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  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Drainage 
  changes, 
  aside 
  from 
  those 
  already 
  described 
  in 
  con- 
  

   nection 
  with 
  the 
  history 
  of 
  lakes, 
  are 
  also 
  numerous 
  in 
  New 
  York. 
  

   It 
  must 
  be 
  remembered 
  that, 
  with 
  few 
  exceptions 
  (for 
  example, 
  the 
  

   basins 
  of 
  Lakes 
  Ontario 
  and 
  Erie, 
  Niagara 
  river, 
  and 
  possibly 
  the 
  

   St 
  Lawrence 
  river), 
  the 
  major 
  drainage 
  lines 
  of 
  the 
  State 
  were 
  

   little 
  changed 
  during 
  the 
  Ice 
  age 
  because 
  the 
  principal 
  valleys 
  were 
  

   mostly 
  the 
  same 
  before 
  and 
  after 
  glaciation. 
  It 
  is 
  the 
  present 
  

   purpose 
  briefly 
  to 
  describe 
  only 
  some 
  of 
  the 
  most 
  important 
  and 
  

   best 
  known 
  cases 
  of 
  stream 
  changes 
  due 
  to 
  the 
  Ice 
  age. 
  1 
  

  

  From 
  the 
  standpoint 
  of 
  both 
  geography 
  and 
  human 
  history, 
  the 
  

   gorge 
  at 
  Little 
  Falls 
  is 
  the 
  most 
  important 
  in 
  New 
  York 
  State 
  (see 
  

   figure 
  7 
  and 
  plate 
  42 
  and 
  also 
  the 
  description 
  in 
  chapter 
  2). 
  Before 
  

   the 
  Ice 
  age 
  there 
  was 
  a 
  divide, 
  instead 
  of 
  the 
  gorge, 
  several 
  hun- 
  

   dred 
  feet 
  above 
  the 
  present 
  river 
  level, 
  which 
  consisted 
  of 
  hard 
  

   Little 
  Falls 
  dolomite. 
  The 
  prominence 
  of 
  this 
  rock 
  barrier 
  was 
  

   greatly 
  increased 
  by 
  the 
  tilting 
  of 
  the 
  strata 
  due 
  to 
  the 
  development 
  

   of 
  the 
  Little 
  Falls 
  fault. 
  The 
  Mohawk 
  river 
  flowed 
  eastward, 
  and 
  

   the 
  now 
  extinct 
  Rome 
  river 
  flowed 
  westward, 
  from 
  this 
  divide 
  (see 
  

   figure 
  36). 
  During 
  the 
  Ice 
  age 
  the 
  divide 
  was 
  somewhat 
  lowered 
  

  

  Fig. 
  36 
  Sketch 
  map 
  of 
  central 
  New 
  York, 
  showing 
  the 
  relation 
  of 
  pre- 
  

   glacial 
  to 
  postglacial 
  drainage. 
  Preglacial 
  streams 
  shown 
  by 
  dotted 
  lines 
  only 
  

   where 
  essentially 
  different 
  from 
  existing 
  streams. 
  

  

  Based 
  upon 
  wo. 
  k 
  of 
  A. 
  P. 
  Brigham 
  

  

  : 
  A11 
  the 
  drainage 
  changes 
  now 
  to 
  be 
  described 
  will 
  be 
  much 
  better 
  under- 
  

   stood 
  by 
  consulting 
  the 
  large 
  government 
  topographic 
  maps 
  of 
  the 
  regions 
  

   considered. 
  

  

  