﻿GEOLOGY 
  OF 
  THE 
  PORT 
  LEYDEN 
  QUADRANGLE 
  IQ 
  

  

  are 
  quartzose 
  and 
  garnetiferous 
  may 
  be 
  accounted 
  for 
  by 
  some 
  

   such 
  process. 
  

  

  Three 
  syenite-Grenville 
  areas 
  are 
  shown 
  on 
  the 
  map. 
  The 
  

   largest 
  of 
  these 
  extends 
  from 
  Denley 
  station 
  to 
  north 
  of 
  Greig, 
  

   a 
  distance 
  of 
  nearly 
  12 
  miles, 
  while 
  the 
  width 
  averages 
  some- 
  

   thing 
  like 
  3 
  miles. 
  In 
  the 
  southern 
  portion 
  of 
  this 
  area 
  the 
  

   Grenville 
  is 
  present 
  in 
  greater 
  force 
  than 
  the 
  syenitic 
  or 
  granitic 
  

   rocks, 
  while 
  in 
  the 
  northern 
  the 
  reverse 
  is 
  true 
  except 
  possibly 
  

   in 
  the 
  vicinity 
  of 
  Greig. 
  Within 
  this 
  area 
  there 
  seems 
  to 
  be 
  good 
  

   evidence 
  for 
  the 
  former 
  existence 
  of 
  very 
  ancient 
  Grenville 
  rock 
  

   belts 
  or 
  structure 
  lines 
  which 
  extended 
  in 
  a 
  northeast-southwest 
  

   direction. 
  Thus 
  pyroxene 
  gneisses 
  are 
  found 
  in 
  the 
  area 
  east 
  

   of 
  Fowlersville 
  ; 
  in 
  small 
  outcrops 
  i^ 
  miles 
  east 
  of 
  Port 
  Ley- 
  

   den; 
  and 
  ij/2 
  miles 
  north 
  of 
  Denley, 
  and 
  these 
  are 
  all 
  arranged 
  

   along 
  a 
  northeast-southwest 
  line. 
  A 
  belt 
  of 
  feldspar-garnet 
  

   gneisses 
  shows 
  a 
  similar 
  strike 
  and 
  extends 
  from 
  Lyonsdale 
  to 
  

   Port 
  Leyden. 
  Quartz-sillimanite 
  rocks 
  much 
  like 
  those 
  at 
  Kos- 
  

   terville 
  have 
  been 
  noted 
  in 
  small 
  exposures 
  from 
  3^ 
  to 
  ^ 
  of 
  a 
  

   mile 
  north 
  of 
  Port 
  Leyden 
  and 
  this 
  suggests 
  another 
  northeast- 
  

   southwest 
  belt. 
  A 
  less 
  well 
  defined 
  belt 
  is 
  garnetiferous 
  and 
  

   passes 
  through 
  Lyons 
  Falls. 
  Still 
  another 
  belt, 
  in 
  which 
  garnet- 
  

   sillimanite 
  gneisses 
  are 
  commonly 
  found, 
  passes 
  northeast 
  and 
  

   southwest 
  through 
  Greig. 
  It 
  seems 
  pretty 
  certain 
  that 
  before 
  

   the 
  intrusion 
  of 
  the 
  syenite, 
  these 
  Grenville 
  belts 
  were 
  continu- 
  

   ous 
  and 
  well 
  defined 
  and 
  that 
  as 
  a 
  result 
  of 
  the 
  intrusion 
  they 
  

   were 
  all 
  cut 
  up 
  leaving 
  only 
  here 
  and 
  there 
  masses 
  of 
  the 
  pure 
  

   Grenville. 
  

  

  Of 
  the 
  two 
  smaller 
  syenite-Grenville 
  areas, 
  one 
  lies 
  about 
  2 
  

   miles 
  north 
  of 
  Fowlersville 
  and 
  the 
  other 
  around 
  East 
  Martins- 
  

   burg. 
  These 
  rocks 
  are 
  quartzose 
  syenites 
  often 
  containing 
  gar- 
  

   nets 
  and 
  more 
  or 
  less 
  intermingled 
  with 
  Grenville. 
  

  

  The 
  great 
  variety 
  of 
  rock 
  types 
  making 
  up 
  this 
  complex 
  and 
  

   their 
  gradations 
  from 
  one 
  type 
  to 
  another 
  make 
  it 
  difficult 
  to 
  

   give 
  a 
  proper 
  idea 
  of 
  them 
  by 
  description. 
  Microscopic 
  study 
  

   of 
  numerous 
  thin 
  sections 
  shows 
  the 
  presence 
  of 
  all 
  the 
  minerals 
  

   of 
  both 
  the 
  Grenville 
  and 
  the 
  syenite 
  and 
  in 
  addition 
  to 
  them 
  

   microcline 
  which 
  often 
  occurs 
  as 
  a 
  prominent 
  feldspar. 
  The 
  fol- 
  

   lowing 
  brief 
  descriptions 
  include 
  most 
  of 
  the 
  leading 
  types 
  : 
  

  

  I 
  Syenitic 
  facies. 
  These 
  are 
  often 
  practically 
  indistinguish- 
  

   able 
  from 
  the 
  normal 
  syenite. 
  They 
  are 
  usually, 
  however, 
  pretty 
  

   fine 
  grained 
  and 
  under 
  the 
  microscope 
  nearly 
  always 
  show 
  a 
  

   highly 
  cataclastic 
  structure. 
  They 
  frequently 
  contain 
  microcline 
  

  

  