﻿52 
  BOSE 
  : 
  GEOLOGY 
  OF 
  THE 
  LOWER 
  NARBADA 
  VALLEY. 
  

  

  with 
  numerous 
  minute, 
  beautiful, 
  little, 
  clear 
  needles, 
  which 
  are 
  un- 
  

   doubtedly 
  of 
  plagioclastic 
  felspar, 
  as 
  they 
  are 
  not 
  unfrequently 
  observed 
  

   to 
  build 
  up 
  by 
  aggregation 
  crystals 
  exhibiting 
  in 
  polarised 
  light 
  the 
  

   colour 
  bands 
  so 
  characteristic 
  of 
  that 
  jmineral. 
  It 
  is 
  also 
  present 
  in 
  

   larger 
  crystals 
  as 
  in 
  the 
  doleritic 
  dyke 
  rock, 
  so 
  large 
  as 
  to 
  be 
  visible 
  to 
  

   the 
  naked 
  eye, 
  and 
  sometimes 
  in 
  such 
  numbers 
  as 
  to 
  render 
  the 
  rock 
  

   almost 
  porphyritic. 
  There 
  can 
  be 
  little 
  doubt 
  that 
  it 
  is 
  this 
  mineral 
  

   which 
  has 
  been 
  sometimes 
  taken 
  for 
  orthoclase 
  looking 
  as 
  it 
  does 
  

   remarkably 
  like 
  sanidin. 
  This 
  species 
  of 
  felspar 
  (orthoclase) 
  is 
  rare, 
  as 
  

   might, 
  indeed, 
  be 
  expected, 
  in 
  the 
  basic 
  rocks 
  under 
  review 
  ; 
  it 
  occurs 
  

   as 
  a 
  normal 
  constituent 
  only 
  in 
  the 
  Kawant 
  rock, 
  and 
  in 
  a 
  few 
  other 
  

   instances 
  to 
  be 
  noticed 
  presently. 
  1 
  Augite, 
  coloured 
  brownish, 
  is 
  com- 
  

   mon, 
  but 
  usually 
  too 
  small 
  to 
  be 
  visible 
  with 
  the 
  naked 
  eye. 
  Very 
  few 
  

   well-developed 
  crystals 
  of 
  the 
  mineral 
  have 
  been 
  observed. 
  They 
  hardly 
  

   ever 
  show 
  the 
  characteristic 
  cleavage, 
  but 
  the 
  cracks 
  of 
  which 
  they 
  

   are 
  full 
  indicate 
  it 
  in 
  some. 
  The 
  only 
  other 
  mineral 
  which, 
  besides 
  

   magnetite, 
  claims 
  notice, 
  is 
  olivine. 
  Its 
  distribution 
  is 
  very 
  local, 
  2 
  but 
  

   when 
  it 
  is 
  present 
  the 
  crystals 
  are 
  good 
  and 
  well 
  formed, 
  and 
  are 
  

   beautifully 
  seen 
  on 
  the 
  weathered 
  face. 
  (See 
  Plate, 
  fig. 
  1.) 
  

  

  The 
  minerals 
  formed 
  by 
  infiltration 
  in 
  the 
  vesicular 
  beds, 
  converting 
  

   these 
  into 
  amygdaloids, 
  have 
  been 
  fully 
  noticed 
  by 
  previous 
  observers, 
  

   being 
  most 
  conspicuous 
  and 
  therefore 
  striking. 
  3 
  

  

  Agglomerates 
  and 
  Ashes. 
  — 
  Beds 
  of 
  considerable 
  thickness 
  formed 
  of 
  

   volcanic 
  ejecta 
  were 
  noticed 
  in 
  the 
  last 
  chapter. 
  Strata 
  of 
  volcanic 
  ash 
  

   occur, 
  especially 
  at 
  the 
  foot 
  of 
  the 
  Yindhyan 
  range, 
  as 
  between 
  Mahesar 
  

   and 
  Jam 
  Ghat. 
  Ferruginous, 
  marly-looking, 
  pinkish 
  beds 
  from 
  an 
  inch 
  

  

  1 
  Mr. 
  Blanford 
  in 
  his 
  paper 
  on 
  the 
  "Traps 
  and 
  Intertrappcans 
  " 
  describes 
  the 
  felspar 
  

   in 
  the 
  trap 
  as 
  " 
  glassy 
  felspar 
  " 
  (Mem., 
  VI, 
  Arts. 
  5, 
  6). 
  The 
  following 
  passage 
  occurs 
  at 
  

  

  p. 
  305 
  of 
  the 
  " 
  Manual 
  " 
  " 
  and 
  the 
  only 
  felspar 
  which 
  occurs 
  in 
  distinct 
  

  

  crystals 
  appears 
  to 
  be 
  the 
  form 
  of 
  orthoclase 
  (glassy 
  felspar), 
  &c." 
  

  

  2 
  Its 
  absence 
  from 
  the 
  Bombay 
  basalts 
  has 
  been 
  noticed 
  by 
  Colonel 
  McMahon 
  (" 
  Rec," 
  

   Vol. 
  XVI.) 
  

  

  8 
  At 
  Muraja, 
  south 
  of 
  Umrali, 
  in 
  the 
  district 
  of 
  Ali 
  Eajpur, 
  I 
  met 
  with 
  curious 
  agate- 
  

   geodes 
  in 
  a 
  calcareous 
  matrix. 
  The 
  calcareous 
  substance 
  has 
  been 
  substituted 
  by 
  infiltra- 
  

   tion 
  for 
  the 
  trappean, 
  until 
  hardly 
  any 
  trace 
  of 
  the 
  latter 
  has 
  been 
  left, 
  by 
  a 
  proces* 
  

   •imilar 
  to 
  the 
  silicification 
  of 
  wood, 
  

  

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  ) 
  

  

  