﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  . 
  1 
  23 
  

  

  During 
  the 
  remainder 
  of 
  the 
  Paleozoic 
  we 
  know 
  but 
  little 
  concern- 
  

   ing 
  the 
  region 
  here, 
  except 
  by 
  comparison 
  with 
  other 
  regions 
  more 
  

   or 
  less 
  remote 
  from 
  it. 
  It 
  may 
  have 
  been 
  somewhat 
  submerged 
  dur- 
  

   ing 
  the 
  Siluric, 
  but 
  certainly, 
  for 
  most 
  of 
  the 
  time, 
  it 
  was 
  a 
  land 
  

   area, 
  and 
  the 
  small 
  amount 
  of 
  wear 
  which 
  it 
  experienced 
  indicates 
  

   that, 
  for 
  most 
  of 
  the 
  time, 
  its 
  altitude 
  was 
  low. 
  

  

  Amount 
  of 
  erosion 
  

  

  The 
  total 
  amount 
  of 
  rock 
  thickness 
  which 
  has 
  been 
  worn 
  away 
  

   since 
  the 
  region 
  became 
  a 
  land 
  area, 
  can 
  not 
  of 
  course 
  be 
  exactly 
  

   determined, 
  though 
  it 
  is 
  thought 
  that 
  it 
  can 
  be 
  approximated. 
  To 
  

   the 
  south 
  the 
  Trenton 
  limestone 
  is 
  overlaid 
  by 
  the 
  Utica 
  and 
  Lor- 
  

   raine 
  shales, 
  and 
  these 
  by 
  the 
  Oswego 
  sandstone 
  and 
  Medina 
  shale 
  

   and 
  sandstone. 
  These 
  are 
  all 
  sufficiently 
  near 
  to 
  make 
  it 
  in 
  high 
  

   degree 
  probable 
  that 
  they 
  were 
  laid 
  down 
  over 
  our 
  district, 
  espe- 
  

   cially 
  since 
  the 
  source 
  of 
  their 
  sediment 
  must 
  have 
  been 
  to 
  the 
  north 
  

   and 
  east. 
  It 
  is 
  regarded 
  as 
  unlikely 
  that 
  they 
  had 
  any 
  greater 
  thick- 
  

   ness 
  here 
  than 
  they 
  now 
  show 
  toward 
  the 
  south, 
  but 
  they 
  may 
  have 
  

   been 
  as 
  thick. 
  We 
  have 
  no 
  evidence 
  that 
  any 
  formations 
  later 
  than 
  

   the 
  Medina 
  were 
  ever 
  deposited 
  here, 
  and 
  even 
  if 
  so, 
  the 
  thickness 
  

   would 
  seem 
  to 
  have 
  been 
  small 
  and 
  the 
  submergence 
  brief. 
  If 
  

   therefore 
  we 
  allow 
  to 
  these 
  formations 
  the 
  full 
  thickness 
  which 
  they 
  

   show 
  to 
  the 
  south, 
  we 
  are 
  likely 
  exaggerating 
  their 
  thickness 
  here 
  

   and 
  allowing 
  a 
  margin 
  to 
  account 
  for 
  any 
  possible 
  later 
  formations 
  

   which 
  may 
  have 
  existed. 
  

  

  The 
  deep 
  wells 
  which 
  have 
  been 
  drilled 
  at 
  various 
  points 
  between 
  

   this 
  district 
  and 
  the 
  Syracuse 
  region, 
  give 
  the 
  data 
  desired. 
  In 
  the 
  

   Monroe 
  well 
  at 
  Baldwinsville 
  the 
  drill 
  went 
  through 
  1740 
  feet 
  of 
  

   sandstone 
  (Medina-Oswego) 
  and 
  shale 
  (Lorraine-Utica), 
  reaching 
  

   the 
  top 
  of 
  the 
  Trenton 
  at 
  2240 
  feet. 
  If 
  we 
  assume 
  them 
  to 
  have 
  

   been 
  deposited 
  over 
  our 
  district 
  in 
  the 
  same 
  thickness, 
  and 
  add 
  the 
  

   thickness 
  of 
  underlying 
  rock 
  (Potsdam-Trenton) 
  we 
  get 
  2600 
  feet 
  

   as 
  an 
  outside 
  measurement 
  of 
  the 
  Paleozoic 
  thickness 
  here 
  origi- 
  

   nally. 
  In 
  all 
  probability 
  this 
  is 
  considerably 
  too 
  high. 
  There 
  were 
  

   1200 
  feet 
  of 
  sandstone 
  and 
  500 
  feet 
  of 
  shale 
  above 
  the 
  Trenton 
  in 
  

   this 
  well, 
  and 
  the 
  full 
  thickness 
  of 
  both 
  was 
  passed 
  through 
  by 
  the 
  

   drill. 
  In 
  the 
  wells 
  further 
  north, 
  as 
  in 
  Orwell 
  and 
  Central 
  Square, 
  

   less 
  sandstone 
  appears 
  but 
  the 
  shales 
  thicken 
  to 
  700 
  feet. 
  Since 
  

   no 
  certainty 
  is 
  possible 
  our 
  purpose 
  is 
  best 
  subserved 
  by 
  a 
  generous 
  

   estimate, 
  and 
  an 
  original 
  thickness 
  of 
  3000 
  feet 
  of 
  Paleozoic 
  rocks 
  

   here 
  will 
  be 
  assumed. 
  Where 
  Precambric 
  rocks 
  are 
  now 
  at 
  the 
  

   surface, 
  3000 
  feet 
  is 
  regarded 
  as 
  the 
  outside 
  limit 
  of" 
  the 
  thickness 
  

  

  