﻿GEOLOGY 
  OF 
  THE 
  PORT 
  LEYDEN 
  QUADRANGLE 
  I3 
  

  

  over 
  pretty 
  large 
  areas 
  and 
  it 
  is 
  clearly 
  the 
  most 
  homogeneous 
  

   rock 
  mass 
  among 
  the 
  Precambrics. 
  The 
  typical 
  rock 
  is 
  a 
  quartz- 
  

   hornblende 
  syenite 
  alwa3^s 
  showing 
  the 
  granitoid 
  texture. 
  The 
  

   quartz 
  content 
  varies 
  a 
  good 
  deal 
  but 
  apparently 
  without 
  other- 
  

   wise 
  affecting 
  the 
  rock. 
  The 
  dark 
  colored 
  minerals 
  are 
  always 
  

   very 
  subordinate 
  in 
  amount. 
  On 
  weathered 
  surfaces 
  the 
  color 
  

   of 
  the 
  rock 
  varies 
  from 
  a 
  light 
  brown 
  to 
  a 
  reddish 
  brown, 
  while 
  

   the 
  color 
  of 
  the 
  fresh 
  rock 
  varies 
  from 
  a 
  sort 
  of 
  greenish 
  gray 
  

   to 
  a 
  light 
  gray. 
  The 
  rock 
  is 
  nearly 
  always 
  medium 
  grained 
  

   although 
  somewhat 
  variable 
  in 
  this 
  respect. 
  In 
  the 
  field 
  the 
  

   rock 
  always 
  clearly 
  exhibits 
  a 
  gneissic 
  structure 
  which 
  usually 
  

   can 
  not 
  be 
  made 
  out 
  in 
  the 
  hand 
  specimen. 
  A 
  distinct 
  banding 
  

   is 
  seldom 
  shown 
  except 
  at 
  times 
  near 
  the 
  borders 
  where 
  the 
  

   syenite 
  grades 
  into 
  the 
  surrounding 
  rocks. 
  The 
  minerals 
  are 
  

   roughly 
  arranged 
  with 
  their 
  long 
  axes 
  parallel 
  to 
  the 
  strike 
  of 
  

   the 
  foliation 
  which 
  ranges 
  from 
  n. 
  30° 
  to^ 
  70° 
  e. 
  Such 
  an 
  

   arrangement 
  of 
  the 
  dark 
  colored 
  minerals 
  causes 
  the 
  foliation 
  

   to 
  be 
  more 
  evident, 
  but 
  they 
  appear 
  like 
  wavy 
  streaks 
  which 
  

   are 
  seldom 
  continuous 
  for 
  more 
  than 
  a 
  few 
  inches 
  or 
  a 
  foot. 
  

   The 
  homogeneity 
  of 
  this 
  syenite 
  and 
  its 
  lack 
  of 
  distinct 
  banding 
  

   serve 
  to 
  separate 
  it 
  from 
  the 
  other 
  Precambric 
  rocks 
  in 
  the 
  field. 
  

  

  The 
  only 
  noteworthy 
  departure 
  from 
  homogeneity 
  is 
  to 
  be 
  

   found 
  in 
  the 
  presence 
  of 
  occasional 
  small 
  dark 
  basic 
  patches 
  in 
  

   the 
  syenite. 
  These 
  (patches 
  nearly 
  always 
  show 
  abrupt 
  termi- 
  

   nations 
  and 
  to 
  all 
  appearances 
  they 
  are 
  true 
  inclusions. 
  They 
  

   are 
  rich 
  in 
  hornblende 
  and 
  biotite 
  and 
  are 
  invariably 
  arranged 
  

   with 
  their 
  long 
  axes 
  parallel 
  to 
  the 
  gneissic 
  bands 
  of 
  the 
  syenite. 
  

   Such 
  inclusions 
  may 
  be 
  seen 
  in 
  the 
  field 
  southeast 
  of 
  Denley; 
  

   near 
  where 
  Miller 
  brook 
  enters 
  the 
  quadrangle; 
  and 
  probably 
  

   best 
  in 
  the 
  large 
  exposures 
  southwest 
  of 
  Partridgeville. 
  Most 
  

   of 
  the 
  syenite 
  outcrops 
  are, 
  however, 
  entirely 
  free 
  from 
  such 
  

   inclusions. 
  

  

  A 
  number 
  of 
  syenite 
  areas 
  are 
  shown 
  on 
  the 
  accompanying 
  

   geologic 
  map. 
  Of 
  these 
  the 
  southernmost 
  one 
  extends 
  from 
  

   Denley 
  southeastward 
  to 
  Hawkinsville 
  and 
  represents 
  probably 
  

   the 
  purest 
  and 
  most 
  typical 
  syenite 
  of 
  the 
  region. 
  Fine 
  expos- 
  

   ures 
  occur 
  in 
  the 
  fields 
  southeast 
  of 
  Denley 
  and 
  in 
  the 
  vicinity 
  

   of 
  Hawkinsville. 
  A 
  large 
  area 
  extends 
  from 
  Miller 
  brook 
  north- 
  

   ward 
  to 
  Moose 
  river 
  with 
  good 
  outcrops 
  along 
  Fall 
  and 
  Miller 
  

   brooks; 
  at 
  Fowlersville 
  and 
  for 
  2 
  miles 
  southward; 
  and 
  just 
  

   east 
  of 
  Lyonsdale. 
  Another 
  large 
  area 
  occupies 
  the 
  northeastern 
  

  

  