﻿GEOLOGY 
  OF 
  THE 
  PORT 
  LEYDEN 
  QUADRANGLE 
  9 
  

  

  liver, 
  one 
  branch 
  of 
  Avhich 
  drains 
  the 
  Fulton 
  chain 
  of 
  lakes. 
  

   Chief 
  among 
  the 
  tributaries 
  from 
  the 
  west 
  are 
  Sugar 
  river. 
  Mill 
  

   creek, 
  House 
  creek, 
  Whetstone 
  creek 
  and 
  Roaring 
  brook. 
  All 
  

   the 
  larger 
  streams 
  which 
  have 
  cut 
  across 
  the 
  steep 
  eastern 
  

   front 
  of 
  Tug 
  hill 
  have 
  there 
  cut 
  out 
  deep 
  narrow 
  gorges 
  locally 
  

   called 
  '* 
  gulfs." 
  More 
  special 
  physiographic 
  features 
  will 
  be 
  

   described 
  later. 
  

  

  PRECAMBRIC 
  ROCKS 
  

  

  The 
  Precambric 
  rocks 
  of 
  the 
  quadrangle 
  represent 
  a 
  portion 
  

   of 
  the 
  great 
  Adirondack 
  crystalline 
  mass 
  along 
  its 
  extreme 
  west- 
  

   ern 
  border. 
  They 
  occupy 
  the 
  eastern 
  side 
  of 
  the 
  quadrangle 
  and 
  

   make 
  up 
  a 
  little 
  less 
  than 
  one 
  half 
  its 
  area. 
  Except 
  at 
  the 
  

   extreme 
  south 
  the 
  Paleozoic-Precambric 
  boundary 
  line 
  is 
  every- 
  

   where 
  to 
  the 
  west 
  of 
  Black 
  river, 
  but 
  it 
  keeps 
  close 
  to 
  the 
  river 
  

   bottom. 
  These 
  crystalline 
  rocks 
  continue 
  westward, 
  under 
  

   cover 
  of 
  the 
  Paleozoics, 
  for 
  many 
  miles. 
  Considerable 
  portions 
  

   of 
  the 
  Precambric 
  area 
  are 
  so 
  deeply 
  buried 
  under 
  glacial 
  drift 
  

   deposits 
  that 
  it 
  is 
  impossible 
  to 
  gain 
  even 
  the 
  slightest 
  clue 
  as 
  

   to 
  the 
  character 
  of 
  the 
  rocks 
  in 
  those 
  places. 
  

  

  Grenville 
  gneiss 
  

  

  The 
  Grenville 
  formation 
  takes 
  its 
  name 
  from 
  Grenville, 
  

   Canada. 
  It 
  comprises 
  a 
  series 
  of 
  gneisses 
  representing 
  very 
  

   ancient 
  sedimentary 
  rocks 
  which 
  have 
  been 
  so 
  profoundly 
  meta- 
  

   morphosed 
  that 
  the 
  original 
  sedimentary 
  features 
  have 
  been 
  

   largely 
  obliterated. 
  So 
  far 
  as 
  can 
  be 
  definitely 
  proved 
  they 
  are 
  

   the 
  oldest 
  exposed 
  rocks 
  in 
  the 
  whole 
  Adirondack 
  region. 
  That 
  

   they 
  are 
  not 
  actually 
  the 
  oldest 
  rocks 
  is 
  evident 
  from 
  the 
  fact 
  

   that 
  these 
  sediments 
  must 
  have 
  been 
  deposited 
  upon 
  a 
  still 
  older 
  

   floor. 
  This 
  very 
  ancient 
  rock 
  floor, 
  which 
  may 
  or 
  may 
  not 
  

   represent 
  a 
  portion 
  of 
  the 
  earth's 
  primitive 
  crust, 
  has 
  thus 
  far 
  

   not 
  been 
  proved 
  to 
  exist 
  in 
  the 
  present 
  exposures 
  of 
  the 
  Adiron- 
  

   dacks. 
  It 
  is 
  barely 
  possible 
  that 
  some 
  of 
  the 
  gneisses 
  still 
  of 
  

   doubtful 
  age 
  and 
  origin 
  may 
  represent 
  that 
  ancient 
  sea-floor. 
  

  

  Within 
  the 
  map 
  limits 
  the 
  Grenville 
  has 
  been 
  mapped 
  in 
  only 
  

   three 
  small 
  areas, 
  one 
  at 
  Kosterville. 
  another 
  at 
  Lyonsdale, 
  and 
  

   a 
  third 
  to 
  the 
  east 
  of 
  Fowlersville. 
  Grenville 
  rocks 
  are 
  unques- 
  

   tionably 
  present 
  in 
  much 
  greater 
  force 
  than 
  these 
  small 
  areas 
  

   seem 
  to 
  indicate 
  but 
  they 
  are 
  aUvays 
  so 
  thoroughly 
  involved 
  

   with 
  other 
  gneisses 
  that 
  they 
  can 
  not 
  be 
  represented 
  on 
  the 
  geo- 
  

  

  