﻿24 
  mallet: 
  volcanoes 
  of 
  barren 
  island 
  and 
  narcondam. 
  

  

  In 
  the 
  lower 
  part 
  of 
  the 
  main 
  gorge, 
  which 
  debouches 
  to 
  the 
  south 
  

   Kecent 
  aqueous 
  depo- 
  o£ 
  the 
  alluvial 
  plain, 
  there 
  is 
  an 
  agglomerate, 
  com- 
  

   Slts 
  * 
  posed 
  of 
  rounded 
  and 
  angular 
  lumps 
  of 
  volcanic 
  

  

  rock 
  in 
  a 
  finer 
  matrix, 
  which 
  appears 
  to 
  be 
  a 
  deposit 
  of 
  the 
  stream 
  itself. 
  

   The 
  water 
  has 
  subsequently 
  cut 
  through, 
  and 
  exposed 
  the 
  rock 
  in 
  section. 
  * 
  

   At 
  the 
  debouchure 
  there 
  is 
  a 
  fan-shaped 
  mass 
  of 
  detrital 
  matter, 
  which 
  

   merges 
  into 
  the 
  alluvial 
  plain 
  to 
  the 
  north. 
  The 
  latter, 
  which, 
  as 
  will 
  be 
  

   seen 
  from 
  the 
  map, 
  is 
  far 
  from 
  level, 
  being 
  250 
  feet 
  above 
  the 
  sea 
  at 
  one 
  end, 
  

   and 
  only 
  80 
  at 
  the 
  other, 
  is 
  formed 
  cf 
  volcanic 
  sand, 
  most 
  of 
  which 
  has 
  

   been 
  washed 
  out 
  of 
  the 
  above 
  gorge, 
  the 
  rest 
  having 
  come 
  from 
  minor 
  

   water-courses 
  to 
  the 
  east. 
  The 
  sand 
  is 
  covered 
  with 
  coarse 
  grass, 
  and 
  occa- 
  

   sional 
  bushes. 
  As 
  previously 
  explained, 
  2 
  the 
  deposit, 
  in 
  as 
  far 
  as 
  it 
  over- 
  

   lies 
  the 
  lava, 
  seems 
  to 
  have 
  been 
  formed 
  within 
  the 
  last 
  century. 
  After 
  

   heavy 
  bursts 
  of 
  tropical 
  rain 
  the 
  amount 
  of 
  detritus 
  swept 
  down 
  the 
  

   gorges 
  is 
  probably 
  very 
  large 
  in 
  proportion 
  to 
  their 
  size, 
  while 
  the 
  frequency 
  

   with 
  which 
  the 
  lava 
  crops 
  through, 
  shows 
  that 
  the 
  sand 
  is 
  not 
  very 
  thick. 
  

  

  At 
  the 
  debouchure 
  of 
  the 
  gorge 
  to 
  the 
  north 
  of 
  the 
  anchorage 
  another 
  

   aqueous 
  deposit 
  may 
  be 
  seen, 
  and 
  doubtless 
  there 
  are 
  many 
  others 
  on 
  the 
  

   island. 
  

  

  The 
  sand 
  on 
  the 
  beach 
  near 
  the 
  anchorage 
  is 
  somewhat 
  remarkable, 
  

   being 
  composed 
  almost 
  entirely 
  of 
  • 
  bottle-green 
  translucent 
  augite, 
  and 
  

   brownish-yellow 
  olivine, 
  with 
  some 
  grains 
  of 
  coral 
  and 
  broken 
  shell, 
  &c. 
  

  

  Taking 
  into 
  account 
  the 
  heavy 
  tropical 
  rains 
  at 
  Barren 
  Island, 
  one 
  

  

  would 
  expect, 
  apriori, 
  a 
  certain 
  amount 
  of 
  drainage- 
  

   Hot 
  spring. 
  . 
  

  

  water 
  from 
  the 
  amphitheatre, 
  which 
  has 
  an 
  area 
  

  

  of 
  rather 
  more 
  than 
  a 
  square 
  mile, 
  and 
  the 
  natural 
  outlet 
  for 
  such 
  drain- 
  

   age 
  would 
  be 
  the 
  breach, 
  towards 
  wdiich, 
  as 
  previously 
  said, 
  the 
  valley 
  

   between 
  the 
  old 
  crater 
  walls 
  and 
  the 
  newer 
  cone, 
  has 
  a 
  tolerably 
  steady 
  

   slope. 
  3 
  But, 
  owing 
  to 
  the 
  porous 
  nature 
  of 
  most 
  of 
  the 
  volcanic 
  products, 
  

   the 
  drainage 
  in 
  the 
  cold 
  weather, 
  and 
  probably 
  at 
  all 
  times, 
  except 
  after 
  

  

  3 
  It 
  is 
  scarcely 
  necessary 
  to 
  say 
  that 
  this, 
  and 
  all 
  the 
  other, 
  streani-heds 
  in 
  the 
  island, 
  

   are 
  perfectly 
  dry 
  in 
  the 
  cold 
  weather, 
  and 
  probably 
  at 
  all 
  times, 
  except 
  after 
  heavy 
  rain. 
  

  

  2 
  p. 
  22. 
  

  

  3 
  p. 
  13. 
  

  

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  274 
  ) 
  

  

  