﻿290 
  PROP. 
  T. 
  G. 
  BO^EV 
  ON 
  SOME 
  XODTJLAK 
  

  

  felspathic 
  constituents) 
  and 
  of 
  films 
  of 
  a 
  glistening 
  pale 
  green 
  mineral, 
  

   together 
  with 
  ' 
  eyes 
  ' 
  of 
  quartz, 
  and 
  seemingly 
  vesicles, 
  about 
  as 
  big 
  

   as 
  a 
  pea 
  (but 
  flattened), 
  sometimes 
  merely 
  lined, 
  sometimes 
  nearly 
  

   filled 
  with 
  a 
  ferruginous 
  mineral, 
  which 
  is 
  often 
  associated 
  with 
  quartz. 
  

   This 
  rock 
  quickly 
  passes 
  into 
  a 
  less 
  fissile 
  and 
  much 
  more 
  coarsely 
  

   spheroidal 
  rock, 
  its 
  nodules 
  being 
  often 
  as 
  large 
  as 
  a 
  pigeon's 
  or 
  

   bantam's 
  egg, 
  ovoid 
  in 
  form 
  and 
  compressed-looking, 
  round 
  which 
  

   the 
  cleavage-planes 
  are 
  bent. 
  A 
  band 
  about 
  a 
  couple 
  of 
  yards 
  wide, 
  

   almost 
  free 
  from 
  " 
  nodules." 
  succeeds 
  ; 
  and 
  then 
  comes 
  another 
  band 
  

   like 
  the 
  former, 
  the 
  upper 
  part 
  of 
  which 
  is 
  crowded 
  with 
  nodules 
  

   (some 
  attaining 
  5 
  inches 
  in 
  longest 
  diameter). 
  These 
  weather 
  out 
  

   from 
  the 
  matrix 
  so 
  as 
  to 
  give 
  the 
  rock 
  the 
  aspect 
  of 
  a 
  coarse 
  

   conglomerate. 
  For 
  a 
  short 
  distance 
  beyond 
  this, 
  the 
  rock 
  (so 
  far 
  

   as 
  I 
  followed 
  it 
  up 
  the 
  hill-side) 
  is 
  not 
  exposed. 
  Then 
  succeed 
  

   some 
  rather 
  compact 
  dark-coloured 
  rocks 
  (cleaved) 
  of 
  ashy 
  aspect 
  

   and 
  evidently 
  sedimentary 
  origin. 
  

  

  Before 
  proceeding 
  to 
  describe 
  the 
  microscopic 
  structure 
  of 
  the 
  

   above 
  rocks 
  it 
  may 
  be 
  well 
  to 
  notice 
  briefly 
  two 
  or 
  three 
  other 
  sec- 
  

   tions. 
  By 
  the 
  wicket-gate 
  leading 
  down 
  to 
  the 
  Conway 
  Palls 
  from 
  

   the 
  road 
  to 
  Pandy 
  Mill 
  a 
  face 
  of 
  rock 
  is 
  exposed 
  in 
  which 
  we 
  find 
  : 
  — 
  

   (1) 
  rather 
  cleaved 
  felsite 
  with 
  many 
  concretions, 
  diameter 
  about 
  

   1 
  inch 
  ; 
  (2) 
  felsite 
  less 
  cleaved, 
  fewer 
  and 
  smaller 
  concretions; 
  (3) 
  

   felsite 
  irregularly 
  jointed, 
  somewhat 
  cleaved 
  ; 
  (4) 
  felsite 
  (?) 
  much 
  

   cleaved 
  ; 
  (5) 
  dark 
  ashy 
  rock, 
  much 
  cleaved. 
  The 
  bedding, 
  if 
  one 
  can 
  

   infer 
  it 
  from 
  (4) 
  and 
  (5), 
  appears 
  to 
  be 
  nearly 
  vertical. 
  The 
  next 
  

