﻿W. 
  Lindgren 
  — 
  Granitic 
  Rooks 
  of 
  California. 
  303 
  

  

  sheet 
  belong. 
  The 
  sedimentary 
  rocks 
  are 
  separated 
  from 
  the 
  

   granite 
  by 
  an 
  extremely 
  irregular 
  contact 
  line. 
  The 
  bays 
  of 
  

   granitic 
  rocks 
  reach 
  far 
  into 
  the 
  schists 
  and 
  slates, 
  and 
  all 
  along 
  

   this 
  contact 
  the 
  sedimentary 
  rocks 
  have 
  been 
  subjected 
  to 
  an 
  

   intense 
  contact 
  metamorphism, 
  but 
  of 
  fusion 
  or 
  absorption 
  

   there 
  is 
  absolutely 
  no 
  evidence. 
  

  

  The 
  whole 
  of 
  the 
  Calaveras 
  formation 
  on 
  the 
  eastern 
  part 
  

   of 
  the 
  Placerville 
  sheet 
  and 
  on 
  this 
  sheet 
  has 
  a 
  pronounced 
  sili- 
  

   ceous 
  character 
  ; 
  it 
  consists 
  of 
  altered 
  sandstones, 
  grading 
  into 
  

   quartzite, 
  and 
  clay 
  slates 
  grading 
  into 
  micaceous 
  schists. 
  

   The 
  cause 
  of 
  the 
  metamorphism 
  is 
  partly 
  of 
  a 
  regional 
  char- 
  

   acter 
  and 
  caused 
  by 
  dynamic 
  movements 
  affecting 
  a 
  large 
  part 
  

   of 
  the 
  Sierra 
  Nevada, 
  chiefly 
  prior 
  to 
  the 
  great 
  granitic 
  intru- 
  

   sions, 
  partly 
  of 
  a 
  local 
  character, 
  and 
  caused 
  by 
  the 
  heat 
  and 
  

   the 
  emanations 
  from 
  the 
  intrusion 
  of 
  enormous 
  massses 
  of 
  gra- 
  

   nitic 
  magmas. 
  While 
  the 
  latter 
  metamorphism 
  is 
  superim- 
  

   posed 
  upon 
  the 
  former, 
  and 
  the 
  phenomena 
  resulting 
  from 
  

   each 
  not 
  always 
  easy 
  to 
  discriminate, 
  it 
  is 
  clearly 
  seen 
  that 
  the 
  

   extremely 
  altered 
  sediments 
  are 
  found 
  only 
  at 
  the 
  contacts 
  

   with 
  the 
  granitic 
  rocks, 
  and 
  that 
  the 
  degree 
  of 
  metamorphism 
  

   gradually 
  decreases 
  away 
  from 
  it. 
  The 
  contact 
  zones 
  are 
  here 
  

   very 
  wide, 
  typical 
  contact 
  metamorphic 
  rocks 
  often 
  being 
  

   found 
  two 
  miles 
  from 
  the 
  contacts, 
  or 
  even 
  more 
  in 
  case 
  of 
  

   projecting 
  masses 
  of 
  sedimentary 
  rocks 
  surrounded 
  on 
  all 
  sides 
  

   by 
  granite. 
  It 
  does 
  not 
  appear 
  probable 
  that 
  any 
  of 
  these 
  

   rocks 
  are 
  old, 
  pre-Carboniferous 
  or 
  Archean 
  schists. 
  

  

  Less 
  altered 
  rocks, 
  the 
  clastic 
  character 
  of 
  which 
  is 
  clearly 
  

   apparent, 
  occur 
  at 
  a 
  few 
  places 
  near 
  the 
  western 
  border 
  of 
  the 
  

   sheet. 
  They 
  are 
  principally 
  dark 
  clay-slates 
  and 
  quartzitic 
  

   rocks, 
  which 
  under 
  the 
  microscope 
  show 
  their 
  f 
  ragmen 
  tal 
  ori- 
  

   gin. 
  Thus 
  on 
  Silver 
  Creek, 
  near 
  the 
  western 
  boundary 
  of 
  the 
  

   sheet, 
  on 
  Sly 
  Park 
  Creek, 
  at 
  Fort 
  Grizzly 
  and 
  southeast 
  of 
  

   Tar's 
  Sawmill. 
  But 
  the 
  larger 
  part 
  of 
  the 
  Calaveras 
  formation 
  

   in 
  this 
  sheet 
  is 
  occupied 
  by 
  the 
  contact 
  metamorphic 
  schists. 
  In 
  

   places 
  especially 
  exposed 
  to 
  the 
  action 
  of 
  the 
  granitic 
  magma, 
  the 
  

   rock 
  is 
  converted 
  to 
  normal, 
  medium-grained 
  gneiss 
  or 
  mica- 
  

   schist, 
  and 
  at 
  these 
  places 
  the 
  contacts 
  with 
  the 
  granite, 
  usually 
  

   sharp, 
  are 
  liable 
  to 
  become 
  indistinct. 
  Somewhat 
  farther 
  away 
  

   the 
  schists 
  are 
  finer-grained, 
  generally 
  of 
  a 
  brownish 
  color, 
  from 
  

   the 
  biotite 
  contained, 
  or 
  of 
  a 
  silvery 
  lustre 
  caused 
  by 
  scales 
  of 
  

   muscovite 
  on 
  the 
  planes 
  of 
  schistosity. 
  The 
  surface 
  is 
  fre- 
  

   quently 
  knotty, 
  changing 
  to 
  normal 
  " 
  Knotenschiefer." 
  They 
  

   often 
  carry 
  andalusite, 
  characteristic 
  for 
  contact 
  rocks, 
  in 
  well- 
  

   developed 
  crystals, 
  and 
  such 
  rocks 
  may 
  be 
  found 
  more 
  than 
  

   one 
  mile 
  distant 
  from 
  the 
  contact. 
  

  

  Excellent 
  exposures 
  are 
  found 
  in 
  the 
  deep 
  canyons 
  of 
  Silver 
  

   Creek, 
  Camp 
  Creek 
  and 
  the 
  north 
  fork 
  of 
  the 
  Cosumnes, 
  

  

  