﻿272 
  Lindgren 
  — 
  Granodiorite 
  and 
  other 
  intermediate 
  rocks. 
  

  

  closely 
  allied 
  to 
  the 
  quartz-mica-diorite 
  than 
  to 
  the 
  granite. 
  

   Comparison 
  of 
  numerous 
  analyses 
  from 
  various 
  parts 
  of 
  the 
  

   Sierra 
  Nevada 
  shows 
  that 
  the 
  chemical 
  composition 
  varies 
  

   between 
  that 
  of 
  a 
  quartz-mica-diorite 
  and 
  a 
  quartz-monzonite 
  

   (adamellite, 
  banatite, 
  Brogger). 
  Its 
  geological 
  occurrence 
  and 
  

   in 
  general 
  entirely 
  similar 
  habit 
  preclude 
  the 
  possibility 
  of 
  

   dividing 
  it 
  into 
  subgroups. 
  

  

  The 
  rock 
  is 
  very 
  characteristic 
  and 
  cannot 
  easily 
  be 
  mistaken. 
  

   The 
  feldspars 
  are 
  generally 
  white 
  ; 
  the 
  quartz 
  is 
  not 
  very 
  con- 
  

   spicuous 
  and 
  does 
  not 
  occur 
  in 
  large 
  grains, 
  as 
  in 
  some 
  true 
  

   granites 
  of 
  the 
  High 
  Sierra 
  ; 
  the 
  hornblende 
  is 
  dark-green, 
  

   often 
  in 
  long, 
  rough 
  prisms 
  ; 
  the 
  biotite 
  is 
  of 
  the 
  usual 
  dark- 
  

   brown 
  color. 
  The 
  general 
  effect 
  is 
  a 
  light-grayish 
  color." 
  

  

  The 
  following 
  table 
  is 
  also 
  quoted 
  from 
  the 
  same 
  place 
  : 
  

  

  Limits 
  of 
  Vabiation 
  and 
  average 
  Composition 
  of 
  Granodiorite. 
  

  

  Limits 
  of 
  variation. 
  Average 
  composition. 
  

  

  Per 
  cent. 
  Per 
  cent. 
  

  

  Si0 
  2 
  59 
  to 
  68^ 
  65- 
  

  

  A1 
  2 
  3 
  14 
  to 
  17 
  16* 
  

  

  Fe 
  2 
  3 
  l£to2i 
  1-50 
  

  

  FeO 
  _.. 
  _ 
  \\ 
  to 
  4| 
  3- 
  

  

  CaO 
  3 
  to 
  6^ 
  5- 
  

  

  MgO 
  1 
  to 
  2-J 
  2- 
  

  

  K 
  2 
  _ 
  1 
  to 
  3| 
  2-25 
  

  

  Na 
  a 
  O 
  2^to4i 
  3-50 
  

  

  Remainder 
  __ 
  1*75 
  

  

  100- 
  

  

  In 
  1897* 
  in 
  a 
  paper 
  on 
  the 
  granitic 
  rocks 
  of 
  the 
  Pyramid 
  

   Peak 
  Folio, 
  I 
  characterized 
  the 
  granodiorite 
  of 
  the 
  High 
  Sierra 
  

   as 
  follows 
  : 
  Comparing 
  the 
  analytical 
  and 
  microscopical 
  results 
  

   with 
  the 
  field 
  notes, 
  it 
  is 
  clear 
  that 
  the 
  granodiorite, 
  as 
  it 
  

   appears 
  in 
  the 
  High 
  Sierra, 
  is 
  a 
  rock 
  of 
  well-defined 
  and 
  fairly 
  

   constant 
  composition, 
  structure 
  and 
  appearance. 
  It 
  is 
  neither 
  

   a 
  normal 
  diorite, 
  nor 
  is 
  it 
  a 
  granite 
  ; 
  it 
  is 
  clearly 
  an 
  intermedi- 
  

   ate 
  type, 
  occupying 
  a 
  place 
  between 
  normal 
  quartz-mica-diorite 
  

   and 
  quartz-monzonite 
  (Brogger). 
  f 
  All 
  transitions 
  toward 
  

  

  *This 
  Journal, 
  vol. 
  iii, 
  1897, 
  p. 
  312. 
  

  

  f 
  Though 
  it 
  is 
  often 
  difficult 
  in 
  practice 
  to 
  separate 
  the 
  normal 
  quartz-mica- 
  

   diorite 
  from 
  the 
  granodiorite, 
  it 
  would 
  seem 
  suitable 
  to 
  restrict 
  granodiorite 
  to 
  the 
  

   following 
  limits 
  : 
  

  

  Si0 
  2 
  . 
  . 
  . 
  .' 
  59-69 
  per 
  cent. 
  

  

  A] 
  2 
  3 
  14-17 
  " 
  

  

  Fe 
  2 
  3 
  H-2J 
  " 
  

  

  FeO 
  H-4£ 
  " 
  

  

  CaO 
  3-6£ 
  

  

  MgO 
  1-24 
  

  

  K 
  2 
  0... 
  l-3f 
  

  

  Na 
  2 
  2^-H 
  " 
  

  

  