﻿NODULAR 
  EELSTONES 
  OF 
  THE 
  LLEYN. 
  

  

  249 
  

  

  especially 
  the 
  larger, 
  are 
  of 
  felsite, 
  resembling, 
  lithologically, 
  the 
  

   neighbouring 
  rocks; 
  thus, 
  one 
  fragment 
  exhibits 
  part 
  of 
  a 
  large 
  

   radialized 
  structure 
  within 
  a 
  spherulitic 
  matrix. 
  

  

  Pig. 
  2. 
  — 
  Pen-y 
  '-chain. 
  Cliff-section, 
  south 
  beach. 
  

  

  a. 
  Compact 
  rhyolitic 
  rock 
  with 
  brecciated 
  veins, 
  b. 
  Agglomerate, 
  c. 
  Ashy 
  beds. 
  

  

  The 
  great 
  mass 
  of 
  the 
  Pen-y-chain 
  felsite 
  which 
  follows 
  consists 
  

   of 
  a 
  compact 
  brownish 
  rock, 
  including 
  small 
  porphyritic 
  quartz 
  and 
  

   felspar. 
  The 
  rock 
  is 
  markedly 
  fluidal, 
  and 
  the 
  weathered 
  surface 
  

   has 
  a 
  slaggy 
  look. 
  The 
  microscope-slides 
  exhibit 
  small 
  elongated 
  

   nests 
  of 
  clear 
  intercrystallized 
  grains, 
  showing 
  in 
  a 
  few 
  cases 
  a 
  

   shaded 
  spherulitic 
  cross 
  when 
  viewed 
  in 
  polarized 
  light. 
  Some, 
  at 
  

   least, 
  of 
  these 
  aggregations 
  appear 
  to 
  be 
  filled-up 
  cavities 
  of 
  the 
  lava. 
  

   The 
  bordering 
  quartz 
  is 
  radial 
  in 
  its 
  arrangement 
  and 
  often 
  pyra- 
  

   midal; 
  the 
  cavities 
  are 
  ranged 
  in 
  irregular 
  bands 
  parallel 
  with 
  

   the 
  flow, 
  and 
  one 
  is 
  bent 
  around 
  the 
  corner 
  of 
  a 
  large 
  felspar 
  at 
  a 
  

   little 
  distance 
  from 
  it. 
  

  

  By 
  the 
  third 
  beach, 
  going 
  northward, 
  brecciated 
  rock 
  occurs, 
  

   possibly 
  a 
  repetition 
  of 
  that 
  first 
  described. 
  Around 
  the 
  point 
  of 
  

   Craig-y-baredy, 
  some 
  of 
  the 
  rock 
  weathers 
  rough 
  and 
  vesicular, 
  but 
  

   others 
  of 
  the 
  old 
  lavas, 
  now 
  much 
  silicified, 
  seem 
  to 
  have 
  been 
  more 
  

   homogeneous, 
  and 
  lines 
  of 
  incipient 
  spherulites 
  mark 
  the 
  even 
  flow, 
  

   diverted 
  at 
  places 
  around 
  included 
  crystals, 
  which 
  contain 
  alteration- 
  

   products 
  of 
  chalcedony 
  and 
  viridite. 
  The 
  coast-section 
  of 
  the 
  rocks 
  

   ends 
  here 
  against 
  low 
  sandy 
  cliffs. 
  

  

  Inland, 
  over 
  the 
  promontory, 
  are 
  many 
  bosses 
  of 
  bare 
  rock, 
  and 
  

   at 
  two 
  places 
  it 
  has 
  been 
  quarried. 
  It 
  is 
  mainly 
  felsite, 
  compact 
  

   and 
  silicified, 
  often 
  breaking 
  with 
  a 
  subconchoidal 
  fracture. 
  Some 
  

   of 
  the 
  fresh 
  rock 
  is 
  grey 
  and 
  flinty-looking, 
  at 
  other 
  places 
  it 
  has 
  

   alternating 
  pinkish 
  and 
  greyish 
  bands. 
  The 
  fluidal 
  character, 
  

   moreover, 
  is 
  often 
  well 
  developed 
  by 
  weathering 
  as 
  a 
  furrowing 
  of 
  

   the 
  surface. 
  

  

  Rocks 
  from 
  Pen-y-chain 
  reminded 
  me, 
  lithologically, 
  of 
  Welsh 
  

   felsites 
  of 
  Bala 
  age, 
  and 
  the 
  neighbouring 
  district 
  is 
  classed 
  as 
  

  

  