﻿Haast,— 
  Ow 
  the 
  Geological 
  Structure 
  of 
  Banks 
  Peninsula, 
  499 
  

  

  •wlilcli 
  towards 
  the 
  centre 
  have 
  the 
  greatest 
  biUk, 
  and 
  are 
  very 
  stony 
  and 
  

   compact, 
  become 
  now 
  gradually 
  more 
  and 
  more 
  numerous, 
  but 
  of 
  smaller 
  

   size 
  and 
  more 
  porpbyritic 
  or 
  scoriaceous, 
  according 
  to 
  the 
  laws 
  by 
  wliich 
  

   the 
  flow, 
  dimensions 
  and 
  cooling 
  of 
  the 
  lava-streams 
  are 
  regulated. 
  It 
  is, 
  

   moreover, 
  evident 
  that 
  many 
  of 
  them, 
  owing 
  to 
  want 
  of 
  material, 
  scarcely 
  

   reach 
  half 
  way 
  down 
  the 
  slopes 
  of 
  the 
  caldera 
  wall, 
  that 
  others 
  rapidly 
  thin 
  

   out, 
  and 
  that 
  many 
  which, 
  for 
  some 
  distance 
  after 
  flowing 
  over 
  the 
  lip 
  of 
  

   the 
  crater, 
  had 
  been 
  of 
  large 
  dimensions 
  and 
  stony, 
  become, 
  long 
  before 
  its 
  

   outer 
  edge 
  is 
  reached, 
  thin 
  and 
  scoriaceous, 
  so 
  that 
  here 
  streams 
  of 
  five 
  feet 
  

   in 
  thickness 
  are 
  not 
  uncommon. 
  Although 
  the 
  tunnel 
  does 
  not 
  offer 
  us 
  the 
  

   necessary 
  data 
  to 
  judge 
  of 
  the 
  breadth 
  of 
  the 
  lava-streams, 
  we 
  have 
  for 
  that 
  

   purpose 
  ample 
  evidence 
  in 
  Godley 
  Heads, 
  the 
  sea-wall 
  near 
  Sumner, 
  and 
  

   many 
  other 
  localities. 
  There 
  are 
  streams 
  which 
  are 
  500 
  feet 
  broad, 
  others 
  

   only 
  30 
  to 
  40, 
  but 
  all 
  without 
  exception 
  are 
  somewhat 
  scoriaceous 
  on 
  the 
  

   bottom, 
  where 
  the 
  lava 
  flowing 
  over 
  cold 
  ground 
  cooled 
  more 
  rapidly. 
  In 
  

   many 
  instances 
  this 
  is 
  well 
  exhibited 
  by 
  the 
  existence 
  of 
  a 
  small 
  bed 
  of 
  

   laterite, 
  a 
  brick-red 
  coloured 
  rock, 
  sometimes 
  only 
  a 
  few 
  inches 
  thick, 
  which 
  

   doubtless 
  was 
  a 
  layer 
  of 
  soil 
  on 
  the 
  decomposed 
  upper 
  portion 
  of 
  the 
  lava- 
  

   stream 
  or 
  agglomerate 
  bed 
  exposed 
  for 
  a 
  considerable 
  time 
  to 
  atmospheric 
  

   action 
  before 
  the 
  new 
  eruption 
  took 
  place. 
  The 
  lava 
  in 
  the 
  larger 
  streams, 
  

   and 
  in 
  its 
  central 
  portion 
  principally, 
  very 
  stony 
  and 
  of 
  a 
  blackish 
  colour, 
  

   gradually 
  becomes, 
  as 
  we 
  approach 
  the 
  surface, 
  more 
  porpbyritic, 
  with 
  a 
  

   more 
  open 
  texture, 
  and 
  assumes 
  pinkish 
  or 
  lilac 
  tints, 
  till 
  it 
  changes 
  into 
  

   scoriffi. 
  The 
  decomposition 
  or 
  alteration 
  is 
  here 
  often 
  so 
  great 
  that 
  it 
  is 
  

   impossible 
  to 
  trace 
  the 
  top 
  of 
  the 
  line 
  of 
  contact 
  between 
  the 
  surface 
  of 
  the 
  

   stream 
  and 
  the 
  bottom 
  of 
  the 
  overlying 
  bed, 
  both 
  forming 
  a 
  layer 
  of 
  coarse 
  

   agglomerate. 
  In 
  other 
  instances 
  the 
  rough, 
  uneven 
  scoriaceous 
  surface 
  of 
  

   the 
  lava-streams 
  has 
  been 
  well 
  preserved, 
  the 
  hollow 
  spaces 
  being 
  filled 
  up 
  

   by 
  ashes 
  and 
  ejecta, 
  in 
  which 
  case 
  they 
  resemble 
  many 
  of 
  the 
  recent 
  lava- 
  

   streams 
  which 
  I 
  examined 
  in 
  Mount 
  Vesuvius 
  and 
  Mount 
  Etna 
  shortly 
  

   after 
  they 
  had 
  issued 
  from 
  the 
  crater. 
  

  

  The 
  lava 
  of 
  which 
  the 
  caldera 
  wall 
  under 
  consideration 
  has 
  been 
  built 
  

   up, 
  consists 
  of 
  basic 
  rocks, 
  changing 
  from 
  a 
  dolerite 
  to 
  a 
  fine-grained 
  basalt. 
  

   Some 
  of 
  the 
  lava-streams, 
  however, 
  as 
  previously 
  pointed 
  out, 
  show 
  also 
  a 
  

   remarkable 
  difference 
  in 
  the 
  structure 
  of 
  the 
  rock 
  of 
  which 
  they 
  are 
  com- 
  

   posed, 
  the 
  central 
  portion 
  being 
  a 
  compact 
  basalt 
  with 
  a 
  few 
  crystals 
  of 
  

   augite, 
  basaltic 
  hornblende, 
  labradorite, 
  whilst 
  the 
  upper 
  portion 
  consists 
  

   of 
  a 
  lighter 
  coloured 
  porpbyritic 
  dolerite, 
  sometimes 
  so 
  replete 
  with 
  good 
  

   sized 
  crystals 
  of 
  labradorite 
  that 
  the 
  greater 
  portion 
  of 
  the 
  rock 
  is 
  formed 
  

   pf 
  that 
  mineral. 
  

  

  