﻿l8o 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  ^ 
  The 
  amount 
  of 
  ferric 
  oxid 
  in 
  the 
  red 
  feldspar 
  is 
  undoubtedly 
  

   very 
  trifling, 
  so 
  that, 
  if 
  chemical 
  combination 
  has 
  taken 
  place 
  and 
  

   the 
  lime 
  has 
  entered 
  into 
  the 
  reaction 
  the 
  quantity 
  involved 
  is 
  so 
  

   small 
  that 
  it 
  would 
  be 
  a 
  comparatively 
  insignificant 
  feature 
  in 
  the 
  

   complete 
  rock 
  analysis. 
  It 
  is 
  to 
  be 
  noted 
  that 
  the 
  lime 
  is 
  some- 
  

   what 
  higher 
  in 
  analysis 
  i 
  than 
  in 
  4, 
  but, 
  while 
  it 
  is 
  possible 
  that 
  

   this 
  is 
  owing 
  to 
  lime 
  taken 
  up 
  from 
  the 
  limestone 
  and 
  going 
  into 
  

   combination 
  with 
  the 
  iron 
  of 
  the 
  feldspar, 
  it 
  must 
  be 
  remembered 
  

   that 
  the 
  variation 
  is 
  well 
  within 
  the 
  limits 
  of 
  variation 
  which 
  all 
  

   the 
  bases 
  show 
  in 
  the 
  general 
  granite 
  mass, 
  hence 
  it 
  is 
  absolutely 
  

   unsafe 
  to 
  generalize 
  in 
  regard 
  to 
  it. 
  We 
  may 
  have 
  a 
  combination 
  

   of 
  lime, 
  iron 
  and 
  alumina 
  in 
  a 
  spinellike 
  mineral, 
  though 
  lime 
  does 
  

   not, 
  in 
  general, 
  occur 
  in 
  spinel: 
  or 
  a 
  small 
  amount 
  of 
  anorthite 
  

   may 
  be 
  formed, 
  with 
  the 
  iron 
  replacing 
  alumina. 
  The 
  iron 
  may 
  

   perhaps 
  be 
  reduced, 
  forming 
  an 
  iron 
  aluminate, 
  the 
  iron 
  reduced 
  

   to 
  the 
  ferrous 
  condition, 
  though 
  it 
  would 
  seem 
  as 
  if 
  this 
  would 
  

   likely 
  give 
  a 
  green 
  color 
  to 
  the 
  feldspar. 
  Warth 
  argues 
  that 
  his 
  

   color 
  changes 
  need 
  not 
  mean 
  chemical 
  combination 
  of 
  the 
  two 
  oxids 
  

   but 
  ratlier 
  a 
  diffusion 
  of 
  one 
  in 
  the 
  other. 
  Hillebrand, 
  however, 
  is 
  

   quite 
  confident 
  that 
  combination 
  takes 
  place. 
  He 
  says, 
  " 
  It 
  is 
  un- 
  

   questionable 
  that 
  both 
  lime 
  and 
  alumina 
  decolorize 
  and 
  combine 
  

   with 
  ferric 
  oxid 
  when 
  they 
  are 
  heated 
  together." 
  Though 
  this 
  

   chemical 
  question 
  must 
  be 
  left 
  indefinite, 
  it 
  does 
  seem 
  to 
  us 
  cer- 
  

   tain 
  that 
  the 
  red 
  color 
  of 
  the 
  feldspar 
  may 
  be 
  made 
  to 
  disappear 
  

   merely 
  by 
  sufficiently 
  high 
  and 
  prolonged 
  heating, 
  that 
  the 
  presence 
  

   of 
  lime 
  facilitates 
  the 
  process, 
  lowering 
  the 
  necessarv' 
  temperature, 
  

   and 
  that 
  with 
  our 
  feldspars 
  here 
  the 
  temperatures 
  were 
  not 
  suf- 
  

   ficiently 
  high 
  to 
  discharge 
  the 
  color, 
  or 
  rather 
  to 
  cause 
  the 
  feldspars 
  

   to 
  crv^stallize 
  with 
  the 
  iron 
  combined, 
  rather 
  than 
  as 
  free 
  hematite, 
  

   under 
  the 
  conditions 
  prevailing 
  at 
  the 
  place 
  and 
  time 
  of 
  solidification 
  ; 
  

   though 
  they 
  were 
  high 
  enough 
  to 
  cause 
  the 
  combination 
  to 
  take 
  

   place 
  when 
  in 
  the 
  vicinitv- 
  of 
  limestone 
  and 
  under 
  its 
  influence. 
  

  

  The 
  only 
  difiference 
  in 
  the 
  mineralog}- 
  of 
  the 
  two 
  rocks 
  is 
  the 
  

   presence 
  in 
  the 
  white 
  rock 
  of 
  occasional, 
  scattered, 
  small 
  black 
  

   tourmalins, 
  which 
  in 
  general 
  do 
  not 
  appear 
  in 
  the 
  other, 
  though 
  

   they 
  are 
  locally 
  present 
  even 
  there. 
  They 
  would 
  seem 
  attributable 
  

   to 
  the 
  presence 
  of 
  mineralizers 
  in 
  the 
  border 
  phase 
  of 
  the 
  granite, 
  

   and 
  in 
  the 
  dikes 
  they 
  occur 
  in 
  the 
  red 
  granites 
  adjacent 
  to 
  other 
  

   rocks^than 
  limestone, 
  such 
  as 
  quartzite 
  for 
  example, 
  and 
  seem 
  to 
  

   havje/nothing 
  whatever 
  to 
  do 
  with 
  the 
  color 
  change. 
  It 
  seems 
  to 
  

   us 
  that 
  the 
  chemical 
  analysis 
  gives 
  no 
  suggestion 
  whatever 
  as 
  to 
  

   the 
  cause 
  of 
  this 
  change. 
  

  

  J 
  

  

  