﻿Notes 
  upon 
  the 
  Lithology 
  of 
  the 
  Adikondacks. 
  91 
  

  

  III. 
  Analyses 
  op 
  the 
  Most 
  Impoetant 
  Minerals 
  and 
  

  

  Rocks. 
  

  

  The 
  first 
  point 
  to 
  be 
  definitely 
  established, 
  was 
  the 
  constitu- 
  

   tion 
  of 
  the 
  feldspars, 
  which 
  occur 
  in 
  this 
  suite 
  of 
  Adirondack 
  

   norites. 
  Their 
  specific 
  gravities, 
  degrees 
  of 
  fusibility, 
  and 
  

   flame-reactions, 
  together 
  with 
  their 
  optical 
  characters, 
  readily 
  

   permitted 
  their 
  reference 
  to 
  that 
  group 
  of 
  feldspars, 
  which 
  on 
  

   account 
  of 
  its 
  crystallographic 
  relationships, 
  has 
  been 
  termed 
  

   Plagioclase, 
  and 
  with 
  a 
  single 
  exception 
  to 
  that 
  species 
  of 
  

   plagioclase, 
  known 
  as 
  Labradorite. 
  But 
  to 
  determine 
  the 
  for- 
  

   mulae 
  of 
  these 
  particular 
  labradorites, 
  together 
  with 
  any 
  

   important 
  variations 
  in 
  their 
  constitution, 
  if 
  such 
  variations 
  

   exist, 
  as 
  numerous 
  quantitative 
  analyses 
  as 
  time 
  would 
  permit, 
  

   were 
  requisite. 
  With 
  this 
  object 
  in 
  view, 
  the 
  two 
  varieties 
  of 
  

   Norian 
  labradorite, 
  which 
  were 
  found 
  to 
  be 
  most 
  widely 
  diver- 
  

   gent 
  in 
  physical 
  characters, 
  were 
  selected. 
  The 
  one, 
  was 
  that 
  

   which 
  occurs 
  in 
  crystalline 
  masses, 
  with 
  faces 
  sometimes 
  seve- 
  

   ral 
  inches 
  in 
  breadth 
  and 
  length. 
  The 
  faces 
  are 
  finely 
  ruled 
  

   with 
  lines, 
  significant 
  of 
  the 
  multitude 
  of* 
  individuals 
  com- 
  

   posing 
  these 
  polysynthetic 
  aggregates. 
  This 
  variety 
  is 
  usually 
  

   dark-grey 
  or 
  smoky, 
  sometimes 
  approaching 
  to 
  bluish 
  in 
  tint, 
  

   and 
  frequently 
  opalescent. 
  Such 
  is 
  the 
  case 
  with 
  the 
  material 
  

   picked 
  out 
  for 
  analysis, 
  from 
  the 
  norite 
  forming 
  the 
  mass 
  and 
  

   summit 
  of 
  Mount 
  Marcy, 
  the 
  highest 
  peak 
  into 
  which 
  the 
  

   Norian 
  System 
  of 
  Northern 
  New 
  York 
  rises, 
  its 
  altitude 
  being 
  

   5,400 
  feet. 
  The 
  results 
  are 
  given 
  under 
  A. 
  

  

  The 
  other 
  variety 
  is 
  less 
  vitreous 
  in 
  lustre, 
  approaching 
  often 
  

   to 
  waxy. 
  This 
  aspect 
  especially 
  characterizes 
  the 
  specimen 
  

   analyzed, 
  which 
  also 
  resembles 
  common 
  wax 
  in 
  color. 
  It 
  is 
  

   crypto-crystalline, 
  forming 
  the 
  'matrix, 
  however, 
  of 
  smoke-col- 
  

   ored 
  crystals 
  analogous 
  to 
  the 
  above. 
  Its 
  microscopic 
  charac- 
  

   ters 
  will 
  be 
  found 
  in 
  Part 
  IV. 
  The 
  plagioclase 
  base, 
  forming 
  

   similar 
  porphyries 
  and 
  probably 
  not 
  differing 
  essentially 
  in 
  

   composition 
  from 
  this 
  type 
  specimen, 
  is 
  also 
  white 
  to 
  grey, 
  

   and 
  light- 
  to 
  dark-green 
  in 
  color, 
  varying 
  from 
  compact 
  (in 
  

   reality 
  crypto-crystalline) 
  to 
  fine- 
  and 
  coarse-granular, 
  and 
  even 
  

   minutely 
  phanero-crystalline 
  in 
  structure. 
  In 
  the 
  latter 
  case, 
  

   the 
  imbedded 
  crystalline 
  masses, 
  are 
  only 
  distinguished 
  by 
  their 
  

   greater 
  size, 
  their 
  darker 
  color 
  and 
  different 
  lustre, 
  from 
  the 
  

  

  