﻿312 
  REV. 
  K. 
  BAEOX 
  OX 
  THE 
  

  

  great 
  thickness, 
  frequently 
  occur 
  among 
  the 
  other 
  rocks. 
  Of 
  

   quartz 
  itself 
  many 
  varieties 
  are 
  found, 
  as 
  (a) 
  rock-crystal 
  (for 
  

   large 
  crystals 
  of 
  which 
  lEadagascar 
  has 
  been 
  well 
  known 
  for 
  

   more 
  than 
  200 
  years*) 
  ; 
  (b) 
  pale 
  blue 
  vitreous 
  quartz, 
  occurring 
  in 
  

   Antsihanaka 
  ; 
  (c) 
  rose 
  quartz, 
  found 
  on 
  the 
  eastern 
  flank 
  of 
  the 
  

   hill 
  rauge 
  of 
  Famoizankova, 
  in 
  west 
  Yalalafotsy, 
  and 
  in 
  Antsihanaka 
  ; 
  

   (cZ) 
  smoky 
  quartz, 
  which 
  occurs 
  in 
  Antsihanaka 
  ; 
  (e) 
  milky 
  quartz, 
  

   a 
  beautiful 
  snow-white 
  variety 
  of 
  which 
  exists 
  at 
  a 
  spot 
  between 
  

   Ankazobe 
  and 
  Maneva, 
  in 
  Yonizongo 
  ; 
  (/) 
  jasper, 
  found 
  on 
  the 
  

   mountain 
  of 
  Yavavato 
  ; 
  (g) 
  amethyst, 
  which 
  occurs 
  in 
  many 
  loca- 
  

   lities 
  ; 
  (li) 
  agate, 
  found 
  in 
  Antsihanaka 
  and 
  on 
  the 
  west 
  bank 
  of 
  

   the 
  River 
  Betsiboka, 
  south 
  of 
  Mahabo. 
  

  

  Geaxite. 
  

  

  Here 
  and 
  there 
  the 
  vast 
  stretches 
  of 
  gneiss 
  and 
  its 
  allied 
  rocks 
  

   are 
  invaded 
  by 
  masses 
  and 
  bosses 
  of 
  granite. 
  The 
  mountain 
  of 
  

   Yombohitra, 
  situated 
  about 
  70 
  or 
  80 
  miles 
  north 
  of 
  the 
  capital, 
  is, 
  

   perhaps, 
  the 
  most 
  remarkable 
  of 
  these 
  eruptive 
  bosses. 
  This 
  moun- 
  

   tain 
  is 
  of 
  a 
  circular 
  shape, 
  is 
  perhaps 
  eighteen 
  miles 
  in 
  circum- 
  

   ference, 
  and 
  rises 
  boldly, 
  with 
  inaccessible 
  sides 
  in 
  many 
  parts 
  of 
  it, 
  

   to 
  a 
  height 
  of 
  about 
  1000 
  feet 
  above 
  the 
  surrounding 
  country. 
  The 
  

   granite 
  is 
  of 
  a 
  reddish 
  or 
  pinkish 
  colour, 
  having 
  flesh-coloured 
  

   orthoclase 
  and 
  black 
  mica 
  f. 
  Within 
  a 
  short 
  distance 
  of 
  this 
  im- 
  

   mense 
  granitic 
  boss 
  there 
  is 
  found 
  a 
  coarsely 
  crystalline 
  variety 
  of 
  

   graphic 
  granite, 
  probably 
  existing 
  in 
  veins 
  running 
  out 
  from 
  Yom- 
  

   bohitra. 
  There 
  is 
  also 
  to 
  be 
  found 
  graphic 
  granite 
  on 
  the 
  north 
  

   side 
  of 
  Yavavato 
  mountain. 
  

  

  Granite 
  similar 
  in 
  appearance 
  to 
  that 
  of 
  Yombohitra 
  also 
  occurs 
  

   rising 
  in 
  the 
  hill-range 
  known 
  as 
  Famoizankova, 
  on 
  the 
  western 
  

   confines 
  of 
  Imerina, 
  to 
  the 
  west 
  of 
  Yalalafotsy, 
  where, 
  in 
  its 
  con 
  ■ 
  

   tact 
  with 
  the 
  gneiss 
  on 
  its 
  eastern 
  border, 
  abundant 
  large 
  crystals 
  

   of 
  black 
  tourmaline 
  have 
  been 
  developed. 
  It 
  exists 
  also 
  from 
  about 
  

   ten 
  miles 
  east 
  of 
  the 
  capital 
  to 
  within 
  three 
  or 
  four 
  miles 
  of 
  the 
  

   large 
  forest 
  — 
  from 
  about 
  Isoavina 
  to 
  near 
  Mantasoa, 
  covering 
  an 
  

   area 
  of 
  perhaps 
  15 
  or 
  16 
  miles 
  in 
  diameter 
  — 
  where 
  it 
  rises 
  in 
  

   numerous 
  rounded 
  or 
  cupola-like 
  masses, 
  of 
  which 
  Ambatovory, 
  

   Ambatoinanga, 
  &c, 
  are 
  examples. 
  In 
  this 
  region 
  the 
  rock 
  for 
  the 
  

   most 
  part 
  contains 
  porphyritic 
  crystals 
  of 
  orthoclase 
  felspar. 
  These 
  

   crystals 
  near 
  the 
  edge 
  of 
  the 
  granite 
  (at 
  least 
  on 
  the 
  northern 
  

   boundary, 
  which 
  alone 
  I 
  have 
  seen) 
  run 
  more 
  or 
  less 
  in 
  a 
  linear 
  

   direction 
  from 
  east 
  to 
  west, 
  and, 
  I 
  believe, 
  parallel 
  with 
  the 
  strike 
  

   of 
  the 
  gneiss 
  in 
  the 
  immediate 
  neighbourhood. 
  This 
  direction 
  of 
  

   the 
  felspar 
  crystals 
  is 
  due 
  to 
  fracture 
  along 
  the 
  margin 
  of 
  the 
  in- 
  

   truding 
  mass, 
  producing 
  a 
  kind 
  of 
  fluxion-structure 
  on 
  a 
  large 
  

   scale, 
  the 
  crystals 
  having 
  been 
  obliged 
  to 
  rearrange 
  themselves 
  in 
  

  

  * 
  I 
  have 
  heard 
  of 
  a 
  specimen 
  of 
  rock-crystal 
  containing 
  liquid-cavities 
  \ 
  or 
  

   ^ 
  inch 
  in 
  diameter. 
  

  

  !" 
  For 
  description 
  of 
  this 
  granite 
  see 
  Dr. 
  Hatch's 
  paper, 
  p. 
  311. 
  

  

  