﻿W. 
  Lindgren 
  — 
  Granitic 
  Rocks 
  of 
  California. 
  311 
  

  

  tite 
  and 
  hornblende, 
  the 
  remainder 
  was 
  calculated 
  as 
  orthoclase 
  

   and 
  albite. 
  Further, 
  1*20 
  per 
  cent 
  lime 
  was 
  tentatively 
  sub- 
  

   tracted 
  from 
  the 
  total 
  as 
  belonging 
  to 
  the 
  hornblende, 
  and 
  0*56 
  

   per 
  cent 
  for 
  titanite 
  and 
  apatite, 
  the 
  remainder 
  being 
  calculated 
  

   as 
  anorthite. 
  The 
  amount 
  of 
  magnetite 
  is 
  estimated. 
  From 
  the 
  

   remaining 
  silica 
  -±'50 
  per 
  cent 
  was 
  subtracted 
  to 
  approximately 
  

   correspond 
  with 
  the 
  A1 
  2 
  3 
  , 
  and 
  MgO 
  available 
  for 
  biotite 
  and 
  

   hornblende. 
  

  

  The 
  analysis 
  is 
  entirely 
  typical 
  for 
  granodiorite 
  and 
  is 
  ex- 
  

   tremely 
  similar 
  to 
  the 
  analyses 
  of 
  the 
  granodiorite 
  from 
  

   Nevada 
  City 
  and 
  Grass 
  Yalley, 
  Nevada 
  County.* 
  

  

  Under 
  No. 
  IV 
  a 
  partial 
  analysis 
  is 
  recorded 
  of 
  a 
  rock 
  near 
  

   the 
  shore 
  of 
  Lake 
  Tahoe, 
  not 
  far 
  from 
  the 
  northern 
  boundary 
  

   line 
  of 
  the 
  sheet. 
  The 
  rock 
  is 
  coarse 
  granular, 
  consisting 
  

   chiefly 
  of 
  slightly 
  reddish 
  feldspar 
  with 
  much 
  quartz. 
  Horn- 
  

   blende 
  and 
  biotite 
  are 
  present 
  in 
  about 
  equal 
  quantities, 
  but 
  

   the 
  hornblende 
  occurs 
  in 
  small 
  grains 
  and 
  prisms 
  only. 
  It 
  was 
  

   thought 
  that 
  this 
  rock 
  presented 
  a 
  certain 
  similarity 
  to 
  the 
  

   granitite 
  and 
  it 
  was 
  therefore 
  analyzed, 
  but 
  the 
  figures 
  ob- 
  

   tained 
  indicate 
  it 
  to 
  be 
  a 
  normal 
  granodiorite. 
  The 
  microscope 
  

   shows 
  a 
  few 
  large 
  carlsbad 
  twins 
  of 
  microcline 
  and 
  microper- 
  

   thite; 
  an 
  abundance 
  of 
  imperfect 
  prisms 
  of 
  plagioclase 
  imbed- 
  

   ded 
  in 
  anhedral 
  quartz, 
  orthoclase, 
  microcline 
  and 
  microper- 
  

   thite, 
  the 
  latter 
  two 
  often 
  as 
  Carlsbad 
  twins 
  ; 
  well-defined 
  foils 
  

   of 
  biotite, 
  a 
  little 
  hornblende 
  and 
  a 
  few 
  grains 
  of 
  titanite. 
  , 
  

  

  Analysis 
  Y 
  shows 
  the 
  composition 
  of 
  a 
  granodiorite 
  from 
  the 
  

   valley 
  of 
  the 
  Rubicon, 
  2 
  miles 
  south 
  of 
  the 
  northern 
  boundary 
  

   line 
  of 
  the 
  sheet. 
  Macroscopically 
  the 
  rock 
  is 
  very 
  similar 
  to 
  

   IV. 
  Under 
  the 
  microscope 
  the 
  same 
  normal 
  granodiorite 
  

   structure 
  is 
  apparent. 
  As 
  in 
  IY 
  much 
  of 
  the 
  potassium 
  feld- 
  

   spar 
  cementing 
  the 
  plagioclase 
  prisms 
  is 
  microcline. 
  The 
  analy- 
  

   sis 
  indicates 
  a 
  normal 
  granodiorite. 
  

  

  Analysis 
  YI 
  shows 
  the 
  composition 
  of 
  the 
  granodiorite 
  6 
  

   miles 
  south 
  of 
  Silver 
  Lake 
  in 
  Bear 
  River 
  canyon. 
  The 
  rock 
  is 
  

   normal 
  except 
  for 
  the 
  fact 
  that 
  the 
  quartz 
  is 
  rather 
  prominent 
  

   in 
  grains 
  up 
  to 
  6 
  millimeters 
  in 
  diameter 
  and 
  that 
  the 
  biotite 
  

   predominates 
  over 
  the 
  hornblende. 
  

  

  Under 
  the 
  microscope 
  it 
  is 
  evident 
  that 
  the 
  cementing 
  ortho- 
  

   clase 
  and 
  microcline 
  are 
  rather 
  abundant, 
  but 
  the 
  granodiorite 
  

   structure 
  is 
  well-defined. 
  Titanite 
  is 
  abundant. 
  The 
  analysis 
  

   shows 
  a 
  closer 
  approach 
  to 
  the 
  granitite 
  than 
  in 
  any 
  other 
  of 
  

   the 
  rocks 
  here 
  examined 
  ; 
  this 
  is 
  expressed 
  in 
  the 
  high 
  percent- 
  

   age 
  of 
  silica 
  and 
  potash, 
  as 
  well 
  as 
  in 
  the 
  relatively 
  low 
  per- 
  

   centage 
  of 
  lime. 
  Still 
  there 
  is 
  a 
  wide 
  gap 
  between 
  this 
  rock 
  

   and 
  a 
  normal 
  granitite. 
  

  

  Analysis 
  YII 
  shows 
  the 
  composition 
  of 
  the 
  granodiorite 
  of 
  

  

  * 
  17th 
  Ann. 
  Kept. 
  TJ. 
  S. 
  Geol. 
  Survey, 
  pp. 
  38 
  and 
  42. 
  

  

  