﻿COLLECTED 
  IN 
  MADAGASCAR 
  BY 
  EEV. 
  R. 
  BARON. 
  

  

  351 
  

  

  refractive 
  granules 
  (augite) 
  ; 
  and 
  3, 
  reddish-brown 
  strongly 
  pleochroic 
  

   microlites 
  (hornblende). 
  Brown 
  pleochroic 
  microlites 
  have 
  been 
  

   observed 
  in 
  the 
  fusion-zones 
  around 
  hornblende 
  by 
  Werweke 
  *, 
  

   Sommerlad 
  f 
  , 
  and 
  Hyland 
  J, 
  all 
  of 
  whom 
  agree 
  in 
  referring 
  them 
  

   to 
  hornblende- 
  

   Fig. 
  9. 
  — 
  Augite 
  with 
  twin-lamella. 
  

  

  <K 
  e 
  ; 
  

  

  

  

  i\ 
  

  

  

  \ 
  , 
  

  

  '\ 
  

  

  \ 
  

  

  X 
  

  

  // 
  

  

  \ 
  

  

  NY 
  

  

  ,M 
  

  

  N 
  

  

  ( 
  

  

  i 
  

  

  V 
  

  

  

  / 
  

  

  / 
  

  

  

  X 
  

  

  (\ 
  

  

  Pig. 
  10. 
  

   Twinned 
  Augite. 
  

  

  The 
  hornblende 
  is 
  of 
  the 
  common 
  basaltic 
  type 
  (basaltine). 
  It 
  is 
  

   strongly 
  pleochroic 
  in 
  the 
  following 
  colours 
  : 
  — 
  

  

  a 
  = 
  pale 
  straw-yellow. 
  

   y>/3 
  = 
  yellowish 
  brown. 
  

  

  The 
  mica 
  is 
  a 
  dark-coloured, 
  strongly 
  pleochroic 
  variety 
  (biotite). 
  

  

  c. 
  Olivine-free 
  Basalt 
  with 
  Hornblende 
  in 
  Porphy?*itie 
  Crystals. 
  

  

  A 
  lava-stream 
  of 
  the 
  volcano 
  Kasige, 
  in 
  the 
  volcanic 
  region 
  to 
  the 
  

   west 
  of 
  Lake 
  Itasy, 
  has 
  this 
  composition 
  : 
  it 
  is 
  a 
  black 
  and 
  finely 
  

   vesicular 
  rock 
  composed 
  of 
  small 
  porphyritic 
  crystals 
  of 
  augite, 
  horn- 
  

   blende, 
  and 
  apatite, 
  imbedded 
  in 
  a 
  brown 
  ground-mass, 
  which, 
  

   besides 
  glassy 
  matter, 
  contains 
  abundant 
  needles 
  of 
  striated 
  felspar, 
  

   microlites 
  of 
  augite, 
  and 
  minute 
  granules 
  of 
  magnetic 
  iron-ore. 
  

   Under 
  a 
  high 
  power 
  the 
  glass 
  appears 
  globulitic 
  and, 
  in 
  places, 
  

   fibrous, 
  the 
  latter 
  appearance 
  being 
  due 
  to 
  the 
  presence 
  of 
  numerous 
  

   minute 
  hair-like 
  bodies 
  (trichites). 
  

  

  Peculiar 
  to 
  this 
  rock 
  is 
  the 
  extraordinarily 
  large 
  amount 
  of 
  apatite. 
  

   This 
  mineral 
  occurs 
  in 
  unusually 
  fine 
  large 
  prisms, 
  showing 
  pyramidal 
  

   terminations 
  and 
  giving 
  hexagonal 
  cross-sections. 
  Longitudinal 
  

  

  * 
  " 
  Beitrag 
  zar 
  Kenntniss 
  der 
  Gesteine 
  der 
  Insel 
  Palma," 
  Neues 
  Jahrb. 
  

   1879, 
  p. 
  824. 
  

  

  t 
  " 
  Ueber 
  kornblendefiihrende 
  Basaltgesteine," 
  Neues 
  Jahrb. 
  Beilage-Band 
  ii. 
  

   1883, 
  p. 
  139. 
  

  

  J 
  " 
  Ueber 
  die 
  Gesteine 
  des 
  Kiliinandscharo 
  und 
  dessen 
  Umgebung," 
  Tsoher- 
  

   mak's 
  'Min. 
  u. 
  petr. 
  Mith.' 
  x. 
  1888, 
  p. 
  236. 
  

  

  Q.J.G.S. 
  No. 
  178. 
  £c 
  

  

  