﻿GEOLOGY 
  OE 
  MADAGASCAR. 
  315 
  

  

  subcorneal 
  hill 
  of 
  columnar 
  trachyte* 
  ; 
  this 
  is 
  possibly 
  the 
  neck 
  of 
  an 
  

   ancient 
  volcano 
  exposed 
  by 
  denudation 
  of 
  its 
  former 
  covering. 
  

  

  Newep. 
  Volcanic 
  Series. 
  

  

  In 
  addition 
  to 
  the 
  above 
  evidences 
  of 
  former 
  volcanic 
  activity 
  

   in 
  the 
  region 
  of 
  Ankaratra, 
  there 
  are 
  many 
  scores 
  of 
  volcanic 
  cones, 
  

   which 
  are 
  probably 
  of 
  later 
  origin 
  than 
  Ankaratra. 
  These 
  are 
  

   situated 
  in 
  two 
  localities 
  especially, 
  in 
  Mandridrano, 
  on 
  the 
  western 
  

   side 
  of 
  Lake 
  Itasy, 
  and 
  in 
  the 
  neighbourhood 
  of 
  Betafo, 
  in 
  Yakin' 
  

   Ankaratra, 
  the 
  former 
  being 
  about 
  sixty 
  miles 
  west, 
  and 
  the 
  latter 
  

   from 
  eighty 
  to 
  ninety 
  miles 
  S.S.W., 
  of 
  the 
  capital. 
  Both 
  localities 
  

   are 
  about 
  130 
  miles 
  from 
  the 
  eastern 
  coast 
  of 
  the 
  island, 
  and 
  150 
  

   from 
  the 
  western 
  coast. 
  It 
  is 
  hardly 
  necessary 
  to 
  say 
  that 
  all 
  

   these 
  volcanoes 
  are 
  extinct, 
  and 
  that 
  there 
  are 
  none 
  in 
  activity 
  at 
  

   the 
  present 
  time 
  in 
  any 
  part 
  of 
  Madagascar 
  t. 
  On 
  the 
  west 
  side 
  

   of 
  Lake 
  Itasy 
  the 
  volcanic 
  cones 
  exist 
  in 
  great 
  numbers, 
  and 
  these 
  

   therefore 
  shall 
  be 
  first 
  described. 
  

  

  The 
  extinct 
  volcanoes 
  of 
  this 
  district 
  of 
  Mandridrano 
  extend 
  for 
  a 
  

   distance 
  of 
  about 
  twenty 
  miles 
  north 
  and 
  south, 
  and 
  perhaps 
  three 
  

   or 
  four 
  east 
  and 
  west. 
  They 
  are, 
  for 
  the 
  most 
  part, 
  scoria-cones. 
  

   The 
  cones 
  are 
  thickly 
  studded 
  over 
  the 
  district, 
  in 
  some 
  parts 
  clus- 
  

   tering 
  together 
  more 
  thickly 
  than 
  in 
  others. 
  Occasionally 
  there 
  is 
  

   a 
  series 
  of 
  cones 
  which 
  have 
  evidently 
  been 
  heaped 
  up 
  by 
  the 
  simul- 
  

   taneous 
  ejection 
  of 
  scoriae 
  from 
  different 
  vents 
  situated 
  on 
  the 
  same 
  

   line 
  of 
  fissure, 
  but 
  so 
  that 
  the 
  cones 
  have 
  run 
  one 
  into 
  the 
  other, 
  

   leaving 
  a 
  ridge, 
  generally 
  curvilinear, 
  at 
  the 
  summit. 
  None 
  of 
  

   these 
  extinct 
  volcanoes 
  reach 
  the 
  height 
  of 
  1000 
  feet. 
  Kasige, 
  

   which 
  is 
  probably 
  the 
  highest, 
  I 
  found 
  by 
  aneroid 
  to 
  be 
  863 
  feet 
  

