﻿

  Lindgren 
  — 
  Granodiorite 
  and 
  other 
  intermediate 
  rocks. 
  281 
  

  

  Owing 
  to 
  the 
  low 
  percentage 
  of 
  CaO 
  and 
  large 
  amount 
  of 
  

   K 
  2 
  this 
  rock 
  would 
  fall 
  outside 
  of 
  the 
  limits 
  of 
  granodiorite 
  

   and 
  may 
  approximately 
  be 
  referred 
  to 
  as 
  a 
  quartz-monzonite. 
  

   This 
  rock 
  has 
  all 
  the 
  appearance 
  of 
  a 
  granite, 
  and 
  from 
  Held 
  

   examination 
  was 
  supposed 
  to 
  belong 
  to 
  that 
  family. 
  

  

  In 
  the 
  critical 
  examination 
  of 
  proposed 
  rock 
  types 
  the 
  defi- 
  

   nition 
  is 
  clearly 
  first 
  to 
  be 
  considered, 
  secondarily 
  the 
  analyses. 
  

   Turning 
  now 
  to 
  the 
  analyses 
  of 
  quartz-monzonites 
  given 
  by 
  

   Brogger, 
  a 
  perusal 
  will 
  convince 
  that 
  representatives 
  of 
  his 
  defi- 
  

   nition 
  are 
  few 
  in 
  number. 
  The 
  group 
  with 
  less 
  silica 
  or 
  the 
  

   banatites 
  is 
  represented 
  by 
  five 
  analyses, 
  four 
  of 
  which 
  easily 
  

   fall 
  within 
  the 
  limits 
  of 
  the 
  granodiorites. 
  The 
  mean 
  of 
  the 
  

   analyses 
  is 
  as 
  follows 
  : 
  

  

  Adaruellite. 
  Banatite. 
  

  

  SiO,-.. 
  69-27 
  64-39 
  

  

  Al 
  o 
  3 
  13-47 
  15-90 
  

  

  Fe" 
  3 
  4-82 
  4-69 
  

  

  CaO 
  3-25 
  . 
  4-15 
  

  

  Mo-0 
  1-02 
  1-93 
  

  

  K 
  o 
  3-85 
  3-52 
  

  

  Na 
  2 
  3-29 
  3*58 
  

  

  By 
  reason 
  of 
  the 
  high 
  potash 
  the 
  adamellite 
  of 
  this 
  average 
  

   falls 
  outside 
  of 
  the 
  granodiorites 
  though 
  it 
  hardly 
  corresponds 
  

   to 
  Broggers 
  definition. 
  The 
  banatite, 
  on 
  the 
  other 
  hand, 
  

   would 
  be 
  identical 
  with 
  some 
  types 
  of 
  granodiorite 
  if 
  the 
  

   analyses 
  were 
  actually 
  representative. 
  Brogger's 
  average 
  of 
  

   banatite 
  is 
  thus 
  not 
  only 
  on 
  one 
  side 
  of 
  his 
  definition 
  but 
  very 
  

   much 
  so, 
  inasmuch 
  as 
  the 
  soda-lime 
  feldspar 
  will 
  be 
  equal 
  to 
  

   about 
  three 
  times 
  the 
  quantity 
  of 
  orthoclase, 
  provided 
  that 
  the 
  

   mineral 
  composition 
  of 
  the 
  rocks 
  is 
  similar 
  to 
  that 
  of 
  a 
  grano- 
  

   diorite. 
  

  

  I 
  think 
  in 
  fact 
  that 
  it 
  will 
  be 
  difficult 
  to 
  obtain 
  any 
  con- 
  

   siderable 
  number 
  of 
  analyses 
  of 
  granular 
  rocks, 
  having 
  the 
  

   average 
  silica 
  content 
  of 
  65 
  per 
  cent 
  and 
  about 
  equal 
  quantities 
  

   of 
  alkali 
  and 
  soda-lime 
  feldspars. 
  In 
  other 
  words, 
  it 
  does 
  not 
  

   appear 
  probable 
  that 
  the 
  banatite, 
  which 
  corresponds 
  to 
  Brog- 
  

   ger's 
  definition, 
  is 
  a 
  very 
  common 
  and 
  widespread 
  family 
  of 
  

   rocks. 
  

  

  Granodiorite 
  porphyry. 
  — 
  Minor 
  intrusive 
  masses 
  and 
  dikes, 
  

   having 
  the 
  composition 
  of 
  granodiorite 
  combined 
  with 
  a 
  por- 
  

   phyrinic 
  noncrystalline 
  groundmass, 
  are 
  not 
  uncommon. 
  For 
  

   these 
  I 
  propose 
  the 
  name 
  granodiorite 
  porphyry, 
  in 
  analogy 
  

   with 
  granite 
  porphyry 
  and 
  diorite 
  porphyry. 
  

  

  Conclusions. 
  — 
  Granodiorite, 
  a 
  member 
  of 
  the 
  great 
  family 
  

   of 
  rocks 
  with 
  predominating 
  soda-lime 
  feldspars, 
  is 
  distin- 
  

   guished 
  by 
  a 
  granular 
  texture, 
  grayish 
  color 
  and 
  a 
  mineral 
  

  

  