﻿CRYSTALLINE 
  ROCKS 
  OP 
  THE 
  ALPS. 
  101 
  

  

  angular 
  (sometimes 
  four-sided) 
  to 
  somewhat 
  rounded 
  in 
  outline, 
  

   often 
  about 
  -03" 
  wide. 
  They 
  contain 
  tiny 
  flakes 
  of 
  brown 
  mica, 
  

   black 
  granules, 
  and 
  (much 
  more 
  abundantly) 
  minute 
  belonites, 
  which, 
  

   with 
  low 
  powers, 
  appear 
  quite 
  black, 
  but 
  with 
  high 
  powers 
  are 
  seen 
  

   to 
  be 
  translucent 
  and 
  of 
  a 
  pale 
  dull 
  tint. 
  These 
  last 
  are 
  sometimes 
  

   so 
  abundant 
  as 
  to 
  completely 
  discolour 
  parts 
  of 
  a 
  grain 
  of 
  kyanite. 
  

   They 
  are 
  arranged 
  in 
  roughly 
  parallel 
  lines 
  or 
  streamers. 
  The 
  

   quartz 
  occurs 
  commonly 
  in 
  clustered 
  grains, 
  with 
  the 
  usual 
  habit 
  of 
  

   mica-schist. 
  All 
  the 
  constituents 
  suggested 
  that 
  the 
  rock 
  has 
  been 
  

   considerably 
  modified 
  by 
  pressure 
  subsequent 
  to 
  its 
  first 
  consolid- 
  

   ation. 
  The 
  mica 
  is 
  often 
  beautifully 
  bent 
  and 
  puckered 
  ; 
  the 
  kyanite 
  

   sometimes 
  appears 
  to 
  have 
  been 
  broken 
  and 
  otherwise 
  disturbed 
  in 
  

   position. 
  This 
  also 
  seems 
  indicated 
  by 
  the 
  fact 
  that 
  the 
  dusky 
  

   black 
  lines 
  mentioned 
  above, 
  while 
  generally 
  lying 
  approximately 
  

   in 
  the 
  same 
  direction 
  in 
  the 
  slide, 
  are 
  sometimes 
  markedly 
  diver- 
  

   gent, 
  as 
  though 
  a 
  grain 
  or 
  a 
  fragment 
  of 
  a 
  crystal 
  had 
  been 
  twisted 
  

   out 
  of 
  its 
  original 
  position. 
  If 
  I 
  am 
  right 
  in 
  regarding 
  these 
  en- 
  

   closures 
  in 
  the 
  kyanite 
  as 
  anterior 
  to 
  the 
  mechanical 
  disturbance, 
  it 
  

   would 
  seem 
  highly 
  probable 
  that 
  they 
  were 
  in 
  some 
  way 
  a 
  record 
  

   of 
  a 
  differential 
  arrangement 
  of 
  constituents 
  prior 
  to 
  the 
  first 
  for- 
  

   mation 
  of 
  the 
  mineral, 
  and 
  belong 
  to 
  a 
  very 
  early 
  epoch 
  in 
  the 
  

   history 
  of 
  the 
  rock. 
  

  

  (6) 
  Schist 
  iviih 
  contorted 
  Quartz-veins 
  by 
  the 
  entrance 
  of 
  Livet 
  (p. 
  72). 
  

   — 
  This 
  rock 
  chiefly 
  consists 
  of 
  quartz, 
  mica, 
  garnet, 
  and 
  felspar. 
  The 
  

   first 
  mineral 
  calls 
  for 
  no 
  special 
  remark. 
  The 
  mica 
  is 
  mainly 
  biotite, 
  

   but 
  there 
  are 
  a 
  few 
  flakes 
  of 
  a 
  pale 
  mica, 
  as 
  above 
  described. 
  The 
  

   garnets 
  are 
  small, 
  often 
  about 
  '02" 
  in 
  diameter, 
  roundish 
  in 
  outline, 
  

   of 
  a 
  pale 
  reddish 
  or 
  yellowish-brown 
  colour, 
  but 
  often 
  darkened 
  with 
  

   dusky 
  enclosures, 
  and 
  frequently 
  showing 
  one 
  rather 
  marked 
  cleav- 
  

   age. 
  But 
  little 
  felspar 
  can 
  now 
  be 
  identified, 
  and 
  that 
  is 
  plagio- 
  

   clase 
  ; 
  but 
  many 
  of 
  the 
  quartz-grains 
  are 
  full 
  of 
  "dusty 
  " 
  particles, 
  

   as 
  if 
  replacing 
  a 
  felspar. 
  The 
  rock 
  has 
  evidentty 
  undergone 
  

   mechanical 
  disturbance, 
  but 
  is 
  not 
  notably 
  crushed. 
  As 
  the 
  above 
  

   description 
  shows, 
  it 
  is 
  intermediate 
  between 
  a 
  mica-schist 
  and 
  a 
  

   kinzigite. 
  

  

  (/3) 
  Gneiss 
  of 
  the 
  Combe 
  de 
  Malasal, 
  $c. 
  

  

  (a) 
  Gneiss 
  in 
  the 
  glen 
  West 
  of 
  Freney 
  (p. 
  72). 
  — 
  The 
  rock 
  consists 
  of 
  

   quartz, 
  felspar, 
  mica, 
  and 
  some 
  epidote. 
  The 
  last 
  occurs 
  in 
  granu- 
  

   lar 
  streaks, 
  and 
  is 
  clearly 
  of 
  later 
  origin. 
  The 
  mica 
  varies 
  from 
  

   brown 
  to 
  nearly 
  colourless, 
  and 
  occurs 
  in 
  rather 
  small 
  flakes 
  ; 
  the 
  

   felspar 
  is 
  rather 
  decomposed, 
  but 
  a 
  plagioclase 
  and 
  probably 
  ortho- 
  

   clase 
  can 
  be 
  recognized. 
  The 
  structure 
  of 
  this 
  rock 
  has 
  been 
  much 
  

   modified 
  by 
  pressure 
  ; 
  in 
  many 
  parts, 
  the 
  original 
  grains 
  of 
  quartz 
  

   and 
  felspar 
  have 
  been 
  broken 
  up 
  into 
  a 
  " 
  mosaic" 
  of 
  granules, 
  and 
  I 
  

   think 
  the 
  mica 
  has 
  similarly 
  suffered. 
  Thus 
  it 
  is 
  very 
  difficult 
  to 
  

   decide 
  upon 
  the 
  antecedent 
  condition 
  of 
  the 
  rock, 
  but 
  I 
  think 
  that 
  

   its 
  constituents 
  were 
  banded, 
  and 
  the 
  relations 
  of 
  the 
  quartz 
  and 
  

   felspar 
  were 
  those 
  usual 
  in 
  an 
  old 
  gneiss, 
  not 
  in 
  a 
  granite 
  ; 
  i. 
  e. 
  I 
  

  

  