﻿248 
  

  

  MISS 
  C. 
  A. 
  EAISIN 
  ON 
  SOME 
  

  

  which 
  shows 
  faint 
  indications 
  of 
  fluidal 
  structure 
  and 
  contains 
  

   porphyritic 
  felspar 
  and 
  quartz. 
  This 
  rhyolitic 
  rock 
  seems 
  to 
  have 
  

   undergone 
  a 
  brecciation 
  in 
  situ 
  ; 
  for 
  some 
  of 
  the 
  neighbouring 
  frag- 
  

   ments 
  were 
  evidently 
  once 
  continuous, 
  and 
  the 
  blackish 
  veins 
  fade 
  

   off 
  at 
  places 
  and 
  are 
  lost 
  in 
  the 
  felstone. 
  The 
  brecciation 
  dies 
  out 
  

   in 
  the 
  beds 
  above, 
  and 
  the 
  last 
  traces 
  of 
  the 
  veining 
  consist 
  of 
  more 
  

   regular 
  lines 
  joining 
  darkened 
  knots, 
  which 
  prove 
  to 
  be 
  porphyritic 
  

   crystals, 
  surrounded 
  and 
  penetrated 
  by 
  the 
  dark 
  granular 
  deposit. 
  

   This 
  deposit 
  similarly 
  aggregates 
  around 
  and 
  within 
  the 
  crust 
  of 
  

   nodules 
  which 
  occur 
  along 
  one 
  band. 
  The 
  dark 
  lines 
  form 
  curves 
  

   of 
  large 
  radius, 
  tangential 
  to 
  the 
  roek-laminse, 
  or 
  to 
  the 
  surfaces 
  of 
  

   porphyritic 
  crystals, 
  as 
  if 
  due 
  to 
  perlitic 
  contraction 
  acting 
  under 
  

   constraint. 
  Along 
  the 
  curves 
  within 
  one 
  quartz 
  grain 
  the 
  deposit 
  

   has 
  formed 
  very 
  minute 
  scales 
  of 
  an 
  irregular 
  stellate 
  appearance, 
  

   possibly 
  a 
  kind 
  of 
  radial 
  or 
  dendritic 
  development 
  (fig. 
  1). 
  

  

  Fig. 
  1. 
  — 
  Chains 
  of 
  Stellate 
  Spherulitoid 
  Enclosures 
  along 
  the 
  curved 
  

   surface 
  of 
  a 
  crack, 
  which 
  crosses 
  a 
  clear 
  porphyritic 
  quartz- 
  

   grain 
  ; 
  the 
  crack 
  seems 
  probably 
  due 
  to 
  perlitic 
  contraction. 
  

   From 
  quartz-felsite 
  of 
  Pen-y-chain, 
  above 
  brecciated 
  rock. 
  (En- 
  

   larged 
  350 
  diameters.) 
  

  

  Along 
  the 
  next 
  beach 
  to 
  the 
  eastward, 
  which 
  is 
  the 
  most 
  southerly 
  

   of 
  the 
  district, 
  some 
  of 
  the 
  lowest 
  rocks 
  are 
  of 
  the 
  brecciated 
  

   character 
  described. 
  Certain 
  bosses 
  below 
  high-water 
  mark 
  consist 
  

   of 
  a 
  very 
  compact, 
  ill-mixed, 
  pink 
  and 
  grey 
  felsite, 
  with 
  flecks 
  of 
  

   pyrites. 
  On 
  surfaces 
  smoothed 
  by 
  the 
  waves 
  are 
  small 
  curved 
  

   furrows, 
  like 
  indentations 
  of 
  finger-nails 
  widened 
  irregularly 
  by 
  

   weathering. 
  These 
  would 
  seem 
  to 
  be 
  perlitic 
  cracks, 
  which 
  the 
  

   microscope 
  shows 
  to 
  be 
  abundant 
  in 
  the 
  rock 
  and 
  even 
  in 
  its 
  porphy- 
  

   ritic 
  quartz. 
  The 
  face 
  of 
  the 
  cliff, 
  which 
  is 
  about 
  in 
  the 
  line 
  of 
  

   strike, 
  exposes 
  horizontal, 
  ashy 
  and 
  agglomeratic 
  layers. 
  The 
  dip 
  is 
  

   northerly, 
  about 
  35° 
  (fig. 
  2). 
  The 
  fragments 
  in 
  the 
  agglomerate 
  

   may 
  be 
  as 
  much 
  as 
  six 
  inches 
  in 
  length. 
  Some 
  are 
  of 
  slate 
  ; 
  many, 
  ' 
  

  

  