﻿28 
  MALLET 
  : 
  VOLCANOES 
  OF 
  BARREN 
  ISLAND 
  AND 
  NARCONDAM, 
  

  

  with 
  certainty 
  much 
  above 
  sea-level, 
  or 
  at 
  a 
  depth, 
  at 
  the 
  point 
  in 
  question 
  

   of- 
  some 
  200 
  feet. 
  

  

  The 
  solfataras 
  have 
  been 
  already 
  described 
  (p. 
  18, 
  20), 
  but 
  it 
  remains 
  

   Economic 
  resources; 
  to 
  discuss 
  their 
  value 
  a9 
  a 
  source 
  of 
  sulphur. 
  We 
  

   Sulphur. 
  have, 
  firstly, 
  the 
  superficial 
  crusts, 
  containing 
  a 
  

  

  high 
  percentage 
  of 
  the 
  mineral 
  ; 
  and, 
  secondly, 
  the 
  ash 
  beneath, 
  through 
  

   which 
  sulphur 
  is 
  more 
  or 
  less 
  disseminated. 
  The 
  aggregate 
  area 
  of 
  the 
  

   solfataras 
  at 
  the 
  crater 
  and 
  at 
  the 
  point 
  of 
  eruption 
  of 
  the 
  northern 
  stream 
  

   of 
  lava, 
  does 
  not, 
  I 
  think, 
  exceed 
  some 
  5,000 
  square 
  feet. 
  The 
  crusts, 
  

   although, 
  in 
  some 
  places, 
  several 
  inches 
  thick, 
  were 
  absent 
  in 
  others, 
  so 
  

   that 
  the 
  average 
  thickness 
  was 
  probably 
  not 
  more 
  than 
  2 
  or 
  3. 
  Taking 
  the 
  

   specific 
  gravity 
  of 
  the 
  loosely 
  coherent 
  sulphur 
  at 
  1*5, 
  the 
  above 
  figures 
  

   would 
  give 
  a 
  total 
  of 
  not 
  more 
  than 
  a 
  few 
  dozen 
  tons, 
  from 
  which 
  some 
  

   deduction 
  would 
  have 
  to 
  be 
  made 
  for 
  impurity. 
  This 
  estimate, 
  although 
  

   crude 
  in 
  the 
  extreme, 
  and 
  without 
  any 
  pretensions 
  to 
  accuracy, 
  at 
  least 
  

   suffices, 
  I 
  think, 
  to 
  show 
  that 
  only 
  a 
  very 
  limited 
  quantity 
  of 
  sulphur 
  is 
  to 
  . 
  

   be 
  obtained. 
  During 
  our 
  stay 
  at 
  the 
  island 
  the 
  party 
  of 
  convicts 
  collected 
  

   97 
  bags-full, 
  weighing 
  6,840 
  lbs., 
  or 
  rather 
  more 
  than 
  3 
  tons. 
  This 
  was 
  

   the 
  creme 
  cle 
  la 
  creme 
  of 
  the 
  deposit 
  (the 
  last 
  10 
  or 
  20 
  bags, 
  even, 
  con- 
  

   taining 
  rather 
  more 
  impurity 
  than 
  the 
  remainder). 
  A 
  sample 
  brought 
  to 
  

   Calcutta 
  yielded 
  on 
  assay 
  — 
  

  

  Sulphur 
  . 
  * 
  . 
  . 
  . 
  .... 
  . 
  . 
  . 
  88-02 
  

  

  Water 
  244 
  

  

  Fixed 
  residue 
  ......... 
  8'64 
  

  

  100*00 
  

  

  The 
  ash 
  beneath 
  the 
  crusts 
  was 
  dug 
  into 
  to 
  a 
  depth 
  of 
  several 
  feet, 
  

  

  and 
  samples 
  taken 
  for 
  assay, 
  which 
  gave 
  — 
  

  

  Sulphur. 
  

  

  p. 
  c. 
  

   Largest 
  solfatara 
  in 
  crater; 
  ash 
  2£ 
  feet 
  from 
  surface 
  (stones 
  

  

  excluded=, 
  say, 
  ^ 
  of 
  the 
  total) 
  ..... 
  1-06 
  

  

  Do. 
  ; 
  ash 
  6 
  feet 
  from 
  surface 
  (stones 
  

  

  excluded=, 
  say, 
  | 
  of 
  the 
  total) 
  ..... 
  12'98 
  

  

  Solfatara 
  on 
  northern 
  outer 
  slope 
  ; 
  ash 
  4 
  feet 
  from 
  surface 
  . 
  -80 
  

  

  Do. 
  do. 
  ; 
  „ 
  7 
  „ 
  „ 
  . 
  -15 
  

  

  Solfatara 
  at 
  point 
  of 
  issue 
  of 
  recent 
  lava 
  ; 
  ash 
  1 
  i 
  feet 
  from 
  surface 
  -04 
  

  

  Do. 
  do. 
  ; 
  ash 
  7 
  „ 
  „ 
  „ 
  . 
  -02 
  

  

  ( 
  278 
  ) 
  

  

  