﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  I9 
  

  

  an 
  abundant 
  marine 
  fauna, 
  the 
  large 
  cephalopods 
  being 
  especially 
  

   conspicuous. 
  

  

  The 
  Watertown 
  limestone 
  is 
  unconformably 
  overlain 
  by 
  the 
  thin 
  

   bedded 
  limestones 
  of 
  the 
  Trenton. 
  The 
  time 
  interval 
  between 
  the 
  

   Lowville 
  and 
  the 
  Trenton 
  was 
  a 
  considerable 
  one, 
  but 
  the 
  surface 
  

   exposures 
  of 
  these 
  rocks 
  in 
  New 
  York 
  are 
  so 
  near 
  the 
  old 
  shore 
  

   lines 
  of 
  the 
  time, 
  that 
  the 
  deposits 
  exposed 
  represent 
  the 
  interval 
  

   very 
  imperfectly. 
  The 
  shore 
  line 
  was 
  one 
  of 
  many 
  and 
  frequent 
  

   local 
  o'scillations, 
  and 
  the 
  rocks 
  which 
  have, 
  of 
  late 
  years, 
  been 
  

   classified 
  as 
  Black 
  River 
  limestone, 
  represent 
  very 
  different 
  parts 
  

   of 
  this 
  general 
  interval. 
  

  

  The 
  Trenton 
  limestone 
  is 
  abundantly 
  fossiliferous 
  and 
  has 
  a 
  thick- 
  

   ness 
  of 
  400 
  feet 
  or 
  more 
  in 
  the 
  immediate 
  region, 
  exceeding 
  the 
  

   combined 
  thickness 
  of 
  the 
  Potsdam, 
  Theresa, 
  Pamelia, 
  Lowville 
  and 
  

   Black 
  River 
  together. 
  Found 
  on 
  all 
  sides 
  of 
  the 
  Adirondacks, 
  and 
  

   with 
  large 
  thickness 
  everywhere, 
  the 
  Mohawk 
  valley 
  excepted, 
  large 
  

   subsidence 
  is 
  shown, 
  with 
  probable 
  great 
  .encroachment 
  of 
  the 
  

   waters 
  upon 
  the 
  Adirondack 
  island, 
  much 
  diminishing 
  its 
  size. 
  

  

  As 
  Trenton 
  time 
  drew 
  to 
  a 
  close 
  fine 
  muds 
  commenced 
  to 
  appear 
  

   in 
  the 
  waters, 
  brought 
  in 
  by 
  currents 
  from 
  the 
  northeast, 
  and 
  in 
  

   slowly 
  increasing 
  amount. 
  Hence 
  the 
  limestones 
  become 
  impure 
  

   and 
  grade 
  upward 
  into 
  black 
  shales, 
  at 
  first 
  strongly 
  calcareous, 
  

   later 
  on 
  lacking 
  lime. 
  This 
  change 
  cSme 
  on 
  the 
  region 
  from 
  the 
  

   eastward, 
  hence 
  shales 
  were 
  forming 
  there 
  while 
  limestone 
  was 
  

   still 
  being 
  deposited 
  on 
  the 
  west. 
  Bu' 
  the 
  change 
  to 
  mud 
  deposit 
  

   spread 
  slowly 
  over 
  the 
  whole 
  region 
  and 
  the 
  Trenton 
  is 
  found 
  

   everywhere 
  to 
  be 
  overlaid 
  by 
  the 
  black 
  Utica 
  shales. 
  This 
  Utica 
  

   submergence 
  seems 
  to 
  have 
  been 
  the 
  most 
  extensive 
  in 
  the 
  State's 
  

   geologic 
  past, 
  and 
  it 
  is 
  quite 
  possible 
  that 
  the 
  entire 
  Adirondack 
  

   island 
  was 
  submerged. 
  If 
  so 
  it 
  seems 
  to 
  have 
  been 
  the 
  last 
  time 
  

   that 
  such 
  was 
  the 
  case, 
  as 
  it 
  was 
  the 
  first. 
  

  

  Above 
  the 
  Utica 
  lie 
  the 
  lighter 
  colored 
  shales 
  and 
  shaly 
  sand- 
  

   stones 
  of 
  the 
  Lorraine 
  formation, 
  the 
  combined 
  thickness 
  of 
  the 
  two 
  

   shale 
  series 
  being 
  several 
  hundred 
  feet. 
  While 
  neither 
  formation 
  

   is 
  found 
  within 
  the 
  limits 
  of 
  the 
  area 
  mapped, 
  in 
  which 
  the 
  lower 
  

   Trenton 
  is 
  the 
  youngest 
  rock 
  found, 
  yet 
  they 
  outcrop 
  in 
  great 
  thick- 
  

   ness 
  on 
  the 
  Watertown 
  quadrangle 
  and 
  reach 
  to 
  within 
  6 
  miles 
  of 
  

   the 
  south 
  margin 
  of 
  the 
  Theresa 
  sheet, 
  and 
  it 
  seems 
  quite 
  certain 
  

   that 
  they 
  were 
  originally 
  deposited 
  over 
  part, 
  and 
  likely 
  all, 
  of 
  the 
  

   district 
  mapped, 
  and 
  are 
  now 
  absent 
  from 
  it 
  because 
  of 
  subsequent 
  

   erosion. 
  It 
  is 
  even 
  probable 
  that 
  the 
  Oswego 
  and 
  Medina 
  sand- 
  

   stones, 
  thick 
  sand 
  formations 
  which 
  overlie 
  the 
  Lorraine 
  shales. 
  

  

  