﻿420 
  Ransome 
  — 
  New 
  Occurrence 
  of 
  Nepheline 
  Syenite. 
  

  

  are 
  indicated 
  on 
  the 
  accompanying 
  sketch-map 
  by 
  the 
  two 
  

   black 
  dots 
  near 
  the 
  edge 
  of 
  the 
  trap 
  area. 
  

  

  Microscopical 
  Petrography. 
  

  

  Nepheline 
  Syenite. 
  — 
  Megascopicallj 
  this 
  is 
  a 
  light 
  gray 
  gran- 
  

   ular 
  rock 
  of 
  medium 
  grain, 
  which 
  bears 
  a 
  very 
  superficial 
  

   resemblance 
  to 
  the 
  nepheline 
  syenite 
  of 
  Moultouboro, 
  N. 
  H. 
  

   Dark 
  amphibole 
  is 
  abundant, 
  usually 
  in 
  slender 
  prisms 
  up 
  to 
  a 
  

   centimeter 
  in 
  length. 
  Biotite, 
  while 
  less 
  abundant, 
  is 
  a 
  con- 
  

   spicuous 
  constituent 
  in 
  most 
  hand-specimens, 
  as 
  it 
  forms 
  irregu- 
  

   lar 
  poikilitic 
  plates, 
  usually 
  about 
  5™°^ 
  in 
  diameter. 
  The 
  dark 
  

   minerals 
  appear 
  to 
  constitute 
  between 
  a 
  fourth 
  and 
  a 
  third 
  of 
  

   the 
  rock, 
  but 
  are 
  not 
  always 
  uniformly 
  distributed. 
  They 
  lie 
  

   in 
  a 
  nearly 
  white 
  granular 
  ground 
  in 
  which 
  the 
  lens 
  reveals 
  

   cleavage 
  faces 
  of 
  feldspars, 
  sometimes 
  finely 
  striated, 
  and 
  light 
  

   brownish 
  grains 
  with 
  greasy 
  luster 
  which 
  presumably 
  are 
  more 
  

   or 
  less 
  altered 
  nepheline. 
  

  

  The 
  microscope 
  shows 
  the 
  rock 
  to 
  have 
  a 
  hypidiomorphic- 
  

   granular 
  structure 
  and 
  to 
  consist 
  of 
  alkali 
  feldspar 
  >nepheline 
  

   (including 
  its 
  alteration 
  products) 
  ><C 
  amphibole 
  > 
  biotite 
  

   >cancrinite 
  ><^ 
  soda-lime 
  feldspar^ 
  muscovite><:^ 
  segirine- 
  

   augite 
  > 
  apatite, 
  titanite, 
  and 
  fluorite. 
  Iron 
  ore 
  is 
  almost 
  

   lacking, 
  although 
  a 
  few 
  grains 
  of 
  magnetite 
  occur 
  included 
  in, 
  

   or 
  close 
  to, 
  the 
  amphibole. 
  Analcite, 
  usually 
  filling 
  triangular 
  

   spaces 
  between 
  the 
  feldspars, 
  is 
  rather 
  abundant 
  in 
  some 
  sec- 
  

   tions. 
  It 
  is 
  probably 
  wholly 
  secondary. 
  Sericite 
  is 
  present 
  as 
  

   a 
  decomposition 
  product 
  of 
  the 
  feldspars. 
  Calcite 
  occurs 
  some- 
  

   what 
  irregularly, 
  usually 
  associated 
  with 
  the 
  analcite. 
  'The 
  

   latter 
  is 
  also 
  accompanied 
  at 
  times 
  by 
  small 
  amounts 
  of 
  a 
  

   librous 
  mineral 
  which 
  is 
  probablj^ 
  natrolite. 
  

  

  All 
  the 
  feldspars 
  show 
  a 
  gray 
  turbidity 
  similar 
  to 
  that 
  which 
  

   is 
  so 
  common 
  a 
  feature 
  of 
  the 
  syenitic 
  rocks 
  of 
  Norway 
  and 
  

   elsewhere. 
  Partly 
  on 
  this 
  account, 
  but 
  more 
  by 
  reason 
  of 
  their 
  

   lack 
  of 
  crystal 
  outline 
  and 
  their 
  confused 
  intercrystallization, 
  

   specific 
  determination 
  of 
  the 
  feldspars 
  by 
  optical 
  means 
  is 
  not 
  

   always 
  possible. 
  Individual 
  grains 
  of 
  orthoclase 
  pass 
  indis- 
  

   tinctly 
  and 
  irregularly 
  into 
  microperthitic 
  patches 
  or 
  are 
  intri- 
  

   cately 
  intergrown 
  with 
  a 
  feldspar 
  showing 
  tine 
  albite 
  lamella? 
  — 
  

   probably 
  anorthoclase. 
  This 
  latter 
  is 
  often 
  partly 
  automorphic 
  

   with 
  reference 
  to 
  the 
  orthoclase 
  and 
  microperthite. 
  One 
  area, 
  

   with 
  fine, 
  shadowy 
  microperthitic 
  structure, 
  showed 
  distinct 
  

   cleavage 
  traces, 
  probably 
  basal, 
  and 
  the 
  emergence 
  of 
  a 
  bisectrix. 
  

   The 
  extinction 
  referred 
  to 
  this 
  cleavage 
  was 
  about 
  12°, 
  which 
  

   would 
  seem 
  to 
  indicate 
  the 
  presence 
  of 
  soda 
  orthoclase. 
  A 
  

   small 
  part 
  of 
  the 
  twinned 
  feldspar 
  may 
  be 
  albite 
  or 
  acid 
  oligo- 
  

   clase. 
  In 
  general 
  the 
  feldspars 
  show 
  tiie 
  lack 
  of 
  optical 
  homo- 
  

  

  