﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  1 
  79 
  

  

  Now 
  on 
  hearing 
  of 
  your 
  problem 
  it 
  occurred 
  to 
  me 
  that 
  such 
  an 
  

   effect 
  might 
  be 
  represented 
  by 
  the 
  bleached 
  dikes 
  in 
  limestone. 
  

   The 
  idea 
  was 
  that, 
  under 
  the 
  influence 
  of 
  the 
  intrusions, 
  the 
  lime- 
  

   stone 
  may 
  have 
  become 
  decarbonated 
  to 
  a 
  slight 
  extent, 
  thus 
  

   facilitating 
  action 
  with 
  the 
  ferric 
  oxid 
  of 
  the 
  feldspar. 
  The 
  ex- 
  

   planation 
  does 
  not, 
  however, 
  satisfy 
  me, 
  for 
  one 
  might 
  expect 
  

   perhaps 
  that 
  the 
  feldspathic 
  material 
  intruded 
  at 
  the 
  elevated 
  

   temperature 
  would 
  have 
  already 
  acted 
  on 
  its 
  iron 
  oxid, 
  and 
  hence 
  

   not 
  show 
  color; 
  still 
  it 
  may 
  be 
  that 
  the 
  silicate 
  molecule 
  of 
  the 
  

   feldspar 
  is 
  far 
  more 
  resistant 
  than 
  the 
  zeolite 
  and 
  limestone 
  in 
  

   respect 
  to 
  ferric 
  oxid, 
  which 
  might 
  thus 
  be 
  in 
  independent 
  exist- 
  

   ence 
  with 
  the 
  feldspar 
  at 
  high 
  temperatures. 
  

  

  Dr 
  Warth's 
  article 
  in 
  the' 
  Chemical 
  News 
  deals 
  with 
  the 
  blowpipe 
  

   ignition 
  of 
  mixtures 
  of 
  alumina 
  and 
  ferric 
  oxid 
  in 
  various 
  pro- 
  

   portions, 
  in 
  which 
  the 
  color 
  invariaibly 
  changed 
  from 
  red 
  to 
  white 
  

   when 
  small 
  amounts 
  of 
  iron 
  were 
  used, 
  while 
  a 
  brownish 
  tint 
  was 
  

   obtained 
  when 
  the 
  proportions 
  were 
  larger. 
  Incidentally 
  it 
  was 
  

   also 
  shown 
  that 
  the 
  alumina 
  prevented 
  reduction 
  of 
  the 
  iron 
  to 
  the 
  

   magnetic 
  oxid. 
  

  

  A 
  sample 
  of 
  finely 
  crushed 
  and 
  sorted 
  red 
  granite 
  was 
  ignited 
  

   by 
  us 
  for 
  three 
  hours 
  over 
  a 
  Bunsen 
  flame 
  in 
  a 
  platinum 
  crucible. 
  

   The 
  portion 
  in 
  close 
  contact 
  with 
  the 
  sides 
  and 
  bottom 
  became 
  

   white, 
  while 
  the 
  bulk 
  of 
  the 
  material, 
  in 
  more 
  central 
  position 
  and 
  

   hence 
  less 
  strongly 
  heated, 
  retained 
  its 
  red 
  color. 
  This 
  we 
  take 
  to 
  

   indicate 
  that, 
  with 
  sufficiently 
  high 
  temperature, 
  even 
  in 
  feldspar, 
  

   the 
  red 
  color 
  will 
  disappear, 
  and 
  that 
  the 
  presence 
  in 
  rocks 
  of 
  

   alkali 
  feldspar 
  colored 
  red 
  by 
  ferric 
  oxid 
  shows 
  that, 
  under 
  the 
  

   conditions 
  of 
  congelation, 
  the 
  temperature 
  was 
  not 
  suflicientb/ 
  high 
  

   to 
  bring 
  about 
  this 
  color 
  change. 
  We 
  then 
  mixed 
  a 
  small 
  quantity 
  

   of 
  powdered 
  limestone 
  with 
  another 
  charge 
  of 
  the 
  crushed 
  granite, 
  

   and 
  ignited 
  in 
  the 
  same 
  crucible 
  over 
  the 
  same 
  burner 
  for 
  the 
  

   same 
  time. 
  Not 
  only 
  was 
  the 
  feldspar 
  of 
  the 
  entire 
  charge 
  bleached, 
  

   but 
  the 
  bleaching 
  seemed 
  complete 
  at 
  the 
  end 
  of 
  one 
  hour. 
  Finally 
  

   we 
  ignited 
  a 
  third 
  charge, 
  in 
  which 
  a 
  very 
  thin 
  coating 
  of 
  lime- 
  

   stone 
  was 
  spread 
  over 
  the 
  top, 
  but 
  not 
  mixed 
  with 
  the 
  granite 
  as 
  

   in 
  the 
  previous 
  case, 
  and 
  here 
  again 
  the 
  bleaching 
  was 
  prompt 
  and 
  

   absolute. 
  It 
  is 
  not 
  intended 
  to 
  imply 
  that 
  the 
  cause 
  of 
  the 
  bleach- 
  

   ing 
  was 
  the 
  same 
  in 
  both 
  cases, 
  but 
  only 
  that, 
  in 
  the 
  presence 
  of 
  

   lime, 
  decoloration 
  took 
  place 
  more 
  readily 
  and 
  at 
  a 
  lower 
  tempera- 
  

   ture 
  ; 
  precisely 
  what 
  the 
  field 
  relations 
  had 
  indicated 
  for 
  the 
  granite 
  

   in 
  place. 
  There 
  is 
  also 
  here, 
  it 
  seems 
  to 
  us, 
  a 
  hint 
  at 
  the 
  reason 
  

   why 
  red 
  coloration 
  is 
  a 
  common 
  feature 
  in 
  alkali 
  feldspars, 
  and 
  

   not 
  in 
  lime 
  soda 
  feldspars. 
  

  

  