﻿256 
  MISS 
  C. 
  A. 
  EAISIN 
  OS 
  S03IE 
  

  

  conditions 
  might 
  thus 
  be 
  somewhat 
  analogous 
  to 
  the 
  secondary 
  

   heating-up 
  of 
  the 
  Arran 
  felsite. 
  

  

  Near 
  the 
  point 
  at 
  Careg-y-defaidfcertain 
  brownish 
  nodules, 
  from 
  

   J 
  inch 
  to 
  \ 
  inch 
  or 
  less 
  in 
  diameter, 
  occur 
  in 
  a 
  compact 
  greyish 
  rock. 
  

   The 
  microscope 
  shows 
  the 
  matrix 
  to 
  be 
  devitrified 
  and 
  perlitic, 
  and 
  

   the 
  nodules 
  prove 
  to 
  be 
  spherulitic 
  ; 
  thus 
  we 
  have 
  here 
  another 
  

   example, 
  to 
  add 
  to 
  those 
  enumerated 
  by 
  Mr. 
  Cole, 
  of 
  ' 
  pyromerides 
  ' 
  

   due 
  to 
  alteration 
  of 
  originally 
  glassy 
  rocks 
  *. 
  Around 
  or 
  towards 
  

   the 
  exterior 
  is 
  generally 
  an 
  irregular 
  and 
  often 
  incomplete 
  ring 
  of 
  

   quartz, 
  and 
  spherulitic 
  tufts 
  are 
  best 
  denned 
  where 
  rooted 
  in 
  the 
  

   outer 
  granules, 
  or, 
  in 
  one 
  example, 
  where 
  starting 
  from 
  a 
  porphyritic 
  

   crystal. 
  Whether 
  the 
  quartz 
  marks 
  what 
  was 
  originally 
  an 
  irregular 
  

   vesicle, 
  or 
  a 
  space 
  primarily 
  due 
  to 
  contraction, 
  the 
  deposit 
  seems 
  to 
  

   have 
  further 
  extended 
  by 
  a 
  kind 
  of 
  replacement 
  : 
  for 
  lines 
  of 
  minute 
  

   enclosures 
  run 
  into 
  it 
  without 
  interruption 
  and 
  continue 
  from 
  grain 
  

   to 
  grain. 
  

  

  Specimens 
  of 
  Jersey 
  nodules 
  t, 
  for 
  which 
  I 
  am 
  indebted 
  to 
  the 
  

   kindness 
  of 
  Professor 
  Bonney 
  J, 
  exhibit 
  the 
  thin 
  and 
  numerous 
  chal- 
  

   cedonic 
  threads 
  which 
  are 
  mentioned 
  by 
  de 
  Lapparent 
  as 
  occurring 
  

   between 
  successive 
  layers 
  §. 
  They 
  are 
  often 
  crenated, 
  and 
  roughly 
  

   concentric 
  with 
  an 
  outer 
  somewhat 
  mamillated 
  surface. 
  It 
  is 
  diffi- 
  

   cult 
  to 
  decide 
  upon 
  the 
  cause 
  or 
  causes 
  of 
  this 
  tendency 
  to 
  concentric 
  

   rings. 
  If 
  in 
  an 
  early 
  stage 
  gas 
  was 
  evolved 
  in 
  these 
  spherulites, 
  after 
  

   they 
  had 
  begun 
  to 
  form, 
  it 
  would 
  be 
  likely 
  to 
  take 
  possession 
  of 
  any 
  

   spaces 
  already 
  existing, 
  possibly 
  filling 
  and 
  enlarging 
  cracks 
  formed 
  

   in 
  some 
  contraction 
  of 
  the 
  spherulite 
  before 
  it 
  had 
  " 
  set." 
  In 
  the 
  

   cavities 
  thus 
  originated, 
  quartz 
  might 
  crystallize 
  out, 
  mostly 
  supplied 
  

   from 
  the 
  adjacent 
  zones 
  ; 
  these 
  are 
  now 
  dark 
  and 
  decomposed, 
  and 
  

   are 
  generally 
  more 
  irregular 
  at 
  their 
  outer 
  boundary. 
  The 
  definition 
  

   of 
  the 
  quartzose 
  arcs 
  is 
  prominently 
  exhibited, 
  on 
  the 
  cut 
  surface 
  

   of 
  several 
  specimens, 
  by 
  a 
  capillary 
  efflorescence, 
  which 
  developed 
  in 
  

   the 
  course 
  of 
  a 
  few 
  days 
  from 
  the 
  intermediate 
  fibrous 
  zones. 
  The 
  

   minute 
  hair-like 
  crystals 
  consist, 
  apparently, 
  of 
  magnesium 
  sulphate 
  

   (epsomite), 
  probably 
  due 
  to 
  a 
  deposit 
  from 
  sea-water 
  within 
  the 
  more 
  

   weathered 
  part 
  of 
  the 
  spherulite. 
  One 
  specimen, 
  which 
  has 
  exhibited 
  

   none 
  of 
  this 
  efflorescence, 
  proves 
  to 
  be 
  clearer 
  and 
  less 
  decomposed, 
  

   more 
  markedly 
  spherulitic, 
  and 
  nearly 
  free 
  from 
  the 
  concentric 
  chal- 
  

   cedonic 
  rings. 
  

  

  Some 
  connexion 
  of 
  spherulites 
  with 
  a 
  kind 
  of 
  perlitic 
  contraction, 
  

   possibly 
  of 
  later 
  date, 
  seems 
  indicated 
  in 
  certain 
  slides, 
  especially 
  in 
  

   a 
  Lea-rock 
  and 
  a 
  Boulay-Bay 
  example, 
  where 
  a 
  sharply-defined 
  

   narrow 
  quartzose 
  vein 
  bounds 
  part 
  of 
  the 
  spherulite, 
  which 
  is 
  

  

  * 
  Geol. 
  Mag. 
  July 
  1887, 
  p. 
  303. 
  

  

  t 
  See 
  " 
  Khvolites 
  of 
  Bouley 
  Bay," 
  by 
  Mr. 
  T. 
  Davies, 
  ' 
  Min. 
  Mag.' 
  1879, 
  vol. 
  iii. 
  

   p. 
  118. 
  

  

  % 
  I 
  hare 
  also 
  had 
  the 
  advantage 
  of 
  studying 
  some 
  additional 
  illustrations 
  

   from 
  Jersey, 
  kindly 
  lent 
  by 
  Mr. 
  Percy 
  F. 
  Kendall, 
  of 
  Owens 
  College, 
  Man 
  - 
  

   Chester. 
  

  

  § 
  Bull. 
  Soc. 
  Geol. 
  de 
  Fr. 
  1884, 
  3 
  e 
  ser. 
  t. 
  xii. 
  p. 
  284. 
  Compare 
  the 
  " 
  concentric 
  

   zones 
  caused 
  bv 
  successive 
  growths 
  " 
  witbin 
  Gargalong 
  pyromerides 
  described 
  

   by 
  M. 
  Levy, 
  Bull. 
  Soc. 
  Geol. 
  de 
  Fr. 
  1875, 
  3^ 
  ser. 
  t. 
  iii. 
  p. 
  223. 
  

  

  