﻿GEOLOGY 
  OF 
  THE 
  NORTH 
  CREEK 
  QUADRANGLE 
  

  

  19 
  

  

  per 
  cent 
  of 
  quartz. 
  By 
  becoming 
  coarse-grained 
  and 
  porphyritic 
  

   it 
  also 
  passes 
  gradually 
  into 
  the 
  granite 
  porphyry. 
  As 
  in 
  the 
  case 
  

   of 
  the 
  syenite, 
  the 
  contact 
  against 
  the 
  Grenville 
  is 
  seldom 
  sharp 
  

   except 
  along 
  the 
  lines 
  of 
  faulting. 
  The 
  area 
  covered 
  by 
  the 
  granite 
  

   is 
  almost 
  the 
  same 
  as 
  that 
  of 
  the 
  syenite 
  or 
  about 
  two-ninths 
  of 
  

   the 
  quadrangle. 
  

  

  This 
  rock, 
  too, 
  is 
  decidedly 
  variable 
  as 
  regards 
  color, 
  granu- 
  

   larity, 
  structure 
  and 
  mineral 
  composition. 
  The 
  colors 
  range 
  

   through 
  greenish 
  gray, 
  light 
  gray, 
  and 
  pinkish 
  to 
  almost 
  red. 
  These 
  

   color 
  varieties 
  are 
  especially 
  well 
  shown 
  in 
  the 
  vicinity 
  of 
  The 
  

   Glen. 
  Pinkish 
  granites 
  are 
  the 
  most 
  abundant. 
  

  

  The 
  granularity 
  of 
  the 
  rocks 
  varies 
  from 
  fine 
  to 
  coarse 
  grain, 
  

   with 
  a 
  medium 
  grain 
  predominating. 
  Coarse-grained 
  types 
  often 
  

   show 
  a 
  tendency 
  toward 
  porphyritic 
  texture 
  and 
  thus 
  approach 
  the 
  

   granite 
  porphyry. 
  The 
  granites 
  are 
  almost 
  always 
  highly 
  granu- 
  

   lated, 
  especially 
  the 
  more 
  gneissoid 
  varieties 
  in 
  which 
  the 
  feldspars 
  

   are 
  most 
  badly 
  crushed. 
  There 
  is 
  a 
  wide 
  range 
  from 
  poorly 
  

   gneissoid 
  rocks 
  to 
  those 
  which 
  are 
  highly 
  foliated 
  and 
  almost 
  

   banded, 
  the 
  latter 
  being 
  particularly 
  true 
  of 
  the 
  commonly 
  occur- 
  

   ring 
  pink 
  granites. 
  

  

  The 
  range 
  in 
  mineral 
  composition 
  is 
  well 
  illustrated 
  by 
  the 
  se- 
  

   lected 
  examples 
  given 
  in 
  table 
  2. 
  As 
  compared 
  with 
  the 
  granitic 
  

   syenite, 
  the 
  chief 
  differences 
  are 
  the 
  high 
  quartz 
  content, 
  the 
  com- 
  

   mon 
  occurrence 
  of 
  microcline, 
  the 
  generally 
  lower 
  content 
  of 
  horn- 
  

   blende, 
  and 
  the 
  almost 
  constant 
  presence 
  of 
  biotite. 
  

  

  table 
  2 
  

   Granite 
  

  

  

  

  

  

  

  is 
  

  

  

  

  ■e 
  

  

  

  

  M 
  

  

  u 
  

  

  a 
  

   

  

  u 
  

  

  

  

  u 
  

  

  3 
  

  

  O 
  

   a 
  

  

  3 
  

   O 
  

  

  C 
  

   4) 
  

  

  c 
  

  

  O 
  

  

  

  

  S 
  

  

  '0 
  

   CS3 
  

  

  G 
  

  

  O 
  

  

  c 
  

   

  

  n 
  

   8P 
  

  

  3 
  

  

  < 
  

  

  

  

  

  

  

  01 
  

  

  

  

  

  

  

  

  

  

  T 
  

  

  21 
  

  

  22 
  

  

  22 
  

  

  

  7 
  

  

  26 
  

  

  20 
  

  

  2 
  

  

  

  

  little 
  

  

  1 
  

  

  

  

  

  

  

  

  01 
  

  

  

  

  

  

  

  

  

  

  2 
  

  

  35 
  

  

  7 
  

  

  30 
  

  

  18 
  

  

  3 
  

  

  28 
  

  

  8 
  

  

  1 
  

  

  1 
  

  

  2 
  

  

  3 
  

  

  L 
  

  

  4 
  

  

  1 
  

  

  1 
  

   4 
  

  

  3 
  

  

  18 
  

  

  17 
  

  

  50 
  

  

  

  

  30 
  

  

  

  2 
  

  

  

  

  little 
  

  

  1 
  

  

  

  

  01 
  -And 
  

  

  

  

  

  4 
  

  

  53 
  

  

  10 
  

  

  45 
  

  

  4 
  

  

  5 
  

   Ol-And 
  

  

  30 
  

  

  5 
  

  

  

  

  1 
  

  

  2 
  

  

  * 
  

  

  1 
  

   4 
  

  

  

  

  

  

  5 
  

  

  32 
  

  

  5 
  

  

  40 
  

  

  

  10 
  

   01 
  

  

  35 
  

  

  7 
  

  

  1 
  

  

  1 
  

   2 
  

  

  

  1 
  

  

  2 
  

  

  1 
  

  

  little 
  

  

  6 
  

  

  3i 
  

  

  10 
  

  

  18 
  

  

  M 
  

  

  10 
  

  

  1 
  

  

  35 
  

  

  6 
  

  

  2 
  

  

  ' 
  

  

  1 
  

  

  1 
  

   2 
  

  

  2 
  

  

  1 
  

   2 
  

  

  