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  Lindgren 
  — 
  Granodiorite 
  and 
  other 
  intermediate 
  rocks. 
  

  

  ing 
  from 
  2*50 
  per 
  cent 
  to 
  4^ 
  per 
  cent. 
  K 
  2 
  varies 
  in 
  the 
  

   analyses 
  from 
  1*18 
  per 
  cent 
  to 
  3'66 
  per 
  cent 
  and 
  may 
  equal 
  or 
  

   even 
  slightly 
  exceed 
  Na 
  2 
  0, 
  especially 
  in 
  the 
  more 
  acidic 
  types 
  

   from 
  the 
  High 
  Sierra. 
  Where 
  the 
  percentage 
  goes 
  below 
  1" 
  

   the 
  rocks 
  should 
  certainly 
  be 
  classed 
  as 
  quartz 
  diorites. 
  

  

  The 
  above 
  tables 
  give 
  complete 
  analyses 
  of 
  six 
  grano- 
  

   diorites, 
  partial 
  analyses 
  of 
  seventeen 
  rocks, 
  and 
  the 
  calculated 
  

   mineral 
  ogical 
  composition 
  of 
  three 
  rocks. 
  

  

  Regarding 
  YI 
  in 
  Table 
  A 
  and 
  I 
  in 
  Table 
  B 
  of 
  incomplete 
  

   analyses, 
  it 
  should 
  be 
  stated 
  that, 
  owing 
  to 
  the 
  low 
  percentage 
  

   of 
  silica 
  and 
  large 
  amount 
  of 
  iron 
  and 
  magnesium, 
  it 
  stands 
  

   close 
  to 
  the 
  limit 
  and 
  may 
  be 
  considered 
  as 
  a 
  quartz-diorite 
  or 
  

   a 
  granodiorite. 
  That 
  it 
  has 
  been 
  included 
  in 
  this 
  table 
  is 
  due 
  

   to 
  the 
  fact 
  that 
  these 
  changes 
  from 
  the 
  composition 
  of 
  a 
  normal 
  

   granodiorite 
  have 
  only 
  been 
  effected 
  by 
  the 
  addition 
  of 
  horn- 
  

   blende 
  without 
  much 
  altering 
  the 
  proportion 
  and 
  composition 
  

   of 
  the 
  feldspars. 
  

  

  Another 
  somewhat 
  doubtful 
  rock 
  is 
  XVI 
  in 
  the 
  second 
  table, 
  

   which 
  has 
  a 
  high 
  percentage 
  of 
  K 
  2 
  coupled 
  with 
  an 
  unusually 
  

   small 
  amount 
  of 
  Na 
  2 
  0, 
  and 
  it 
  is 
  probable 
  that 
  it 
  represents 
  a 
  

   local 
  facies 
  of 
  the 
  prevailing 
  rock. 
  Its 
  composition 
  would 
  

   probably 
  place 
  the 
  rock 
  close 
  to 
  the 
  quartz-monzonites. 
  

  

  The 
  last 
  tables 
  give 
  the 
  calculated 
  mineralogical 
  composition 
  

   of 
  three 
  representative 
  rocks. 
  For 
  the 
  determination 
  of 
  the 
  

   potash 
  feldspar 
  all 
  of 
  the 
  K 
  2 
  except 
  the 
  quantity 
  needed 
  for 
  

   biotite 
  has 
  been 
  used. 
  Similarly 
  all 
  of 
  the 
  Na 
  2 
  0, 
  deducting 
  a 
  

   small 
  amount 
  for 
  the 
  hornblende, 
  has 
  been 
  calculated 
  as 
  albite. 
  

   All 
  of 
  the 
  albite 
  has 
  been 
  added 
  to 
  the 
  anorthite 
  as 
  soda-lime 
  

   feldspar. 
  The 
  potash-feldspar 
  undoubtedly 
  contains 
  some 
  soda 
  

   but 
  that 
  it 
  is 
  only 
  a 
  small 
  amount, 
  is 
  shown 
  by 
  the 
  fact 
  

   that 
  microperthite, 
  albite 
  and 
  anorthoclase 
  are 
  not 
  generally 
  

   present 
  and, 
  furthermore, 
  because 
  the 
  calculated 
  soda-lime 
  

   feldspar 
  closely 
  agrees 
  in 
  composition 
  with 
  that 
  inferred 
  from 
  

   optical 
  measurements. 
  

  

  Regarding 
  the 
  "average 
  composition" 
  quoted 
  above 
  from 
  

   my 
  report 
  on 
  Nevada 
  City 
  and 
  Grass 
  Valley, 
  it 
  should 
  be 
  borne 
  

   in 
  mind 
  that 
  most 
  of 
  the 
  analyses 
  available 
  in 
  1896 
  were 
  made 
  

   of 
  the 
  more 
  basic 
  type 
  of 
  granodiorite, 
  so 
  that 
  the 
  lime 
  is 
  a 
  

   little 
  higher 
  and 
  potash 
  lower 
  than 
  would 
  be 
  the 
  case 
  if 
  the 
  

   large 
  areas 
  of 
  the 
  somewhat 
  more 
  acidic 
  type 
  of 
  the 
  High 
  

   Sierra 
  were 
  considered. 
  It 
  is 
  clear 
  besides 
  that 
  it 
  will 
  be 
  very 
  

   difficult 
  to 
  obtain 
  such 
  an 
  average, 
  for 
  not 
  only 
  the 
  analyses 
  but 
  

   the 
  weight 
  in 
  proportion 
  to 
  the 
  rock 
  masses 
  should 
  be 
  consid- 
  

   ered. 
  

  

  I 
  have 
  no 
  radical 
  change 
  to 
  propose 
  in 
  the 
  chemical 
  limits 
  of 
  

   the 
  rock 
  given 
  in 
  the 
  paper 
  on 
  the 
  Pyramid 
  Peak 
  region, 
  

   referred 
  to 
  on 
  page. 
  272. 
  Only, 
  as 
  to 
  the 
  percentage 
  of 
  silica 
  it 
  

  

  