﻿Lindgren 
  — 
  Granodiorite 
  and 
  other 
  intermediate 
  rocks. 
  271 
  

  

  hornblende. 
  The 
  soda-lime 
  feldspars 
  are 
  usually 
  considerably 
  

   and 
  to 
  a 
  variable 
  extent 
  in 
  excess 
  of 
  the 
  alkali 
  feldspar. 
  This 
  

   granitoid 
  rock 
  occupies 
  a 
  position 
  intermediate 
  between 
  a 
  

   granite 
  and 
  a 
  quartz-diorite, 
  and 
  is 
  in 
  fact 
  closely 
  related 
  to 
  the 
  

   latter. 
  The 
  large 
  areas 
  occupied 
  by 
  it 
  and 
  the 
  constancy 
  of 
  

   the 
  type 
  justify 
  the 
  special 
  name." 
  

  

  In 
  1893 
  I 
  attempted 
  to 
  limit 
  the 
  rocks 
  from 
  a 
  chemical 
  

   point 
  of 
  view.* 
  On 
  account 
  of 
  the 
  few 
  analyses 
  available 
  

   this 
  first 
  attempt 
  could 
  not 
  be 
  as 
  precise 
  as 
  the 
  later 
  definitions, 
  

   but 
  requires 
  only 
  slight 
  correction. 
  The 
  statement 
  is 
  as 
  fol- 
  

   lows 
  : 
  " 
  A 
  light 
  gray 
  granitic 
  rock 
  occupies 
  the 
  larger 
  part 
  of 
  

   the 
  area 
  of 
  the 
  map 
  . 
  . 
  . 
  The 
  rock 
  is 
  in 
  general 
  identical 
  

   with 
  the 
  gray 
  so-called 
  granite 
  that 
  occupies 
  such 
  large 
  areas 
  in 
  

   the 
  Sierra 
  Nevada 
  and 
  which 
  probably 
  extends 
  through 
  

   Southern 
  California 
  far 
  down 
  into 
  the 
  peninsula 
  of 
  Lower 
  

   California. 
  The 
  rock 
  consists 
  in 
  typical 
  development 
  of 
  feld- 
  

   spar, 
  quartz, 
  biotite 
  and 
  hornblende 
  with 
  medium-grained, 
  

   hypidiomorphic 
  structure. 
  The 
  soda-lime 
  feldspars 
  are 
  usually 
  

   considerably 
  and 
  to 
  a 
  variable 
  extent 
  in 
  excess 
  of 
  the 
  alkali 
  

   feldspars. 
  The 
  silica 
  varies 
  between 
  60 
  and 
  73 
  per. 
  cent; 
  the 
  

   amount 
  of 
  lime 
  is 
  variable 
  but 
  it 
  rarely 
  exceeds, 
  while 
  it 
  usually 
  

   falls 
  somewhat 
  short 
  of, 
  the 
  sum 
  of 
  the 
  alkalies. 
  While 
  in 
  

   some 
  varieties 
  that 
  cannot 
  be 
  distinguished 
  from 
  the 
  others 
  in 
  

   the 
  field 
  there 
  is 
  more 
  potash 
  than 
  soda, 
  a 
  frequently 
  occurring 
  

   relation 
  is 
  2 
  per 
  cent 
  K 
  2 
  to 
  1 
  per 
  cent 
  Na 
  2 
  0. 
  It 
  will 
  be 
  seen 
  

   that 
  the 
  rock 
  very 
  closely 
  approaches 
  some 
  quartz- 
  mica-diorites 
  

   and 
  often 
  might 
  be 
  indicated 
  by 
  that 
  name. 
  This 
  term, 
  how- 
  

   ever, 
  besides 
  being 
  clumsy 
  does 
  not 
  sufficiently 
  express 
  its 
  close 
  

   relationship 
  to 
  granite, 
  brought 
  out 
  by 
  its 
  frequently 
  high 
  per- 
  

   centage 
  of 
  silica 
  and 
  low 
  percentage 
  of 
  lime, 
  by 
  its 
  variable 
  

   percentage 
  of 
  alkali 
  feldspar, 
  and 
  by 
  the 
  muscovite 
  sometimes 
  

   occurring 
  in 
  it." 
  

  

  The 
  last 
  part 
  of 
  this 
  sentence 
  refers 
  to 
  a 
  facies 
  from 
  Rocklin, 
  

   Placer 
  County 
  and 
  other 
  places 
  which 
  probably 
  should 
  not 
  be 
  

   included 
  in 
  the 
  granodiorites. 
  

  

  In 
  a 
  report 
  on 
  the 
  veins 
  of 
  Grass 
  Valley 
  and 
  Nevada 
  City, 
  

   Cal.,"r 
  the 
  following 
  definition 
  is 
  given 
  : 
  

  

  "Under 
  the 
  name 
  granodiorite 
  are 
  included 
  coarsely 
  granu- 
  

   lar 
  rocks, 
  intruded 
  and 
  consolidated 
  at 
  considerable 
  depths 
  

   below 
  the 
  surface, 
  having 
  a 
  normal 
  granitic 
  (eu-granitic) 
  struc- 
  

   ture, 
  and 
  a 
  mineralogical 
  composition 
  of 
  quartz, 
  soda-lime 
  

   feldspars, 
  orthoclase, 
  hornblende, 
  and 
  nearly 
  always 
  biotite. 
  

   Titanite 
  and 
  magnetite 
  are 
  always 
  present 
  as 
  accessory 
  con- 
  

   stituents. 
  This 
  rock, 
  which 
  in 
  the 
  Sierra 
  Nevada 
  occurs 
  in 
  

   enormous 
  areas, 
  forms 
  an 
  intermediate 
  group 
  between 
  the 
  

   quartz-mica-diorites 
  and 
  the 
  granites, 
  being, 
  however, 
  more 
  

  

  *This 
  Journal, 
  lxvi, 
  201. 
  The 
  Auriferous 
  Veins 
  of 
  Meadow 
  Lake, 
  Cal. 
  

   f 
  17th 
  Adu. 
  Rept., 
  1896, 
  TJ. 
  S. 
  G. 
  S., 
  Part 
  IT, 
  p. 
  35. 
  

  

  