﻿CRYSTALLINE 
  ROCKS 
  OF 
  THE 
  ALPS. 
  81 
  

  

  (/3) 
  Section 
  of 
  the 
  Col 
  de 
  Sestrieres. 
  

  

  The 
  road, 
  not 
  long 
  after 
  leaving 
  Cesanne, 
  crosses 
  over 
  a 
  great 
  mass 
  

   of 
  serpentine. 
  On 
  the 
  west 
  side 
  of 
  this 
  is 
  the 
  usual 
  mica-schist, 
  

   which 
  can 
  be 
  seen 
  cropping 
  out 
  very 
  near 
  the 
  serpentine, 
  though 
  the 
  

   actual 
  junction, 
  at 
  any 
  rate 
  about 
  here, 
  is 
  masked 
  by 
  debris. 
  But 
  the 
  

   latter 
  appears 
  to 
  cut 
  across 
  the 
  schist 
  like 
  an 
  intrusive 
  mass. 
  The 
  

   serpentine 
  at 
  first 
  is 
  greatly 
  crushed, 
  but 
  the 
  effects 
  of 
  this 
  gradually 
  

   disappear, 
  and 
  fairly 
  normal 
  specimens 
  can 
  be 
  obtained. 
  It 
  is 
  of 
  

   the 
  usual 
  Alpine 
  type, 
  a 
  dull 
  greenish-black 
  rock 
  containing 
  crystals 
  

   of 
  bronzite 
  or 
  bastite. 
  In 
  its 
  peculiar 
  joint-planes, 
  its 
  mode 
  of 
  

   weathering, 
  its 
  brown 
  rugged 
  surfaces, 
  it 
  exactly 
  resembles 
  the 
  

   Lizard 
  serpentine 
  *. 
  The 
  rock 
  on 
  the 
  eastern 
  side 
  of 
  the 
  mass 
  

   l)eoomes 
  greatly 
  brecciated, 
  and 
  is 
  associated 
  — 
  apparently 
  intrusively 
  

   (but 
  the 
  effects 
  of 
  subsequent 
  disturbance 
  obscure 
  the 
  relation) 
  — 
  

   with 
  a 
  compact 
  green 
  schist 
  (Appendix, 
  p. 
  103), 
  which 
  now 
  and 
  then 
  

   is 
  reddish 
  in 
  colour, 
  and 
  reminded 
  me 
  much 
  of 
  a 
  rock 
  which 
  occurs 
  on 
  

   the 
  west 
  side 
  of 
  the 
  Julier 
  Pass 
  (Engadine) 
  To 
  this 
  succeeds 
  a 
  calc- 
  

   mica 
  schist, 
  like 
  that 
  below 
  Cesanne, 
  much 
  disturbed 
  and 
  crushed, 
  

   and 
  exhibiting 
  " 
  sheen 
  surfaces." 
  Higher 
  up 
  another 
  variety, 
  which 
  

   in 
  general 
  appearance 
  reminded 
  me 
  of 
  some 
  of 
  the 
  calc-mica 
  schists 
  

   of 
  the 
  Central 
  Alps 
  (e. 
  g. 
  the 
  mass 
  north 
  of 
  Olivone), 
  proved 
  that 
  a 
  

   cleavage-foliation 
  had 
  been 
  superinduced 
  in 
  a 
  rock 
  already 
  foliated, 
  

   for 
  in 
  places 
  the 
  former 
  structure 
  clearly 
  cut 
  across 
  the 
  contortions 
  

   of 
  the 
  latter 
  (fig. 
  4). 
  Calc-mica-schists 
  of 
  one 
  general 
  character 
  

   (Appendix, 
  p. 
  103), 
  but 
  with 
  minor 
  variations, 
  as 
  when, 
  for 
  example, 
  

   the 
  rock 
  reverts 
  to 
  the 
  anthracitic 
  type 
  near 
  Charaplain 
  du 
  Col, 
  

   continue 
  till 
  the 
  trough 
  on 
  the 
  upper 
  part 
  of 
  the 
  pass 
  is 
  reached. 
  

   The 
  " 
  stratification-f 
  oliation 
  " 
  strikes 
  generally 
  between 
  N.N.W. 
  and 
  

   N.W., 
  dipping 
  at 
  about 
  45° 
  on 
  the 
  average 
  to 
  the 
  western 
  side. 
  

  

  In 
  the 
  first 
  part 
  of 
  the 
  descent 
  from 
  the 
  Col 
  very 
  little 
  rock 
  

   crops 
  out 
  near 
  the 
  road, 
  and 
  as 
  far 
  as 
  Pragelas 
  we 
  saw 
  nothing 
  but 
  

   schists 
  of 
  the 
  above-mentioned 
  type 
  ; 
  sometimes 
  one 
  of 
  the 
  more 
  

   anthracitic 
  varieties, 
  like 
  that 
  below 
  Cesanne, 
  sometimes 
  one 
  of 
  the 
  

   more 
  micaceous, 
  like 
  that 
  on 
  the 
  east 
  side 
  of 
  the 
  Mont 
  Genevre, 
  some- 
  

   times 
  one 
  rather 
  more 
  massive, 
  which 
  recalled 
  to 
  mind 
  the 
  " 
  brown- 
  

   bedded" 
  rock 
  of 
  Olivone 
  f 
  . 
  There 
  is 
  nothing 
  needing 
  special 
  remark 
  

   between 
  Pragelas 
  and 
  Fenestrelle, 
  near 
  to 
  which 
  mica-schists 
  occur, 
  

   dipping 
  apparently 
  at 
  about 
  50° 
  rather 
  to 
  the 
  S. 
  of 
  W.J 
  At 
  the 
  

  

  * 
  It 
  is 
  needless 
  to 
  give 
  a 
  description 
  of 
  the 
  microscopic 
  structure 
  ; 
  it 
  is 
  a 
  per- 
  

   fectly 
  typical 
  serpentine, 
  such 
  as 
  the 
  dark 
  serpentine 
  from 
  the 
  north 
  of 
  Cadgwith, 
  

   the 
  similar 
  rocks 
  from 
  near 
  Genoa, 
  near 
  Figline, 
  and 
  the 
  Engadine 
  — 
  a 
  serpen- 
  

   tine, 
  varieties 
  of 
  which 
  occur 
  here 
  and 
  there 
  throughout 
  the 
  Alps. 
  This 
  one 
  is 
  

   an 
  altered 
  olivine-enstatite-augite 
  rock 
  (Buchnerite 
  of 
  Wadsworth), 
  the 
  first 
  

   and 
  second 
  minerals 
  being 
  completely 
  serpentinized. 
  

  

  t 
  Quart. 
  Journ. 
  Greol. 
  Soc. 
  1886, 
  Presid. 
  Address, 
  p. 
  47. 
  

  

  \ 
  These 
  differ 
  greatly 
  from 
  the 
  schists 
  described 
  above. 
  Under 
  the 
  micro- 
  

   scope 
  their 
  structure 
  is 
  coarser, 
  " 
  cleaner," 
  and 
  more 
  like 
  that 
  of 
  schists 
  at 
  a 
  

   lower 
  horizon, 
  e. 
  g. 
  a 
  silvery 
  mica-schist 
  which 
  I 
  have 
  found 
  in 
  various 
  localities 
  

   in 
  the 
  Lepontine 
  and 
  Noric 
  Alps. 
  The 
  specimen 
  examined 
  consists 
  of 
  quartz 
  

   and 
  white 
  mica 
  with 
  some 
  kyanite. 
  

  

  Q. 
  J. 
  G. 
  S. 
  No. 
  177. 
  ' 
  a 
  

  

  