﻿Vol. 
  53.] 
  IGNEOUS 
  ROCKS 
  IN 
  NORTH 
  PEMBROKESHIRE. 
  467 
  

  

  irregular 
  spherulitic 
  growths, 
  the 
  matrix 
  in 
  which 
  they 
  are 
  set 
  

   containing 
  an 
  inert 
  green 
  ' 
  chlorite 
  'in 
  some 
  quantity. 
  The 
  arrange- 
  

   ment 
  of 
  this 
  ' 
  chlorite 
  ' 
  in 
  places 
  strongly 
  recalls 
  the 
  perlitic 
  patch 
  

   figured 
  by 
  Mr. 
  Eutley 
  in 
  a 
  spherulitic 
  rock 
  from 
  Beddgelert 
  and 
  an 
  

   epidositic 
  felsite 
  from 
  the 
  Herefordshire 
  Beacon, 
  1 
  and 
  there 
  can 
  be 
  

   little 
  doubt 
  that 
  much 
  of 
  the 
  present 
  structure 
  is 
  due 
  to 
  the 
  

   causes 
  which 
  he 
  describes 
  in 
  those 
  instances. 
  The 
  spherulites 
  as 
  a 
  

   rule 
  are 
  rather 
  confusedly 
  crystalline, 
  and 
  show 
  but 
  little 
  approach 
  

   to 
  a 
  radial 
  structure 
  ; 
  their 
  outlines 
  are 
  usually 
  elliptical 
  rather 
  than 
  

   circular, 
  and 
  they 
  are 
  free 
  from 
  the 
  secondary 
  chloritic 
  mineral. 
  It 
  

   is 
  perhaps 
  worth 
  mentioning 
  that 
  the 
  microlites 
  forming 
  a 
  large 
  part 
  

   of 
  the 
  bands 
  which 
  characterize 
  the 
  rock 
  macroscopically 
  lie 
  in 
  a 
  

   direction 
  not 
  parallel 
  to, 
  but 
  at 
  an 
  angle 
  with, 
  the 
  length 
  of 
  the 
  

   band, 
  indicating 
  — 
  as 
  Prof. 
  Bonney 
  has 
  suggested 
  to 
  me 
  — 
  a 
  slight 
  

   movement 
  of 
  the 
  rock 
  in 
  a 
  new 
  direction, 
  immediately 
  prior 
  to 
  

   consolidation, 
  but 
  which 
  has 
  not 
  been 
  sufficient 
  to 
  disturb 
  the 
  

   parallel 
  regularity 
  of 
  the 
  bands 
  themselves. 
  

  

  Consideration 
  of 
  this 
  not 
  very 
  markedly 
  spherulitic 
  rock 
  leads 
  to 
  

   those 
  in 
  which 
  the 
  spherulites 
  are 
  conspicuous. 
  In 
  a 
  slide 
  from 
  

   one 
  of 
  these 
  a 
  band 
  about 
  \ 
  inch 
  across, 
  with 
  spherulites 
  yL- 
  inch 
  

   in 
  diameter, 
  is 
  cut. 
  

  

  The 
  larger 
  of 
  these 
  spherulites 
  occur 
  either 
  singly 
  or 
  grouped 
  

   in 
  twos 
  and 
  threes, 
  in 
  the 
  latter 
  case 
  arranged 
  often 
  in 
  a 
  linear 
  

   manner 
  and 
  shading 
  off 
  into 
  axiolites. 
  They 
  show 
  concentric 
  lines 
  

   of 
  growth, 
  with 
  generally 
  a 
  narrow 
  outer 
  border 
  of 
  clear 
  matter 
  in 
  

   contrast 
  to 
  the 
  darker 
  and 
  finely 
  fibrous 
  nature 
  of 
  the 
  internal 
  

   portion. 
  

  

  Interstitially, 
  between 
  the 
  above, 
  are 
  closely-packed 
  clear 
  spheru- 
  

   lites, 
  showing 
  commonly 
  concentric 
  lines 
  of 
  growth 
  rather 
  markedly. 
  

   In 
  the 
  majority 
  of 
  cases 
  these, 
  like 
  their 
  larger 
  representatives, 
  have 
  

   a 
  clear 
  but 
  broader 
  edge, 
  which 
  is 
  distinctly 
  separated 
  from 
  the 
  

   less 
  translucent 
  central 
  portion. 
  The 
  sharpness 
  of 
  the 
  definition 
  

   between 
  the 
  zones 
  suggests 
  occasional 
  concentric 
  fracture 
  and 
  infil- 
  

   tration. 
  These 
  smaller 
  spherulites 
  are 
  in 
  some 
  instances 
  grouped 
  

   linearly, 
  giving 
  a 
  scalloped 
  appearance, 
  on 
  each 
  side 
  of 
  a 
  line 
  of 
  

   granular 
  and 
  less 
  definite 
  crystallization, 
  of 
  some 
  width 
  in 
  proportion 
  

   to 
  the 
  size 
  of 
  the 
  spherulites, 
  and 
  which 
  may 
  extend 
  for 
  nearly 
  the 
  

   entire 
  breadth 
  of 
  the 
  slide. 
  As 
  Prof. 
  Bonney 
  has 
  pointed 
  out, 
  2 
  this 
  

   kind 
  of 
  arrangement 
  may 
  be 
  simulated 
  in 
  sheets 
  of 
  glass 
  fused 
  by 
  

   fire, 
  a 
  surface 
  of 
  discontinuity 
  being 
  formed 
  between 
  two 
  layers. 
  

   In 
  this 
  case 
  it 
  would 
  appear 
  as 
  if 
  a 
  crack 
  had 
  formed 
  the 
  necessary 
  

   starting-point. 
  

  

  A 
  variety 
  of 
  this 
  rock, 
  showing 
  minor 
  differences 
  in 
  the 
  spheru- 
  

   lites, 
  but 
  considerable 
  differences 
  in 
  the 
  character 
  of 
  the 
  matrix 
  in 
  

   which 
  they 
  are 
  embedded, 
  presents 
  a 
  few 
  points 
  which 
  may 
  be 
  of 
  

   interest. 
  

  

  1 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xliw 
  (1888} 
  p. 
  740 
  & 
  pi. 
  xvii. 
  

  

  2 
  Pres. 
  Addr., 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xli. 
  (1885) 
  Proc. 
  p. 
  91. 
  

  

  £l 
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