﻿GEOLOGY 
  OF 
  THOUSAND 
  ISLANDS 
  REGION 
  I4I 
  

  

  Physiography 
  

  

  Glacial 
  diversion 
  of 
  the 
  Black 
  river. 
  The 
  history 
  of 
  the 
  Black 
  

   river 
  is 
  not 
  only 
  the 
  most 
  interesting 
  problem 
  connected 
  with 
  the 
  

   evolution 
  of 
  the 
  physiography 
  of 
  the 
  region 
  but 
  specially 
  important 
  

   as 
  it 
  may 
  supply 
  the 
  key 
  to 
  Tertiary 
  drainage 
  of 
  the 
  entire 
  area. 
  

  

  In 
  only 
  the 
  middle 
  portion 
  of 
  its 
  course 
  has 
  the 
  present 
  Black 
  

   river 
  any 
  pronounced 
  valley. 
  The 
  headwaters 
  and 
  upper 
  section, 
  

   about 
  30 
  miles 
  long, 
  lie 
  on 
  the 
  crystahines 
  of 
  the 
  southwest 
  slope 
  

   of 
  the 
  Adirondacks, 
  with 
  no 
  conspicuous 
  valley. 
  The 
  lower 
  section, 
  

   below 
  Carthage, 
  has 
  only 
  a 
  shallow 
  postglacial 
  channel. 
  The 
  great 
  

   valley 
  begins 
  at 
  about 
  Forestport 
  and 
  extends 
  northwest 
  to 
  Car- 
  

   thage, 
  a 
  distance 
  of 
  more 
  than 
  40 
  miles, 
  and 
  steadily 
  deepens 
  and 
  

   widens 
  northward. 
  At 
  Glenfield 
  or 
  Lowville, 
  near 
  the 
  middle 
  part 
  

   of 
  the 
  valley, 
  the 
  altitude 
  of 
  the 
  river 
  is 
  740 
  feet, 
  while 
  the 
  great 
  

   ridge 
  on 
  the 
  west, 
  separating 
  this 
  valley 
  from 
  the 
  Ontario, 
  rises 
  to 
  

   2000 
  feet, 
  and 
  the 
  breadth 
  of 
  the 
  valley 
  is 
  at 
  least 
  10 
  miles 
  on 
  

   the 
  1300 
  foot 
  contour. 
  

  

  Former 
  writers 
  have 
  regarded 
  the 
  Black 
  river 
  as 
  the 
  trunk 
  stream 
  

   of 
  the 
  early 
  drainage 
  which 
  headed 
  the 
  Ontario 
  valley.^ 
  It 
  appears 
  

   to 
  the 
  writer 
  that 
  that 
  view 
  is 
  a 
  mistake 
  and 
  that 
  quite 
  the 
  oppo- 
  

   site 
  is 
  the 
  fact, 
  that 
  the 
  Black 
  river 
  w^as 
  the 
  headwater 
  of 
  the 
  St 
  

   Lawrence 
  drainage, 
  at 
  least 
  for 
  New 
  York 
  State. 
  

  

  Plate 
  43 
  shows 
  the 
  present 
  hydrography 
  of 
  the 
  region 
  and 
  the 
  

   divide 
  between 
  northward 
  and 
  southward 
  streams 
  of 
  the 
  Ontario- 
  

   St 
  Lawrence 
  valley. 
  Plates 
  44 
  and 
  47 
  show 
  portions 
  of 
  the 
  divide 
  

   on 
  the 
  larger 
  scale 
  of 
  the 
  topographic 
  sheets. 
  On 
  plate 
  43 
  the 
  

   heavy, 
  broken 
  line 
  south 
  of 
  the 
  Black 
  river 
  marks 
  what 
  was 
  the 
  pre- 
  

   glacial 
  divide 
  between 
  Ontario 
  and 
  St 
  Lawrence 
  drainage 
  before 
  

   the 
  Black 
  river 
  was 
  forced 
  by 
  the 
  interference 
  of 
  the 
  ice 
  sheet 
  across 
  

   the 
  divide. 
  The 
  light, 
  continuous 
  line 
  indicates 
  the 
  present 
  and 
  

   shifted 
  divide. 
  It 
  is 
  apparent 
  that 
  below 
  Great 
  Bend 
  the 
  river 
  has 
  

   peculiar 
  and 
  anomalous 
  relationship, 
  and 
  that 
  the 
  divide 
  leading 
  

   east 
  up 
  the 
  Adirondacks 
  slope 
  is 
  newly 
  established. 
  

  

  In 
  discussion 
  of 
  this 
  problem 
  the 
  theoretic 
  evolution 
  of 
  the 
  drain- 
  

   age 
  will 
  be 
  considered 
  first 
  and 
  then 
  the 
  recent 
  history 
  and 
  the 
  

   present 
  features. 
  

  

  The 
  Black 
  valley 
  was 
  initiated 
  and 
  developed, 
  at 
  least 
  as 
  early 
  

   as 
  the 
  Tertiary 
  uplift, 
  along 
  the 
  contact 
  or 
  overlap 
  of 
  the 
  Ordovicic 
  

   sedimentaries 
  on 
  the 
  ancient 
  crystallines. 
  The 
  west 
  wall 
  of 
  the 
  

  

  1 
  Specially 
  the 
  paper 
  by 
  A. 
  W. 
  G. 
  Wilson, 
  Trent 
  River 
  Sj^stem 
  and 
  the 
  

   St 
  Lawrence 
  Outlet. 
  Geol. 
  Soc. 
  Am. 
  Bui. 
  15:211-42. 
  Pages 
  236-38 
  refer 
  

   to 
  our 
  district. 
  With 
  the 
  entire 
  article 
  excepting 
  the 
  point 
  of 
  the 
  Black 
  

   river 
  relationship 
  we 
  are 
  in 
  hearty 
  accord. 
  

  

  