﻿GEOLOGY 
  OF 
  WASHINGTON, 
  WARREN 
  COUNTIES, 
  ETC. 
  523 
  

  

  and 
  to 
  have 
  developed 
  biotite 
  along 
  the 
  folia, 
  but 
  it 
  is 
  a 
  minor 
  

   component. 
  Where 
  shearing 
  has 
  been 
  very 
  pronounced 
  a 
  black 
  

   shaly 
  streak 
  may 
  be 
  observed. 
  This 
  same 
  rock 
  occurs 
  in 
  some 
  

   of 
  the 
  cuts 
  along 
  the 
  D. 
  & 
  H. 
  railroad 
  just 
  before 
  it 
  crosses 
  South 
  

   bay, 
  and 
  where 
  faults 
  cross 
  the 
  ledges 
  the 
  same 
  black, 
  crushed 
  

   product 
  appears. 
  These 
  exposures 
  mark 
  the 
  southern 
  extension 
  

   of 
  this 
  type, 
  as 
  it 
  runs 
  out 
  before 
  the 
  south 
  line 
  of 
  Whitehall 
  

   township 
  is 
  crossed. 
  

  

  Another 
  gneiss 
  is 
  granitic 
  in 
  composition 
  and 
  is 
  strongly 
  con- 
  

   trasted 
  with 
  the 
  variety 
  just 
  described. 
  Instead 
  of 
  dark 
  green 
  

   it 
  is 
  light 
  gray 
  or 
  almost 
  white, 
  depending 
  on 
  the 
  amount 
  of 
  bio- 
  

   tite 
  that 
  is 
  present. 
  The 
  more 
  biotite, 
  the 
  more 
  pronounced 
  are 
  

   the 
  dark 
  folia, 
  and 
  the 
  darker 
  the 
  shade. 
  The 
  feldspar 
  is 
  in 
  

   marked 
  lenticular 
  masses 
  yielding 
  corresponding 
  eyes 
  or 
  augen, 
  

   and 
  is 
  also 
  in 
  general 
  dissemination 
  through 
  the 
  rock. 
  Its 
  exces- 
  

   sive 
  granulation 
  has 
  given 
  it 
  a 
  milky 
  white 
  color 
  when 
  its 
  amount 
  

   is 
  large, 
  and 
  when 
  it 
  is 
  not 
  stained 
  with 
  iron 
  oxid. 
  When 
  it 
  is 
  

   more 
  sparsely 
  distributed 
  through 
  the 
  leaflets 
  of 
  biotite 
  is 
  is 
  gray. 
  

   Cleavage 
  surfaces 
  of 
  any 
  marked 
  size, 
  say 
  5-10 
  mm 
  (J 
  in.) 
  in 
  

   diameter 
  are 
  rare, 
  so 
  complete 
  is 
  the 
  granulation. 
  Orthoclase 
  is 
  

   the 
  commonest 
  feldspar 
  present 
  and 
  it 
  may 
  be 
  microperthitic 
  but 
  

   commonly 
  is 
  not. 
  Plagioclase 
  is 
  less 
  abundant. 
  Quartz 
  is 
  fre- 
  

   quent 
  and 
  may 
  be 
  excessively 
  rich 
  as 
  will 
  be 
  later 
  brought 
  out 
  in 
  

   several 
  varieties. 
  The 
  dark 
  silicate 
  is 
  biotite 
  and 
  its 
  amount 
  is 
  

   variable. 
  Garnets 
  are 
  practically 
  omnipresent 
  and 
  at 
  times 
  are 
  

   thickly 
  strewn 
  through 
  the 
  rock. 
  They 
  are 
  a 
  light 
  pink 
  and 
  not 
  

   so 
  deepiy 
  colored 
  as 
  those 
  in 
  the 
  basic 
  rocks. 
  Magnetite, 
  apatite 
  

   and 
  zircon 
  are 
  sparingly 
  present. 
  There 
  is 
  little 
  question 
  that 
  

   these 
  gneisses 
  have 
  resulted 
  from 
  the 
  excessive 
  granulation 
  and 
  

   shearing 
  of 
  granites 
  or 
  from 
  the 
  metamorphism 
  of 
  a 
  sediment 
  

   related 
  to 
  arkose. 
  The 
  augen 
  or 
  eyes 
  of 
  feldspar 
  would 
  lead 
  

   to 
  the 
  inference 
  that 
  the 
  granites 
  were 
  porphyritic 
  from 
  large 
  

   feldspars. 
  

  

  In 
  two 
  places, 
  no. 
  54 
  and 
  60 
  on 
  the 
  east 
  side 
  of 
  South 
  bay, 
  

   the 
  feldspar 
  has 
  relatively 
  diminished 
  and 
  the 
  quartz 
  has 
  become 
  

   prominent 
  till 
  the 
  rock 
  is 
  almost 
  entirely 
  quartz, 
  the 
  " 
  South 
  Bay 
  

  

  