﻿NODULAR 
  FELSTONES 
  OP 
  THE 
  LLEIN. 
  261 
  

  

  marking 
  the 
  continuation 
  of 
  the 
  rock-laminse. 
  As 
  has 
  been 
  noticed 
  

   in 
  other 
  cases, 
  the 
  lamination 
  appears 
  interrupted 
  by 
  the 
  interior 
  of 
  

   the 
  nodules 
  * 
  ; 
  a 
  breaking 
  of 
  the 
  laminae 
  across 
  vesicles 
  is, 
  however, 
  

   by 
  no 
  means 
  an 
  unfamiliar 
  circumstance 
  in 
  vesicular 
  pumice. 
  

  

  Fig. 
  6. 
  — 
  Section 
  of 
  Nodule 
  with 
  protuberant 
  ridges 
  ; 
  from 
  near 
  rift 
  

   along 
  East 
  coast 
  of 
  Pen-y-chain. 
  (Nat. 
  size.) 
  

  

  The 
  crust 
  of 
  the 
  nodule 
  shows 
  concentric 
  banding, 
  and, 
  when 
  magnified, 
  radial 
  

   structure, 
  as 
  well 
  as 
  faint 
  traces 
  of 
  the 
  continuation 
  of 
  rock-laminse 
  (not 
  

   shown 
  in 
  diagram). 
  It 
  contains 
  porphyritic 
  felspars 
  much 
  decomposed 
  

   and 
  chalcedonized. 
  

  

  a. 
  (?) 
  Portion 
  of 
  altered 
  matrix, 
  not 
  spherulitic. 
  

  

  The 
  chalcedonic 
  deposit 
  within 
  consists 
  of: 
  — 
  

  

  b. 
  Layer 
  of 
  fibrous 
  chalcedony. 
  

  

  c. 
  Chalcedony 
  in 
  mamillated 
  or 
  spherulitic 
  masses, 
  meeting 
  along 
  

  

  polygonal 
  boundaries. 
  

  

  In 
  a 
  baylet 
  a 
  short 
  distance 
  northward 
  of 
  this 
  small 
  rift 
  agate 
  

   nodules 
  are 
  found, 
  developed 
  along 
  certain 
  beds 
  (fig. 
  7). 
  In 
  the 
  

   northern 
  cliff 
  the 
  specimens 
  are 
  small, 
  from 
  half 
  an 
  inch 
  to 
  one 
  inch 
  

   across, 
  and 
  are 
  crowded 
  through 
  a 
  finely 
  laminated 
  matrix. 
  The 
  beds 
  

   are 
  crumpled 
  into 
  an 
  S 
  _sna 
  P 
  e 
  5 
  an 
  d 
  become 
  approximately 
  vertical, 
  

   marking 
  probably 
  the 
  position 
  of 
  a 
  fault. 
  Westward, 
  at 
  the 
  head 
  

   of 
  the 
  recess, 
  the 
  nodules 
  are 
  larger, 
  two 
  or 
  three 
  inches 
  across. 
  

   They 
  are 
  sparsely 
  developed 
  in 
  certain 
  firmer 
  layers, 
  in 
  one 
  of 
  which 
  

   I 
  found 
  an 
  aggregated 
  spherulitic 
  hemisphere 
  (of 
  about 
  one 
  inch 
  

   radius) 
  apparently 
  without 
  a 
  central 
  cavity; 
  but 
  the 
  transitions 
  

   between 
  solid 
  spherulites 
  and 
  those 
  with 
  unfilled 
  hollow 
  centres 
  

   quoted 
  from 
  other 
  localities 
  f 
  seem 
  to 
  be 
  not 
  common 
  in 
  the 
  Lleyn. 
  

  

  * 
  Mr. 
  Cole, 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xlii. 
  p. 
  188. 
  Mr. 
  Iddings, 
  Amer. 
  

   Journ. 
  of 
  Sci. 
  vol. 
  xxxiii. 
  p. 
  36. 
  

  

  t 
  The 
  "normal" 
  and 
  "abnormal" 
  globules 
  of 
  Delesse. 
  Mem. 
  Soc. 
  Geol. 
  de 
  

   Fr. 
  2 
  e 
  ser. 
  t. 
  iv. 
  p. 
  300 
  ; 
  and 
  Bull. 
  Soc. 
  Geol. 
  de 
  Fr. 
  2 
  e 
  ser. 
  t. 
  ix. 
  p. 
  432 
  ; 
  (Thur. 
  

   Wald.) 
  Zeitschr. 
  d. 
  d. 
  geol. 
  Gesell. 
  1877, 
  Bd. 
  xxix. 
  p. 
  420; 
  (Jersey) 
  Bull. 
  Soc. 
  Geol. 
  

   de 
  Fr. 
  3 
  e 
  ser. 
  t. 
  xii. 
  p. 
  287 
  ; 
  (Hungary) 
  Jahrb. 
  k.-k. 
  geol. 
  Eeichs. 
  1866, 
  p. 
  90. 
  

  

  