﻿GEOLOGY 
  OF 
  THE 
  NORTH 
  CREEK 
  QUADRANGLE 
  1 
  3 
  

  

  Feldspar-biotite-garnet 
  gneisses 
  There 
  are 
  a 
  number 
  of 
  rather 
  

   distinct 
  fades 
  of 
  these 
  gneisses 
  which 
  show 
  all 
  sorts 
  of 
  gradations 
  

   from 
  one 
  to 
  another. 
  One 
  common 
  facies 
  is 
  a 
  fine 
  to 
  medium- 
  

   grained 
  gneiss 
  in 
  dark 
  gray 
  and 
  nearly 
  white 
  alternating 
  bands. 
  

   The 
  biotite 
  is 
  wholly 
  confined 
  to 
  the 
  dark 
  layers, 
  while 
  small 
  scat- 
  

   tering 
  garnets 
  appear 
  in 
  both. 
  Such 
  rock 
  is 
  common 
  in 
  the 
  gneiss 
  

   areas, 
  being 
  especially 
  abundant 
  on 
  the 
  mountain 
  side 
  east 
  and 
  

   south 
  of 
  Valentine 
  pond 
  and 
  northeast 
  of 
  Fuller 
  pond. 
  

  

  Another 
  facies 
  is 
  medium 
  to 
  coarse-grained 
  and 
  not 
  so 
  per- 
  

   fectly 
  banded. 
  It 
  is 
  best 
  shown 
  in 
  the 
  small 
  mountain 
  \]/ 
  2 
  miles 
  

   north 
  of 
  Valentine 
  pond. 
  

  

  A 
  third 
  facies 
  is 
  a 
  fine 
  to 
  rather 
  coarse-grained, 
  gray 
  to 
  dark 
  

   gray 
  rock, 
  clearly 
  gneissoid, 
  usually 
  banded 
  and 
  with 
  numerous 
  

   pink 
  to 
  amethyst 
  garnets 
  up 
  to 
  five 
  millimeters 
  across. 
  Such 
  rocks 
  

   are 
  very 
  common 
  in 
  the 
  Grenville 
  gneiss 
  areas 
  as, 
  for 
  example, 
  in 
  

   the 
  quarry 
  near 
  the 
  southeastern 
  end 
  of 
  Loon 
  lake 
  and 
  at 
  the 
  west- 
  

   ern 
  base 
  of 
  Prospect 
  mountain. 
  

  

  Hornblende-feldspar 
  gneiss. 
  The 
  most 
  common 
  facies 
  of 
  these 
  

   rocks 
  is 
  a 
  fine 
  to 
  medium-grained, 
  dark 
  gray 
  gneiss 
  almost 
  wholly 
  

   devoid 
  of 
  garnets. 
  It 
  is 
  very 
  gneissoid 
  and 
  amphibolite-like 
  but 
  

   not 
  at 
  all 
  banded. 
  It 
  is 
  closely 
  associated 
  with 
  limestone, 
  some- 
  

   times 
  with 
  thin 
  layers 
  of 
  that 
  rock 
  interbedded. 
  The 
  whole 
  ridge 
  

   extending 
  for 
  five 
  miles 
  southeastward 
  from 
  North 
  Creek 
  is 
  prac- 
  

   tically 
  made 
  up 
  of 
  this 
  rock. 
  

  

  Another 
  but 
  similar 
  looking 
  gneiss 
  contains 
  orthoclase, 
  plagi- 
  

   oclase, 
  hornblende, 
  and 
  hypersthene 
  together 
  with 
  small 
  amounts 
  

   of 
  magnetite 
  and 
  graphite. 
  This 
  is 
  a 
  much 
  more 
  locally 
  developed 
  

   gneiss 
  as, 
  for 
  example, 
  immediately 
  under 
  the 
  limestone 
  at 
  the 
  Nat- 
  

   ural 
  Bridge. 
  

  

  Feldspar-quartz 
  gneisses. 
  These 
  are 
  the 
  white 
  or 
  very 
  light 
  gray 
  

   gneisses 
  of 
  the 
  district. 
  Perhaps 
  the 
  most 
  typical 
  examples 
  are 
  

   found 
  in 
  excellent 
  exposures 
  along 
  the 
  road 
  near 
  the 
  quarry 
  at 
  

   the 
  southeastern 
  end 
  of 
  Loon 
  lake. 
  This 
  is 
  a 
  fine 
  to 
  medium 
  

   grained, 
  very 
  light 
  gray 
  gneiss 
  with 
  some 
  tiny 
  biotite 
  flakes 
  and 
  

   small 
  brown 
  garnets 
  scattered 
  through 
  the 
  mass. 
  A 
  slide 
  shows 
  

   about 
  80 
  per 
  cent 
  of 
  orthoclase, 
  microcline, 
  and 
  microperthite 
  in 
  

   nearly 
  equal 
  amounts; 
  13 
  per 
  cent 
  quartz 
  ; 
  together 
  with 
  small 
  

   amounts 
  of 
  plagioclase, 
  biotite 
  and 
  garnet. 
  This 
  light 
  gneiss 
  is 
  

   in 
  thin 
  to 
  thick 
  beds 
  and 
  repeatedly 
  interbedded 
  with 
  biotite-garnet 
  

   gneisses. 
  A 
  very 
  similar 
  light 
  gneiss, 
  but 
  with 
  graphite 
  flakes, 
  

   occurs 
  a 
  mile 
  farther 
  northward 
  along 
  the 
  same 
  road. 
  

  

  