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  Lvndgren 
  — 
  Granodiorite 
  and 
  other 
  intermediate 
  rocks. 
  

  

  In 
  view 
  of 
  this 
  it 
  may 
  be 
  profitable 
  to 
  inquire 
  into 
  the 
  limits 
  

   assigned 
  to 
  this 
  rock 
  and 
  to 
  its 
  relation 
  to 
  granodiorite. 
  

  

  In 
  order 
  to 
  make 
  accurate 
  comparisons 
  it 
  is 
  necessary 
  to 
  have 
  

   accurately 
  defined 
  standards 
  ; 
  the 
  lack 
  of 
  these 
  is 
  very 
  much 
  

   felt 
  in 
  attempts 
  at 
  rock 
  classification. 
  "Granite" 
  is 
  a 
  term 
  

   concerning 
  the 
  petrographic 
  meaning 
  of 
  which 
  there 
  can 
  be 
  

   little 
  doubt. 
  True, 
  certain 
  geologists 
  have 
  fallen 
  into 
  the 
  habit 
  

   of 
  using 
  this 
  name 
  as 
  a 
  synonym 
  for 
  "granular 
  rocks," 
  but 
  this 
  

   is 
  a 
  practice 
  which 
  should 
  not 
  be 
  encouraged.* 
  

  

  A 
  granite 
  means 
  petrographically 
  a 
  granular 
  rock 
  composed 
  

   of 
  quartz 
  and 
  alkali 
  feldspar 
  with 
  a 
  micaceous 
  mineral 
  or 
  horn- 
  

   blende. 
  There 
  are, 
  however, 
  but 
  few 
  rocks 
  which 
  exactly 
  

   correspond 
  to 
  this 
  type, 
  more 
  or 
  less 
  soda-lime 
  feldspar 
  being 
  

   ordinarily 
  present 
  ; 
  it 
  may 
  be 
  referred 
  to 
  as 
  an 
  extreme 
  type 
  

   from 
  which 
  the 
  rock 
  can 
  vary 
  only 
  one 
  way, 
  and 
  the 
  majority 
  of 
  

   our 
  granites 
  are 
  therefore 
  more 
  or 
  less 
  pronouncedly 
  interme- 
  

   diate 
  between 
  granite 
  and 
  diorite. 
  

  

  Diorite 
  is 
  ordinarily 
  defined 
  (Rosenbusch) 
  as 
  a 
  granular 
  rock 
  

   composed 
  of 
  soda-lime 
  feldspar, 
  and 
  biotite, 
  pyroxene, 
  or 
  

   amphibole 
  singly 
  or 
  severally 
  ; 
  with 
  added 
  quartz 
  the 
  family 
  of 
  

   the 
  quartz-diorites 
  is 
  formed. 
  While 
  this 
  is 
  the 
  most 
  generally 
  

   accepted 
  definition, 
  some 
  petrographers 
  deny 
  admission 
  into 
  

   this 
  family 
  to 
  the 
  varieties 
  carrying 
  pyroxene. 
  It 
  will 
  be 
  

   apparent 
  at 
  a 
  glance 
  that 
  unless 
  the 
  very 
  wide 
  term 
  soda-lime 
  

   feldspar 
  is 
  qualified, 
  this 
  family 
  would 
  include 
  diabases 
  and 
  

   gabbros 
  as 
  well, 
  and 
  to 
  make 
  separate 
  families 
  of 
  the 
  latter 
  is 
  to 
  

   sacrifice 
  logical 
  classification. 
  What 
  is 
  really 
  done 
  for 
  prac- 
  

   tical 
  purposes 
  is 
  expressed 
  by 
  Brogger 
  as 
  follows 
  :f 
  " 
  Die 
  

   einzige 
  moegliche 
  Trennung 
  wird 
  hier 
  nach 
  meiner 
  ansicht 
  

   diejenige 
  sein, 
  den 
  Begriff 
  Diorit 
  fiir 
  mittelsaure 
  Tiefen- 
  

   gesteine, 
  den 
  Begriff 
  Gabbro 
  fiir 
  basische 
  Tiefengesteine 
  der 
  

   Plagioklasreihe, 
  den 
  Namen 
  Diabas 
  fiir 
  entsprechende 
  hypa- 
  

   byssische 
  Gesteine 
  und 
  fur 
  palaiotypej 
  Ergussteine 
  zu 
  reser- 
  

   viren." 
  Assenting 
  to 
  this 
  limitation, 
  it 
  is 
  still 
  true 
  that 
  diorite 
  

   and 
  quartz-diorite, 
  owing 
  to 
  the 
  variation 
  of 
  soda-lime 
  feldspars, 
  

   is 
  a 
  less 
  precise 
  term 
  than 
  granite. 
  

  

  It 
  became 
  apparent 
  to 
  Prof. 
  Brogger, 
  as 
  it 
  did 
  to 
  the 
  Cali- 
  

   fornian 
  geologists, 
  that 
  the 
  terms 
  granite, 
  diorite 
  and 
  quartz- 
  

   diorite 
  were 
  no 
  longer 
  sufficient 
  for 
  present 
  purposes, 
  and 
  this 
  

   necessity 
  of 
  special 
  names 
  for 
  transition 
  types 
  or 
  intermediate 
  

   rocks 
  is 
  often 
  expressed 
  in 
  his 
  writings. 
  The 
  result 
  was 
  the 
  

  

  * 
  " 
  Granolites 
  " 
  has 
  been 
  proposed 
  as 
  a 
  convenient 
  word, 
  embracing 
  all 
  rocks 
  

   of 
  granular 
  structure, 
  and 
  though 
  open 
  to 
  criticism 
  in 
  some 
  respects 
  certainly 
  

   offers 
  some 
  advantages. 
  See 
  H. 
  W. 
  Turner, 
  Journal 
  of 
  Geology, 
  1899, 
  p. 
  141. 
  

  

  fl. 
  c. 
  p. 
  17. 
  

  

  % 
  American 
  petrographers 
  will 
  probably 
  object 
  to 
  this 
  limiting 
  of 
  diabase 
  ; 
  the 
  

   Columbia 
  (Miocene) 
  lava 
  formation, 
  for 
  example, 
  contains 
  abundant 
  instances 
  of 
  

   diabase 
  flows. 
  

  

  