﻿PLEISTOCENE 
  GEOLOGY 
  OF 
  NASSAU 
  CO. 
  AND 
  BOROUGH 
  OF 
  QUEENS 
  623 
  

  

  the 
  limits 
  of 
  tliis 
  part 
  of 
  the 
  island 
  naturally 
  precludes 
  any 
  observa- 
  

   tion 
  of 
  glacial 
  striae 
  indicating 
  the 
  direction 
  of 
  local 
  ice 
  movement. 
  

   The 
  ledges 
  of 
  gneiss 
  in 
  Long 
  Island 
  City 
  bear 
  striae 
  whose 
  direc- 
  

   tion 
  is 
  s. 
  s. 
  e. 
  and 
  presumably 
  a 
  similar 
  course 
  was 
  followed 
  over 
  this 
  

   tract. 
  

  

  Glacial 
  formations 
  

  

  The 
  glacial 
  formations 
  of 
  this 
  area 
  are 
  divisible 
  into 
  two 
  great 
  

   groups 
  : 
  those 
  of 
  an 
  unassorted, 
  unstratified 
  structure, 
  composed 
  of 
  

   mixtures 
  of 
  boulders, 
  pebbles, 
  sand 
  and 
  clay, 
  frequently, 
  when 
  

   covering 
  the 
  surface, 
  witli 
  a 
  knob 
  and 
  basin 
  topography, 
  forming 
  in 
  

   general 
  terms 
  till, 
  or 
  boulder 
  clay 
  when 
  boulders 
  are 
  mixed 
  with 
  

   clay 
  ; 
  and 
  those 
  composed 
  of 
  gravels 
  and 
  sand 
  with 
  a 
  stratified 
  struc- 
  

   ture 
  showing 
  their 
  evident 
  deposition 
  by 
  running 
  water. 
  

  

  Till 
  constitutes 
  the 
  larger 
  part 
  of 
  the 
  ridges 
  or 
  moraines 
  already 
  

   described. 
  Boulder 
  clay 
  occurs 
  as 
  a 
  thin 
  layer 
  in 
  the 
  bluffs 
  on 
  

   either 
  side 
  of 
  Hempstead 
  harbor 
  and 
  in 
  the 
  area 
  between 
  Searing- 
  

   ton 
  and 
  the 
  main 
  ridge 
  near 
  Lake 
  Surprise. 
  Ordinary 
  till, 
  largely 
  

   in 
  the 
  form 
  of 
  scattered 
  boulders, 
  covers 
  the 
  terraced 
  plains 
  and 
  

   the 
  ridges 
  and 
  valleys 
  north 
  of 
  the 
  main 
  moraine. 
  The 
  rest 
  of 
  the 
  

   area 
  is 
  largely 
  composed 
  of 
  gravel 
  and 
  sand 
  with 
  local 
  deposits 
  of 
  

   blackish 
  or 
  bluish 
  black 
  clay 
  not 
  certainly 
  of 
  glacial 
  origin 
  and 
  per- 
  

   haps 
  to 
  be 
  regarded 
  as 
  of 
  Tertiary 
  or 
  older 
  age. 
  Gravel 
  and 
  sand 
  

   constitute 
  bj^ 
  far 
  the 
  greater 
  portion 
  of 
  the 
  glacial 
  deposits 
  both 
  as 
  

   regards 
  the 
  surficial 
  extent 
  and 
  cubic 
  contents 
  of 
  the 
  Pleistocene. 
  

  

  Since 
  these 
  deposits 
  appear 
  by 
  their 
  structure 
  and 
  relations 
  to 
  

   have 
  been 
  deposited 
  in 
  succession, 
  some 
  till 
  having 
  been 
  made 
  under 
  

   tlie 
  ice 
  or 
  at 
  the 
  ice 
  front 
  while 
  gravels 
  and 
  sands 
  were 
  being 
  laid 
  

   down 
  by 
  water 
  running 
  through 
  or 
  pouring 
  out 
  of 
  the 
  ice, 
  it 
  will 
  be 
  

   necessary 
  to 
  consider 
  them 
  in 
  the 
  order 
  of 
  their 
  development 
  in 
  

   time. 
  In 
  the 
  chronologic 
  succession, 
  the 
  glacial 
  deposits 
  exhibit 
  

   three 
  marked 
  phases 
  of 
  Pleistocene 
  history 
  in 
  this 
  area 
  : 
  1) 
  a 
  group 
  

   of 
  older 
  gravels 
  and 
  sands 
  with 
  an 
  intercalated 
  till 
  bed, 
  the 
  evident 
  

   equivalent 
  of 
  the 
  Columbia 
  formation 
  ; 
  2) 
  the 
  moraines 
  and 
  their 
  

   attendant 
  stratified 
  gravels 
  and 
  sands, 
  forming 
  the 
  topographic 
  

   details 
  of 
  the 
  surface 
  ; 
  3) 
  between 
  these 
  deposits 
  in 
  the 
  order 
  of 
  

   time, 
  evidences 
  of 
  erosion 
  by 
  other 
  than 
  glacial 
  action, 
  which 
  

   demand 
  separate 
  treatment. 
  

  

  