﻿42 
  ME. 
  T. 
  L. 
  WAiKEE 
  OX 
  THE 
  [Feb. 
  1 
  89 
  7, 
  

  

  (i) 
  The 
  Gneisses 
  near 
  Wahnapitae 
  Station. 
  

  

  These 
  rocks 
  are 
  well 
  bedded, 
  and 
  show 
  considerable 
  folding 
  on 
  

   .a 
  large 
  scale. 
  Biotite 
  is 
  by 
  far 
  the 
  most 
  prominent 
  constituent. 
  

   ■Over 
  large 
  areas 
  reddish 
  almandine-garnet 
  is 
  so 
  common 
  that 
  the 
  

   Wahnapitae 
  rocks 
  may 
  be 
  designated 
  ' 
  garnetiferous 
  biotite-gneiss/ 
  

   The 
  garnets 
  vary 
  from 
  J 
  to 
  11 
  inch 
  in 
  diameter, 
  and 
  are 
  often 
  

   so 
  abundant 
  as 
  to 
  constitute 
  20 
  per 
  cent, 
  of 
  the 
  rock. 
  When 
  in 
  

   micaceous 
  bands 
  they 
  are 
  crystallized 
  in 
  rhombic 
  dodecahedra 
  go 
  0, 
  

   while 
  when 
  in 
  quartzose 
  or 
  felspathic 
  bands 
  they 
  are 
  always 
  

   icositetrahedra 
  2 
  2. 
  As 
  a 
  rule, 
  garnets 
  are 
  inclined 
  to 
  crystallize 
  

   in 
  rhombic 
  dodecahedra 
  when 
  in 
  schistose 
  or 
  basic 
  bands, 
  while 
  

   when 
  in 
  acid 
  or 
  granular 
  bands 
  there 
  is 
  a 
  tendency 
  to 
  take 
  the 
  

   form 
  of 
  icositetrahedra. 
  

  

  The 
  microscope 
  shows 
  that 
  the 
  biotite 
  is 
  strongly 
  pleochroic 
  and 
  

   nearly 
  uniaxial. 
  It 
  occurs 
  as 
  comparatively 
  large 
  independent 
  

   individuals, 
  and 
  never 
  forms 
  continuous 
  films 
  composed 
  of 
  innu- 
  

   merable 
  small 
  individuals. 
  The 
  biotite 
  is 
  sometimes 
  altered 
  to 
  

   chlorite. 
  Muscovite 
  is 
  occasional. 
  The 
  quartzes 
  abound 
  in 
  liquid 
  

   inclusions, 
  which 
  are 
  often 
  characterized 
  by 
  moving 
  bubbles 
  or 
  

   small 
  cube-like 
  crystals. 
  Felspar 
  plays 
  an 
  important 
  part, 
  and 
  is 
  

   frequently 
  perthitic 
  or 
  microclinic. 
  Kyanite 
  is 
  often 
  abundant, 
  and 
  

   presents 
  in 
  rock-sections 
  long, 
  highly-polarizing 
  individuals 
  which 
  

   generally, 
  but 
  not 
  always, 
  conform 
  to 
  the 
  schistosity. 
  Inclusions 
  of 
  

   quartz 
  and 
  felspar 
  are 
  quite 
  common. 
  The 
  colour 
  is 
  different 
  in 
  

   different 
  individuals, 
  and 
  even 
  in 
  different 
  parts 
  of 
  the 
  same 
  indi- 
  

   vidual. 
  Some 
  are 
  water-clear, 
  while 
  others 
  are 
  water-clear 
  with 
  

   irregular 
  sky-blue 
  flecks. 
  No 
  twinning 
  could 
  be 
  detected. 
  Silli- 
  

   manite 
  is 
  frequent 
  on 
  slickensides. 
  The 
  long, 
  colourless, 
  acicular 
  

   crystals 
  show 
  the 
  effect 
  of 
  pressure 
  in 
  being 
  broken 
  into 
  large 
  

   numbers 
  of 
  short 
  prismatic 
  fragments 
  which 
  are 
  drawn 
  apart, 
  so 
  

   that 
  the 
  disjointed 
  crystal 
  is 
  about 
  twice 
  as 
  long 
  as 
  the 
  original 
  

   erystal. 
  Zircon 
  in 
  rounded 
  grains 
  is 
  frequent, 
  and 
  seems 
  to 
  be 
  

   largely 
  confined 
  to 
  the 
  neighbourhood 
  of 
  biotite. 
  When 
  the 
  zircon- 
  

   grains 
  are 
  included 
  in 
  the 
  biotite, 
  they 
  are 
  usually 
  surrounded 
  by 
  

   pleochroic 
  areas 
  (' 
  pleochroitische 
  Hofe 
  '). 
  

  

  (ii) 
  Gneiss 
  near 
  Onaping 
  Station. 
  

  

  The 
  gneiss 
  exposed 
  west 
  of 
  Onaping 
  Station 
  is 
  largely 
  composed 
  

   of 
  quartz 
  and 
  felspar, 
  which 
  form 
  pinkish- 
  white 
  bands 
  : 
  these 
  

   alternate 
  with 
  comparatively 
  small 
  bands 
  of 
  biotite. 
  The 
  Onaping 
  

   gneiss 
  is 
  thus 
  very 
  much 
  lighter 
  in 
  colour 
  than 
  the 
  gneiss 
  at 
  

   Wahnapitae. 
  The 
  microscope 
  shows 
  that 
  these 
  rocks 
  are 
  true 
  

   gneisses 
  and 
  not 
  crushed 
  granites. 
  Biotite 
  occurs 
  in 
  large 
  indi- 
  

   viduals, 
  whose 
  prismatic 
  sections 
  show 
  a 
  well-developed 
  system 
  of 
  

   partings 
  which 
  form 
  a 
  cross-hatching, 
  probably 
  the 
  result 
  of 
  

   pressure. 
  The 
  gliding-plane 
  is 
  apparently 
  a 
  pyramidal 
  face, 
  as 
  has 
  

   been 
  proved 
  to 
  be 
  the 
  case 
  for 
  large 
  mica-individuals 
  by 
  Tschermak. 
  

   JBiotite 
  is 
  sometimes 
  changed 
  to 
  an 
  aggregate 
  of 
  chlorite, 
  epidote, 
  

  

  