﻿Notes 
  upon 
  the 
  Lithology 
  of 
  the 
  Adikondacks. 
  87 
  

  

  These 
  gravities 
  were 
  determined 
  upon 
  masses 
  weighing 
  from 
  

   5 
  to 
  15 
  grammes, 
  and 
  are 
  all 
  reduced 
  to 
  0°C. 
  They 
  vary 
  from 
  

   2.67, 
  a 
  figure 
  agreeing 
  with 
  the 
  lowest 
  limit 
  of 
  the 
  numbers, 
  

   which 
  have 
  been 
  obtained 
  in 
  determinations 
  of 
  the 
  specific 
  

   gravities 
  of 
  any 
  labradorites, 
  to 
  3.459, 
  the 
  specific 
  gravity 
  of 
  

   diallage. 
  These 
  figures 
  may 
  be 
  taken 
  as 
  the 
  extremes, 
  within 
  

   which 
  the 
  specific 
  gravities 
  of 
  norian 
  rocks, 
  composed 
  of 
  mix- 
  

   tures 
  of 
  labradorite 
  and 
  pyroxene 
  in 
  all 
  proportions 
  whatsoever, 
  

   will 
  vary. 
  A 
  lower 
  specific 
  gravity 
  will 
  be 
  attributable 
  to 
  some 
  

   other 
  variety 
  of 
  feldspar, 
  or 
  an 
  admixture 
  of 
  quartz 
  : 
  a 
  higher, 
  

   to 
  an 
  unusual 
  percentage 
  of 
  garnet, 
  menaccanite 
  or 
  magnetite. 
  

   As 
  an 
  instance 
  of 
  the 
  former, 
  a 
  specimen 
  (a), 
  analyzed 
  in 
  Part 
  

   III, 
  and 
  microscopically 
  examined 
  in 
  Part 
  IV, 
  may 
  be 
  men- 
  

   tioned, 
  which 
  strikingly 
  diners 
  in 
  its 
  characters 
  from 
  any 
  of 
  

   those 
  contained 
  in 
  the 
  above 
  table. 
  It 
  resembles, 
  in 
  appear- 
  

   ance, 
  a 
  vitreous 
  ferruginous 
  quartzite 
  of 
  a 
  dark 
  red 
  color, 
  for 
  

   which 
  at 
  first 
  sight 
  it 
  was 
  mistaken. 
  It 
  is 
  readily 
  distinguished, 
  

   however, 
  by 
  the 
  finely 
  striated 
  surfaces 
  of 
  the 
  minute 
  crystal- 
  

   line 
  masses, 
  of 
  which 
  it 
  is 
  composed. 
  The 
  specific 
  gravity 
  of 
  

   the 
  powdered 
  rock, 
  such 
  as 
  was 
  used 
  in 
  its 
  chemical 
  analysis, 
  

   is 
  2.635, 
  while 
  that 
  of 
  the 
  original 
  mass 
  is 
  2.65. 
  The 
  difference 
  

   is 
  due 
  to 
  the 
  crystals 
  of 
  magnetite 
  and 
  menaccanite^ 
  picked 
  out 
  

   by 
  the 
  magnet 
  prior 
  to 
  analysis, 
  many 
  being 
  large 
  enough 
  to 
  

   be 
  visible 
  to 
  the 
  naked 
  eye. 
  It 
  fused 
  more 
  difficultly 
  than 
  

   labradorite, 
  with 
  the 
  formation 
  of 
  a 
  clear 
  white 
  glass, 
  the 
  red 
  

   color 
  disappearing, 
  and 
  the 
  metallic 
  constituent 
  rendering 
  the 
  

   remaining 
  partially 
  fused 
  portion 
  black. 
  It 
  gives 
  a 
  strong 
  

   flame-reaction, 
  indicative 
  of 
  the 
  presence 
  of 
  sodium. 
  In 
  these 
  

   respects 
  it 
  resembles 
  oligoclase, 
  which 
  is 
  sometimes 
  reddish, 
  

   has 
  a 
  fusibility 
  of 
  3.5, 
  a 
  specific 
  gravity 
  of 
  2.56-2.72, 
  and 
  con- 
  

   tains 
  much 
  more 
  soda 
  than 
  lime. 
  

  

  Nos. 
  1, 
  4, 
  8 
  and 
  39 
  are 
  similar 
  to 
  one 
  another 
  in 
  composition, 
  

   and 
  somewhat, 
  though 
  less 
  so, 
  in 
  appearance. 
  They 
  consist 
  of 
  

   labradorite 
  chiefly, 
  and 
  hornblende, 
  disposed 
  in 
  parallel 
  masses, 
  

   the 
  latter 
  mineral 
  increasing 
  with 
  the 
  specific 
  gravity. 
  The 
  

   gravity 
  of 
  No. 
  1 
  is 
  2.67, 
  while 
  that 
  of 
  labradorite 
  itself 
  varies 
  

   between 
  2.67 
  and 
  2.76. 
  This 
  extremely 
  low 
  result 
  is 
  due 
  to 
  the 
  

   mineral 
  having 
  lost 
  some 
  of 
  its 
  earthy 
  bases 
  by 
  weathering, 
  a 
  

   change 
  also 
  shown 
  by 
  the 
  iron 
  stains 
  on 
  a 
  fresh 
  fracture 
  of 
  the 
  

   decomposing 
  rock, 
  and 
  by 
  the 
  white 
  flinty 
  exterior, 
  from 
  which 
  

  

  