﻿328 
  

  

  EEV. 
  K. 
  EAEON 
  ON 
  THE 
  

  

  ties 
  by 
  a 
  rough 
  process 
  of 
  sublimation) 
  it 
  is 
  used 
  in 
  the 
  manufacture 
  

   of 
  gunpowder. 
  Nitre 
  or 
  saltpetre 
  is 
  obtained 
  by 
  lixiviating" 
  the 
  soil 
  

   (the 
  decayed 
  gneiss) 
  and 
  allowing 
  the 
  solution 
  to 
  crystallize. 
  There 
  

   is 
  no 
  special 
  locality 
  whence 
  the 
  nitre 
  is 
  obtained, 
  though 
  the 
  

   natives 
  say 
  that 
  certain 
  soils, 
  probably 
  those 
  rich 
  in 
  nitrogenous 
  

   matter, 
  yield 
  it 
  in 
  greater 
  abundance 
  than 
  others. 
  Graphite 
  and 
  

   iron 
  pyrites, 
  as 
  has 
  been 
  stated 
  above, 
  are 
  found 
  in 
  various 
  places. 
  

   Mr. 
  Ellis 
  says 
  that 
  oxide 
  of 
  manganese 
  has 
  been 
  found 
  about 
  50 
  

   miles 
  south 
  of 
  the 
  capital. 
  Lime 
  is 
  obtained 
  from 
  the 
  deposit 
  of 
  

   travertine 
  at 
  Antsirabe, 
  but 
  as 
  yet 
  it 
  seems 
  only 
  to 
  have 
  been 
  em- 
  

   ployed 
  in 
  the 
  erection 
  of 
  the 
  Queen's 
  palaces 
  and 
  a 
  few 
  other 
  

   buildings. 
  A 
  beautiful 
  variety 
  of 
  Amazon 
  stone 
  is 
  found 
  somewhere 
  

   to 
  the 
  south 
  of 
  Lake 
  Itasy. 
  A 
  kind 
  of 
  ferruginous 
  clay 
  (kaolinite) 
  

   known 
  as 
  tanimanga, 
  now 
  much 
  used 
  for 
  roofing- 
  tiles, 
  is 
  obtained 
  in 
  

   many 
  places, 
  but 
  it 
  seems 
  that 
  it 
  is 
  not 
  of 
  very 
  excellent 
  quality, 
  

   owing 
  perhaps 
  to 
  the 
  large 
  proportion 
  of 
  iron 
  present. 
  Tourma- 
  

   line 
  (schorl 
  and 
  rubellite), 
  corundum, 
  sapphire, 
  spinel, 
  rutile, 
  &c. 
  

   are 
  also 
  found. 
  

  

  Lagooxs. 
  

  

  Any 
  paper 
  dealing 
  with 
  the 
  geology 
  of 
  ^Madagascar 
  would 
  be 
  in- 
  

   complete 
  without 
  a 
  notice 
  of 
  the 
  remarkable 
  series 
  of 
  narrow 
  lagoons 
  

   which 
  form 
  so 
  prominent 
  a 
  feature 
  in 
  the 
  character 
  of 
  the 
  east 
  

   coast. 
  I 
  have 
  no 
  new 
  facts 
  to 
  mention 
  in 
  regard 
  to 
  these 
  lagoons, 
  

   but 
  their 
  importance 
  demands 
  a 
  word 
  or 
  two 
  of 
  desertion 
  *. 
  The 
  

   lagoons 
  are 
  formed 
  by 
  the 
  numerous 
  rivers 
  which 
  flow 
  from 
  the 
  

   mountains 
  in 
  the 
  interior 
  in 
  their 
  endeavour 
  to 
  discharge 
  their 
  

   waters 
  into 
  the 
  Indian 
  Ocean. 
  They 
  are 
  found 
  from 
  16° 
  52' 
  to 
  

   22° 
  25' 
  S. 
  lat. 
  It 
  seems 
  that 
  there 
  are 
  more 
  than 
  twenty 
  of 
  these 
  

   lagoons 
  between 
  the 
  rivers 
  Ivondrona 
  and 
  Matitanana 
  (a 
  distance 
  of 
  

   300 
  miles), 
  the 
  total 
  length 
  of 
  the 
  isthmuses 
  between 
  them 
  only 
  

   amounting 
  to 
  28 
  j 
  miles, 
  or 
  about 
  one 
  eleventh 
  part 
  of 
  the 
  whole 
  dis- 
  

   tance. 
  With 
  a 
  comparatively 
  small 
  outlay 
  these 
  lagoons 
  might 
  be 
  

   turned 
  into 
  a 
  continuous 
  canal, 
  which 
  would 
  be 
  an 
  immense 
  boon 
  

   to 
  merchants 
  and 
  others 
  resident 
  in 
  this 
  part 
  of 
  the 
  island. 
  

  

  Coxcltjsions. 
  

  

  From 
  what 
  has 
  been 
  stated 
  in 
  the 
  preceding 
  pages, 
  it 
  will 
  be 
  

   seen 
  that 
  the 
  eastern 
  half 
  of 
  Madagascar 
  must 
  be 
  classed 
  as 
  one 
  

   of 
  those 
  extensive 
  regions 
  of 
  crystalline 
  rocks 
  known 
  as 
  metamor- 
  

   phic. 
  To 
  what 
  period 
  of 
  geological 
  time, 
  then, 
  do 
  the 
  rocks 
  of 
  this 
  

   region 
  belong, 
  and 
  when 
  were 
  they 
  elevated 
  above 
  the 
  sea 
  ? 
  

  

  AYith 
  our 
  present 
  imperfect 
  knowledge 
  of 
  the 
  country, 
  these 
  are 
  

   questions 
  more 
  easily 
  propounded 
  than 
  answered. 
  As 
  there 
  are, 
  so 
  

   far 
  as 
  yet 
  known, 
  no 
  rocks 
  older 
  than 
  Jurassic 
  resting 
  upon 
  them, 
  

   we 
  are 
  left 
  without 
  one 
  of 
  the 
  most 
  valuable 
  aids 
  in 
  helping 
  us 
  to 
  

   determine 
  their 
  antiquity. 
  The 
  rocks, 
  however, 
  present 
  the 
  closest 
  

  

  * 
  For 
  particulars 
  and 
  maps 
  see 
  M. 
  Grandidier's 
  paper 
  read 
  before 
  the 
  Aca- 
  

   demie 
  des 
  Sciences. 
  

  

  