﻿W. 
  Lindgren 
  — 
  Granitic 
  Rocks 
  of 
  California. 
  301 
  

  

  Art. 
  XXVIII. 
  — 
  The 
  Granitic 
  Rocks 
  of 
  the 
  Pyramid 
  Peak 
  

   District, 
  Sierra 
  Nevada, 
  California 
  ; 
  by 
  Waldemar 
  Lind- 
  

   gren. 
  

  

  [Published 
  by 
  permission 
  of 
  the 
  Director 
  of 
  the 
  U. 
  S. 
  Geological 
  Survey.] 
  

  

  It 
  has 
  long 
  been 
  known 
  that 
  the 
  summit 
  region 
  of 
  the 
  

   Sierra 
  Nevada 
  is 
  occupied 
  by 
  an 
  enormous 
  mass 
  of 
  granitic 
  

   rocks, 
  and 
  that 
  a 
  large 
  part 
  of 
  it 
  consists 
  of 
  granodiorite, 
  a 
  rock 
  

   intermediate 
  between 
  a 
  granite 
  and 
  a 
  diorite, 
  but 
  no 
  detailed 
  

   maps 
  have 
  thus 
  far 
  been 
  made 
  of 
  the 
  granitic 
  areas. 
  An 
  

   opportunity 
  was 
  offered 
  for 
  the 
  study 
  of 
  these 
  granitic 
  rocks 
  

   during 
  the 
  survey 
  of 
  Pyramid 
  Peak 
  atlas 
  sheet, 
  which 
  was 
  

   undertaken 
  in 
  the 
  summer 
  of 
  1894 
  by 
  the 
  writer, 
  assisted 
  by 
  

   Mr. 
  H. 
  C. 
  Hoover. 
  The 
  results 
  are 
  shown 
  in 
  the 
  accompany- 
  

   ing 
  map 
  (p. 
  302), 
  compiled 
  from 
  the 
  Pyramid 
  Peak 
  folio 
  now 
  

   in 
  press. 
  

  

  The 
  region 
  embraces 
  half 
  a 
  degree 
  of 
  latitude 
  by 
  half 
  a 
  

   degree 
  of 
  longitude, 
  and 
  contains 
  927 
  square 
  miles. 
  The 
  

   southern 
  end 
  of 
  Lake 
  Tahoe 
  falls 
  within 
  the 
  northern 
  corner, 
  

   and 
  the 
  main 
  divide 
  of 
  the 
  mountain 
  range 
  runs 
  near 
  the 
  east- 
  

   ern 
  boundary 
  of 
  the 
  sheet. 
  While 
  the 
  western 
  part 
  is 
  occu- 
  

   pied 
  by 
  an 
  approximate 
  plateau 
  deeply 
  trenched 
  by 
  canyons 
  

   and 
  gulches, 
  the 
  crest 
  of 
  the 
  Sierra 
  Nevada 
  rises 
  in 
  the 
  eastern 
  

   part 
  to 
  lofty 
  snow-capped 
  mountains. 
  The 
  drainage 
  of 
  the 
  

   western 
  part 
  is 
  toward 
  the 
  Sacramento 
  and 
  San 
  Joaquin 
  rivers, 
  

   while 
  the 
  drainage 
  toward 
  Lake 
  Tahoe 
  eventually 
  finds 
  its 
  way 
  

   to 
  the 
  deserts 
  of 
  the 
  Great 
  Basin. 
  

  

  The 
  older 
  bed-rock 
  series 
  consists 
  of 
  slates, 
  schists 
  and 
  gra- 
  

   nitic 
  rocks. 
  These 
  are 
  extensively 
  covered 
  by 
  Tertiary 
  erup- 
  

   tives, 
  andesite, 
  rhyolite 
  and 
  basalt, 
  which 
  have 
  not 
  been 
  indi- 
  

   cated 
  in 
  the 
  map 
  accompanying 
  this 
  paper. 
  To 
  the 
  west 
  the 
  

   slates, 
  schists 
  and 
  accompanying 
  basic 
  eruptive 
  rocks 
  continue 
  

   down 
  to 
  the 
  foothills 
  of 
  the 
  range 
  and 
  contain 
  several 
  small 
  

   masses 
  of 
  granitic 
  rocks. 
  Toward 
  the 
  east 
  the 
  latter 
  continue 
  

   over 
  to 
  the 
  eastern 
  escarpment 
  of 
  the 
  Sierra 
  Nevada. 
  The 
  

   range 
  in 
  this 
  vicinity 
  contains 
  two 
  summit-ridges. 
  The 
  west- 
  

   erly, 
  dividing 
  the 
  Pacific 
  from 
  the 
  Great 
  Basin, 
  is 
  found 
  on 
  

   this 
  sheet, 
  while 
  the 
  easterly 
  summit 
  divides 
  the 
  drainage 
  flow- 
  

   ing 
  into 
  Lake 
  Tahoe 
  from 
  that 
  running 
  into 
  the 
  Carson 
  River. 
  

  

  The 
  Sedimentary 
  Areas. 
  

  

  No 
  fossils 
  have 
  been 
  found 
  in 
  any 
  of 
  the 
  sedimentary 
  rocks 
  

   of 
  the 
  bed-rock 
  series 
  within 
  the 
  limit 
  of 
  this 
  sheet, 
  and 
  the 
  

   age 
  assigned 
  is 
  in 
  all 
  cases 
  tentative 
  only. 
  The 
  determinations 
  

   are, 
  however, 
  based 
  upon 
  a 
  comparison 
  with 
  formations 
  of 
  

  

  Am. 
  Jour. 
  Sol 
  — 
  Fourth 
  Series, 
  Vol. 
  Ill, 
  No. 
  16.— 
  April, 
  1897. 
  

   21 
  

  

  