﻿£0 
  MALLET 
  : 
  VOLCANOES 
  OF 
  BARREN 
  ISLAND 
  AND 
  NAllCONDAM. 
  

  

  streams. 
  In 
  general 
  appearance 
  they 
  are 
  all 
  very 
  similar 
  to 
  each 
  other, 
  

   presenting 
  the 
  same 
  exceedingly 
  rough, 
  hummocky, 
  and 
  fissured 
  surface, 
  

   with 
  the 
  black, 
  scoriaceous 
  crust 
  broken 
  into 
  pieces 
  of 
  every 
  size 
  up 
  to 
  

   those 
  many 
  tons 
  in 
  weight. 
  Great 
  hollows 
  are 
  seen 
  in 
  places, 
  where, 
  the 
  

   lava 
  having 
  flowed 
  away 
  from 
  underneath, 
  the 
  crust 
  has 
  given 
  way 
  and 
  

   fallen 
  in. 
  The 
  streams 
  have 
  the 
  lateral 
  and 
  terminal 
  ' 
  banks' 
  1 
  so 
  frequently 
  

   noticed 
  in 
  the 
  descriptions 
  of 
  other 
  volcanoes. 
  The 
  lava 
  is 
  almost 
  perfectly 
  

   bare 
  of 
  vegetation, 
  even 
  a 
  stray 
  blade 
  of 
  grass 
  being 
  rarely 
  seen 
  upon 
  it. 
  

  

  The 
  macroscopic 
  and 
  microscopic 
  examination 
  of 
  the 
  recent 
  lavas 
  does 
  

   not 
  indicate 
  any 
  essential 
  difference 
  between 
  them 
  and 
  those 
  from 
  the 
  

   ancient 
  cone. 
  There 
  is 
  the 
  same 
  association 
  of 
  white, 
  translucent, 
  

   triclinic 
  felspar 
  crystals, 
  and 
  bottle-green 
  translucent 
  augite, 
  with 
  fre- 
  

   quently 
  a 
  little 
  olivine, 
  in 
  a 
  micro-crystalline 
  ground-mass 
  composed 
  of 
  

   triclinic 
  felspar, 
  augite, 
  magnetite, 
  opacite, 
  apatite, 
  &c. 
  An 
  average 
  

   sample 
  was 
  found 
  to 
  contain 
  50*10 
  per 
  -cent, 
  of 
  silica. 
  

  

  The 
  age 
  of 
  the 
  eastern 
  flow, 
  with 
  reference 
  to 
  the 
  others, 
  cannot 
  be 
  

   determined 
  with 
  certainty, 
  as 
  it 
  does 
  not 
  come 
  in 
  contact 
  with 
  either. 
  

  

  The 
  southern 
  stream 
  broke 
  out 
  a 
  little 
  more 
  than 
  half 
  way 
  up 
  the 
  

   cone, 
  at 
  a 
  point 
  now 
  marked 
  by 
  sliglit 
  projection. 
  After 
  pouring 
  down 
  

   the 
  side 
  of 
  the 
  cone, 
  it 
  followed 
  the 
  course 
  of 
  the 
  valley 
  into 
  the 
  sea, 
  

   which 
  has, 
  since 
  then, 
  cut 
  the 
  face 
  into 
  a 
  cliff 
  10 
  or 
  15 
  feet 
  in 
  height. 
  

   This 
  was 
  the 
  largest 
  flow 
  of 
  all, 
  a 
  considerable 
  part 
  of 
  the 
  area 
  covered 
  

   by 
  it 
  being 
  obscured 
  by 
  the 
  sand, 
  which 
  has 
  been 
  washed 
  down 
  from 
  the 
  

   old 
  crater 
  walls 
  to 
  the 
  south. 
  There 
  seems 
  to 
  have 
  been 
  a 
  subse- 
  

   quent 
  minor 
  gush 
  from 
  the 
  same 
  orifice, 
  which 
  scarcely 
  reached 
  beyond 
  

   the 
  base 
  of 
  the 
  cone. 
  

  

  The 
  northern 
  stream 
  broke 
  forth 
  about 
  £50 
  feet 
  below 
  the 
  crater; 
  

   close 
  to 
  the 
  point 
  of 
  issue 
  there 
  is 
  a 
  solfatara, 
  at 
  one 
  part 
  of 
  which, 
  

   about 
  25 
  feet 
  in 
  diameter, 
  was 
  the 
  richest 
  crust 
  of 
  sulphur 
  met 
  with 
  

   anywhere, 
  averaging 
  perhaps 
  4 
  inches 
  in 
  thickness. 
  Beneath 
  was 
  bleach- 
  

   ed 
  ash, 
  and, 
  on 
  digging 
  through 
  this, 
  in 
  the 
  centre 
  of 
  the 
  crust, 
  to 
  a 
  

   depth 
  of 
  7 
  feet, 
  an 
  open 
  hole 
  8 
  or 
  9 
  inches 
  in 
  diameter 
  was 
  disclosed, 
  into 
  

  

  1 
  Vide 
  sections 
  (drawn 
  on 
  a 
  horizontal 
  and 
  vertical 
  scale 
  of 
  4 
  inches 
  to 
  the 
  mile) 
  at 
  end 
  

   of 
  report. 
  

  

  ( 
  £70 
  ) 
  

  

  