﻿CRYSTALLINE 
  EOCKS 
  OF 
  THE 
  ALPS. 
  105 
  

  

  the 
  pass 
  to 
  Mitiersill, 
  contains 
  also 
  a 
  fair 
  amount 
  of 
  black 
  mica, 
  the 
  

   flakes 
  being 
  without 
  definite 
  orientation, 
  also 
  a 
  little 
  epidote. 
  The 
  

   remark 
  just 
  made 
  applies 
  also 
  to 
  this 
  specimen. 
  A 
  " 
  dark 
  variety 
  " 
  

   from 
  near 
  the 
  summit 
  contains 
  more 
  epidote 
  ; 
  the 
  quartz-grains 
  

   give 
  very 
  distinct 
  indications 
  of 
  an 
  old 
  crush-structure. 
  

  

  Two 
  specimens 
  of 
  the 
  more 
  granitoid 
  rocks 
  which 
  occur 
  near 
  the 
  

   top 
  of 
  the 
  pass 
  have 
  been 
  examined. 
  The 
  ground-mass 
  is 
  a 
  mosaic 
  

   of 
  quartz, 
  felspar 
  (rather 
  decomposed), 
  and 
  occasional 
  flakes 
  of 
  

   white 
  or 
  brown 
  mica, 
  in 
  which 
  occur 
  streaky 
  aggregates 
  of 
  quartz- 
  

   granules, 
  irregularly 
  bordered 
  grains, 
  sometimes 
  rather 
  elongated, 
  

   of 
  felspar, 
  in 
  one 
  specimen 
  of 
  microcline 
  or 
  of 
  orthoclase, 
  in 
  another 
  

   probably 
  of 
  plagioclase. 
  These 
  occasionally 
  contain 
  rounded 
  in- 
  

   clusions 
  of 
  quartz, 
  flakes 
  of 
  brown 
  or 
  green 
  mica, 
  and 
  in 
  one 
  case 
  

   (rather 
  abundantly) 
  of 
  white 
  mica. 
  The 
  structure 
  of 
  the 
  rocks 
  in- 
  

   dicates 
  modification 
  by 
  pressure, 
  but 
  at 
  no 
  recent 
  date, 
  for 
  the 
  con- 
  

   solidation 
  is 
  complete. 
  Anterior 
  to 
  that, 
  it 
  may 
  have 
  been 
  either 
  a 
  

   normal 
  granite 
  or 
  a 
  gneiss 
  of 
  Lauren 
  tian 
  type. 
  

  

  (/3) 
  Mica-schist 
  and 
  Gneiss 
  (Yon 
  Hauer) 
  (pp. 
  86, 
  89, 
  94). 
  

  

  I 
  have 
  examined 
  but 
  few 
  specimens 
  microscopically, 
  because, 
  in 
  

   one 
  case, 
  I 
  believe 
  the 
  gneiss 
  to 
  be 
  a 
  modified 
  granite, 
  in 
  others 
  

   because 
  the 
  specimens 
  were 
  not 
  collected 
  in 
  situ. 
  As 
  it 
  happened, 
  I 
  

   did 
  not 
  actually 
  cross 
  extensive 
  outcrops 
  of 
  the 
  group, 
  though 
  I 
  saw 
  

   its 
  rocks 
  frequently 
  in 
  moraines 
  and 
  torrent-debris, 
  as 
  well 
  as 
  in 
  the 
  

   Innsbruck 
  Museum. 
  It 
  may 
  suffice 
  to 
  say 
  of 
  these 
  that, 
  as 
  a 
  rule, 
  

   had 
  they 
  been 
  shown 
  me 
  as 
  coming 
  from 
  the 
  St.-Gothard 
  district, 
  I 
  

   should 
  have 
  seen 
  no 
  reason 
  to 
  doubt 
  the 
  statement. 
  The 
  specimens 
  

   examined 
  came 
  from 
  the 
  base 
  of 
  the 
  Rauberberg, 
  from 
  near 
  St. 
  

   Johann 
  and 
  Landeggsage, 
  in 
  the 
  Iselthal, 
  and 
  from 
  Matrei 
  on 
  the 
  

   Brenner. 
  They 
  all 
  contain 
  quartz, 
  white 
  and 
  brown 
  mica, 
  and 
  gar- 
  

   nets, 
  with 
  some 
  felspar, 
  the 
  constituents 
  being 
  commonly 
  about 
  *02" 
  

   in 
  diameter, 
  sometimes 
  a 
  little 
  more. 
  

  

  The 
  details 
  of 
  their 
  accessories, 
  and 
  the 
  minor 
  structures, 
  are 
  of 
  no 
  

   general 
  interest; 
  (a) 
  and 
  (c) 
  give 
  indications 
  of 
  mechanical 
  disturb- 
  

   ances 
  subsequent 
  to 
  the 
  production 
  of 
  their 
  foliated 
  structure 
  ; 
  (b) 
  is 
  

   not 
  quite 
  so 
  markedly 
  foliated 
  or 
  banded. 
  

  

  (y) 
  "Thonc/limmerscMefer" 
  series 
  (Thonschiefer, 
  Sfc. 
  of 
  Yon 
  Hauer). 
  

  

  As 
  intimated 
  in 
  the 
  text, 
  the 
  rocks 
  of 
  this 
  widely 
  spread 
  series 
  

   may 
  be 
  roughly 
  grouped 
  under 
  five 
  lithological 
  divisions 
  — 
  (a) 
  the 
  

   quartz-schists 
  and 
  quartzose 
  mica-schists, 
  (b) 
  the 
  lead-coloured 
  mica- 
  

   schists, 
  which 
  appear 
  to 
  be 
  the 
  most 
  characteristic 
  of 
  the 
  series 
  as 
  a 
  

   whole, 
  (c) 
  the 
  calc-mica-schists, 
  (d) 
  the 
  crystalline 
  limestones, 
  and 
  

   (e) 
  the 
  green 
  schists. 
  These 
  groups 
  may 
  be 
  briefly 
  described 
  as 
  

   follows 
  : 
  — 
  

  

  (a) 
  This 
  rock 
  is 
  chiefly 
  composed 
  of 
  quartz-grains 
  of 
  rather 
  

   irregular 
  outline, 
  which 
  with 
  crossing 
  nicols 
  commonly 
  exhibit 
  a 
  

   differently 
  tinted 
  border, 
  and 
  of 
  flakes 
  of 
  a 
  colourless 
  or 
  very 
  pale 
  

  

  