﻿660 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  SUMMARY 
  OF 
  GLACIAL 
  HISTOEY 
  

  

  From 
  what 
  has 
  been 
  stated 
  of 
  this 
  district, 
  it 
  appears 
  that 
  rela- 
  

   tively 
  early 
  in 
  the 
  Glacial 
  period 
  the 
  area 
  now 
  forming 
  the 
  western 
  

   part 
  of 
  Long 
  Island 
  received 
  a 
  thick 
  coating 
  of 
  gravels 
  and 
  sands, 
  

   some 
  of 
  the 
  debris 
  being 
  eroded 
  from 
  the 
  deposits 
  of 
  the 
  coast 
  plain 
  

   remaining 
  in 
  the 
  area, 
  some 
  of 
  them 
  being 
  borne 
  from 
  the 
  main- 
  

   land 
  on 
  the 
  north 
  ; 
  that 
  probably 
  somewhere 
  near 
  the 
  middle 
  of 
  this 
  

   time, 
  as 
  indicated 
  by 
  the 
  occurrence 
  of 
  the 
  deposits 
  in 
  the 
  section, 
  

   there 
  was 
  an 
  actual 
  invasion 
  of 
  the 
  district 
  by 
  ice, 
  either 
  floating 
  ice 
  

   or 
  land 
  ice, 
  in 
  either 
  cj^ge 
  probably 
  the 
  margin 
  or 
  detached 
  floating 
  

   portions 
  of 
  the 
  front 
  of 
  an 
  ice 
  sheet 
  laying 
  down 
  till 
  in 
  the 
  district. 
  

   These 
  deposits 
  as 
  a 
  whole 
  underlie 
  the 
  moraines 
  and 
  are 
  apparently 
  

   the 
  Columbia 
  formation 
  of 
  McGee. 
  Certain 
  aspects 
  of 
  the 
  deposits 
  

   seem 
  to 
  be 
  paralleled 
  in 
  'New 
  Jersey 
  by 
  the 
  yellow 
  gravel 
  forma- 
  

   tions 
  described 
  by 
  Salisbury.^ 
  Subsequent 
  to 
  their 
  deposition, 
  which 
  

   locally 
  affords 
  no 
  decisive 
  evidence 
  of 
  the 
  relation 
  of 
  land 
  to 
  sea- 
  

   level, 
  they 
  appear 
  to 
  have 
  been 
  somewhat 
  dissected 
  by 
  open 
  air 
  

   streams, 
  indicating 
  an 
  epoch 
  of 
  deglaciation 
  or 
  ice 
  retreat 
  of 
  indefi- 
  

   nite 
  duration. 
  Following 
  this 
  came 
  the 
  deposition 
  of 
  two 
  lines 
  of 
  

   moraines 
  in 
  the 
  area, 
  an 
  outer 
  and 
  inner 
  or 
  earlier 
  and 
  later, 
  but 
  in 
  

   the 
  western 
  part 
  of 
  the 
  field 
  the 
  later 
  ice 
  front 
  depassed 
  the 
  position 
  

   of 
  the 
  earlier 
  advance. 
  The 
  land 
  appears 
  to 
  have 
  been 
  as 
  high 
  

   above 
  sealevel 
  as 
  it 
  is 
  now, 
  if 
  not 
  higher 
  ; 
  and 
  during 
  the 
  retreat 
  of 
  

   the 
  ice 
  one 
  or 
  more 
  temporary 
  lakes 
  existed 
  back 
  of 
  the 
  moraine, 
  

   first 
  at 
  80 
  feet 
  above 
  the 
  present 
  sealevel, 
  then 
  possibly 
  at 
  about 
  40 
  

   feet. 
  This 
  lower 
  body 
  of 
  water 
  may 
  have 
  been 
  at 
  sealevel 
  as 
  

   stated 
  above. 
  With 
  the 
  retreat 
  of 
  the 
  ice 
  front 
  across 
  East 
  river, 
  

   the 
  region 
  escaped 
  from 
  the 
  field 
  of 
  glacial 
  action, 
  and 
  its 
  latest 
  

   glacial 
  deposits 
  and 
  features 
  pertain 
  to 
  the 
  very 
  beginnings 
  of 
  the 
  

   ice 
  retreat, 
  a 
  time 
  but 
  slightly 
  past 
  the 
  culminating 
  phase 
  of 
  the 
  

   last 
  or 
  Wisconsin 
  glacial 
  epoch. 
  Of 
  any 
  such 
  distinctions 
  as 
  a 
  Cham- 
  

   plain 
  and 
  Terrace 
  epoch 
  there 
  appears 
  here 
  no 
  trace, 
  for 
  the 
  over- 
  

   wash 
  plain 
  was 
  making 
  while 
  the 
  ice 
  was 
  at 
  its 
  maximum 
  extension, 
  

   and 
  the 
  glacial 
  terraces 
  marked 
  by 
  the 
  small 
  deltas 
  described 
  in 
  this 
  

  

  1 
  Salisbury, 
  R. 
  D. 
  N. 
  J. 
  geol. 
  sur. 
  An. 
  rep't 
  state 
  geol. 
  1895. 
  p. 
  67-72. 
  

  

  