﻿610 
  Transactions, 
  — 
  Geology, 
  

  

  end, 
  but 
  in 
  connection 
  witli 
  it 
  I 
  may 
  here 
  mention 
  timt 
  the 
  first 
  shaft 
  sunk 
  

   by 
  Messrs. 
  Smith 
  and 
  Knight, 
  tlie 
  Englisli 
  contractors, 
  unfortunately 
  

   readied 
  it 
  soon 
  below 
  the 
  surface 
  of 
  the 
  ground, 
  and 
  continued 
  all 
  the 
  way 
  

   through 
  it 
  to 
  the 
  roof 
  of 
  the 
  tunnel. 
  This 
  was 
  one 
  of 
  the 
  principal 
  causes 
  

   that 
  the 
  firm, 
  being 
  unacquainted 
  with 
  the 
  formation 
  of 
  the 
  crater 
  wall, 
  

   abandoned 
  the 
  contract 
  so 
  soon. 
  The 
  first 
  stony 
  lava 
  in 
  the 
  tunnel, 
  flowing 
  

   down 
  the 
  slopes 
  of 
  the 
  crater 
  wall, 
  is 
  a 
  small 
  stream, 
  No. 
  214, 
  about 
  22 
  

   chains 
  from 
  the 
  Lyttelton 
  end. 
  Several 
  others 
  of 
  similar 
  dimensions 
  follow, 
  

   till 
  we 
  reach 
  stream 
  206, 
  which 
  might 
  be 
  the 
  continuation 
  of 
  No. 
  237, 
  11^ 
  

   chains 
  from 
  the 
  Lyttelton 
  end. 
  This 
  stream 
  throws 
  a 
  great 
  deal 
  of 
  light 
  by 
  

   its 
  COD 
  figuration 
  on 
  the 
  manner 
  of 
  the 
  flow 
  of 
  liquid 
  lava. 
  After 
  flowing 
  

   down 
  the 
  slopes, 
  we 
  see 
  it 
  shortly 
  afterwards 
  ascend 
  again 
  (No. 
  202) 
  over 
  a 
  

   bed 
  of 
  agglomerate, 
  and, 
  after 
  having 
  reached 
  the 
  apex 
  of 
  the 
  latter, 
  

   descend 
  again 
  (No. 
  200), 
  diminishing 
  rapidly 
  in 
  size, 
  the 
  rock 
  now 
  becoming 
  

   highly 
  porphyritic 
  and 
  lighter 
  in 
  colour. 
  The 
  largest 
  stony 
  lava-stream 
  of 
  

   the 
  whole 
  series 
  begins 
  about 
  41 
  chains 
  from 
  the 
  Lyttelton 
  end, 
  and 
  con- 
  

   tinues 
  without 
  interruption 
  to 
  52i- 
  chains. 
  Consequently, 
  taking 
  its 
  angle 
  of 
  

   dip 
  into 
  account, 
  it 
  is 
  more 
  than 
  500 
  feet 
  thick. 
  More 
  or 
  less 
  porphyritic 
  on 
  

   both 
  sides, 
  the 
  whole 
  central 
  portion 
  consists 
  of 
  a 
  very 
  hard 
  basaltic 
  rock, 
  

   ringing 
  to 
  the 
  hammer, 
  irregularly 
  jointed, 
  with 
  here 
  and 
  there 
  a 
  tendency 
  

   towards 
  spheroidal 
  structure. 
  This 
  huge 
  stream 
  gains 
  an 
  additional 
  interest 
  

   from 
  the 
  existence 
  of 
  three 
  caves 
  in 
  its 
  centre, 
  which, 
  however, 
  have 
  partly 
  

   been 
  filled 
  up 
  with 
  thin 
  plates 
  of 
  basalt 
  of 
  the 
  same 
  texture 
  as 
  the 
  lava- 
  

   stream, 
  and 
  which 
  lie 
  more 
  or 
  less 
  horizontal. 
  They 
  are 
  coated 
  over 
  and 
  

   often 
  cemented 
  together 
  by 
  sphasrosiderite. 
  Sometimes 
  they 
  lie 
  in 
  such 
  

   regular 
  order, 
  and 
  so 
  loosely 
  upon 
  each 
  other, 
  as 
  if 
  they 
  had 
  been 
  artificially 
  

   placed 
  in 
  that 
  position. 
  The 
  open 
  space, 
  or 
  cave 
  proper, 
  is 
  always 
  on 
  the 
  

   southern 
  side 
  of 
  each 
  cavity. 
  The 
  only 
  explanation 
  I 
  can 
  offer 
  as 
  to 
  their 
  

   formation 
  is 
  that 
  gases 
  have 
  been 
  enclosed 
  in 
  this 
  portion 
  of 
  the 
  lava 
  

   stream, 
  which 
  in 
  course 
  of 
  time 
  were 
  absorbed, 
  and 
  that 
  liquid 
  matter 
  

   from 
  the 
  upper 
  portion 
  of 
  the 
  stream 
  found 
  access 
  to 
  the 
  cavities, 
  gradually 
  

   filling 
  them 
  up, 
  but 
  that 
  the 
  channels 
  of 
  communication 
  were 
  stopped 
  before 
  

   the 
  whole 
  of 
  the 
  gases 
  still 
  remaining 
  in 
  the 
  southern 
  parts 
  of 
  each 
  had 
  

   been 
  absorbed. 
  

  

  Another 
  stream 
  of 
  large 
  dimensions 
  is 
  No. 
  14, 
  beginning 
  20 
  chains 
  from 
  

   the 
  Heathcote 
  end. 
  It 
  is 
  over 
  100 
  feet 
  thick, 
  has 
  a 
  jointed 
  structure, 
  the 
  

   central 
  portion 
  beiug 
  spheroidal, 
  with 
  concentric 
  layers. 
  All 
  the 
  stony 
  

   streams 
  in 
  the 
  tunnel 
  above 
  the 
  latter 
  are 
  very 
  thin, 
  but 
  it 
  is 
  possible 
  that 
  

   the 
  scoriaceous 
  basaltic 
  lava 
  (the 
  violet 
  beds 
  of 
  the 
  section) 
  which 
  overlie 
  

   them, 
  are 
  only 
  their 
  upper 
  portion, 
  the 
  bottom 
  of 
  the 
  streams, 
  owing 
  to 
  

   their 
  thinness 
  and 
  to 
  the 
  distance 
  from 
  the 
  centre 
  of 
  eruption, 
  not 
  having 
  

  

  