﻿"^°1» 
  53'1 
  THE 
  SITMMIT 
  OP 
  THE 
  PTTEKA. 
  PASS. 
  19 
  

  

  loses 
  even 
  its 
  subcrystalline 
  character 
  in 
  the 
  more 
  argillaceous 
  

   bands. 
  Both 
  rocks 
  are 
  ' 
  slabby,' 
  but 
  this 
  character 
  seems 
  due, 
  in 
  

   the 
  marble 
  to 
  pressure, 
  in 
  the 
  limestone 
  more 
  immediately 
  to 
  the 
  

   presence 
  of 
  soft 
  shaly 
  layers, 
  though 
  it 
  may 
  have 
  been 
  augmented 
  

   by 
  pressure. 
  Moreover, 
  to 
  fracture 
  a 
  slab 
  of 
  the 
  marble 
  requires 
  a 
  

   hard 
  blow 
  with 
  the 
  hammer. 
  The 
  other 
  rock 
  breaks 
  more 
  easily 
  

   and 
  splits 
  up 
  into 
  thinner 
  slabs. 
  In 
  other 
  words, 
  the 
  marble, 
  

   except 
  perhaps 
  within 
  a 
  few 
  inches 
  of 
  the 
  junction, 
  in 
  the 
  zone 
  of 
  

   exceptional 
  crushing, 
  is 
  the 
  less 
  fissile 
  of 
  the 
  two 
  rocks. 
  These 
  

   remarks 
  apply 
  especially 
  to 
  the 
  most 
  crystalline 
  variety 
  of 
  the 
  

   Jurassic 
  limestone, 
  which 
  appears, 
  as 
  stated 
  in 
  my 
  former 
  paper, 
  to 
  

   come 
  immediately 
  above 
  the 
  marble. 
  The 
  rest 
  of 
  it 
  is 
  so 
  totally 
  

   different 
  from 
  the 
  latter 
  rock 
  that 
  no 
  confusion 
  can 
  arise. 
  

  

  The 
  distinctions 
  which 
  are 
  observed 
  in 
  the 
  field 
  are 
  confirmed 
  by 
  

   study 
  with 
  the 
  microscope. 
  I 
  collected 
  some 
  additional 
  specimens 
  

   last 
  year, 
  which 
  have 
  been 
  compared 
  with 
  those 
  obtained 
  on 
  former 
  

   occasions. 
  As 
  regards 
  the 
  marble, 
  I 
  have 
  really 
  nothing 
  to 
  add 
  to 
  

   my 
  previous 
  description. 
  If 
  allowance 
  be 
  made 
  for 
  the 
  effects 
  of 
  

   crushing 
  (which 
  are 
  more 
  conspicuous 
  near 
  the 
  exterior), 
  this 
  rock 
  

   everywhere 
  has 
  marked 
  characteristics 
  of 
  its 
  own. 
  The 
  mica, 
  when 
  

   it 
  occurs, 
  is 
  usually 
  well 
  developed, 
  seemingly 
  authigenous, 
  varying' 
  

   from 
  colourless 
  to 
  a 
  pale 
  brown 
  tint 
  ; 
  the 
  grains 
  of 
  quartz 
  (with 
  no 
  

   hint 
  of 
  a 
  fragmental 
  origin) 
  are 
  larger 
  than 
  in 
  the 
  other 
  rock 
  ; 
  so 
  

   also 
  are 
  those 
  of 
  calcite, 
  as 
  well 
  as 
  being 
  more 
  uniform 
  in 
  size 
  and 
  

   aspect. 
  This 
  rock, 
  in 
  short, 
  corresponds 
  very 
  closely 
  with 
  the 
  

   marble 
  and 
  the 
  purer 
  parts 
  of 
  the 
  calc-mica 
  schists, 
  which 
  are 
  so 
  

   abundant 
  in 
  association 
  with 
  various 
  crystalline 
  schists 
  in 
  many 
  parts 
  

   of 
  the 
  Pennine 
  Alps, 
  not 
  to 
  mention 
  other 
  districts. 
  Even 
  the 
  most 
  

   crystalline 
  variety 
  of 
  the 
  Jurassic 
  rock 
  is 
  altogether 
  less 
  regular, 
  and 
  

   generally 
  is 
  more 
  fine-grained 
  in 
  structure 
  than 
  it 
  ; 
  the 
  mica 
  is 
  in 
  

   smaller 
  flakes 
  and 
  of 
  doubtful 
  origin 
  ; 
  the 
  calcite-grains 
  vary 
  much 
  

   in 
  size, 
  several 
  certainly 
  are 
  fragments 
  of 
  organisms, 
  among 
  which 
  

   crinoidal 
  structure 
  occasionally 
  can 
  be 
  recognized 
  : 
  here 
  and 
  there 
  

   dark 
  films 
  and 
  small 
  lenticles 
  mark 
  the 
  presence 
  of 
  ' 
  earthy 
  ' 
  carbo- 
  

   naceous 
  material, 
  as 
  in 
  any 
  ordinary 
  impure 
  limestone. 
  Some 
  

   mineral 
  changes 
  have 
  undoubtedly 
  occurred; 
  the 
  quartz, 
  for 
  in- 
  

   stance, 
  in 
  its 
  present 
  form, 
  does 
  not 
  indicate 
  a 
  clastic 
  origin, 
  but 
  

   the 
  alteration 
  never 
  exceeds, 
  if 
  indeed 
  it 
  equals, 
  that 
  in 
  the 
  matrix 
  

   of 
  the 
  Jurassic 
  ' 
  knotenschiefer 
  ' 
  near 
  the 
  Nufenen 
  Pass. 
  1 
  

  

  Omitting 
  for 
  the 
  moment 
  one 
  character, 
  which 
  has 
  no 
  immediate 
  

   bearing 
  on 
  the 
  present 
  question, 
  we 
  may 
  thus 
  sum 
  up 
  the 
  dif- 
  

   ferences 
  : 
  that 
  while 
  both 
  rocks 
  have 
  been 
  affected 
  to 
  some 
  extent 
  

   by 
  pressure, 
  the 
  marble 
  always 
  seems 
  tending 
  to 
  ally 
  itself 
  with 
  

   a 
  thoroughly 
  crystalline 
  rock, 
  such 
  as 
  elsewhere 
  in 
  the 
  Alps 
  would 
  

   be 
  associated 
  with 
  typical 
  mica-schists, 
  quartz-schists, 
  etc., 
  and 
  the 
  

   limestone 
  with 
  the 
  ordinary 
  members 
  of 
  the 
  Jurassic 
  system. 
  

  

  The 
  subcrystalline 
  limestone 
  seems 
  to 
  occupy 
  the 
  same 
  position 
  

   in 
  regard 
  to 
  the 
  marble, 
  so 
  far 
  as 
  it 
  can 
  be 
  traced 
  in 
  this 
  district, 
  

   1 
  Op. 
  cit. 
  p. 
  288, 
  and 
  vol. 
  xlvi. 
  (1890)-pp. 
  213-221. 
  

  

  c2 
  

  

  