﻿250 
  MISS 
  C. 
  A. 
  RAISIN 
  OX 
  SOME 
  

  

  belonging 
  to 
  that 
  formation; 
  but 
  the 
  nearest 
  fossiliferous 
  outcrop 
  

   recorded- 
  is 
  distant 
  two 
  or 
  three 
  miles. 
  The 
  country 
  around 
  is 
  

   drift-covered, 
  but 
  I 
  found 
  some 
  indications 
  of 
  stratigraphical 
  position 
  

   near 
  the 
  streamlet 
  which 
  flows 
  to 
  Llym-gwyn. 
  Felsite 
  of 
  the 
  

   usual 
  type 
  occurs 
  close 
  by 
  the 
  cottages, 
  although 
  further 
  south, 
  just 
  

   beyond 
  the 
  railway, 
  is 
  one 
  outcrop, 
  which 
  seems 
  probably 
  an 
  ash, 
  

   consisting 
  of 
  broken 
  felstone 
  and 
  some 
  slate. 
  Walking 
  northward 
  

   for 
  about 
  thirty 
  yards, 
  along 
  the 
  path 
  east 
  of 
  the 
  stream, 
  we 
  pass 
  

   over 
  a 
  small 
  exposure 
  of 
  a 
  peculiar 
  black 
  and 
  white 
  rock, 
  which 
  

   has 
  a 
  squeezed 
  look. 
  The 
  milk-white 
  fragments 
  of 
  felstone 
  exhibit, 
  

   under 
  the 
  microscope, 
  traces 
  of 
  banding, 
  possibly 
  fluidal 
  ; 
  they 
  are, 
  

   at 
  places, 
  spherulitized, 
  and 
  contain 
  abundant 
  microliths 
  or 
  globulites. 
  

   Slat} 
  T 
  fragments 
  are 
  entangled, 
  which 
  are 
  often 
  rounded, 
  and 
  some 
  

   are 
  beginning 
  to 
  crack 
  along 
  curving 
  boundaries. 
  This 
  rock 
  seems 
  

   to 
  be 
  a 
  volcanic 
  agglomerate, 
  which 
  has 
  become 
  schistose 
  from 
  

   pressure. 
  

  

  Along 
  the 
  next 
  200 
  yards, 
  well-banded 
  ashy 
  and 
  slaty 
  beds 
  occur 
  

   here 
  and 
  there, 
  in 
  which 
  I 
  found 
  a 
  few 
  small 
  fossils. 
  These 
  were 
  

   several 
  squeezed 
  examples 
  of 
  Trinudeus 
  concentricus, 
  small 
  specimens 
  

   of 
  Leptcena 
  sericea, 
  a 
  distorted 
  Orthis 
  elega?itula, 
  and 
  other 
  young 
  

   forms 
  of 
  Ortliis 
  (sp. 
  ?). 
  This 
  assemblage 
  has 
  a 
  Bala 
  facies, 
  and 
  Mr. 
  

   Etheridge, 
  who 
  very 
  kindly 
  identified 
  some 
  of 
  the 
  specimens 
  for 
  

   me, 
  gave 
  his 
  opinion, 
  from 
  the 
  fossil 
  and 
  lithological 
  characters, 
  

   that 
  the 
  strata 
  may 
  be 
  taken 
  as 
  belonging, 
  in 
  all 
  probability, 
  to 
  that 
  

   formation. 
  The 
  microscope 
  shows 
  quartz 
  and 
  plagioclase 
  felspar 
  in 
  

   small 
  angular 
  fragments 
  and 
  a 
  minute 
  secondary 
  mineral 
  ; 
  the 
  

   meshwork 
  of 
  dark 
  cleavage-planes 
  crosses 
  the 
  beds 
  almost 
  at 
  right 
  

   angles. 
  

  

  Some 
  30 
  yards 
  succeed, 
  occupied 
  by 
  a 
  felspathic 
  rock, 
  part 
  of 
  

   which 
  forms 
  two 
  small 
  craglets 
  overlooking 
  the 
  stream. 
  The 
  beds, 
  

   although 
  uniform, 
  are 
  well 
  marked, 
  dipping 
  about 
  ET.N'.E. 
  at 
  an 
  

   angle 
  of 
  45° 
  or 
  50°. 
  They 
  are 
  crossed 
  by 
  a 
  cleavage 
  similar 
  to 
  

   that 
  of 
  the 
  slaty 
  and 
  ashy 
  strata, 
  and 
  the 
  subsequent 
  pressure, 
  

   which 
  thus 
  modified 
  the 
  rock, 
  doubtless 
  caused 
  the 
  fracturing 
  of 
  

   the 
  included 
  felspar. 
  The 
  appearance 
  of 
  the 
  slide 
  is 
  suggestive, 
  as 
  

   Professor 
  Bonney 
  pointed 
  out 
  to 
  me, 
  of 
  a 
  very 
  porphyritic 
  rhyolite, 
  

   now 
  devitrified 
  and 
  crushed. 
  

  

  The 
  next 
  outcrop 
  is 
  of 
  a 
  compact 
  pale 
  grey 
  rock, 
  which 
  proves 
  to 
  

   be 
  a 
  felstone, 
  enclosing 
  small 
  fragments 
  of 
  slate, 
  quartz, 
  and 
  felspar. 
  

   The 
  fluidal 
  layers 
  are 
  much 
  contorted, 
  and 
  exhibit 
  a 
  deposit 
  of 
  a 
  

   minute 
  secondary 
  mineral. 
  

  

  Thus 
  the 
  Pen-y-chain 
  felsites 
  seem 
  to 
  pass 
  upward 
  into 
  a 
  series 
  

   of 
  agglomerates 
  and 
  lavas, 
  with 
  interbedded 
  slates 
  and 
  grits, 
  including 
  

   Bala 
  fossils. 
  If 
  the 
  igneous 
  strata 
  of 
  the 
  Snowdon 
  district 
  once 
  

   extended 
  over 
  the 
  Lleyn, 
  as 
  suggested 
  in 
  the 
  Survey 
  Memoir 
  *, 
  the 
  

   Pen-y-chain 
  mass 
  may 
  be 
  a 
  remnant 
  of 
  such 
  volcanic 
  accumu- 
  

   lations. 
  

  

  The 
  small 
  area 
  of 
  Careg-y-defaid 
  does 
  not 
  need 
  separate 
  detailed 
  

   description. 
  • 
  A 
  fine 
  fluidal 
  structure 
  in 
  a 
  porphyritic 
  rock 
  is 
  well 
  

   * 
  The 
  Geology 
  of 
  tfortk 
  Wales, 
  pp. 
  218, 
  221. 
  

  

  