﻿94 
  PEOF. 
  T. 
  G. 
  BONNET 
  ON 
  TWO 
  TEAVEESES 
  OF 
  THE 
  

  

  duced. 
  If 
  the 
  porphyritic 
  rock 
  be 
  igneous, 
  the 
  gneisses 
  and 
  mica- 
  

   schists 
  in 
  this 
  glen 
  are, 
  as 
  a 
  rule, 
  of 
  a 
  rather 
  less 
  ancient 
  type 
  than 
  

   those 
  in 
  the^Grschlossthal 
  and 
  on 
  the 
  Yelber-Tauern 
  pass, 
  and 
  resemble 
  

   those 
  which 
  occur 
  on 
  the 
  south 
  side 
  of 
  the 
  former. 
  Porphyritic 
  

   gneissoid 
  rock, 
  similar 
  to 
  the 
  above-mentioned, 
  occasionally 
  asso- 
  

   ciated 
  with 
  a 
  fine-grained 
  gneiss 
  — 
  as 
  if 
  the 
  one 
  were 
  intrusive 
  in 
  the 
  

   other 
  prior 
  to 
  the 
  final 
  pressure 
  — 
  occurs 
  in 
  the 
  Zemmthal 
  as 
  far 
  as 
  

   Ginsling, 
  and 
  in 
  the 
  lower 
  part 
  of 
  the 
  Moitenthal, 
  and 
  was 
  the 
  

   chief 
  rock 
  seen 
  by 
  us 
  in 
  situ 
  ; 
  but 
  below 
  that 
  hamlet 
  in 
  the 
  one, 
  and 
  

   above 
  the 
  "Klamm" 
  in 
  the 
  other, 
  lateral 
  torrents 
  bring 
  down 
  

   gneisses 
  and 
  schists 
  of 
  Lepontine 
  type, 
  similar 
  to 
  those 
  just 
  men- 
  

   tioned. 
  Thus 
  it 
  seems 
  that 
  on 
  both 
  sides 
  of 
  the 
  watershed 
  the 
  

   Central 
  Gneiss 
  becomes 
  less 
  strong 
  and 
  massive 
  as 
  we 
  proceed 
  outward, 
  

   and 
  is 
  otherwise 
  modified 
  ; 
  in 
  short, 
  it 
  changes 
  from 
  a 
  Laurentian 
  

   towards 
  a 
  Montalban 
  tj 
  T 
  pe, 
  without, 
  however, 
  quite 
  attaining 
  to 
  the 
  

   latter. 
  

  

  "We 
  made 
  a 
  short 
  expedition 
  from 
  Innsbriick 
  up 
  the 
  north 
  side 
  of 
  

   the 
  Brenner 
  pass 
  in 
  order 
  to 
  examine 
  the 
  " 
  Thonglimmerschiefer 
  " 
  and 
  

   the 
  mica-schist. 
  The 
  former 
  rock, 
  which 
  we 
  saw 
  in 
  many 
  places 
  from 
  

   the 
  railway 
  and 
  examined 
  in 
  situ 
  above 
  Steinach, 
  is 
  the 
  usual 
  lead- 
  

   coloured 
  schist, 
  generally 
  greatly 
  crushed 
  (Appendix, 
  p. 
  106), 
  but 
  in 
  

   which 
  occasionally 
  the 
  two 
  foliations 
  may 
  be 
  distinguished. 
  The 
  

   mica-schist 
  was 
  examined 
  in 
  a 
  quarry 
  near 
  Alatrei. 
  It 
  is 
  a 
  fairly 
  

   well-banded 
  rock, 
  the 
  cleavage-foliation 
  apparently 
  coinciding 
  gene- 
  

   rally 
  with 
  the 
  stratification-foliation 
  and 
  both 
  dipping 
  roughly 
  S."W. 
  

   at 
  about 
  25°, 
  an 
  unusually 
  low 
  angle. 
  In 
  it 
  occur 
  lenticular 
  masses, 
  

   sometimes 
  from 
  1 
  foot 
  to 
  2 
  feet 
  thick, 
  which 
  we 
  considered 
  to 
  be 
  

   an 
  intrusive 
  granite 
  modified 
  by 
  subsequent 
  pressure. 
  On 
  the 
  right 
  

   bank 
  of 
  the 
  valley, 
  according 
  to 
  Yon 
  Hauer, 
  is 
  an 
  outlier 
  of 
  Triassic 
  

   rock, 
  in 
  which 
  are 
  two 
  rounded 
  patches 
  of 
  serpentine. 
  One 
  of 
  the 
  

   latter 
  we 
  examined 
  carefully 
  in 
  a' 
  large 
  quarry. 
  It 
  was 
  tremen- 
  

   dously 
  crushed 
  and 
  veined 
  with 
  calcite. 
  Here 
  also 
  schist 
  is 
  seen, 
  

   apparently 
  overlain 
  by 
  the 
  serpentine. 
  The 
  last 
  great 
  crushing 
  and 
  

   the 
  subsequent 
  mineral 
  changes 
  make 
  the 
  relations 
  of 
  these 
  rocks 
  

   extremely 
  puzzling, 
  but 
  I 
  believe 
  the 
  following 
  to 
  be 
  the 
  most 
  pro- 
  

   bable 
  account. 
  The 
  serpentine 
  was 
  probably 
  intrusive 
  in 
  the 
  schist, 
  

   the 
  former 
  rock 
  was 
  subjected 
  to 
  pressure, 
  and 
  the 
  fissures 
  afterwards 
  

   were 
  filled 
  with 
  calcite 
  (perhaps 
  obtained 
  from 
  overlying 
  limestones)*. 
  

   Then 
  all 
  the 
  rocks 
  were 
  folded 
  together 
  and 
  rendered 
  fissile 
  by 
  

   crushing. 
  The 
  resulting 
  structure 
  has 
  the 
  usual 
  S."W. 
  strike. 
  Ac- 
  

   cording 
  to 
  Yon 
  Hauer's 
  map 
  the 
  serpentine 
  appears 
  to 
  be 
  also 
  in- 
  

   trusive 
  in 
  the 
  Trias 
  ; 
  but 
  on 
  this 
  point 
  the 
  sections 
  which 
  we 
  saw 
  

   unfortunately 
  threw 
  no 
  light. 
  

  

  "We 
  left 
  the 
  Tyrol 
  by 
  the 
  railway 
  over 
  the 
  Yorarlberg 
  pass, 
  and 
  so 
  

   skirted 
  or 
  traversed 
  for 
  some 
  distance 
  the 
  " 
  Thonglimmerschiefer 
  " 
  

   series, 
  which 
  occurs 
  mainly 
  on 
  the 
  right 
  bank 
  of 
  the 
  Inn, 
  the 
  Triassic 
  

   limestones 
  rising 
  in 
  grand 
  cliffs 
  on 
  the 
  opposite 
  side. 
  The 
  former 
  

   rock 
  is 
  the 
  usual 
  lead-coloured 
  schist, 
  exactly 
  like 
  that 
  so 
  often 
  

  

  * 
  Cf. 
  " 
  The 
  history 
  of 
  the 
  brecciated 
  serpentine 
  in 
  the 
  hills 
  above 
  Bonasola 
  

   (Apennines)," 
  Geol. 
  Mag. 
  dec. 
  ii. 
  vol. 
  vi. 
  p. 
  362. 
  

  

  