﻿308 
  W. 
  Lindgren 
  — 
  Granitic 
  Rocks 
  of 
  California. 
  

  

  Ti0 
  2 
  -14 
  

  

  SiO,__ 
  -n 
  

  

  CaO 
  -10 
  

  

  Titanite 
  -35 
  

  

  Biotite 
  3-10 
  

  

  Magnetite 
  -61 
  

  

  Quartz 
  39'80 
  

  

  Water 
  -31 
  

  

  

  100-15 
  

  

  From 
  the 
  total 
  amount 
  of 
  potash 
  0*24 
  was 
  tentatively 
  sub- 
  

   tracted 
  for 
  the 
  biotite. 
  The 
  total 
  lime, 
  after 
  subtraction 
  of 
  

   amount 
  needed 
  for 
  titanite, 
  was 
  counted 
  to 
  CaA],Si 
  a 
  O 
  e 
  ; 
  the 
  

   total 
  soda 
  as 
  NaAlSi,0 
  8 
  . 
  On 
  basis 
  of 
  remaining 
  A1,0, 
  a 
  

   portion 
  of 
  the 
  silica 
  was 
  referred 
  to 
  the 
  biotite 
  and 
  half 
  the 
  

   amount 
  of 
  iron 
  oxide 
  and 
  sesquioxide 
  subtracted 
  as 
  magnetite. 
  

  

  There 
  remains 
  then 
  for 
  the 
  biotite 
  : 
  

  

  40-32 
  

   26*13 
  

  

  2000 
  

  

  5-81 
  

  

  V-74 
  

  

  SiO 
  Q 
  

  

  

  1-25 
  

  

  Al 
  O 
  

  

  

  •81 
  

  

  FeX>, 
  

  

  ) 
  

  

  

  FeO 
  

  

  M^O 
  

  

  f 
  

  

  •62 
  

   •18 
  

  

  K 
  2 
  0._ 
  

  

  

  •24 
  

  

  

  

  

  3-10 
  100-00 
  

  

  This 
  corresponds 
  fairly 
  well 
  with 
  a 
  normal 
  biotite. 
  

  

  A 
  specimen 
  from 
  the 
  south 
  side 
  of 
  Pyramid 
  Peak 
  was 
  sub- 
  

   jected 
  to 
  a 
  partial 
  analysis 
  (II), 
  which 
  shows 
  it 
  to 
  be 
  of 
  practically 
  

   the 
  same 
  composition 
  as 
  (I), 
  though 
  a 
  little 
  more 
  of 
  the 
  anor- 
  

   thite 
  molecule 
  is 
  present. 
  The 
  granite 
  is 
  on 
  the 
  whole 
  very 
  

   constant 
  in 
  mineral 
  composition 
  and 
  it 
  is 
  believed 
  that 
  these 
  

   analyses 
  well 
  indicate 
  its 
  average 
  composition. 
  

  

  Granocliorite* 
  — 
  As 
  mentioned 
  before, 
  the 
  granodiorite 
  is 
  the 
  

   prevailing 
  rock, 
  occupying 
  a 
  broad 
  belt 
  extending 
  across 
  the 
  

   whole 
  area 
  from 
  north 
  to 
  south. 
  It 
  is 
  of 
  a 
  crumbling 
  nature, 
  

   falling 
  an 
  easy 
  prey 
  to 
  the 
  destructive 
  forces 
  of 
  weathering 
  and 
  

  

  * 
  The 
  name 
  of 
  granodiorite 
  was 
  first 
  proposed 
  by 
  Messrs. 
  G-. 
  F. 
  Becker, 
  H. 
  W. 
  

   Turner 
  and 
  W. 
  Lindgren 
  in 
  1892. 
  References 
  to 
  the 
  rock 
  may 
  he 
  found 
  in 
  the 
  

   following 
  places: 
  

  

  Geologic 
  Atlas 
  of 
  the 
  U. 
  S., 
  Folios 
  3, 
  5, 
  11, 
  18, 
  29. 
  

  

  W. 
  Lindgren: 
  The 
  Auriferous 
  Veins 
  of 
  Meadow 
  Lake, 
  this 
  Journal, 
  III, 
  vol. 
  

   xlvi, 
  p. 
  201, 
  1893 
  ; 
  U. 
  S. 
  Geol. 
  Survey, 
  14th 
  Ann. 
  Rep., 
  pt. 
  2, 
  p. 
  243 
  ; 
  TJ. 
  S. 
  Geol. 
  

   Survey, 
  17th 
  Ann. 
  Rept., 
  pt. 
  1, 
  p. 
  35. 
  

  

  H. 
  W. 
  Turner: 
  U. 
  S. 
  Geol. 
  Survey, 
  14th 
  Ann. 
  Rept., 
  p. 
  478; 
  TJ. 
  S. 
  Geol. 
  

   Survey, 
  17th 
  Ann. 
  Rept., 
  pt. 
  I, 
  p. 
  724. 
  

  

  