﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  21 
  

  

  over 
  3000 
  feet 
  of 
  rock 
  thickness 
  has 
  been 
  removed, 
  and 
  Hkely 
  con- 
  

   siderably 
  less. 
  Since 
  the 
  overlying 
  rock 
  has 
  been 
  worn 
  away 
  down 
  

   to 
  the 
  Precambric 
  over 
  only 
  a 
  small 
  portion 
  of 
  the 
  whole 
  district, 
  

   it 
  follows 
  that 
  in 
  the 
  remainder 
  the 
  erosion 
  has 
  been 
  less 
  than 
  the 
  

   above 
  amount 
  by 
  the 
  remaining 
  thickness 
  of 
  such 
  overlying 
  rock. 
  

   The 
  character 
  of 
  the 
  district 
  to 
  the 
  south 
  of 
  the 
  map 
  limits 
  however 
  

   indicates 
  an 
  uplift 
  of 
  the 
  land 
  of 
  comparative 
  recency 
  to 
  the 
  amount 
  

   of 
  several 
  hundreds 
  of 
  feet, 
  and 
  the 
  present-day 
  stream 
  valleys 
  

   of 
  the 
  region 
  have 
  been 
  worn 
  down 
  below 
  this 
  old 
  level 
  in 
  this 
  

   comparatively 
  recent 
  period. 
  This 
  relatively 
  considerable 
  recent 
  

   elevation 
  and 
  erosion 
  makes 
  still 
  more 
  emphatic 
  the 
  necessity 
  for 
  

   assuming 
  slight 
  elevation 
  of 
  the 
  region 
  during 
  the 
  much 
  longer 
  in- 
  

   terval 
  which 
  preceded 
  it. 
  As 
  compared 
  with 
  much 
  of 
  the 
  district 
  

   surrounding 
  it 
  this 
  area 
  has 
  been 
  one 
  of 
  but 
  slight 
  changes 
  of 
  level 
  

   during 
  its 
  past 
  history. 
  While 
  in 
  their 
  early 
  history 
  these 
  surround- 
  

   ing 
  districts 
  were 
  submerged 
  and 
  subsiding, 
  allowing 
  thick 
  accumu- 
  

   lations 
  of 
  deposits, 
  this 
  area 
  subsided 
  less 
  and 
  received 
  but 
  scanty 
  

   deposit. 
  Only 
  during 
  middle 
  and 
  late 
  Lower 
  Siluric 
  time, 
  during 
  

   Lowville, 
  Trenton, 
  Utica 
  and 
  Lorraine 
  deposition, 
  was 
  it 
  a 
  dis- 
  

   trict 
  of 
  considerable 
  subsidence 
  and 
  deposit. 
  Li 
  its 
  subsequent 
  

   history 
  as 
  a 
  land 
  area 
  it 
  seems 
  to 
  have 
  been 
  one 
  of 
  but 
  small 
  

   uplift 
  as 
  compared 
  with 
  much 
  of 
  the 
  adjacent 
  region. 
  

  

  As 
  has 
  been 
  stated, 
  in 
  the 
  comparatively 
  recent 
  past 
  the 
  district 
  

   experienced 
  uplift 
  to 
  the 
  amount 
  of 
  several 
  hundred 
  feet. 
  Prior 
  

   to 
  this 
  it 
  had 
  been 
  worn 
  down 
  to 
  a 
  surface 
  of 
  comparatively 
  slight 
  

   relief. 
  The 
  uplift 
  gave 
  the 
  streams 
  power 
  to 
  deepen 
  their 
  valleys 
  

   by 
  an 
  equivalent 
  amount, 
  and 
  the 
  processes 
  of 
  wear 
  which 
  have 
  

   given 
  the 
  present 
  relief 
  to 
  the 
  region 
  were 
  set 
  in 
  motion. 
  Then, 
  

   as 
  now, 
  the 
  Black 
  river 
  was 
  the 
  chief 
  stream 
  of 
  the 
  neighborhood, 
  

   and 
  perhaps 
  turned 
  west 
  into 
  the 
  Ontario 
  lowland 
  as 
  it 
  now 
  does 
  ; 
  

   but 
  the 
  lake 
  was 
  not 
  in 
  existence 
  then, 
  nor 
  was 
  the 
  drainage 
  of 
  the 
  

   lowland 
  to 
  the 
  eastward, 
  but 
  the 
  Black 
  river 
  flowed 
  through 
  it 
  in 
  a 
  

   westerly 
  direction, 
  receiving 
  many 
  tributaries 
  from 
  the 
  north 
  and 
  

   the 
  south. 
  There 
  were 
  also 
  easterly 
  flowing 
  waters 
  in 
  the 
  district, 
  

   however, 
  the 
  beginnings 
  of 
  streams 
  which 
  drained 
  down 
  the 
  St 
  

   Lawrence 
  valley. 
  But 
  the 
  St 
  Lawrence 
  of 
  the 
  time 
  had 
  its 
  sources 
  

   in 
  the 
  immediate 
  region, 
  and 
  contained 
  no 
  waters 
  coming 
  from 
  

   farther 
  west, 
  the 
  divide 
  between 
  the 
  easterly 
  and 
  westerly 
  flowing 
  

   waters 
  being 
  here, 
  crossing 
  the 
  present 
  St 
  Lawrence 
  in 
  the 
  Thou- 
  

   sand 
  Island 
  region 
  on 
  the 
  hard 
  rock 
  barrier 
  which 
  the 
  Precam- 
  

   bric 
  rocks 
  furnish. 
  On 
  the 
  New 
  York 
  side 
  the 
  divide 
  can 
  be 
  traced 
  

   across 
  the 
  Clayton, 
  Alexandria 
  and 
  Theresa 
  quadrangles 
  in 
  a 
  south- 
  

  

  