﻿PLEISTOCENE 
  GEOLOGY 
  OF 
  NASSAU 
  CO. 
  AND 
  BOROUGH 
  OF 
  QUEENS 
  625 
  

  

  Quartz 
  pebbles 
  predominate 
  in 
  this 
  formation, 
  particularly 
  those 
  

   etained 
  yellow 
  by 
  the 
  oxid 
  of 
  iron 
  ; 
  hence 
  the 
  term, 
  " 
  yellow 
  

   gravel," 
  which 
  has 
  been 
  sometimes 
  given 
  to 
  it. 
  This 
  discoloration 
  

   will 
  be 
  treated 
  more 
  at 
  length 
  later. 
  White 
  quartz 
  pebbles 
  are 
  not 
  

   uncommon, 
  pebbles 
  which 
  appear 
  never 
  to 
  have 
  been 
  stained. 
  The 
  

   silicified 
  fossils 
  and 
  cherts 
  are 
  relatively 
  rare, 
  but 
  search 
  carried 
  

   over 
  a 
  few 
  square 
  yards 
  of 
  surface 
  in 
  any 
  gravel 
  pit 
  in 
  the 
  forma- 
  

   tion 
  north 
  of 
  the 
  moraine 
  will 
  usually 
  reveal 
  two 
  or 
  three 
  of 
  these 
  

   erratics. 
  The 
  gneissic 
  and 
  granitic 
  pebbles 
  are 
  at 
  least 
  in 
  the 
  mass 
  

   of 
  the 
  formation 
  not 
  much 
  decayed. 
  On 
  the 
  whole, 
  the 
  materials 
  

   are 
  like 
  those 
  in 
  the 
  moraine 
  and 
  in 
  the 
  gravel 
  and 
  sand 
  terraces 
  on 
  

   the 
  mainland 
  except 
  for 
  local 
  staining 
  by 
  iron 
  oxids. 
  The 
  com- 
  

   parison 
  with 
  the 
  moraines 
  is 
  perhaps 
  hardly 
  just, 
  because 
  the 
  

   moraines 
  are 
  locally 
  largely 
  composed 
  of 
  rearranged 
  drift 
  from 
  

   these 
  same 
  beds, 
  as 
  in 
  Harbor 
  hill. 
  The 
  inference 
  from 
  the 
  sands 
  

   and 
  gravels 
  is 
  that 
  they 
  are 
  of 
  glacial 
  origin, 
  modified 
  by 
  the 
  work 
  

   of 
  running 
  water, 
  either 
  ice-born 
  streams 
  or 
  extraglacial 
  waters. 
  

   This 
  conclusion 
  as 
  to 
  their 
  glacial 
  origin 
  amounts 
  to 
  a 
  certainty 
  

   when 
  the 
  intermediate 
  boulder 
  clay 
  bed 
  is 
  taken 
  into 
  the 
  account. 
  

  

  That 
  the 
  beds 
  extend 
  southward 
  beyond 
  the 
  Harbor 
  hill 
  ridge 
  

   or 
  moraine 
  can 
  hardly 
  be 
  questioned 
  ; 
  but 
  it 
  is 
  difficult 
  to 
  distin- 
  

   guish 
  the 
  formation 
  in 
  front 
  of 
  the 
  moraines 
  from 
  the 
  later 
  gravels 
  

   and 
  sands 
  washed 
  out 
  from 
  the 
  ice 
  front. 
  At 
  one 
  point 
  in 
  the 
  

   mounded 
  drift 
  southwest 
  of 
  Koslyn 
  an 
  exposure 
  by 
  the 
  roadside 
  of 
  

   a 
  coarse 
  cobble 
  bed 
  with 
  yellow 
  pebbles 
  contains 
  also 
  iron 
  stone 
  con- 
  

   cretions 
  which 
  have 
  evidently 
  not 
  been 
  rolled, 
  showing 
  that 
  they 
  

   are 
  probably 
  in 
  place, 
  though 
  loosened 
  by 
  exposure 
  to 
  surface 
  

   actions 
  from 
  the 
  surrounding 
  pebbles. 
  Beds 
  of 
  this 
  character 
  are 
  

   found 
  at 
  the 
  base 
  of 
  the 
  Pleistocene 
  on 
  Marthas 
  Vineyard 
  in 
  the 
  

   Gay 
  head 
  section,^ 
  where 
  the 
  origin 
  of 
  the' 
  concretions 
  is 
  clear. 
  The 
  

   concretions 
  arise 
  from 
  the 
  erosion 
  of 
  light 
  colored 
  clays 
  of 
  the 
  

   underlying 
  Cretaceous 
  or 
  Potomac 
  beds 
  and 
  their 
  deposition 
  with 
  

   the 
  coarse 
  gravels 
  as 
  pebbles 
  permeable 
  to 
  percolating 
  water 
  charged 
  

   with 
  iron 
  salts. 
  Cementation 
  takes 
  place 
  by 
  deposition 
  of 
  iron 
  

   oxids 
  around 
  all 
  of 
  the 
  pebbles, 
  involving 
  the 
  outer 
  part 
  of 
  the 
  clay 
  

  

  1 
  Woodworth, 
  J. 
  B. 
  Geol. 
  soc. 
  Am. 
  Biil. 
  1897. 
  8 
  : 
  205-6. 
  

  

  