﻿SOS 
  Transactions, 
  -^^Oeology, 
  

  

  the 
  Lyttelton-Snmner 
  road 
  at 
  riglit-angles, 
  on 
  the 
  very 
  summit 
  of 
  Evans 
  

   Pass, 
  and 
  which 
  is 
  repeatedly 
  passed 
  by 
  the 
  road 
  winding 
  in 
  and 
  out 
  of 
  the 
  

   different 
  bays 
  before 
  reaching 
  that 
  pass. 
  It 
  can 
  be 
  followed 
  to 
  Taylor's 
  

   Mistake. 
  Everywhere 
  along 
  the 
  sea 
  cliffs 
  at 
  and 
  near 
  the 
  entrance 
  of 
  

   Lyttelton 
  Harbour, 
  numerous 
  dykes, 
  mostly 
  all 
  in 
  a 
  vertical 
  position, 
  can 
  

   be 
  seen 
  pointing 
  towards 
  the 
  centre 
  of 
  that 
  harbour. 
  A 
  few, 
  however, 
  

   stand 
  in 
  a 
  slanting 
  position, 
  and 
  others 
  have 
  a 
  tortuous 
  course. 
  As 
  one 
  of 
  

   the 
  remarkable 
  changes 
  which 
  some 
  of 
  the 
  dykes 
  have 
  undergone 
  since 
  their 
  

   formation, 
  I 
  may 
  also 
  mention 
  one 
  which 
  is 
  well 
  exposed 
  in 
  the 
  sea 
  cliffs 
  at 
  

   Ohinitahi, 
  Governor's 
  Bay 
  ; 
  here 
  a 
  dyke 
  of 
  domite, 
  about 
  nine 
  feet 
  broad, 
  

   crosses 
  in 
  a 
  nearly 
  vertical 
  position 
  the 
  so-called 
  trachyte 
  sandstone 
  de- 
  

   posited 
  on 
  the 
  slopes 
  of 
  the 
  quartziferous 
  porphyry. 
  After 
  its 
  solidifica- 
  

   tion, 
  a 
  new 
  fissure, 
  about 
  three 
  feet 
  broad, 
  has 
  been 
  formed 
  parallel 
  to 
  its 
  

   direction, 
  and 
  running 
  along 
  its 
  centre, 
  which 
  has 
  been 
  injected 
  from 
  below 
  

   by 
  domitic 
  matter, 
  but 
  slightly 
  different 
  from 
  the 
  former 
  ; 
  however, 
  instead 
  

   of 
  continuing 
  to 
  the 
  top 
  of 
  the 
  cliff, 
  about 
  twelve 
  feet 
  above 
  the 
  sea 
  level, 
  the 
  

   dyke 
  is 
  seen 
  to 
  turn 
  from 
  its 
  vertical 
  to 
  a 
  nearly 
  horizontal 
  position, 
  and 
  to 
  

   thin 
  out 
  considerably 
  at 
  the 
  same 
  time, 
  disappearing 
  altogether 
  when 
  it 
  

   touches 
  the 
  side 
  wall 
  of 
  the 
  bed-rock. 
  The 
  older 
  dyke, 
  above 
  this 
  change 
  

   of 
  direction, 
  is 
  considerably 
  shattered 
  and 
  broken. 
  

  

  Before 
  proceeding, 
  it 
  v/ill 
  perhaps 
  be 
  useful 
  if 
  I 
  offer 
  a 
  few 
  remarks 
  on 
  

   the 
  causes 
  which 
  led 
  to 
  the 
  formation 
  of 
  these 
  remarkable 
  dykes. 
  I 
  con- 
  

   sider 
  this 
  the 
  more 
  important, 
  as 
  nowhere, 
  as 
  far 
  as 
  I 
  am 
  aware, 
  do 
  they 
  

   exist 
  in 
  such 
  great 
  numbers, 
  nor 
  do 
  they 
  possess 
  such 
  a 
  large 
  longitudinal 
  

   extent, 
  as 
  in 
  the 
  volcanic 
  system 
  under 
  consideration. 
  It 
  appears 
  to 
  me 
  

   that 
  the 
  immediate 
  cause 
  of 
  the 
  formation 
  of 
  a 
  radiating 
  system 
  of 
  dykes 
  

   may 
  be 
  traced 
  to 
  the 
  choked-up 
  vent 
  or 
  chimney 
  of 
  a 
  volcano, 
  the 
  mouth 
  

   of 
  which, 
  after 
  an 
  eruption 
  of 
  considerable 
  dimensions, 
  is 
  thoroughly 
  filled 
  

   up, 
  either 
  by 
  its 
  sides 
  falling 
  in, 
  by 
  the 
  cooling 
  of 
  ascending 
  lava-streams, 
  or 
  

   by 
  both 
  causes 
  combined. 
  When, 
  from 
  abyssological 
  origination, 
  masses 
  of 
  

   steam 
  and 
  gases 
  have 
  collected 
  below 
  this 
  vent, 
  and 
  new 
  matter 
  is 
  ready 
  to 
  

   be 
  erupted, 
  an 
  enormous 
  effort 
  of 
  nature 
  will 
  be 
  necessary 
  to 
  clear 
  out 
  the 
  

   old, 
  or 
  form 
  a 
  new 
  chimney, 
  which 
  cannot 
  be 
  accomplished 
  without 
  a 
  series 
  

   of 
  violent 
  earthquakes, 
  succeeded 
  by 
  an 
  enormous 
  explosion, 
  by 
  which 
  the 
  

   mouth 
  of 
  the 
  volcano 
  is 
  cleared 
  out 
  or 
  newly 
  formed, 
  and 
  of 
  the 
  magnitude 
  

   of 
  which 
  we 
  can 
  scarcely 
  form 
  a 
  conception. 
  A 
  similar 
  effect, 
  on 
  a 
  gigantic 
  

   scale, 
  must 
  have 
  been 
  produced 
  repeatedly 
  by 
  the 
  compressed 
  masses 
  of 
  

   gases 
  and 
  steam 
  during 
  the 
  formation 
  of 
  the 
  Lyttelton 
  caldera 
  wall, 
  when 
  

   the 
  upper 
  portion 
  of 
  the 
  closed-up 
  volcano 
  was 
  not 
  only 
  removed, 
  but 
  vast 
  

   quantities 
  of 
  ashes, 
  scori®, 
  and 
  lapilli 
  were 
  thrown 
  out, 
  together 
  with 
  lava- 
  

   streams 
  which 
  flowed 
  in 
  various 
  directions. 
  Before, 
  or 
  during 
  these 
  

  

  