﻿106 
  PKOF. 
  T. 
  G. 
  BONNET 
  ON 
  TWO 
  TEAVEESES 
  OF 
  THE 
  

  

  greenish-grey 
  mica, 
  "which 
  are 
  often 
  about 
  -01" 
  long, 
  the 
  former 
  

   being 
  sometimes 
  a 
  little 
  larger. 
  Here 
  and 
  there 
  is 
  a 
  little 
  ferrite 
  

   and 
  (rarely) 
  a 
  cluster 
  of 
  minute 
  mica-films, 
  with 
  perhaps 
  one 
  or 
  

   two 
  very 
  small 
  colourless 
  garnets. 
  The 
  structure 
  suggests 
  that 
  the 
  

   rock 
  has 
  been 
  to 
  some 
  extent 
  sheared 
  by 
  pressure. 
  It 
  bears 
  a 
  

   general 
  resemblance 
  to 
  certain 
  of 
  the 
  quartz-schists 
  of 
  the 
  " 
  newer 
  

   gneiss 
  " 
  series 
  of 
  the 
  Highlands, 
  especially 
  those 
  which 
  seem 
  less 
  

   affected 
  by 
  the 
  results 
  of 
  the 
  overthrust. 
  It 
  is 
  difficult 
  to 
  say 
  how 
  

   far 
  the 
  mica 
  is 
  a 
  secondary 
  product 
  ; 
  I 
  incline 
  to 
  regard 
  it 
  as 
  in 
  the 
  

   main 
  anterior 
  to 
  the 
  pressure-modification, 
  but 
  to 
  some 
  extent 
  sub- 
  

   sequently 
  recrystallized 
  ; 
  for 
  the 
  outline 
  of 
  the 
  flakes 
  is 
  commonly 
  

   distinctly 
  rectilineal. 
  

  

  Of 
  the 
  more 
  micaceous 
  varieties, 
  specimens 
  have 
  been 
  examined 
  

   from 
  the 
  quarry 
  near 
  Brunecken 
  (p. 
  85), 
  and 
  from 
  above 
  the 
  castle 
  

   on 
  the 
  route 
  from 
  Mittersill 
  to 
  Kitzbiihel 
  (p. 
  91). 
  Both 
  consist 
  

   mainly 
  of 
  quartz 
  and 
  mica, 
  chiefly 
  colourless 
  or 
  very 
  pale 
  green. 
  A 
  

   few 
  grains 
  may 
  be 
  felspar 
  or 
  kyanite. 
  Among 
  the 
  microliths, 
  zircon 
  

   and 
  rubite 
  are 
  probably 
  present. 
  In 
  the 
  former 
  rock 
  the 
  mica 
  is 
  

   often 
  slightly 
  coloured, 
  and 
  the 
  bands 
  are 
  frequently 
  more 
  or 
  less 
  

   ferrite-stained, 
  sometimes 
  rendered 
  almost 
  opaque. 
  Both 
  have 
  evi- 
  

   dently 
  been 
  much 
  disturbed 
  subsequent 
  to 
  the 
  first 
  foliation 
  ; 
  the 
  

   former, 
  as 
  described, 
  shows 
  a 
  cleavage-foliation 
  superinduced 
  on 
  a 
  

   stratification-foliation. 
  The 
  latter 
  has 
  been 
  so 
  much 
  crushed 
  that 
  

   the 
  first-named 
  foliation 
  dominates, 
  while 
  the 
  latter 
  can 
  only 
  here 
  

   and 
  there 
  be 
  traced. 
  As 
  might 
  be 
  expected, 
  the 
  quartz 
  constituent 
  

   varies 
  in 
  size, 
  much 
  of 
  it 
  being 
  quite 
  minute. 
  This 
  gives 
  the 
  rock 
  

   at 
  first 
  sight 
  a 
  clastic 
  aspect, 
  but 
  I 
  have 
  no 
  doubt 
  this 
  is 
  secondary 
  

   — 
  the 
  result 
  of 
  crushing. 
  At 
  the 
  same 
  time 
  I 
  believe 
  the 
  rock 
  to 
  

   have 
  begun 
  its 
  history 
  as 
  a 
  sediment, 
  though 
  the 
  original 
  constituents 
  

   can 
  no 
  longer 
  be 
  recognized. 
  

  

  (6) 
  Specimens 
  of 
  this 
  group 
  have 
  been 
  examined 
  from 
  various 
  

   localities. 
  Perhaps 
  the 
  most 
  characteristic 
  are 
  those 
  from 
  the 
  en- 
  

   trance 
  of 
  the 
  Iselthal 
  (p. 
  86), 
  and 
  from 
  near 
  Steinach 
  on 
  the 
  Brenner 
  

   (p. 
  94). 
  The 
  chief 
  constituents 
  are 
  quartz 
  and 
  mica, 
  the 
  latter 
  com- 
  

   monly 
  white, 
  but 
  occasionally 
  pale 
  green. 
  The 
  Iselthal 
  specimen 
  

   contains 
  a 
  fair 
  amount 
  of 
  hydrous 
  green 
  mica 
  or 
  chlorite 
  and 
  more 
  

   or 
  less 
  " 
  ferrite 
  " 
  with 
  a 
  little 
  kyanite. 
  The 
  Steinach 
  specimen 
  has 
  

   its 
  mica 
  associated 
  with 
  considerable 
  quantities 
  of 
  opacite, 
  so 
  that 
  

   the 
  slide 
  is 
  in 
  parts 
  streaked 
  with 
  black. 
  Grains 
  of 
  kyanite 
  are 
  

   fairly 
  abundant. 
  This 
  rock, 
  in 
  short, 
  has 
  a 
  remarkable 
  resemblance 
  

   to 
  some 
  of 
  the 
  lead-coloured 
  schists 
  from 
  South 
  Devon 
  *. 
  Evidently 
  

   it 
  was 
  once 
  a 
  foliated 
  rock, 
  with 
  alternating 
  quartzose 
  and 
  mica- 
  

   ceous 
  bands 
  ; 
  these 
  have 
  been 
  crumpled 
  and 
  " 
  van 
  dyked," 
  and 
  a 
  

   strain-slip 
  cleavage 
  developed 
  in 
  parts, 
  parallel, 
  of 
  course, 
  with 
  the 
  

   cleavage-foliation, 
  which 
  now 
  dominates 
  in 
  the 
  mass. 
  The 
  Iselthal 
  

   specimen 
  has 
  a 
  similar 
  history, 
  though 
  it 
  is 
  not 
  quite 
  so 
  markedly 
  

   banded. 
  Specimens 
  from 
  the 
  Zillerthal 
  and 
  from 
  the 
  ascent 
  from 
  

   Kitzbiihel 
  are 
  a 
  little 
  more 
  quartzose, 
  and 
  brown 
  mica 
  seems 
  more 
  

  

  * 
  Quart. 
  Joum. 
  Geol. 
  Soc. 
  vol. 
  xl. 
  p. 
  1, 
  & 
  vol. 
  xliii. 
  p. 
  715. 
  

  

  