﻿314 
  W. 
  Lindgren 
  — 
  Granitic 
  Rocks 
  of 
  California. 
  

  

  There 
  is 
  no 
  doubt 
  that 
  all 
  of 
  the 
  granitic 
  rocks 
  are 
  later 
  

   than 
  the 
  altered 
  sedimentary 
  rocks 
  and 
  the 
  augite-por- 
  

   phyrite, 
  but 
  it 
  must 
  be 
  confessed 
  that 
  in 
  spite 
  of 
  good 
  expo- 
  

   sures 
  the 
  evidence 
  as 
  to 
  the 
  relative 
  age 
  of 
  the 
  granite, 
  grano- 
  

   diorite, 
  diorite 
  and 
  gabbro 
  is 
  not 
  decisive, 
  and 
  even 
  in 
  some 
  

   respects 
  contradictory. 
  There 
  is 
  some 
  evidence, 
  based 
  on 
  the 
  

   general 
  form 
  of 
  the 
  Pyramid 
  Peak 
  granite 
  area 
  and 
  the 
  man- 
  

   ner 
  in 
  which 
  it 
  includes 
  the 
  slate 
  fragments, 
  as 
  well 
  as 
  on 
  the 
  

   occurrence 
  in 
  it 
  of 
  dikes 
  of 
  a 
  rock 
  allied 
  to 
  granodiorite, 
  tend- 
  

   ing 
  to 
  show 
  that 
  the 
  granite 
  was 
  intruded 
  earlier 
  than 
  the 
  

   granodiorite. 
  On 
  the 
  other 
  hand, 
  it 
  is 
  unquestionably 
  true 
  

   that 
  the 
  granite 
  of 
  the 
  southwestern 
  corner 
  sends 
  out 
  numer- 
  

   ous 
  dikes 
  into 
  the 
  diorite 
  of 
  the 
  south 
  fork 
  of 
  the 
  American 
  

   Kiver 
  ; 
  this 
  diorite 
  again 
  shows 
  numerous 
  local 
  transitions 
  to 
  

   apparently 
  normal 
  granodiorite, 
  so 
  that 
  if 
  it 
  be 
  conceded 
  that 
  

   this 
  diorite 
  area 
  is 
  of 
  approximately 
  the 
  same 
  age 
  as 
  the 
  main 
  

   granodiorite 
  mass, 
  it 
  would 
  follow 
  that 
  the 
  granite 
  would 
  be 
  

   later 
  than 
  the 
  granodiorite. 
  The 
  probability 
  is 
  that 
  the 
  intru- 
  

   sion 
  both 
  of 
  the 
  granite 
  and 
  of 
  the 
  granodiorite 
  was 
  accom- 
  

   panied 
  by 
  minor 
  intrusions 
  of 
  acid 
  and 
  basic 
  magmas, 
  and 
  that 
  

   there 
  are 
  diorites, 
  pegmatites 
  and 
  aplites 
  of 
  the 
  age 
  of 
  the 
  

   granodiorite 
  and 
  of 
  that 
  of 
  the 
  granite, 
  the 
  latter 
  being 
  the 
  

   older 
  rock 
  ; 
  only 
  on 
  this 
  supposition 
  can 
  the 
  contradictory 
  tes- 
  

   timony 
  be 
  explained 
  ; 
  the 
  diorites 
  of 
  the 
  canyon 
  of 
  the 
  South 
  

   Fork 
  and 
  in 
  the 
  smaller 
  areas 
  along 
  the 
  western 
  boundary 
  

   would 
  then 
  belong 
  to 
  the 
  period 
  of 
  granitic 
  intrusions, 
  while 
  

   those 
  of 
  Pound 
  Top 
  and 
  the 
  Pyramid 
  Peak 
  range 
  would 
  

   belong 
  to 
  the 
  granodiorite. 
  

  

  Washington, 
  D. 
  C, 
  Jan., 
  1897. 
  

  

  

  