﻿GEOLOGY 
  OF 
  THE 
  NORTH 
  CREEK 
  QUADRANGLE 
  8l 
  

  

  All 
  modes 
  of 
  occurrence 
  of 
  garnets 
  observed 
  by 
  the 
  writer 
  on 
  the 
  

   North 
  Creek 
  and 
  Thirteenth 
  lake 
  sheets 
  may 
  be 
  summarized 
  as 
  

   follows 
  : 
  ( 
  i 
  ) 
  as 
  crystals 
  or 
  grains 
  in 
  various 
  Grenville 
  rocks, 
  as 
  the 
  

   garnet-pyroxene 
  gneisses, 
  the 
  dark 
  hornblende-garnet 
  gneiss, 
  the 
  

   gray 
  feldspar-biotite-garnet 
  gneisses 
  or 
  schists, 
  and 
  the 
  white 
  or 
  

   very 
  light 
  gray 
  feldspar 
  gneisses; 
  (2) 
  as 
  distinct 
  crystals 
  fre- 
  

   quently 
  occurring 
  in 
  all 
  types 
  of 
  intrusive 
  rocks 
  — 
  syenite, 
  granite, 
  

   granite 
  porphyry, 
  and 
  gabbro 
  — 
  except 
  the 
  diabase; 
  (3) 
  as 
  large 
  

   more 
  or 
  less 
  rounded 
  masses, 
  with 
  distinct 
  hornblende 
  rims, 
  in 
  the 
  

   long, 
  lenslike 
  inclusions 
  of 
  Grenville 
  hornblende 
  gneiss 
  in 
  syenite 
  

   or 
  granite 
  ; 
  and 
  (4) 
  as 
  more 
  or 
  less 
  distinct 
  crystals, 
  without 
  horn- 
  

   blende 
  rims, 
  in 
  a 
  certain 
  special 
  basic 
  syenitelike 
  or 
  acidic 
  diorite- 
  

   like 
  rock. 
  

  

  In 
  case 
  no. 
  1 
  (for 
  example 
  Sanders 
  Brothers 
  and 
  Parker 
  mines) 
  

   the 
  garnets 
  have, 
  in 
  the 
  usual 
  way, 
  crystallized 
  out 
  of 
  masses 
  of 
  

   sediments 
  under 
  conditions 
  of 
  thermal 
  and 
  dynamic 
  metamorphism. 
  

  

  In 
  case 
  no. 
  2 
  the 
  garnets 
  appear 
  mostly 
  to 
  have 
  crystallized 
  

   out 
  of 
  the 
  original 
  magmas, 
  their 
  presence 
  possibly 
  being 
  due 
  to 
  

   some 
  assimilation 
  of 
  Grenville 
  sediments, 
  though 
  this 
  is 
  by 
  no 
  

   means 
  proved. 
  Sometimes, 
  as 
  in 
  the 
  gabbros, 
  the 
  garnets 
  may 
  

   have 
  been 
  produced 
  secondarily 
  after 
  the 
  cooling 
  of 
  the 
  igneous 
  

   masses. 
  

  

  Case 
  no. 
  3 
  (for 
  example, 
  Oven 
  mountain, 
  Rexford, 
  and 
  Rogers 
  

   mines) 
  is 
  of 
  particular 
  interest 
  because 
  of 
  the 
  very 
  large 
  garnets 
  

   surrounded 
  by 
  reaction 
  rims. 
  Without 
  question 
  the 
  garnets 
  occur 
  

   in 
  lenses 
  of 
  Grenville 
  sediment 
  which 
  were 
  caught 
  up 
  or 
  included 
  

   in 
  the 
  great 
  igneous 
  masses 
  at 
  the 
  time 
  of 
  their 
  intrusion, 
  the 
  

   tremendous 
  heat 
  and 
  pressure 
  being 
  especially 
  favorable 
  for 
  a 
  

   very 
  complete 
  rearrangement 
  and 
  crystallization 
  of 
  the 
  masses 
  of 
  

   sediment 
  which 
  were 
  rather 
  low 
  in 
  silica. 
  The 
  hornblende 
  rims 
  

   or 
  envelops 
  are 
  quite 
  certainly 
  great 
  reaction 
  rims 
  around 
  the 
  gar- 
  

   nets, 
  but 
  just 
  at 
  what 
  stage 
  of 
  the 
  metamorphism 
  they 
  were 
  pro- 
  

   duced 
  is 
  not 
  at 
  all 
  clear 
  to 
  the 
  writer. 
  The 
  rounded 
  and 
  granulated 
  

   condition 
  of 
  the 
  garnets 
  suggest 
  that 
  the 
  reaction 
  rims 
  of 
  horn- 
  

   blende 
  may 
  have 
  formed 
  some 
  time 
  after 
  the 
  crystallization 
  of 
  the 
  

   garnets 
  and 
  possibly 
  at 
  the 
  time 
  when 
  the 
  great 
  pressure 
  producing 
  

   the 
  foliation 
  was 
  brought 
  to 
  bear. 
  

  

  A 
  clew 
  to 
  the 
  origin 
  of 
  the 
  garnets 
  in 
  case 
  no. 
  4 
  (for 
  example, 
  

   Hooper's 
  mine) 
  is 
  furnished 
  by 
  a 
  study 
  of 
  the 
  wall 
  rock 
  in 
  the 
  

   mine 
  on 
  Gore 
  mountain. 
  The 
  typical 
  garnet-bearing 
  rock 
  of 
  the 
  

   mine 
  passes 
  by 
  perfect 
  gradations 
  through 
  an 
  8 
  or 
  10 
  foot 
  zone 
  

  

  