﻿522 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Series 
  1. 
  The 
  gneisses 
  are 
  the 
  chief 
  representatives 
  among 
  the 
  

   crystallines. 
  They 
  present 
  not 
  a 
  few 
  examples 
  that 
  resemble 
  

   quartzites 
  so 
  closely 
  as 
  to 
  lead 
  us 
  to 
  believe 
  in 
  the 
  extended 
  de- 
  

   velopment 
  of 
  the 
  latter 
  while 
  we 
  were 
  in 
  the 
  field. 
  More 
  care- 
  

   ful 
  study 
  in 
  the 
  laboratory 
  with 
  thin 
  sections 
  has 
  in 
  some 
  cases 
  

   thrown 
  doubt 
  over 
  this 
  interpretation, 
  and 
  it 
  seems 
  more 
  prob- 
  

   able 
  that 
  some 
  at 
  least 
  are 
  squeezed 
  and 
  granulated 
  eruptives, 
  

   but 
  the 
  question 
  is 
  not 
  yet 
  fully 
  decided. 
  Along 
  the 
  east 
  side 
  

   of 
  South 
  bay 
  at 
  52 
  and 
  53, 
  the 
  gneisses 
  resemble 
  most 
  closely 
  

   sheared 
  porphyritic 
  types. 
  The 
  rock 
  is 
  strongly 
  gneissoid 
  and 
  

   broken 
  by 
  innumerable 
  cross-fractures 
  with 
  noticeable 
  displace- 
  

   ment. 
  It 
  is 
  dark 
  blackish 
  green 
  in 
  general 
  color, 
  with 
  lighter 
  

   green 
  augen 
  or 
  phenocrysts. 
  The 
  matrix 
  is 
  largely 
  biotite, 
  with 
  

   some 
  feldspar. 
  The 
  augen 
  are 
  flattened 
  lenses 
  of 
  green 
  feldspar 
  

   that 
  may 
  be 
  more 
  than 
  an 
  inch 
  across. 
  Chips 
  prove 
  it 
  to 
  be 
  

   microcline 
  when 
  examined 
  under 
  the 
  microscope 
  and 
  lead 
  one 
  to 
  

   infer 
  that 
  the 
  original 
  rock 
  was 
  a 
  rather 
  basic 
  syenite 
  porphyry, 
  

   presumably 
  belonging 
  with 
  other 
  syenitic 
  gneisses, 
  in 
  the 
  out- 
  

   skirts 
  of 
  Whitehall. 
  The 
  latter 
  occur 
  along 
  the 
  eastern 
  edge 
  

   of 
  the 
  ridge 
  that 
  bounds 
  the 
  village 
  on 
  the 
  west 
  and 
  have 
  been 
  

   quite 
  extensively 
  quarried 
  at 
  no. 
  74 
  on 
  the 
  enlarged 
  map 
  of 
  

   the 
  town, 
  plate 
  4. 
  The 
  quarry 
  is 
  the 
  locality 
  for 
  our 
  "Whitehall 
  

   type." 
  They 
  are 
  finely 
  and 
  regularly 
  laminated- 
  rocks 
  that 
  are 
  

   green 
  in 
  color 
  and 
  that 
  look 
  extremely 
  like 
  a 
  dark 
  quartzite. 
  

   They 
  have 
  lenticular 
  augen 
  of 
  shining 
  orthoclase, 
  that 
  has 
  a 
  bril- 
  

   liant 
  luster. 
  Rarely 
  streaks 
  of 
  gray 
  quartz 
  run 
  parallel 
  to 
  the 
  

   foliation. 
  Under 
  the 
  microscope 
  they 
  are 
  found 
  to 
  be 
  very 
  finely 
  

   granulated 
  and 
  to 
  consist 
  of 
  small 
  particles 
  .1 
  mm 
  in 
  diameter 
  

   (.004 
  in.). 
  When 
  examined 
  with 
  a 
  high 
  power 
  these 
  grains 
  are 
  

   found 
  to, 
  be 
  chiefly 
  microperthitic 
  orthoclase. 
  Granules 
  of 
  green 
  

   augite 
  of 
  about 
  the 
  same 
  size 
  are 
  present 
  and 
  some 
  magnetite 
  

   can 
  be 
  detected. 
  Zircons 
  are 
  rather 
  noticeable 
  and 
  are 
  charged 
  

   with 
  inclusions 
  of 
  still 
  older 
  minerals. 
  There 
  is 
  little 
  doubt 
  that 
  

   these 
  rocks 
  were 
  originally 
  the 
  rocks 
  often 
  cited 
  in 
  the 
  preceding 
  

   townships 
  and 
  from 
  Mt 
  Defiance, 
  and 
  that 
  they 
  have 
  been 
  gran- 
  

   ulated 
  by 
  pressure. 
  The 
  layers 
  seem 
  to 
  have 
  slipped 
  sometimes 
  

  

  