﻿W. 
  Linclgren 
  — 
  Granitic 
  Rocks 
  of 
  California. 
  305 
  

  

  these 
  schist 
  areas 
  is 
  usually 
  reddish 
  brown, 
  contrasting 
  strongly 
  

   with 
  the 
  light-gray 
  granodiorite. 
  

  

  The 
  two 
  small 
  areas 
  at 
  the 
  northern 
  boundary 
  consist 
  of 
  

   quartzite 
  and 
  black 
  slate, 
  the 
  latter 
  altered 
  near 
  the 
  contacts 
  to 
  

   gneissoid 
  micaceous 
  schist 
  ; 
  the 
  contacts 
  are 
  usually 
  sharp, 
  

   extremely 
  so 
  where 
  the 
  road 
  crosses 
  the 
  western 
  area. 
  At 
  

   other 
  places, 
  as 
  for 
  instance, 
  on 
  the 
  west 
  side 
  of 
  Loon 
  Lake, 
  

   the 
  contact 
  is 
  very 
  unsatisfactory, 
  the 
  reddish 
  granitic 
  outcrops 
  

   being 
  everywhere 
  mixed 
  with 
  schistose 
  fragments. 
  

  

  The 
  long 
  and 
  narrow 
  area 
  west 
  of 
  Tells 
  Peak 
  is 
  strongly 
  

   metamorphosed 
  and 
  composed 
  of 
  gneissoid 
  schists, 
  quartzites 
  

   and 
  mica-chlorite-andalusite 
  schists. 
  

  

  The 
  largest 
  area 
  of 
  supposed 
  Jura-trias 
  lies 
  in 
  Rockbound 
  

   "Valley 
  between 
  Mount 
  Tallac 
  and 
  the 
  Pyramid 
  Peak 
  Range 
  ; 
  

   it 
  has 
  a 
  roughly 
  triangular 
  form 
  and 
  is 
  distinguished 
  by 
  out- 
  

   crops 
  of 
  dull 
  gray 
  or 
  brown 
  color. 
  The 
  rocks 
  consist 
  of 
  a 
  

   series 
  of 
  clearly 
  stratified 
  black 
  slates 
  and 
  white 
  quartzitic 
  

   rocks 
  ; 
  beautifully 
  banded 
  hard 
  rocks, 
  dark-gray 
  and 
  white, 
  

   also 
  occcur 
  in 
  Rockbound 
  Valley. 
  The 
  normal 
  strike 
  appears 
  

   to 
  be 
  N.N.W., 
  with 
  a 
  dip 
  of 
  about 
  45° 
  to 
  the 
  east; 
  the 
  

   schistosity 
  is 
  not 
  prominent. 
  In 
  the 
  western 
  point 
  of 
  the 
  area 
  

   the 
  rocks 
  are 
  disturbed 
  and 
  dip 
  in 
  different 
  directions. 
  In 
  the 
  

   vicinity 
  of 
  Suzy 
  Lake 
  white 
  quartzitic 
  rocks 
  crop, 
  less 
  clearly 
  

   stratified, 
  often 
  indeed 
  appearing 
  massive. 
  The 
  microscope 
  

   shows 
  that 
  the 
  banded 
  rocks 
  from 
  Rockbound 
  Valley 
  and 
  in 
  

   the 
  Suzy 
  Lake 
  region 
  are 
  porphyrite 
  tuffs, 
  probably 
  depos- 
  

   ited 
  contemporaneously 
  with 
  the 
  eruption 
  of 
  the 
  large 
  por- 
  

   phyrite 
  mass 
  of 
  Mount 
  Tallac. 
  Dikes 
  of 
  typical 
  diabase 
  

   porphyrite 
  were 
  noted 
  on 
  the 
  west 
  shore 
  of 
  Suzy 
  Lake 
  ; 
  on 
  the 
  

   western 
  slope 
  of 
  Rockbound 
  Valley 
  uralite-porphy 
  rites 
  appear 
  

   which 
  would 
  seem 
  to 
  lie 
  conformably 
  in 
  the 
  sedimentary 
  series 
  

   and 
  are 
  made 
  somewhat 
  schistose 
  by 
  pressure. 
  

  

  The 
  Granitic 
  .Rocks. 
  

  

  The 
  granitic 
  rocks 
  exhibit 
  a 
  rather 
  unexpected 
  variety 
  in 
  

   composition 
  and 
  structure. 
  They 
  include 
  granites, 
  aplites, 
  grano- 
  

   diorites, 
  diorites, 
  and 
  gabbro, 
  by 
  far 
  the 
  largest 
  areas 
  being, 
  how- 
  

   ever, 
  occupied 
  by 
  the 
  granodiorite. 
  The 
  structure 
  is 
  always 
  

   massive, 
  a 
  well 
  defined 
  schistosity 
  being 
  nowhere 
  observed. 
  

   Joints 
  are 
  frequent, 
  however, 
  and 
  near 
  the 
  summit 
  the 
  rocks 
  

   are 
  intersected 
  by 
  extensive 
  fissure 
  systems. 
  

  

  Granite. 
  — 
  A 
  normal 
  biotite-granite 
  or 
  granitite 
  occupies 
  sev- 
  

   eral 
  large 
  areas 
  along 
  the 
  Pyramid 
  Peak 
  Range 
  at 
  Echo 
  Lake, 
  

   at 
  Mokelumne 
  Peak, 
  and 
  about 
  the 
  headwaters 
  of 
  the 
  Cosum- 
  

   nes 
  River. 
  Its 
  outcrops 
  are 
  generally 
  distinguished 
  by 
  a 
  light- 
  

   yellowish 
  or 
  reddish 
  color, 
  due 
  to 
  the 
  sesquioxide 
  of 
  iron 
  con- 
  

   tained 
  in 
  the 
  orthoclase. 
  It 
  is 
  harder 
  and 
  of 
  a 
  firmer 
  texture 
  

  

  