﻿IT. 
  Lindgren 
  — 
  Granitic 
  Rocks 
  of 
  California. 
  307 
  

  

  VII. 
  177 
  Pyramid 
  Peak 
  collection; 
  granodiorite 
  ; 
  Meek's 
  

   Creek, 
  2 
  miles 
  up 
  from 
  mouth 
  at 
  Lake 
  Tahoe. 
  

   Lat. 
  39° 
  0-8'; 
  Long. 
  120° 
  9'. 
  

   VIII. 
  24 
  Pyramid 
  Peak 
  collection 
  ; 
  diorite 
  ; 
  Pyramid 
  Peak 
  

   bears 
  S. 
  50° 
  E. 
  and 
  is 
  3 
  miles 
  distant. 
  Head 
  of 
  

   Blakeley 
  Creek. 
  Lat. 
  38° 
  52-3'; 
  Long. 
  120° 
  3 
  2'. 
  

   IX. 
  93 
  Pyramid 
  Peak 
  collection 
  ; 
  Glen 
  Alpine 
  Spring 
  bear 
  

   N. 
  40° 
  W. 
  and 
  is 
  f 
  mile 
  distant. 
  Lat. 
  38° 
  51-9'; 
  

   Long. 
  120° 
  5"2\ 
  

  

  Under 
  I 
  in 
  the 
  table 
  of 
  analyses 
  is 
  given 
  one 
  of 
  these 
  gran- 
  

   ites 
  of 
  an 
  unusually 
  fresh 
  type. 
  It 
  is 
  a 
  light-gray, 
  hard, 
  gran- 
  

   ular 
  rock 
  with 
  an 
  approximation 
  to 
  a 
  porphyritic 
  habit. 
  Macro- 
  

   scopically 
  are 
  noted 
  large 
  quartz 
  grains 
  up 
  to 
  five 
  millimeters 
  

   in 
  diameter, 
  large 
  grains 
  and 
  imperfect 
  prisms 
  of 
  feldspar 
  up 
  

   to 
  ten 
  milimeters 
  in 
  length. 
  Between 
  these 
  larger 
  grains 
  lie 
  

   the 
  remaining 
  feldspar-quartz 
  mass 
  with 
  somewhat 
  finer 
  grain. 
  

   Biotite 
  in 
  foils 
  up 
  to 
  three 
  millimeters 
  in 
  diameter 
  are 
  scattered 
  

   through 
  the 
  rock. 
  Microscopically, 
  the 
  structure 
  is 
  almost 
  

   allotriomorphic, 
  the 
  rock 
  being 
  principally 
  made 
  up 
  of 
  large, 
  

   irregular 
  and 
  very 
  interlocking 
  grains 
  of 
  microcline, 
  microper- 
  

   thite, 
  and 
  quartz. 
  In 
  the 
  microline 
  lie 
  imbedded 
  smaller 
  

   grains 
  and 
  prisms 
  of 
  an 
  acid 
  plagioclase, 
  as 
  well 
  as 
  some 
  quartz. 
  

   Between 
  the 
  larger 
  grains 
  lie 
  in 
  places 
  aggregates 
  of 
  quartz, 
  

   microcline, 
  albite, 
  and'oligoclase, 
  also 
  with 
  interlocking 
  struc- 
  

   ture. 
  Biotite 
  is 
  sparingly 
  present. 
  The 
  analysis 
  may 
  be 
  cal- 
  

   culated 
  as 
  follows 
  : 
  

  

  Per 
  Cent. 
  

  

  Si0 
  o 
  18-23 
  

  

  A1 
  2 
  3 
  5-18 
  

  

  K 
  2 
  G 
  4-76 
  

  

  KAlSi 
  3 
  O 
  s 
  28-17 
  

  

  Si0 
  2 
  17-24 
  

  

  Al 
  O 
  __ 
  4-89 
  

  

  NaO 
  2-96 
  

  

  Na 
  Al 
  Si 
  3 
  O 
  s 
  25-09 
  

  

  Si0 
  2 
  1-05 
  

  

  A1 
  2 
  3 
  -93 
  

  

  CaO 
  -49 
  

  

  Ca 
  Al 
  2 
  Si 
  2 
  8 
  2-47 
  

  

  P.O. 
  _. 
  -10 
  

  

  CaO..._ 
  -13 
  

  

  CI 
  -02 
  

  

  Apatite 
  -25 
  

  

  