﻿304 
  LT.-GEN, 
  C. 
  A. 
  MCMAHON 
  & 
  CAPT. 
  A. 
  H. 
  MCMAHON 
  [Aug. 
  1 
  897, 
  

  

  Oligoclase 
  is 
  the 
  most 
  abundant 
  mineral. 
  The 
  quartz 
  and 
  ortho- 
  

   clase 
  are 
  present 
  in 
  about 
  equal 
  proportions, 
  but 
  each 
  taken 
  

   separately 
  is 
  very 
  subordinate 
  to 
  the 
  plagioclase. 
  The 
  latter, 
  by 
  its 
  

   extinctions 
  and 
  specific 
  gravity, 
  is 
  seen 
  to 
  be 
  oligoclase. 
  

  

  Both 
  felspars 
  are 
  fairly 
  fresh, 
  and 
  as 
  a 
  rule 
  are 
  allotriomorphic 
  ; 
  

   but 
  there 
  are 
  two 
  crystals 
  enclosed 
  in 
  biotite 
  which 
  possess 
  crys- 
  

   tallographic 
  outlines. 
  

  

  In 
  transmitted 
  light 
  the 
  hornblende 
  is 
  of 
  a 
  green 
  to 
  brownish- 
  

   green, 
  and 
  the 
  biotite 
  of 
  a 
  greenish 
  to 
  reddish-brown 
  colour. 
  The 
  

   biotite 
  is 
  altered 
  in 
  places 
  to 
  chlorite. 
  Epidote 
  occurs, 
  intergrown 
  

   with 
  chlorite 
  in 
  elongated 
  granules 
  running 
  in 
  the 
  direction 
  of 
  the 
  

   biotite 
  and 
  chlorite 
  cleavage-planes. 
  The 
  hornblende 
  and 
  biotite 
  

   are 
  deeply 
  corroded 
  by 
  both 
  the 
  quartz 
  and 
  the 
  plagioclase. 
  (See 
  

   PI. 
  XX, 
  figs. 
  3 
  & 
  4.) 
  

  

  Apatite 
  is 
  abundant, 
  and 
  occurs 
  in 
  the 
  biotite, 
  felspar, 
  and 
  quartz, 
  

   while 
  the 
  magnetite, 
  as 
  one 
  so 
  often 
  sees 
  in 
  igneous 
  rocks, 
  is 
  often 
  

   formed 
  upon 
  the 
  apatite. 
  

  

  Sphene 
  is 
  somewhat 
  abundant, 
  and 
  is 
  in 
  good-sized 
  grains 
  ; 
  it 
  

   rarely 
  shows 
  any 
  approximation 
  to 
  crystalline 
  shape. 
  It 
  is 
  dis- 
  

   tinctly 
  dichroic, 
  and 
  exhibits 
  a 
  tendency 
  to 
  a 
  fibrous 
  habit. 
  It 
  

   has 
  the 
  prism-cleavage 
  strongly 
  developed 
  in 
  one 
  direction, 
  with 
  

   traces 
  of 
  another 
  cleavage 
  crossing 
  it 
  at 
  an 
  angle 
  of 
  111° 
  to 
  117°. 
  

  

  The 
  quartz 
  contains 
  liquid 
  cavities 
  with 
  small 
  moving 
  bubbles 
  

   and 
  fine 
  needle-shaped 
  crystals 
  which 
  are 
  probably 
  rutile. 
  

  

  Sedimentary 
  Rocks. 
  

  

  No. 
  1410. 
  From 
  Amir 
  Chah. 
  

  

  „ 
  1411. 
  

  

  „ 
  1412. 
  

  

  „ 
  1414. 
  

  

  „ 
  1415. 
  

  

  „ 
  1449. 
  ,, 
  the 
  east 
  side 
  of 
  the 
  great 
  fault. 
  

  

  „ 
  1453. 
  ,, 
  the 
  west 
  side 
  of 
  the 
  great 
  fault. 
  

  

  The 
  first 
  five 
  samples 
  are 
  apparently 
  very 
  fine-grained 
  sedi- 
  

   mentary 
  rocks 
  of 
  the 
  character 
  of 
  indurated 
  muds. 
  They 
  are 
  

   porcellanous-looking, 
  and 
  not 
  unlike 
  felsites. 
  They 
  do 
  not 
  exhibit 
  

   cleavage 
  or 
  lamination. 
  They 
  are 
  brittle, 
  and 
  fuse 
  at 
  the 
  edges, 
  but 
  

   the 
  fused 
  edge 
  is 
  not 
  magnetic. 
  

  

  The 
  groundmass 
  of 
  some 
  felsites 
  and 
  porphyries 
  resembles 
  the 
  

   structure 
  of 
  these 
  rocks 
  as 
  seen 
  under 
  the 
  microscope 
  ; 
  but 
  these 
  

   samples 
  do 
  not 
  contain 
  any 
  embedded 
  crystals, 
  or 
  other 
  indication 
  of 
  

   igneous 
  structure. 
  

  

  No. 
  1449 
  is 
  a 
  glossy, 
  silty 
  shale, 
  with 
  much 
  of 
  the 
  aspect 
  of 
  a 
  

   slate. 
  Under 
  the 
  microscope 
  it 
  is 
  seen 
  to 
  be 
  extremely 
  fine-grained. 
  

  

  No. 
  1453 
  is 
  a 
  fine-grained, 
  indurated 
  silt, 
  formed 
  of 
  flaky 
  silica 
  

   deeply 
  impregnated 
  and 
  stained 
  a 
  reddish-brown 
  colour 
  with 
  limo- 
  

   nite. 
  The 
  groundmass 
  contains 
  a 
  number 
  of 
  round, 
  oval, 
  and 
  

   angular 
  grains 
  and 
  elongated 
  fibres 
  of 
  calcite 
  scattered 
  through 
  it. 
  

   In 
  some 
  cases 
  opal 
  has 
  replaced 
  the 
  calcite. 
  The 
  quartz 
  is 
  in 
  

   irregularly-shaped 
  flakes. 
  

  

  