﻿Content 
  oj 
  Igneous 
  RocJcs 
  from 
  Sub-Antarctic 
  Jslands. 
  815 
  

  

  are 
  mostly 
  igneous 
  in 
  character, 
  the 
  indication 
  appears 
  to 
  be 
  

   that 
  the 
  distribution 
  of 
  radium 
  in 
  the 
  rocks 
  of 
  this 
  region 
  is 
  

   in 
  excess 
  o£ 
  that 
  required 
  to 
  maintain 
  the 
  constanc}^ 
  of 
  the 
  

   heat 
  of 
  the 
  Earth 
  ; 
  and 
  the 
  necessity 
  of 
  an 
  examination 
  of 
  rocks 
  

   from 
  all 
  places 
  and 
  of 
  all 
  ages 
  is 
  emphasized. 
  The 
  mean 
  

   radium 
  content 
  of 
  these 
  rocks 
  approximates 
  very 
  closely 
  to 
  

   that 
  found 
  for 
  others 
  by 
  Strutt 
  and 
  by 
  Eve 
  and 
  Mcintosh, 
  

   but 
  differs 
  considerably 
  from 
  Joly's 
  values. 
  Further 
  inves- 
  

   tigations 
  are 
  being 
  made 
  on 
  the 
  rocks 
  of 
  these 
  regions 
  ; 
  

   and 
  it 
  is 
  hoped 
  to 
  examine 
  the 
  distribution 
  of 
  radium 
  

   in 
  the 
  material 
  encountered 
  in 
  piercing 
  the 
  Lyttleton 
  Tunnel, 
  

   which 
  will 
  give 
  a 
  range 
  of 
  time 
  from 
  the 
  earliest 
  sedimentary 
  

   rocks 
  to 
  the 
  last 
  flow 
  of 
  the 
  volcano, 
  through 
  the 
  wall 
  of 
  

   whose 
  crater 
  the 
  tunnel 
  is 
  bored. 
  

  

  The 
  following 
  notes 
  on 
  the 
  geological 
  properties 
  of 
  these 
  

   rocks 
  by 
  Mr. 
  E. 
  Speight, 
  F.G.S., 
  may 
  be 
  of 
  interest. 
  

  

  The 
  two 
  granites 
  are 
  both 
  biotite 
  granites 
  of 
  ordinary 
  type 
  

   and 
  of 
  uncertain 
  age. 
  The 
  other 
  plutonic 
  rocks 
  — 
  the 
  gabbros 
  

   — 
  though 
  coming 
  from 
  widely 
  separated 
  localities 
  of 
  the 
  same 
  

   region, 
  exhibit 
  marked 
  similarities: 
  both 
  are 
  olivine 
  gabbros, 
  

   but 
  that 
  from 
  Auckland 
  Island 
  is 
  very 
  coarse-grained 
  at 
  

   times. 
  The 
  coincidence 
  of 
  their 
  radium 
  content 
  is 
  very 
  

   striking. 
  

  

  The 
  porphyry 
  from 
  Campbell 
  Island 
  contains 
  large 
  numbers 
  

   of 
  zircon 
  phenocrj^sts. 
  

  

  The 
  trachytes 
  are 
  all 
  of 
  highly 
  alkaline 
  type. 
  Those 
  from 
  

   Auckland 
  Island 
  contain 
  a 
  very 
  high 
  percentage 
  of 
  soda 
  

   and 
  a 
  very 
  iow^ 
  percentage 
  of 
  alumina 
  (11 
  per 
  cent.) 
  and 
  a 
  

   small 
  quantity 
  of 
  free 
  quartz 
  ; 
  they 
  are 
  decidedly 
  acid. 
  

   Anorthoclase 
  is 
  a 
  common 
  constituent 
  as 
  well 
  as 
  an 
  alkaline 
  

   hornblende. 
  The 
  pitchstone 
  belongs 
  to 
  the 
  same 
  group 
  but 
  

   is 
  somewhat 
  more 
  basic 
  in 
  composition, 
  and 
  contains 
  abundant 
  

   J3egerine-augite 
  microlites. 
  The 
  Campbell 
  Island 
  trachytes, 
  

   according 
  to 
  Dr. 
  Marshall, 
  are 
  slightly 
  more 
  alkaline 
  and 
  

   contain 
  less 
  iron. 
  They 
  are 
  all 
  augite 
  trachyte 
  wdth 
  anor- 
  

   thoclase 
  and 
  occasional 
  riebeckite 
  and 
  cossyrite. 
  These 
  rocks 
  

   together 
  with 
  the 
  melilite 
  basalt 
  all 
  appear 
  to 
  have 
  similar 
  

   amounts 
  of 
  radium 
  present. 
  

  

  The 
  other 
  rocks 
  from 
  Auckland 
  Island 
  are 
  basic 
  in 
  character 
  

   and 
  include 
  flows 
  and 
  dykes. 
  They 
  are 
  generally 
  marked 
  

   by 
  a 
  high 
  percentage 
  of 
  titaniferous 
  magnetite. 
  No. 
  8 
  is 
  a 
  

   diabase 
  of 
  greater 
  age 
  than 
  the 
  rest, 
  and 
  No. 
  5 
  a 
  porphyrite 
  

   approaching 
  an 
  augite-camptonite 
  in 
  character 
  and 
  basic 
  

   com'position, 
  found 
  penetrating 
  the 
  more 
  recent 
  basalts. 
  

   The 
  age 
  of 
  these 
  basalts 
  is 
  probably 
  from 
  middle 
  to 
  late 
  

   Tertiary. 
  There 
  is 
  no 
  marked 
  difference 
  between 
  the 
  earlier 
  

  

  