differing 
  therein 
  that 
  the 
  grooves 
  do 
  not 
  extend 
  to 
  the 
  edge 
  of 
  the 
  

   limb. 
  

  

  In 
  front 
  of 
  the 
  glabella 
  the 
  pits 
  of 
  the 
  three 
  outer 
  rows 
  lie 
  in 
  

   these 
  radiating 
  grooves, 
  but 
  behind 
  them, 
  and 
  also 
  on 
  the 
  upturned 
  

   portion 
  of 
  the 
  limb, 
  lie 
  one 
  or 
  two 
  independent 
  rows 
  of 
  pits 
  not 
  in 
  

   grooves. 
  In 
  front 
  of 
  the 
  glabella 
  and 
  cheeks 
  the 
  inner 
  convex 
  portion 
  

   of 
  the 
  limb 
  also 
  has 
  three 
  or 
  four 
  concentric 
  rows 
  of 
  pits 
  arranged 
  in 
  

   similar 
  radiating 
  grooves, 
  as 
  in 
  the 
  variety 
  of 
  Tr. 
  seticornis 
  from 
  the 
  

   limestone 
  at 
  the 
  spot 
  marked 
  C. 
  

  

  EXPLANATION 
  OF 
  PLATES 
  XLII 
  & 
  XLHI. 
  

  

  Plate 
  XLII. 
  

  

  Section 
  along 
  the 
  coast, 
  Portraine 
  (Co. 
  Dublin), 
  on 
  the 
  scale 
  of 
  

   12 
  inches 
  to 
  1 
  mile. 
  

  

  Plat 
  e 
  XLII 
  I. 
  

   Geological 
  Map 
  of 
  the 
  Portraine 
  Inlier 
  on 
  the 
  scale 
  of 
  4 
  inches 
  to 
  1 
  mile. 
  

  

  Discussion. 
  

  

  Mr. 
  Lampltjgh 
  was, 
  in 
  the 
  main, 
  able 
  from 
  personal 
  observation, 
  

   under 
  the 
  guidance 
  of 
  Mr. 
  McHenry, 
  to 
  corroborate 
  the 
  Authors 
  as 
  

   to 
  the 
  effect 
  of 
  earth-movement 
  in 
  these 
  sections. 
  The 
  readiness 
  of 
  

   the 
  thin-bedded 
  limestones 
  to 
  break 
  up 
  into 
  crush 
  -conglomerate 
  was 
  

   striking. 
  In 
  areas 
  affected 
  by 
  shearing, 
  he 
  thought 
  that 
  the 
  origin 
  

   of 
  every 
  conglomerate 
  should 
  be 
  carefully 
  investigated, 
  and 
  was 
  glad 
  

   to 
  find 
  that 
  this 
  was 
  the 
  attitude 
  of 
  the 
  Authors. 
  Though 
  the 
  lower 
  

   ashy 
  conglomerate 
  might 
  have 
  been 
  an 
  originally 
  fragmental 
  deposit, 
  

   he 
  thought 
  that 
  it 
  had 
  undergone 
  some 
  subsequent 
  modification. 
  

   To 
  distinguish 
  between 
  the 
  original 
  and 
  the 
  superimposed 
  structure 
  

   in 
  such 
  cases 
  was, 
  as 
  he 
  knew 
  by 
  experience, 
  difficult. 
  He 
  doubted 
  

   whether 
  the 
  distinction 
  drawn 
  by 
  the 
  Authors 
  between 
  crush- 
  

   conglomerate 
  and 
  thrust- 
  conglomerate 
  could 
  be 
  generally 
  main- 
  

   tained. 
  

  

  Mr. 
  W. 
  W. 
  Watts 
  also 
  spoke, 
  and 
  Mr. 
  C. 
  I. 
  Gardiner 
  replied. 
  

  

  