﻿Notes 
  upon 
  the 
  Lithology 
  of 
  the 
  Adikondacks. 
  107 
  

  

  been 
  given. 
  t 
  A 
  large 
  portion 
  of 
  the 
  transparent 
  base 
  of 
  this 
  

   rock, 
  could 
  not 
  be 
  definitely 
  referred 
  by 
  its 
  optical 
  characters 
  

   to 
  plagioclase. 
  It 
  presents 
  a 
  considerable 
  admixture 
  of 
  quartz. 
  

   The 
  dark 
  color 
  of 
  the 
  section 
  and 
  rock 
  is 
  due 
  in 
  part 
  to 
  the 
  

   magnetite 
  and 
  menaccanite, 
  but 
  in 
  still 
  greater 
  degree 
  to 
  very 
  

   minute 
  light- 
  to 
  dark-green 
  and 
  yellowish-red 
  masses. 
  The 
  

   former 
  are 
  probably 
  pyroxene, 
  the 
  latter, 
  which 
  are 
  by 
  far 
  the 
  

   most 
  abundant, 
  hornblende. 
  

  

  36. 
  A 
  rock-section 
  of 
  the 
  very 
  common 
  variety 
  of 
  norite, 
  

   consisting 
  of 
  a 
  waxy-looking 
  green 
  feldspathic 
  base 
  with 
  

   brownish-yellow 
  hornblende. 
  Alteration 
  has 
  proceeded 
  to 
  

   such 
  an 
  extent, 
  that 
  a 
  recombination 
  and 
  re-arrangement 
  of 
  

   the 
  constituents 
  has 
  in 
  part 
  taken 
  place. 
  The 
  labradorite 
  is 
  

   represented 
  by 
  translucent 
  areas 
  clouded 
  with 
  a 
  greenish 
  color, 
  

   but 
  containing 
  no 
  definite 
  green 
  particles. 
  The 
  structure 
  of 
  

   the 
  labradorite 
  is 
  faintly 
  recognizable, 
  and 
  the 
  banded 
  arrange- 
  

   ment 
  of 
  the 
  colors 
  still 
  visible 
  around 
  the 
  edges 
  of 
  the 
  clouded 
  

   portions, 
  when 
  viewed 
  with 
  polarized 
  light. 
  The 
  amount 
  of 
  

   free 
  quartz 
  is 
  large, 
  presenting 
  a 
  granular 
  appearance. 
  The 
  

   diallage 
  has 
  almost 
  disappeared, 
  the 
  original 
  masses 
  being 
  

   represented 
  only 
  by 
  small 
  areas 
  of 
  deep 
  green 
  color. 
  Instead 
  

   of 
  them, 
  extensive 
  areas 
  of 
  reddish-brown 
  hornblende, 
  in 
  color 
  

   resembling 
  some 
  varieties 
  of 
  garnet, 
  are 
  found. 
  This 
  horn- 
  

   blende, 
  in 
  the 
  blowpipe-flame 
  fuses 
  readily 
  with 
  intumescence 
  

   to 
  a 
  black 
  globule 
  attractable 
  by 
  the 
  magnet. 
  

  

  3. 
  This 
  rock- 
  section 
  is 
  from 
  a 
  mass 
  similar 
  in 
  character 
  to 
  5, 
  

   which 
  is 
  the 
  yellowish 
  labradorite, 
  the 
  matrix 
  of 
  the 
  smoky- 
  

   grey 
  crystals 
  in 
  the 
  porphyritic 
  rock. 
  The 
  composition 
  of 
  this 
  

   matrix 
  has 
  already 
  been 
  given. 
  It 
  has 
  been 
  seen 
  that 
  it 
  differs 
  

   in 
  a 
  small 
  but 
  important 
  degree, 
  from 
  the 
  composition 
  of 
  the 
  

   more 
  highly 
  crystalline 
  portion. 
  The 
  microscope 
  shows 
  that 
  

   No. 
  3 
  contains 
  some 
  free 
  quartz. 
  With 
  a 
  high 
  power, 
  minute 
  

   crystals 
  of 
  menaccanite 
  are 
  found, 
  along 
  with 
  some 
  black 
  amor- 
  

   phous 
  specks, 
  the 
  character 
  of 
  which 
  was 
  not 
  determined. 
  

   The 
  diallage 
  is 
  represented 
  by 
  imperfectly 
  crystalline 
  and 
  feebly 
  

   dichroic 
  masses, 
  which 
  in 
  a 
  few 
  places 
  are 
  slightly 
  altered. 
  

  

  In 
  5, 
  quartz 
  is 
  also 
  present 
  in 
  the 
  labradorite, 
  and 
  the 
  num- 
  

   ber 
  of 
  crystals 
  of 
  menaccanite, 
  and 
  possibly 
  magnetite, 
  much 
  

   larger 
  than 
  in 
  the 
  preceding 
  section. 
  A 
  few 
  masses 
  of 
  pyroxene 
  

   are 
  apparent, 
  but 
  a 
  slight 
  yellow 
  is 
  imparted 
  to 
  the 
  section 
  by 
  

  

  