﻿20 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  zX 
  1200 
  feet, 
  has 
  a 
  little 
  swash 
  channel 
  across 
  it, 
  but 
  was 
  never 
  cut 
  

   by 
  a 
  river. 
  The 
  failure 
  of 
  flow 
  across 
  this 
  col 
  seems 
  to 
  be 
  due 
  to 
  

   the 
  Hudson 
  ice 
  flow 
  blockading 
  the 
  Catskill 
  valley. 
  

  

  When 
  the 
  ice 
  front 
  receded 
  on 
  the 
  Helderberg 
  scarp 
  the 
  Mohawk 
  

   lake 
  (including 
  the 
  Schoharie 
  waters) 
  found 
  escape 
  to 
  the 
  Hudson 
  

   valley. 
  The 
  face 
  of 
  the 
  Helderberg 
  is 
  strongly 
  terraced 
  by 
  cen- 
  

   turies 
  of 
  river 
  work. 
  This 
  channeling 
  continues 
  southward 
  along 
  

   the 
  west 
  side 
  of 
  the 
  Hudson 
  valley 
  where 
  the 
  rivers 
  flowed 
  along- 
  

   side 
  the 
  ice 
  tongue. 
  

  

  The 
  lowest 
  pass 
  of 
  this 
  episode 
  lies 
  between 
  Esperance 
  and 
  

   Delanson 
  at 
  840 
  feet, 
  now 
  utilized 
  by 
  the 
  Delaware 
  and 
  Hudson 
  

   Railroad. 
  This 
  outlet 
  correlates 
  with 
  numerous 
  delta 
  plains 
  in 
  the 
  

   Mohawk 
  valley, 
  striking 
  examples 
  of 
  which 
  may 
  be 
  seen 
  about 
  

   Prospect 
  and 
  Trenton 
  Falls, 
  at 
  iioo 
  to 
  900 
  feet. 
  

  

  The 
  Delanson 
  outlet 
  was 
  abandoned 
  when 
  the 
  ice 
  front 
  weakened 
  

   on 
  the 
  rock 
  scarp 
  west 
  of 
  Schenectady 
  and 
  at 
  Rotterdam 
  Junction. 
  

   The 
  blockade 
  at 
  this 
  stage 
  correlates 
  with 
  many 
  plains 
  in 
  the 
  upper 
  

   Mohawk 
  valley 
  and 
  with 
  broad 
  plains 
  in 
  the 
  Sacandaga 
  valley, 
  

   already 
  noted 
  by 
  Brigham. 
  These 
  have 
  altitudes 
  of 
  900 
  down 
  to 
  

   700 
  feet. 
  

  

  The 
  low 
  altitude 
  of 
  the 
  glacial 
  waters 
  in 
  the 
  upper 
  Mohawk 
  

   region 
  forces 
  us 
  to 
  the 
  conclusion 
  that 
  the 
  rock 
  barrier 
  at 
  Little 
  

   Falls 
  must 
  have 
  been 
  removed 
  early 
  in 
  the 
  history 
  of 
  the 
  Postwis- 
  

   consin 
  drainage 
  through 
  the 
  Mohawk 
  valley, 
  and 
  long 
  before 
  it 
  

   received 
  the 
  flood 
  from 
  the 
  area 
  of 
  the 
  Great 
  Lakes. 
  It 
  appears 
  to 
  

   he 
  more 
  likely 
  that 
  the 
  pass 
  was 
  chiefly 
  cut 
  by 
  Prewisconsin 
  

   drainage. 
  

  

  By 
  the 
  study 
  of 
  the 
  several 
  points 
  of 
  outflow 
  of 
  the 
  glacial 
  waters 
  

   as 
  indicated 
  above, 
  in 
  comparison 
  with 
  their 
  correlating 
  sand 
  

   plains 
  reaching 
  west 
  to 
  beyond 
  Rome, 
  it 
  becomes 
  possible 
  to 
  deter- 
  

   mine 
  with 
  some 
  degree 
  of 
  exactness 
  the 
  limits 
  of 
  the 
  two 
  ice 
  lobes 
  

   (Ontario 
  and 
  Hudson) 
  at 
  certain 
  critical 
  stages 
  of 
  their 
  waning. 
  

   A 
  series 
  of 
  large 
  maps 
  has 
  been 
  prepared 
  to 
  show 
  in 
  a 
  general 
  

   way 
  the 
  recession 
  of 
  the 
  ice 
  sheet 
  over 
  New 
  York. 
  

  

  Industrial 
  geology 
  

   Iron 
  ores. 
  The 
  investigation 
  of 
  the 
  State's 
  iron 
  ore 
  fields 
  — 
  a 
  

   work 
  that 
  has 
  been 
  under 
  way 
  for 
  some 
  time 
  — 
  was 
  brought 
  to 
  

   part'al 
  completion 
  during 
  the 
  past 
  year 
  by 
  the 
  publication 
  of 
  final 
  

   reports 
  upon 
  the 
  Adirondack 
  magnetite 
  district 
  and 
  the 
  Clinton 
  

   belt 
  of 
  hematite 
  ores. 
  These 
  are 
  the 
  two 
  largest 
  fields 
  and 
  have 
  

   the 
  greatest 
  commercial 
  importance 
  at 
  present 
  as 
  well 
  as 
  for 
  the 
  

  

  