﻿496 
  Transactions. 
  — 
  Geology. 
  

  

  deep 
  indentations, 
  forming 
  splendid 
  harbours, 
  enter 
  far 
  into 
  the 
  outer 
  rim 
  

   of 
  the 
  mountains, 
  passing 
  for 
  a 
  considerable 
  distance 
  along 
  the 
  higher 
  

   central 
  range. 
  Similar 
  indentations 
  are 
  also 
  found 
  to 
  exist 
  towards 
  the 
  

   Canterbury 
  plains, 
  but 
  they 
  have 
  either 
  been 
  already 
  filled 
  by 
  alluvial 
  

   deposits 
  forming 
  fertile 
  valleys, 
  such 
  as 
  the 
  Kaituna 
  valley, 
  or 
  they 
  appear 
  

   in 
  the 
  form 
  of 
  a 
  lake 
  (Lake 
  Forsyth). 
  In 
  examining 
  the 
  nature 
  of 
  the 
  rocks 
  

   of 
  which 
  the 
  system 
  under 
  consideration 
  is 
  composed, 
  we 
  find 
  that, 
  with 
  

   the 
  exception 
  of 
  a 
  small 
  zone 
  at 
  the 
  head 
  of 
  Lyttelton 
  Harbour, 
  the 
  whole 
  

   is 
  composed 
  of 
  volcanic 
  rocks 
  ; 
  that 
  the 
  deep 
  indentations 
  are 
  ancient 
  crater 
  

   walls, 
  so-called 
  calderas, 
  into 
  which 
  a 
  channel 
  with 
  precipitous 
  walls, 
  the 
  

   barranco, 
  leads 
  ; 
  and 
  tliat 
  they 
  consist 
  of 
  a 
  series 
  of 
  lava 
  streams, 
  with 
  

   agglomerates 
  consisting 
  of 
  scori®, 
  lapilli, 
  ashes, 
  and 
  tufas 
  interstratified 
  

   with 
  them. 
  These 
  beds 
  have 
  all 
  a 
  qua-qua 
  versal 
  dip, 
  that 
  is 
  to 
  say, 
  they 
  

   all 
  incline 
  outwards 
  from 
  the 
  centre 
  of 
  the 
  cavity. 
  The 
  higher 
  mountains 
  

   in 
  the 
  centre 
  consist 
  also 
  of 
  volcanic 
  rocks 
  of 
  a 
  similar 
  composition, 
  which 
  

   appear 
  either 
  horizontal 
  or, 
  when 
  the 
  direction 
  of 
  the 
  lava-streams 
  com- 
  

   posing 
  them 
  can 
  be 
  ascertained, 
  are 
  found 
  to 
  flow 
  into 
  the 
  calderas 
  

   previously 
  formed, 
  from 
  which 
  we 
  can 
  at 
  once 
  conclude 
  that 
  they 
  are 
  of 
  

   younger 
  origin. 
  Finally, 
  we 
  find 
  mostly 
  in 
  or 
  near 
  the 
  centre 
  of 
  these 
  deep 
  

   cavities, 
  or 
  calderas, 
  either 
  a 
  small 
  island 
  or 
  a 
  peninsula 
  stretching 
  so 
  far 
  

   into 
  these 
  harbours. 
  They 
  consist 
  also 
  of 
  volcanic 
  rocks, 
  having 
  been 
  

   preserved 
  above 
  the 
  last 
  centre 
  of 
  eruption. 
  This 
  last 
  sign 
  of 
  vulcanicity 
  is 
  

   on 
  a 
  smaller 
  scale 
  than 
  the 
  previous 
  ones. 
  The 
  whole 
  of 
  Banks 
  Peninsula, 
  

   measuring 
  along 
  its 
  longest 
  axis 
  from 
  north-west 
  to 
  south-east, 
  has 
  a 
  length 
  

   of 
  31 
  miles, 
  with 
  a 
  greatest 
  breadth 
  of 
  20 
  miles, 
  and 
  if 
  we 
  do 
  not 
  take 
  the 
  

   numerous 
  indentations 
  into 
  account, 
  it 
  has 
  a 
  circumference 
  of 
  88 
  miles, 
  

   which 
  corresponds 
  closely 
  with 
  that 
  of 
  the 
  base 
  of 
  Mount 
  Etna. 
  

  

  Having 
  thus 
  given 
  an 
  outline 
  of 
  the 
  general 
  features 
  of 
  the 
  volcanic 
  

   system 
  under 
  consideration, 
  I 
  shall 
  now 
  proceed 
  to 
  offer 
  a 
  short 
  history 
  of 
  

   its 
  origin. 
  

  

  The 
  oldest 
  rocks 
  in 
  Banks 
  Peninsula 
  form 
  a 
  small 
  zone 
  of 
  palaeozoic 
  

   sedimentary 
  strata, 
  possessing 
  a 
  slightly 
  altered 
  -structure, 
  many 
  of 
  them 
  

   forming 
  beds 
  of 
  chert, 
  others, 
  peculiar 
  light-coloured 
  brecciated 
  schists 
  ; 
  

   however, 
  sandstones 
  and 
  dark 
  clay-slates 
  are 
  also 
  re|)resented. 
  This 
  zone 
  

   has 
  a 
  north 
  and 
  south 
  direction, 
  and 
  reaches 
  to 
  the 
  southern 
  watershed 
  of 
  

   McQueen's 
  Pass, 
  which 
  leads 
  from 
  the 
  head 
  of 
  Lyttelton 
  Harbour 
  to 
  Lake 
  

   Ellesmere. 
  Near 
  this 
  pass, 
  slates 
  appear 
  as 
  high 
  as 
  600 
  feet 
  above 
  the 
  

   sea-level. 
  On 
  the 
  western 
  slopes 
  of 
  Castle 
  Hill, 
  the 
  south-western 
  cotinua- 
  

   tion 
  of 
  Mount 
  Herbert, 
  2,900 
  feet 
  high, 
  which 
  rises 
  so 
  conspicuously 
  above 
  

   Lyttelton 
  Harbour, 
  they 
  reach 
  an 
  altitude 
  of 
  nearly 
  1,000 
  feet, 
  where 
  they 
  

   are 
  overlaid 
  by 
  the 
  older 
  lavas, 
  forming 
  the 
  Lyttelton 
  Harbour 
  caldera. 
  

  

  