﻿COLLECTED 
  IN 
  MADAGASCAR 
  BY 
  REV. 
  R. 
  BARON. 
  

  

  347 
  

  

  the 
  rock 
  while 
  in 
  the 
  molten 
  condition 
  are 
  indicated 
  by 
  the 
  presence 
  

   of 
  fractured 
  crystals. 
  

  

  The 
  augite, 
  which, 
  in 
  thin 
  sections, 
  is 
  of 
  a 
  pale 
  purplish-brown 
  

   colour, 
  seldom 
  occurs 
  in 
  well-shaped 
  crystals. 
  As 
  in 
  the 
  " 
  glomero- 
  

   porphyritic" 
  structure 
  of 
  Prof. 
  Judd, 
  the 
  grains 
  are 
  frequently 
  

   so 
  aggregated 
  as 
  to 
  entirely 
  exclude 
  the 
  ground-mass. 
  Hero 
  

   and 
  there 
  a 
  more 
  decided 
  " 
  centric 
  structure 
  " 
  is 
  produced 
  by 
  the 
  

  

  Pig. 
  1. 
  — 
  Corroded 
  Olivine 
  

   with 
  glass-inclusion. 
  

  

  Pig. 
  2. 
  — 
  Corroded 
  Olivine 
  

   with 
  glass-inclusion. 
  

  

  Pig. 
  4. 
  — 
  Twin 
  of 
  Olivine. 
  

  

  Pig. 
  3. 
  — 
  Twin 
  of 
  Olivine. 
  

  

  radiate 
  grouping 
  of 
  augite-individuals 
  around 
  a 
  central 
  grain 
  of 
  

   olivine. 
  Enclosed 
  in 
  the 
  augite 
  are 
  abundant 
  granules 
  of 
  magnetic 
  

   iron-ore 
  and 
  glass. 
  Less 
  frequent 
  are 
  microlites 
  of 
  a 
  colourless 
  

   mineral 
  (apatite). 
  

  

  Occurring 
  sporadically 
  are 
  grains 
  of 
  quartz 
  with 
  liquid-inclusions. 
  

   These 
  grains 
  have 
  suffered 
  considerable 
  corrosion 
  in 
  the 
  basic 
  magma 
  

   in 
  which 
  they 
  floated 
  ; 
  for 
  their 
  contours 
  are 
  rounded 
  off, 
  and 
  they 
  

   are 
  surrounded 
  by 
  a 
  narrow 
  zone 
  (what 
  the 
  Germans 
  call 
  a 
  Schmelz- 
  

   zone) 
  of 
  minute 
  yellowish 
  microlites 
  (? 
  augite), 
  evidently 
  produced 
  

   by 
  a 
  change 
  in 
  the 
  chemical 
  composition 
  of 
  the 
  magma. 
  

  

  The 
  sporadic 
  occurrence 
  of 
  corroded 
  grains 
  of 
  quartz 
  in 
  basalt 
  has 
  

   been 
  noticed 
  by 
  several 
  observers, 
  who, 
  as 
  a 
  rule, 
  have 
  regarded 
  them 
  

   as 
  inclusions 
  of 
  foreign 
  quartz 
  taken 
  up 
  by 
  the 
  lava 
  during 
  its 
  

  

  