﻿GEOLOGY 
  OF 
  THE 
  PORT 
  LEYDEN 
  QUADRANGLE 
  II 
  

  

  Specimen 
  to 
  be 
  made 
  up 
  as 
  follows: 
  quartz 
  75;^; 
  sillimanite 
  12^; 
  

   and 
  with 
  the 
  long 
  axes 
  of 
  the 
  glistening 
  needles 
  parallel 
  to 
  the 
  

   rock 
  bands; 
  enstatite 
  5;^; 
  magnetite 
  3^/, 
  and 
  changing 
  to 
  leucox- 
  

   ene; 
  pyrite 
  2;^; 
  garnet 
  2;/, 
  and 
  often 
  completely 
  enveloping 
  the 
  

   magnetite 
  ; 
  together 
  with 
  a 
  little 
  zircon 
  and 
  badly 
  decomposed 
  

   biotite. 
  Another 
  specimen 
  shows 
  from 
  85 
  to 
  90;^ 
  of 
  badly 
  cracked 
  

   quartz 
  ; 
  i 
  or 
  2;^ 
  each 
  of 
  hornblende, 
  pyrite 
  and 
  sillimanite 
  with 
  

   a 
  little 
  zircon 
  ; 
  while 
  the 
  rest 
  of 
  the 
  rock 
  is 
  made 
  up 
  of 
  gray, 
  

   uncrystallized, 
  yellow-stained, 
  decomposition 
  products 
  of 
  horn- 
  

   blende 
  and 
  biotite. 
  Certain 
  other 
  layers 
  are 
  slightly 
  feldspathic. 
  

   The 
  most 
  striking 
  features 
  in 
  the 
  composition 
  are 
  the 
  very 
  high 
  

   quartz 
  content, 
  the 
  almost 
  complete 
  absence 
  of 
  feldspar, 
  and 
  

   the 
  dearth 
  of 
  dark 
  colored 
  minerals. 
  The 
  rock 
  thus 
  appears 
  

   to 
  have 
  been 
  an 
  almost 
  pure 
  sandstone 
  Avhich 
  has 
  been 
  meta- 
  

   morphosed 
  to 
  a 
  quartzite. 
  The 
  rock 
  is 
  highly 
  cataclastic 
  and 
  

   that 
  the 
  mass 
  has 
  been 
  subjected 
  to 
  a 
  great 
  pressure 
  is 
  proved 
  

   by 
  the 
  local 
  folds 
  and 
  by 
  the 
  general 
  crushed 
  appearance 
  of 
  the 
  

   exposures 
  [see 
  pi. 
  i]. 
  In 
  the 
  field 
  the 
  rock 
  has 
  a 
  decidedly 
  sedi- 
  

   mentar}^ 
  look 
  and 
  we 
  have 
  here 
  a 
  fine 
  example 
  of 
  the 
  Grenville 
  

   which 
  does 
  not 
  appear 
  to 
  have 
  been 
  very 
  profoundly 
  changed 
  

   from 
  the 
  original 
  sediment. 
  Where 
  these 
  gneisses 
  grade 
  into 
  

   the 
  surrounding 
  mixed 
  gneisses 
  some 
  feldspar 
  and 
  a 
  larger 
  per- 
  

   centage 
  of 
  dark 
  colored 
  minerals 
  are 
  present. 
  

  

  The 
  Grenville 
  rocks 
  in 
  the 
  Lyonsdale 
  area 
  are 
  chiefly 
  feldspar- 
  

   garnet-mica 
  gneisses. 
  The 
  gneissic 
  structure 
  is 
  here 
  greatly 
  

   accentuated 
  by 
  the 
  alternation 
  of 
  light 
  and 
  very 
  dark 
  gray 
  layers 
  

   which 
  are 
  usually 
  from 
  a 
  few 
  inches 
  to 
  a 
  foot 
  or 
  more 
  in 
  thick- 
  

   ness. 
  A 
  thin 
  section 
  of 
  the 
  light 
  gneiss 
  shows 
  quartz 
  75^; 
  feld- 
  

   spar 
  15 
  to 
  18;/, 
  mostly 
  oligoclase 
  to 
  labradorite, 
  but 
  with 
  a 
  little 
  

   microperthite; 
  biotite 
  5;^, 
  and 
  garnet 
  2 
  or 
  3;^. 
  In 
  the 
  dark 
  

   gneisses 
  the 
  quartz 
  is 
  proportionately 
  less 
  prominent 
  while 
  the 
  

   biotite 
  may 
  run 
  as 
  high 
  as 
  35 
  or 
  40;^. 
  Both 
  the 
  light 
  and 
  dark 
  

   rocks 
  are 
  often 
  very 
  garnetiferous. 
  In 
  some 
  specimens 
  a 
  few 
  

   small 
  flakes 
  of 
  graphite 
  were 
  noted. 
  The 
  original 
  sediments 
  

   here 
  were 
  probably 
  somewhat 
  carbonaceous 
  shales 
  and 
  shah- 
  

   sandstones. 
  

  

  The 
  rock 
  bands 
  show^ 
  a 
  northward 
  dip 
  at 
  a 
  high 
  angle 
  and 
  a 
  

   strike 
  of 
  n. 
  40° 
  e. 
  On 
  the 
  north 
  side 
  the 
  exposures 
  are 
  not 
  good 
  

   but 
  the 
  Grenville 
  does 
  not 
  seem 
  to 
  be 
  sharply 
  separated 
  from 
  

   the 
  surrounding 
  rocks, 
  while 
  on 
  the 
  south 
  side, 
  along 
  Moose 
  

   river, 
  there 
  is 
  exhibited 
  a 
  very 
  sharp 
  contact 
  between 
  the 
  Gren- 
  

  

  