﻿Vol. 
  53.] 
  THE 
  PORTRAINE 
  INLIER 
  (CO. 
  DUBLIN). 
  531 
  

  

  VI. 
  The 
  Grit 
  Series. 
  

  

  Between 
  Priest's 
  Chamber 
  and 
  St. 
  Kenny's 
  Well, 
  a 
  distance 
  of 
  

   about 
  600 
  yards, 
  the 
  coast 
  is 
  formed 
  of 
  green 
  and 
  brown 
  grits 
  and 
  

   slates, 
  which 
  dip, 
  on 
  the 
  whole, 
  E. 
  20° 
  S., 
  but 
  roll 
  slightly. 
  The 
  

   coast-line 
  in 
  the 
  main 
  follows 
  the 
  strike, 
  and 
  only 
  about 
  220 
  feet 
  

   is 
  seen. 
  There 
  is 
  a 
  marked 
  discordance, 
  as 
  observed 
  by 
  the 
  

   officers 
  of 
  the 
  Geological 
  Survey, 
  between 
  the 
  dip 
  of 
  the 
  series 
  and 
  

   the 
  dip 
  of 
  the 
  cleavage 
  of 
  the 
  interbedded 
  slate-bands. 
  These 
  

   beds 
  yielded 
  no 
  fossils, 
  and 
  are 
  separated 
  by 
  a 
  mass 
  of 
  thrust- 
  

   conglomerate 
  from 
  the 
  underlying 
  limestone 
  series, 
  so 
  that 
  we 
  have 
  

   no 
  direct 
  evidence 
  of 
  their 
  age, 
  but 
  their 
  resemblance 
  to 
  the 
  grits 
  

   and 
  slates 
  which 
  occur 
  near 
  Balbriggan, 
  some 
  8 
  miles 
  to 
  the 
  

   north, 
  is 
  worth 
  noting. 
  These 
  latter 
  beds 
  contain 
  bands 
  of 
  black 
  

   slate 
  yielding 
  Monograptus 
  Becki, 
  M. 
  triangulatus, 
  M. 
  Hisingeri, 
  

   M. 
  jaculum, 
  Diplograptus 
  tamariscus, 
  and 
  Petalograptus 
  palmeus, 
  

   and 
  apparently 
  therefore 
  belong 
  to 
  the 
  Middle 
  or 
  Lower 
  Birkhill 
  

   Series. 
  1 
  

  

  Two 
  small 
  exposures 
  of 
  grit 
  occur 
  a 
  short 
  distance 
  inland, 
  and 
  

   the 
  spring 
  at 
  St. 
  Kenny's 
  Well 
  is 
  probably 
  thrown 
  out 
  at 
  the 
  base 
  

   of 
  the 
  series. 
  

  

  VII. 
  The 
  Conglomerates 
  due 
  to 
  Earth-movements. 
  

  

  The 
  strip 
  of 
  coast 
  which 
  we 
  are 
  describing 
  has 
  been 
  subjected 
  to 
  

   so 
  much 
  disturbance 
  that 
  conglomerate-like 
  rocks 
  produced 
  by 
  earth- 
  

   movements 
  occur 
  almost 
  wherever 
  the 
  lithological 
  character 
  of 
  the 
  

   beds 
  admits 
  of 
  their 
  being 
  formed. 
  

  

  These 
  beds, 
  as 
  already 
  noted 
  (p. 
  527), 
  we 
  divide 
  into 
  two 
  classes: 
  

   (a) 
  crush-conglomerates 
  and 
  (b) 
  thrust-conglomerates. 
  

  

  The 
  crush- 
  conglomerates, 
  in 
  this 
  area, 
  are 
  those 
  formed 
  by 
  the 
  

   separation 
  of 
  a 
  bed 
  of 
  limestone 
  into 
  parts, 
  the 
  parts 
  having 
  been 
  

   subsequently 
  rounded. 
  , 
  All 
  stages 
  in 
  the 
  formation 
  of 
  such 
  beds 
  

   may 
  be 
  traced. 
  Compact 
  bands 
  of 
  limestone 
  may 
  be 
  seen, 
  at 
  first 
  

   cracked, 
  but 
  not 
  displaced 
  ; 
  then, 
  a 
  short 
  distance 
  farther 
  along, 
  

   the 
  cracks 
  become 
  more 
  obvious 
  ; 
  and 
  at 
  length 
  the 
  portions 
  of 
  what 
  

   must 
  have 
  been 
  a 
  continuous 
  band 
  have 
  become 
  separated 
  one 
  from 
  

   another 
  by 
  a 
  gap, 
  now 
  filled 
  with 
  the 
  shaly 
  material 
  derived 
  from 
  

   the 
  shale-bands 
  above 
  and 
  below. 
  

  

  It 
  is 
  very 
  clearly 
  seen 
  on 
  the 
  south 
  side 
  of 
  the 
  bay, 
  just 
  south 
  of 
  

   the 
  northern 
  martello 
  tower, 
  that 
  where 
  the 
  bands 
  of 
  limestone 
  

   differ 
  in 
  thickness 
  the 
  wider 
  bands, 
  here 
  about 
  10 
  inches 
  thick, 
  have 
  

   merely 
  been 
  cracked, 
  their 
  portions 
  having 
  suffered 
  no 
  displacement 
  ; 
  

   while 
  the 
  intermediate 
  bands 
  have 
  not 
  only 
  been 
  fractured, 
  but 
  their 
  

   fragments 
  have 
  undergone 
  a 
  certain 
  amount 
  of 
  displacement 
  ; 
  

   and 
  the 
  narrower 
  bands, 
  here 
  some 
  2 
  or 
  3 
  inches 
  thick, 
  have 
  been 
  

   cracked, 
  and 
  their 
  fragments 
  are 
  now 
  separated 
  by 
  several 
  inches 
  

   of 
  shale. 
  These 
  fragments 
  are 
  now 
  thoroughly 
  rounded, 
  and 
  pre- 
  

  

  1 
  These 
  graptolites 
  have 
  been 
  determined 
  for 
  us 
  by 
  Miss 
  E. 
  M. 
  E. 
  Wood 
  and 
  

   Miss 
  G. 
  L. 
  Elles. 
  

  

  2n 
  2 
  

  

  