﻿THE 
  GEOLOGICAL 
  HISTORY 
  OF 
  NEW 
  YORK 
  STATE 
  

  

  97 
  

  

  lake 
  basins 
  were 
  appreciably 
  deepened. 
  Even 
  so, 
  however, 
  we 
  have 
  

   not 
  yet 
  accounted 
  for 
  the 
  present 
  closed 
  basins. 
  In 
  the 
  writer's 
  

   opinion 
  the 
  two 
  most 
  important 
  phenomena 
  which 
  have 
  contributed 
  

   to 
  the 
  formation 
  of 
  the 
  closed 
  basins 
  of 
  the 
  Great 
  Lakes 
  are 
  the 
  

   great 
  drift 
  accumulations 
  along 
  the 
  south 
  side 
  and 
  the 
  tilting 
  of 
  

   the 
  land 
  downward 
  on 
  the 
  north 
  side 
  of 
  this 
  region. 
  The 
  deep 
  

   drift 
  deposits 
  must 
  certainly 
  have 
  been 
  very 
  effective 
  in 
  damming 
  

   up 
  the 
  south 
  or 
  southwesterly-flowing 
  preglacial 
  streams 
  of 
  the 
  

   region. 
  For 
  example, 
  the 
  deep 
  channel 
  of 
  the 
  so-called 
  Dundas 
  

  

  <-.---^-^«i^-- 
  x. 
  

  

  Fig. 
  30 
  The 
  first 
  stage 
  in 
  the 
  formation 
  of 
  the 
  Great 
  Lakes, 
  

   when 
  most 
  of 
  the 
  region 
  was 
  still 
  buried 
  under 
  the 
  ice. 
  

  

  After 
  Taylor 
  & 
  Leverett 
  

  

  river 
  (see 
  figure 
  27) 
  has 
  been 
  drift-filled 
  as 
  proved 
  by 
  many 
  well 
  

   borings, 
  and 
  a 
  distinct 
  moraine 
  extends 
  around 
  the 
  southern 
  half 
  

   of 
  Lake 
  Michigan. 
  The 
  great 
  clumping 
  ground 
  of 
  ice-transported 
  

   materials 
  from 
  the 
  north 
  was 
  in 
  general 
  along 
  the 
  southern 
  side 
  of 
  

   the 
  Great 
  Lakes 
  and 
  southward. 
  Late 
  in 
  the 
  Ice 
  age 
  the 
  land 
  on 
  

   the 
  northern 
  side 
  of 
  the 
  Great 
  Lakes 
  region 
  was 
  lower 
  than 
  it 
  is 
  

   today 
  as 
  proved 
  by 
  the 
  tilted 
  character 
  of 
  certain 
  well-known 
  

   beaches 
  of 
  extinct 
  glacial 
  lakes 
  (see 
  below). 
  Such 
  a 
  differential 
  

   tilting 
  or 
  warping 
  of 
  the 
  land 
  must 
  have 
  helped 
  to 
  form 
  the 
  closed 
  

   basins 
  by 
  tending 
  to 
  stop 
  the 
  southward 
  or 
  southwestward 
  drainage 
  

  

  