﻿294 
  PROF. 
  T. 
  G. 
  BONNET 
  ON 
  SOME 
  NODULAR 
  

  

  in 
  1878, 
  opposite 
  to 
  the 
  gate 
  of 
  the 
  Diganwy 
  Hotel. 
  A 
  little 
  below 
  

   this 
  the 
  felsite 
  is 
  also 
  very 
  spheroidal, 
  the 
  ovoid 
  balls 
  being 
  often 
  

   almost 
  in 
  contact, 
  from 
  1 
  to 
  1*5 
  inch 
  in 
  diameter, 
  and 
  sometimes 
  even 
  

   double 
  the 
  latter 
  size. 
  Where 
  not 
  decomposed, 
  they 
  have 
  within 
  a 
  

   cherty 
  aspect. 
  The 
  structure 
  occurs 
  most 
  conspicuously 
  in 
  a 
  band 
  

   several 
  feet 
  thick. 
  Here 
  also 
  the 
  surface 
  of 
  the 
  mass 
  is 
  overlain 
  by 
  a 
  

   grit 
  derived 
  from 
  the 
  felsite, 
  in 
  which 
  pebbles 
  of 
  that 
  rock 
  occur 
  ; 
  and 
  

   then 
  comes, 
  apparently 
  in 
  immediate 
  succession, 
  a 
  black 
  slaty 
  rock. 
  

   Specimens 
  of 
  the 
  spheroidal 
  rock 
  from 
  the 
  upper 
  part 
  of 
  Conway 
  

   Mountain, 
  and 
  of 
  a 
  spheroid 
  from 
  Diganwy, 
  have 
  been 
  examined 
  

   microscopically. 
  Both 
  are 
  considerably 
  decomposed. 
  The 
  outer 
  

   part 
  of 
  the 
  spheroid 
  (like 
  a 
  kind 
  of 
  envelope, 
  more 
  regular 
  on 
  the 
  

   outer 
  than 
  on 
  the 
  inner 
  side) 
  exhibits 
  a 
  very 
  well-marked 
  fluidal 
  

   structure, 
  which 
  shows 
  a 
  general 
  parallelism 
  to 
  the 
  bounding 
  surfaces, 
  

   bending 
  up 
  into 
  wave-like 
  crests 
  in 
  the 
  interior. 
  This, 
  in 
  the 
  former 
  

   specimen, 
  is 
  hollow, 
  with 
  more 
  or 
  less 
  of 
  a 
  lining 
  of 
  minutely 
  crys- 
  

   tallized 
  quartz. 
  The 
  matrix 
  of 
  the 
  rock, 
  among 
  the 
  spheroids, 
  shows 
  

   also 
  a 
  fluidal 
  structure 
  ; 
  but 
  this 
  is 
  more 
  irregular 
  and 
  more 
  decom- 
  

   posed 
  than 
  in 
  the 
  Diganwy 
  specimen. 
  The 
  " 
  husk 
  " 
  of 
  this 
  ex- 
  

   hibits 
  a 
  very 
  fine 
  fluidal 
  structure, 
  rather 
  more 
  corrugated 
  than 
  in 
  

   the 
  other 
  case 
  ; 
  the 
  interior 
  is 
  occupied 
  by 
  a 
  pale 
  brown, 
  more 
  

   homogeneous 
  material, 
  with 
  occasional 
  lacuna?. 
  This, 
  with 
  crossed 
  

   Mcols, 
  exhibits 
  many 
  minute 
  bright 
  specks, 
  with 
  others 
  that 
  are 
  

   colourless. 
  It 
  would 
  seem 
  as 
  if 
  a 
  little 
  of 
  a 
  glassy 
  base 
  still 
  remained. 
  

   As 
  in 
  places 
  the 
  boundary 
  between 
  this 
  and 
  the 
  " 
  husk 
  " 
  is 
  very 
  sharp, 
  

   I 
  have 
  doubted 
  whether 
  it 
  may 
  not 
  be 
  formed 
  by 
  subsequent 
  in- 
  

   filtration 
  ; 
  but 
  since 
  in 
  other 
  places 
  the 
  one 
  seems 
  to 
  pass 
  into 
  the 
  

   other, 
  and 
  the 
  structure 
  more 
  resembles 
  that 
  of 
  a 
  glassy 
  rock 
  with 
  

   minute 
  devitrification-structure, 
  I 
  incline 
  to 
  the 
  opinion 
  that 
  it 
  is 
  

   merely 
  a 
  more 
  compact 
  and 
  homogeneous 
  form 
  of 
  the 
  parent 
  rock. 
  

   These 
  rocks, 
  then, 
  present 
  us 
  with 
  structures 
  resembling 
  in 
  some 
  

   respects 
  those 
  already 
  described 
  from 
  the 
  felsites 
  of 
  the 
  Bettws-y- 
  

   Coed 
  district*. 
  

  

  A 
  specimen 
  of 
  the 
  ordinary 
  cream-coloured 
  felsite 
  of 
  the 
  Conway 
  

   Mountain 
  has 
  also 
  been 
  examined. 
  The 
  rock 
  is 
  often 
  very 
  platy, 
  so 
  that 
  

   it 
  might 
  almost 
  be 
  mistaken 
  for 
  a 
  bedded 
  mudstone 
  ; 
  occasionally 
  (as 
  

   notably 
  in 
  a 
  quarry 
  near 
  a 
  foot-bridge 
  which 
  crosses 
  the 
  railway 
  a 
  

   little 
  west 
  of 
  Conway) 
  it 
  is 
  a 
  pale 
  greenish-grey 
  colour, 
  showing 
  that 
  

   the 
  yellowish 
  tint 
  is 
  the 
  result 
  of 
  decomposition. 
  Under 
  the 
  micro- 
  

   scope 
  it 
  exhibits 
  innumerable 
  minute 
  semitransparent 
  dusty 
  granules, 
  

   and, 
  with 
  crossing 
  Nicols, 
  a 
  patchy, 
  very 
  minute 
  devitrified 
  structure, 
  

   giving 
  indications 
  of 
  banding, 
  the 
  patches 
  apparently 
  composed 
  of 
  

   ill-defined 
  microliths 
  so 
  arranged 
  that 
  each 
  patch 
  is 
  approximately 
  

   of 
  one 
  tintf. 
  

  

  * 
  I 
  have 
  not 
  entered 
  into 
  other 
  details 
  of 
  the 
  more 
  minute 
  mineral 
  structures, 
  

   the 
  results 
  of 
  devitrification, 
  infiltration, 
  &c, 
  deeming 
  them 
  of 
  no 
  very 
  special 
  

   interest. 
  

  

  t 
  I 
  have 
  also 
  examined 
  the 
  dark 
  felsite 
  further 
  west, 
  on 
  the 
  other 
  side 
  of 
  the 
  

   fault 
  crossing 
  the 
  western 
  end 
  of 
  Conway 
  Mountain. 
  It 
  differs 
  from 
  those 
  

   described 
  above 
  in 
  having 
  its 
  base 
  (1 
  incline 
  to 
  the 
  opinion 
  that 
  there 
  is 
  still 
  a 
  

  

  