﻿252 
  

  

  inss 
  c. 
  a. 
  kaisin 
  on 
  soue 
  

  

  curves, 
  and 
  appears 
  also 
  minutely 
  broken, 
  like 
  crackled 
  china, 
  with 
  

   small 
  spherulites 
  within 
  the 
  finer 
  network. 
  

  

  Other 
  spherulites, 
  unmarked 
  by 
  the 
  black 
  cross, 
  and 
  exhibiting 
  

   radial 
  fibres, 
  are 
  connected 
  with 
  various 
  micrographic 
  or 
  dendritic 
  

   formations. 
  These 
  are 
  occasionally 
  developed 
  in 
  relation 
  to 
  dark 
  

   perlitic 
  lines. 
  Some 
  groups 
  form 
  incipient 
  spherulites 
  within 
  

   angular 
  spaces. 
  Prom 
  others 
  of 
  the 
  lines, 
  microlithic 
  tufts 
  start, 
  

   like 
  sedge-plants 
  along 
  the 
  water's 
  edge, 
  similar 
  to 
  the 
  dendritic 
  

   growth 
  described 
  in 
  Arran 
  rocks 
  *. 
  One 
  slide, 
  cut 
  from 
  the 
  junction 
  

   of 
  a 
  non-spherulitic 
  with 
  a 
  spherulitic 
  stratum, 
  shows 
  that 
  the 
  

   boundary 
  has 
  given 
  rise 
  to 
  a 
  continuous 
  series 
  of 
  fibrous 
  tufts, 
  like 
  

   those 
  formed 
  along 
  the 
  border 
  of 
  adherent 
  layers 
  of 
  glass 
  t. 
  

  

  Some 
  of 
  the 
  micrographic 
  structure 
  in 
  the 
  Pen-y-chain 
  slides 
  has 
  

   resulted 
  from 
  an 
  alteration 
  of 
  felspar 
  : 
  of 
  such 
  development, 
  Prof. 
  

   Judd 
  has 
  given 
  one 
  illustration 
  — 
  and 
  seems 
  to 
  promise 
  further 
  

   examples 
  — 
  from 
  rocks 
  of 
  the 
  "Western 
  Islands 
  of 
  Scotland 
  $. 
  In 
  

   the 
  Lleyn 
  specimens 
  the 
  alterations 
  may 
  result 
  in 
  granular 
  pseudo- 
  

   morphs 
  ; 
  but 
  these 
  are 
  related 
  to 
  examples, 
  as 
  in 
  those 
  described 
  by 
  

   aEt. 
  R. 
  D. 
  Irving, 
  in 
  which 
  the 
  " 
  corrosion 
  or 
  secondary 
  quartz 
  " 
  

   forms 
  " 
  rows 
  of 
  graphic 
  particles 
  " 
  along 
  the 
  cleavage-directions, 
  or 
  

   develops 
  as 
  "fine 
  lines 
  "§. 
  One 
  group 
  of 
  felspars 
  has 
  been 
  thus 
  

   metamorphosed 
  (fig. 
  3). 
  A 
  square 
  end 
  of 
  one 
  crystal 
  shows 
  three 
  

  

  Pig. 
  3. 
  — 
  Micrographic 
  Structure 
  modifying 
  successive 
  zones 
  of 
  a 
  

   Porphyritic 
  Felspar. 
  From 
  Pen-y-chain 
  beach. 
  (Enlarged 
  

   40 
  diameters.) 
  

  

  (MMB0K 
  

  

  n 
  

  

  

  WMk^-^^^^yn: 
  

  

  distinct 
  zones, 
  the 
  outermost 
  of 
  which 
  presents 
  a 
  rather 
  irregular 
  

   fimbriate 
  growth. 
  The 
  zone 
  next 
  within 
  has 
  finer 
  striae, 
  which 
  

   meet 
  at 
  the 
  corners 
  along 
  diagonal 
  lines, 
  forming 
  in 
  miniature 
  a 
  

  

  * 
  " 
  On 
  Rock 
  Structures 
  in 
  Arran," 
  Prof. 
  Bonney, 
  Geol. 
  Mag. 
  Nov. 
  1877, 
  

   p. 
  508. 
  

  

  t 
  Pres. 
  Addr. 
  Geol. 
  Soc, 
  Prof. 
  Bonney, 
  1885, 
  p. 
  6o. 
  

  

  i 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  1886, 
  p. 
  73, 
  pi. 
  vii. 
  fig. 
  8. 
  

  

  § 
  U. 
  S. 
  Geol. 
  Surv. 
  Copper-bearing 
  Rocks 
  of 
  L. 
  Superior, 
  R. 
  D. 
  Irving, 
  

   p. 
  113, 
  pi. 
  xiv. 
  figs. 
  1, 
  2, 
  pi. 
  xy. 
  fig. 
  4. 
  See 
  also 
  Min. 
  Micr. 
  pL 
  ix., 
  pi. 
  x. 
  fig. 
  2, 
  

   pi. 
  xi. 
  fig. 
  1. 
  Brit. 
  Petrogr. 
  Micro-pegmatite 
  in 
  pi. 
  xxxv. 
  ' 
  

  

  f.2. 
  

  

  