﻿314 
  EET. 
  K. 
  BAEON 
  ON 
  THE 
  

  

  cellular. 
  Here 
  and 
  there 
  basaltic 
  columns 
  may 
  be 
  seen, 
  some 
  of 
  which, 
  

   are 
  now 
  decomposing 
  into 
  wacke. 
  In 
  some 
  places, 
  too, 
  there 
  are 
  

   extensive 
  sheets 
  of 
  a 
  red 
  ferruginous 
  conglomerate. 
  Some 
  portions 
  

   of 
  the 
  basalt 
  are 
  amygdaloidal 
  ; 
  and 
  in 
  one 
  specimen, 
  which 
  I 
  believe 
  

   is 
  from 
  Ankaratra, 
  the 
  cavities 
  are 
  lined 
  with 
  radiating 
  zeolites. 
  

   Some 
  of 
  the 
  basalt 
  is 
  also 
  porphyritic 
  with 
  augite, 
  and 
  also 
  with 
  

   small 
  crystals 
  of 
  an 
  amber-coloured 
  mineral 
  (possibly 
  zircon), 
  which 
  

   is 
  infusible 
  before 
  the 
  blowpipe. 
  But 
  besides 
  basalt, 
  there 
  may 
  be 
  

   found, 
  lying 
  in 
  the 
  bed 
  of 
  some 
  of 
  the 
  streams 
  running 
  down 
  the 
  

   sides 
  of 
  the 
  mountain, 
  pieces 
  of 
  vesicular 
  trachytic 
  lava, 
  the 
  erupted 
  

   fragments 
  of 
  the 
  now 
  extinct 
  volcano. 
  The 
  three 
  highest 
  points 
  

   of 
  Ankaratra 
  are 
  Tsiafajavona, 
  8494 
  feet 
  above 
  the 
  sea; 
  Tsiafakafo, 
  

   8330 
  feet; 
  and 
  Ambohitrakoholahy, 
  7730 
  feet*. 
  Tsiafajavona, 
  the 
  

   highest 
  peak, 
  and 
  Tsiafakafo 
  consist 
  of 
  olivine 
  basalt, 
  Ambohitra- 
  

   koholahy 
  of 
  sanidine 
  trachyte 
  f 
  . 
  But 
  black 
  compact 
  basaltic 
  lavas 
  

   certainly 
  constitute 
  by 
  far 
  the 
  greater 
  part 
  of 
  the 
  mountain. 
  

  

  It 
  would 
  be 
  interesting 
  to 
  know 
  at 
  what 
  period 
  of 
  Tertiary 
  time 
  

   Ankaratra 
  was 
  in 
  a 
  state 
  of 
  eruption 
  ; 
  but 
  our 
  knowledge 
  of 
  the 
  

   mountain 
  and 
  the 
  surrounding 
  district 
  is, 
  as 
  yet, 
  too 
  scanty 
  to 
  help 
  

   us 
  to 
  any 
  conclusion 
  on 
  the 
  matter. 
  There 
  is 
  evidence 
  sufficient, 
  

   however, 
  to 
  show 
  that 
  the 
  volcano 
  is 
  of 
  ancient 
  date 
  ; 
  for, 
  in 
  the 
  

   first 
  place, 
  all 
  signs 
  of 
  craters 
  or 
  cones 
  seem 
  to 
  have 
  been 
  effaced 
  

   through 
  denudation, 
  though 
  the 
  presence 
  of 
  fragmentary 
  materials 
  

   (which, 
  however, 
  have 
  largely 
  disappeared) 
  manifest 
  their 
  former 
  

   existence. 
  Then, 
  again, 
  numerous 
  deep 
  valleys 
  have 
  been 
  excavated 
  

   out 
  of 
  the 
  hard 
  basaltic 
  covering 
  by 
  the 
  many 
  streams 
  that 
  come 
  

   down 
  from 
  the 
  mountain, 
  leaving 
  long 
  tongues 
  of 
  lava 
  diverging 
  

   from 
  the 
  central 
  mass. 
  Many 
  of 
  these 
  streams 
  have 
  cut 
  clean 
  

   through 
  the 
  beds 
  of 
  lava, 
  bringing 
  into 
  view 
  the 
  gneiss 
  upon 
  which 
  

   they 
  are 
  superimposed. 
  

  

  Some 
  thirty 
  or 
  forty 
  miles 
  to 
  the 
  south 
  of 
  Ankaratra 
  there 
  are 
  

   to 
  be 
  seen 
  about 
  a 
  dozen 
  remarkably 
  conical 
  hills 
  without 
  craters. 
  

   Whether 
  they 
  are 
  the 
  cores 
  of 
  former 
  volcanoes 
  or 
  mere 
  eruptive 
  

   bosses, 
  it 
  would 
  be 
  difficult 
  to 
  say, 
  though 
  I 
  am 
  inclined 
  to 
  

   regard 
  them 
  as 
  the 
  former. 
  Votovorona 
  and 
  Iakiana 
  (or 
  Ihan- 
  

   kiana 
  ?) 
  are 
  probably 
  the 
  highest 
  of 
  these 
  cones, 
  though 
  even 
  these 
  

   are 
  of 
  no 
  great 
  height. 
  Votovorona 
  is 
  350 
  feet 
  high, 
  and 
  has 
  been 
  

   protruded 
  through 
  granite. 
  The 
  rock 
  is 
  of 
  the 
  nature 
  of 
  diorite, 
  

   being 
  composed 
  of 
  felspar 
  and 
  green 
  hornblende. 
  The 
  angle 
  of 
  its 
  

   slope 
  is 
  over 
  50°. 
  About 
  twenty 
  or 
  twenty-five 
  miles 
  N.N.E. 
  

   of 
  Ankaratra, 
  and 
  some 
  seven 
  or 
  eight 
  miles 
  W.S.W. 
  of 
  Antana- 
  

   narivo, 
  there 
  is 
  another 
  of 
  these 
  probably 
  eruptive 
  bosses. 
  It 
  is 
  a 
  low 
  

   conical 
  knob 
  of, 
  perhaps, 
  150 
  or 
  200 
  feet 
  high, 
  and 
  is 
  also 
  known 
  

   by 
  the 
  name 
  of 
  Votovorona. 
  There 
  seem 
  to 
  have 
  been 
  a 
  few 
  small 
  

   outflows 
  of 
  lava 
  from 
  the 
  hill, 
  and 
  it 
  not 
  improbably 
  forms 
  the 
  core 
  

   of 
  an 
  old 
  volcano. 
  

  

  Between 
  the 
  mountains 
  of 
  Ankaratra 
  and 
  Vavavato 
  there 
  exists 
  a 
  

  

  * 
  Dr. 
  Mullens's 
  estimates 
  exceed 
  these 
  by 
  about 
  500 
  feet, 
  

   t 
  Described 
  by 
  Dr. 
  Hatch, 
  p. 
  354. 
  

  

  