   above 
  the 
  plain 
  J. 
  This 
  is 
  a 
  remarkably 
  perfect 
  and 
  fresh-looking 
  

   volcano, 
  whose 
  sides 
  slope 
  at 
  an 
  angle 
  of 
  32° 
  or 
  33°. 
  The 
  scoriae 
  on 
  

   the 
  sides 
  have 
  become 
  sufficiently 
  disintegrated 
  to 
  form 
  a 
  soil, 
  on 
  

   which 
  is 
  found 
  a 
  by 
  no 
  means 
  scanty 
  flora 
  ; 
  for, 
  among 
  other 
  plants 
  

   growing 
  here, 
  I 
  gathered 
  an 
  Aloe 
  (A. 
  macroclada), 
  a 
  Clematis 
  (C. 
  

   trifidct), 
  two 
  or 
  three 
  composite 
  herbs 
  (Senecio 
  cochlearifolius, 
  Heli- 
  

   chrysum 
  lycopoclioides, 
  Laggera 
  alata, 
  &c), 
  some 
  grasses 
  (Imperata 
  

  

  * 
  Described 
  by 
  Dr. 
  Hatch, 
  p. 
  354. 
  

  

  t 
  Scrope, 
  in 
  his 
  ' 
  Volcanoes,' 
  2nd 
  edition, 
  p. 
  428, 
  says 
  of 
  Madagascar: 
  — 
  

   " 
  There 
  is 
  some 
  reason 
  to 
  believe 
  in 
  the 
  existence 
  of 
  active 
  volcanic 
  vents 
  in 
  this 
  

   great 
  island;" 
  and 
  Dr. 
  Daubeny, 
  in 
  the 
  2nd 
  edition 
  of 
  his 
  ' 
  Volcanoes,' 
  p. 
  433, 
  

   in 
  referring 
  to 
  the 
  islands 
  on 
  the 
  eastern 
  coast 
  of 
  Africa, 
  says 
  : 
  — 
  " 
  The 
  prin- 
  

   cipal 
  of 
  these 
  are 
  the 
  great 
  island 
  of 
  Madagascar, 
  the 
  isle 
  of 
  Bourbon, 
  and 
  the 
  

   Mauritius, 
  the 
  first 
  of 
  which 
  has 
  been 
  too 
  little 
  explored 
  to 
  allow 
  of 
  my 
  an- 
  

   nouncing 
  with 
  certainty 
  anything 
  respecting 
  its 
  physical 
  structure 
  ; 
  " 
  and, 
  in 
  a 
  

   note, 
  he 
  adds, 
  " 
  Madagascar 
  is 
  stated 
  by 
  Daubuisson 
  to 
  contain 
  volcanoes, 
  on 
  the 
  

   authority 
  of 
  Ebel 
  (' 
  Bau 
  der 
  Erde,' 
  torn. 
  ii. 
  p. 
  289), 
  who 
  reports 
  that 
  in 
  this 
  

   island 
  tbere 
  is 
  a 
  volcano 
  ejecting 
  a 
  stream 
  of 
  water 
  to 
  a 
  sufficient 
  height 
  to 
  be 
  

   visible 
  twenty 
  leagues 
  out 
  at 
  sea." 
  It 
  is 
  needless 
  to 
  say 
  that 
  no 
  such 
  volcano 
  

   exists. 
  Dr. 
  Daubeny 
  continues, 
  " 
  Sir 
  Roderick 
  Murchison, 
  Dec. 
  1827, 
  exhibited 
  

   at 
  the 
  Geological 
  Society 
  some 
  specimens 
  of 
  a 
  volcanic 
  nature 
  said 
  to 
  have 
  come 
  

   from 
  this 
  island, 
  but 
  the 
  locality 
  was 
  not 
  mentioned." 
  

  

  t 
  For 
  description 
  of 
  lava 
  from 
  Kasige 
  see 
  Dr. 
  Hatch's 
  paper, 
  p. 
  351. 
  

  

  