﻿The 
  Pyromerides 
  of 
  Boiday 
  Bay. 
  283 
  

  

  December 
  loth. 
  — 
  Dr. 
  Henry 
  Hicks, 
  F.R.S., 
  President, 
  

   in 
  the 
  Chair. 
  

  

  The 
  following 
  communications 
  were 
  read 
  : 
  — 
  

  

  1. 
  'On 
  the 
  Pyromerides 
  of 
  Boulay 
  Bay, 
  Jersey/ 
  By 
  John 
  

   Parkinson, 
  Esq., 
  F.G.S. 
  

  

  After 
  briefly 
  noticing 
  the 
  literature 
  of 
  the 
  subject, 
  the 
  author 
  

   describes 
  the 
  altered 
  rhyoiites 
  of 
  Boulay 
  Bay. 
  One 
  variety, 
  the 
  

   commonest, 
  is 
  of 
  a 
  dark 
  red 
  colour, 
  showing 
  flow-structure 
  ; 
  another 
  

   is 
  porphyritic 
  ; 
  a 
  third, 
  near 
  the 
  centre 
  of 
  the 
  Bay, 
  has 
  a 
  pale 
  

   greenish 
  matrix 
  enclosing 
  fragments, 
  which, 
  however, 
  are 
  due 
  to 
  

   flow-brecciation. 
  Large 
  pyromerides 
  occur 
  in 
  two 
  localities 
  : 
  in 
  

   the 
  more 
  interesting, 
  that 
  north 
  of 
  the 
  jetty, 
  the 
  structure 
  of 
  the 
  

   rock 
  indicates 
  either 
  a 
  very 
  peculiar 
  magmatic 
  differentiation 
  in 
  situ 
  

   or 
  (more 
  probably) 
  the 
  mixture 
  of 
  two 
  magmas 
  differing 
  in 
  their 
  

   stage 
  of 
  consolidation. 
  

  

  From 
  study 
  of 
  a 
  series 
  of 
  specimens 
  of 
  the 
  pyromeridal 
  rock, 
  the 
  

   author 
  arrives 
  at 
  the 
  following 
  conclusions 
  : 
  — 
  (1) 
  The 
  rock 
  shows 
  

   marked 
  flow-structure 
  and 
  at 
  times 
  bands 
  which 
  indicate 
  a 
  slight 
  

   difference 
  in 
  its 
  composition, 
  the 
  latter 
  tending 
  to 
  assume 
  a 
  

   moniliform 
  outline. 
  In 
  such 
  the 
  microscopic 
  structure 
  corre- 
  

   sponds 
  with 
  that 
  of 
  the 
  pyromerides, 
  and 
  exhibits 
  traces 
  of 
  radial 
  

   crystallization. 
  (2) 
  These 
  afford 
  a 
  passage 
  into 
  somewhat 
  oval 
  

   pyromerides, 
  with 
  rather 
  tapering 
  ends 
  and 
  irregularly 
  mammillated 
  

   surfaces. 
  (3) 
  From 
  these 
  sometimes 
  a 
  single 
  one 
  seems 
  to 
  be 
  

   thrown 
  off, 
  while 
  lines 
  of 
  pyromerides 
  or 
  little 
  lumps 
  of 
  similar 
  

   material 
  are 
  scattered 
  about 
  the 
  matrix. 
  (4) 
  Many 
  of 
  the 
  

   pyromerides 
  are 
  solid 
  throughout 
  ; 
  others 
  have 
  a 
  central 
  cavity 
  

   filled 
  with 
  quartz. 
  

  

  The 
  author 
  describes 
  varieties 
  of 
  the 
  pyromerides. 
  They 
  are 
  

   generally 
  deep 
  red 
  in 
  colour, 
  and 
  exhibit 
  (a) 
  fluxion-structure, 
  

   made 
  more 
  distinct 
  by 
  minute 
  black 
  microliths; 
  (b) 
  a 
  radial 
  

   structure; 
  (c) 
  a 
  'patchy' 
  devitrifled 
  structure 
  (with 
  crossed 
  nicols); 
  

   the 
  second 
  being 
  not 
  always 
  present. 
  The 
  matrix 
  is 
  usually 
  of 
  a 
  

   greenish 
  tint, 
  showing 
  devitrification-structure 
  and 
  sometimes 
  a 
  trace 
  

   of 
  perlitic 
  structure. 
  

  

  The 
  pyromerides 
  frequently 
  exhibit 
  more 
  or 
  less 
  crescentic 
  cracks, 
  

   due 
  apparently 
  to 
  contraction, 
  which 
  have 
  been 
  filled 
  by 
  quartz. 
  

   Sometimes 
  also 
  they 
  scale 
  off 
  in 
  rudely 
  crescentic 
  shells. 
  In 
  one 
  

   locality 
  a 
  variety 
  with 
  good 
  spherulites, 
  about 
  as 
  large 
  as 
  a 
  pea, 
  

   passes 
  into 
  one 
  showing 
  a 
  fluxion 
  -structure 
  and 
  pyromerides, 
  

   having 
  traces 
  of 
  radial 
  structure 
  as 
  well 
  as 
  clots 
  and 
  irregular 
  

   t 
  wisps/ 
  suggestive 
  of 
  a 
  stiffer 
  material 
  broken 
  up 
  by 
  one 
  more 
  

   liquid. 
  

  

  As 
  the 
  result 
  of 
  his 
  studies, 
  the 
  author 
  thinks 
  that 
  while 
  very 
  

   regular 
  spherulites 
  do 
  occur, 
  apparently 
  in 
  consequence 
  of 
  radial 
  

   crystallization 
  round 
  a 
  centre, 
  the 
  pyromerides 
  are 
  due 
  to 
  the 
  mixture 
  

   of 
  two 
  magmas 
  slightly 
  different 
  in 
  composition 
  and 
  fluidity, 
  the 
  

   less 
  plastic 
  of 
  the 
  two 
  being 
  sometimes 
  drawn 
  out 
  into 
  streaks, 
  but 
  

   at 
  others 
  forming 
  lumps, 
  in 
  which, 
  where 
  their 
  form 
  is 
  suitable, 
  a 
  

  

  