   section 
  occurs 
  in 
  the 
  Lledr 
  valley, 
  on 
  the 
  left 
  bank, 
  about 
  half 
  a 
  mile 
  

   above 
  the 
  new 
  viaduct. 
  Here 
  a 
  mass 
  of 
  felsite 
  occurs 
  (not 
  less 
  and 
  

   perhaps 
  more 
  than 
  forty 
  feet 
  thick) 
  between 
  ' 
  slabby 
  ' 
  ashy 
  slates 
  of 
  

   darker 
  colours 
  ; 
  nodules 
  abound 
  in 
  the 
  upper 
  part 
  of 
  this 
  rock, 
  which 
  

   forms 
  a 
  bold 
  cliff 
  with 
  a 
  talus 
  of 
  fallen 
  blocks 
  below. 
  Part 
  of 
  the 
  rock 
  

   appears 
  to 
  be 
  crowded 
  with 
  ovoid 
  or 
  almost 
  shuttle-shaped 
  nodules, 
  

   defined 
  in 
  part 
  by 
  the 
  bending 
  of 
  the 
  cleavage-surfaces 
  round 
  them. 
  

   Sometimes 
  these 
  are 
  hollow, 
  sometimes 
  wholly 
  filled 
  by 
  one 
  or 
  more 
  

   of 
  the 
  following 
  minerals 
  — 
  quartz, 
  a 
  brown 
  iron 
  oxide, 
  and 
  a 
  com- 
  

   pact 
  dull-green 
  flinty 
  substance. 
  I 
  found, 
  about 
  four 
  years 
  since, 
  

   on 
  the 
  slopes 
  at 
  the 
  head 
  of 
  Llyn 
  Idwal*, 
  a 
  fallen 
  block 
  of 
  a 
  similar 
  

   rock 
  which 
  had 
  evidently 
  come 
  from 
  the 
  crags 
  of 
  the 
  Glydyr. 
  

  

  I 
  proceed 
  now 
  to 
  describe 
  the 
  above 
  rocks 
  more 
  minutely, 
  and 
  take 
  

   first 
  a 
  specimen 
  of 
  the 
  normal 
  felsite 
  from 
  a 
  little 
  pit 
  close 
  to 
  the 
  

   Conway 
  Palls 
  Inn. 
  This 
  is 
  a 
  compact, 
  bluish-grey 
  rock, 
  weathering 
  

   to 
  a 
  paler 
  tint, 
  with 
  only 
  a 
  few 
  small 
  felspar 
  crystals 
  and 
  specks 
  of 
  a 
  

   dull 
  green 
  colour 
  scattered 
  throughout 
  the 
  ground-mass. 
  Under 
  the 
  

   microscope 
  the 
  rock 
  (Pl.X.fig.l) 
  exhibits 
  traces 
  of 
  a 
  fluidal 
  structure. 
  

   The 
  bands, 
  wavy 
  or 
  corrugated, 
  are 
  mainly 
  indicated 
  by 
  microliths 
  of 
  

   a 
  pale 
  gold-green 
  mineral, 
  apparently 
  of 
  rather 
  irregular 
  outline. 
  A 
  

   mineral, 
  presumably 
  the 
  same, 
  occurs 
  sparsely 
  in 
  small 
  aggregated 
  

   patches 
  (the 
  dull 
  green 
  specks 
  visible 
  to 
  the 
  naked 
  eye) 
  and 
  resembles 
  

   one 
  of 
  the 
  chlorite 
  group 
  rather 
  then 
  a 
  hornblende. 
  The 
  slide 
  

  

  * 
  The 
  Museum 
  of 
  Economic 
  Geology, 
  Jermyn 
  Street, 
  contains 
  a 
  specimen 
  

   from 
  the 
  Glydyr 
  Fawr, 
  as 
  well 
  as 
  specimens 
  from 
  Digoed, 
  near 
  Bettws-y-Coed. 
  

  

  