﻿COLLECTED 
  IN 
  MADAGASCAR 
  BY 
  REV. 
  R. 
  BAROtf. 
  353 
  

  

  yellow 
  in 
  colour. 
  Its 
  crystals 
  are 
  remarkably 
  well 
  contoured 
  ; 
  they 
  

   are 
  bounded 
  by 
  faces 
  out 
  of 
  the 
  prismatic 
  zone, 
  terminated 
  by 
  a 
  

   dome 
  or 
  hemipyramid. 
  

  

  Large 
  pseudomorphs 
  after 
  hornblende 
  occur 
  sporadically. 
  They 
  

   are 
  crowded 
  with 
  minute 
  cubes 
  of 
  iron-ore, 
  distributed 
  uniformly 
  

   through 
  the 
  crystal-section 
  (see 
  fig. 
  11). 
  Between 
  crossed 
  nicols 
  

  

  Fig. 
  11. 
  — 
  Fused 
  Hornblende-crystal 
  recrystallized 
  as 
  Magnetite 
  

   and 
  Augite 
  in 
  Magma-basalt. 
  ( 
  X 
  70.) 
  

  

  they 
  usually 
  give 
  aggregate-polarization. 
  The 
  polarizing 
  substance 
  

   resembles 
  augite, 
  probably 
  produced 
  by 
  a 
  melting-down 
  of 
  the 
  

   hornblende 
  substance. 
  

  

  A. 
  few 
  grains 
  of 
  quartz, 
  similar 
  to 
  those 
  already 
  described, 
  are 
  met 
  

   with 
  occasionally. 
  The 
  corroded 
  grains 
  are 
  surrounded 
  by 
  a 
  zone 
  

   of 
  colourless 
  glass 
  containing 
  augite-microlites 
  ; 
  this 
  is 
  succeeded 
  by 
  

   a 
  second 
  zone 
  of 
  brown 
  glass, 
  containing 
  microlites 
  and 
  crystals 
  of 
  

   augite, 
  together 
  with 
  granules 
  of 
  magnetite 
  (see 
  fig. 
  12). 
  

  

  Fig. 
  12. 
  — 
  Quartz-grain 
  melted 
  down 
  and 
  surrounded 
  by 
  light 
  and, 
  

   dark 
  zones 
  of 
  Glass 
  ivith 
  Augite-microlites. 
  

  

  

  

  

  The 
  amount 
  of 
  glass 
  increases 
  in 
  certain 
  parts 
  of 
  the 
  rock. 
  The 
  

   elongated 
  shape 
  of 
  these 
  more 
  yitreous 
  portions 
  points 
  to 
  fluidal 
  

   movements 
  during 
  the 
  hardening 
  of 
  the 
  rock. 
  The 
  central 
  portions 
  

   of 
  these 
  patches 
  are 
  often 
  filled 
  with 
  a 
  network 
  of 
  minute, 
  opaque 
  

   trichites, 
  crossing 
  one 
  another 
  at 
  angles 
  of 
  60°, 
  90°, 
  and 
  120° 
  (fig. 
  13). 
  

  

  Felspar-free 
  basalts 
  or 
  magma-basalts 
  (Boficky 
  ) 
  have 
  a 
  wide-spread 
  

   occurrence. 
  They 
  have 
  been 
  described, 
  for 
  instance, 
  from 
  the 
  

   Kaiserstuhl 
  (Rosenbusch), 
  the 
  Ehon 
  and 
  Vogelsberg 
  (Bucking), 
  

  

  2c2 
  

  

  