﻿258 
  hiss 
  c. 
  a. 
  eaisls" 
  ox 
  soite 
  

  

  would 
  be 
  liable, 
  I 
  should 
  have 
  thought, 
  to 
  yield 
  to 
  corrosion 
  (as 
  in 
  

   small 
  examples 
  which 
  I 
  have 
  mentioned), 
  if 
  such 
  extensive 
  decom- 
  

   position 
  had 
  acted 
  at 
  the 
  heart 
  of 
  the 
  nodules. 
  

  

  It 
  seems 
  also 
  as 
  if, 
  in 
  any 
  differential 
  action 
  upon 
  the 
  spherulite 
  

   and 
  its 
  environment, 
  the 
  matrix 
  is 
  far 
  more 
  readily 
  altered, 
  and 
  thus 
  

   it 
  so 
  often 
  acquires 
  a 
  schistose 
  character, 
  as 
  if 
  squeezed 
  between 
  the 
  

   more 
  compact 
  nodules. 
  Professor 
  Bonney 
  tells 
  me 
  that 
  at 
  Boulay 
  

   Bay 
  the 
  pyromerides 
  are 
  often 
  only 
  faintly 
  traceable 
  on 
  a 
  fresh 
  

   surface 
  of 
  the 
  rock, 
  but 
  are 
  well 
  developed 
  after 
  weathering. 
  A 
  

   microscope 
  slide 
  from 
  one 
  specimen 
  shows 
  a 
  very 
  clear 
  granular 
  

   aggregation 
  deposited 
  in 
  the 
  perlitic 
  ground-mass, 
  while 
  alteration 
  

   of 
  the 
  spherulite 
  seems 
  much 
  less 
  marked. 
  In 
  one 
  of 
  the 
  Lea-rock 
  

   slides 
  greenish 
  oblong 
  microliths, 
  with 
  a 
  rectilinear 
  arrangement, 
  

   seem 
  to 
  mark 
  an 
  original 
  structure, 
  sealed 
  up 
  in 
  the 
  firm 
  spherulite, 
  

   while 
  a 
  contorted 
  fluidal 
  development 
  has 
  been 
  set 
  up 
  in 
  the 
  less 
  

   resisting 
  matrix, 
  which 
  thus 
  seems 
  to 
  flow 
  around 
  the 
  imbedded 
  

   spheres. 
  The 
  minute 
  black 
  microliths, 
  like 
  knobbed 
  sticks, 
  which 
  

   are 
  found 
  within 
  certain 
  spherulites, 
  and 
  not 
  within 
  the 
  surrounding 
  

   matrix 
  (as, 
  for 
  example, 
  in 
  some 
  Boulay-Bay 
  specimens), 
  may 
  per- 
  

   haps 
  be 
  similarly 
  explained, 
  since 
  their 
  orientation 
  is 
  generally 
  

   uninfluenced 
  by 
  the 
  radial 
  growth. 
  Again, 
  as 
  I 
  have 
  described, 
  

   spherulites 
  have 
  become 
  subsequently 
  fissured, 
  as 
  if 
  they 
  were 
  less 
  

   plastic 
  than 
  the 
  matrix. 
  Sometimes 
  a 
  continuation 
  of 
  the 
  rock-mass 
  

   seems 
  to 
  extend 
  around 
  a 
  displaced 
  fragment, 
  as 
  if, 
  after 
  the 
  

   spherulite 
  had 
  begun 
  to 
  form, 
  the 
  glassy 
  matrix 
  was 
  still 
  in 
  a 
  some- 
  

   what 
  viscous 
  condition, 
  and 
  able 
  to 
  penetrate 
  into 
  cracks 
  of 
  the 
  

   nodules 
  *. 
  

  

  Spherulites 
  can 
  be 
  found 
  occasionally 
  not 
  complete, 
  and 
  some 
  of 
  

   these 
  might 
  perhaps 
  be 
  compared 
  with 
  the 
  arrangement 
  of 
  material 
  

   found 
  in 
  napoleonite, 
  or 
  in 
  the 
  spheroids 
  described 
  by 
  Dr. 
  Hatch 
  t. 
  

   It 
  may 
  be, 
  however, 
  that 
  in 
  some 
  cases 
  the 
  development, 
  in 
  accord- 
  

   ance 
  with 
  the 
  principle 
  suggested 
  by 
  Professor 
  Bonney 
  t, 
  started 
  

   from 
  the 
  exterior, 
  but 
  ceased 
  before 
  it 
  had 
  advanced 
  far 
  towards 
  the 
  

   centre, 
  so 
  that 
  a 
  spherulitic 
  rind 
  would 
  be 
  formed. 
  A 
  breach 
  of 
  

   continuity 
  from 
  the 
  internal 
  " 
  residuum 
  " 
  might 
  result, 
  and 
  the 
  dis- 
  

   tinction 
  of 
  the 
  two 
  parts 
  might 
  be 
  further 
  accentuated 
  by 
  granular 
  

   devitrification 
  of 
  the 
  substance 
  within. 
  Weiss 
  speaks 
  of 
  a 
  greenish 
  

   mass 
  (similar, 
  except 
  in 
  colour, 
  to 
  the 
  matrix) 
  contained 
  within 
  a 
  

   fibrous 
  crust 
  § 
  ; 
  and 
  in 
  a 
  specimen 
  from 
  Pen-y-chain 
  a 
  darkened 
  

   part, 
  bounded 
  by 
  spherulitic 
  arcs, 
  is 
  evidently 
  a 
  portion 
  of 
  the 
  

   ground-mass. 
  In 
  the 
  rock 
  the 
  perlitic 
  cracks 
  are 
  mainly 
  chalce- 
  

   donized 
  ; 
  but 
  within 
  the 
  enclosed 
  fragment 
  they 
  contain 
  a 
  greenish 
  

   deposit, 
  which 
  gives 
  it 
  the 
  darkened 
  colour, 
  and 
  thus 
  heightens 
  the 
  

   contrast 
  with 
  the 
  surrounding 
  border. 
  Thus, 
  in 
  these 
  incomplete 
  

   nodules, 
  a 
  spherulitic 
  crust 
  encloses 
  a 
  central 
  mass, 
  which 
  certainly 
  

   could 
  not 
  here 
  be 
  a 
  decomposition-product. 
  

  

  * 
  Compare 
  Amer. 
  Joum. 
  of 
  Sci. 
  vol. 
  xxxiii. 
  p. 
  42, 
  Mr. 
  Iddings, 
  1887. 
  

  

  •f 
  Quart. 
  Journ. 
  Greol. 
  Soc. 
  vol. 
  xliv. 
  p. 
  557, 
  Aug. 
  1888. 
  

  

  $ 
  Geol. 
  Mag. 
  dec. 
  2, 
  rol. 
  iv. 
  1877, 
  p. 
  510. 
  

  

  § 
  " 
  Thur. 
  Wald. 
  Porph.," 
  Zeitschr. 
  d. 
  d. 
  geol. 
  G-esell. 
  1877, 
  Bd. 
  xxix. 
  p. 
  422. 
  

  

  