﻿PLEISTOCENE 
  GEOLOGY 
  OF 
  NASSAU 
  CO. 
  AND 
  BOROUGH 
  OF 
  QUEENS 
  639 
  

  

  on 
  the 
  Malaspina 
  glacier 
  ; 
  or 
  3) 
  deposits 
  made 
  in 
  water-eaten 
  cavities 
  

   in 
  the 
  ice 
  front. 
  As 
  a 
  rule, 
  the 
  gravels 
  are 
  seldom 
  so 
  well 
  exposed 
  

   as 
  to 
  reveal 
  the 
  structures 
  on 
  which 
  a 
  decision 
  as 
  to 
  their 
  precise 
  

   character 
  can 
  be 
  arrived 
  at 
  ; 
  and 
  their 
  origin 
  in 
  the 
  presence 
  of 
  the 
  

   ice 
  ill 
  all 
  cases 
  being 
  so 
  intimate 
  as 
  to 
  permit 
  the 
  falling 
  of 
  erratics 
  

   on 
  their 
  surfaces 
  makes 
  it 
  difficult 
  to 
  discriminate 
  them 
  from 
  the 
  

   gravelly 
  till. 
  This 
  is 
  particularly 
  true 
  where 
  the 
  growth 
  of 
  trees 
  

   and 
  the 
  overturning 
  of 
  the 
  superiicial 
  deposits 
  have 
  broken 
  up 
  tlie 
  

   original 
  stratification 
  in 
  the 
  surficial 
  portion 
  so 
  that 
  the 
  materials 
  

   have 
  the 
  structural 
  appearance 
  of 
  till 
  or 
  at 
  least 
  ice-deposited 
  

   gravels. 
  The 
  deposition 
  of 
  the 
  surface 
  gravels 
  by 
  direct 
  ice 
  action 
  

   is 
  sometimes 
  shown 
  by 
  the 
  scratches 
  on 
  hard 
  silicious 
  pebbles. 
  

   These 
  scratclies 
  are 
  usually 
  miscroscopic 
  and 
  would 
  have 
  been 
  

   quickly 
  effaced 
  by 
  water 
  action. 
  Such 
  pebbles 
  occur 
  in 
  the 
  churned 
  

   up 
  gravelly 
  drift 
  on 
  the 
  surface 
  of 
  the 
  Columbia 
  north 
  of 
  the 
  

   moraine. 
  The 
  structure 
  of 
  the 
  principal 
  knob 
  in 
  this 
  moraine 
  

   chanced 
  to 
  be 
  revealed 
  in 
  the 
  summer 
  of 
  1900, 
  and 
  the 
  following 
  

   notes 
  on 
  Harbor 
  hill 
  show 
  the 
  surprising 
  development 
  of 
  these 
  

   water-worn 
  gravels 
  in 
  the 
  deposit. 
  

  

  Harbor 
  hill. 
  The 
  precise 
  mode 
  of 
  accumulation 
  of 
  the 
  materials 
  

   in 
  the 
  terminal 
  moraine 
  still 
  demands 
  explanation 
  in 
  numerous 
  

   details, 
  particularly 
  in 
  i-egard 
  to 
  those 
  portions 
  which 
  are 
  mainly 
  

   composed 
  of 
  stratified 
  gravels 
  and 
  sands. 
  Now^iere 
  in 
  the 
  moraines 
  

   on 
  the 
  islands 
  off 
  the 
  southern 
  shore 
  of 
  New 
  England 
  does 
  this 
  

   problem 
  become 
  more 
  urgent 
  for 
  a 
  satisfactory 
  answer 
  than 
  in 
  

   Harbor 
  hill, 
  a 
  towering 
  mass 
  of 
  stratified 
  gravels, 
  forming 
  the 
  cul- 
  

   minating 
  point 
  of 
  the 
  moraine 
  on 
  this 
  quadrangle 
  at 
  the 
  eastern 
  

   side 
  of 
  the 
  pass 
  through 
  which 
  the 
  glacial 
  drainage 
  escaped 
  from 
  

   Roslyn 
  bay 
  to 
  the 
  great 
  south 
  plain. 
  This 
  hill 
  rises 
  with 
  steep 
  

   slopes 
  into 
  four 
  knobs, 
  the 
  highest 
  of 
  which 
  has 
  an 
  elevation 
  of 
  391 
  

   feet, 
  its 
  base 
  on 
  the 
  out 
  wash 
  plain 
  being 
  roughly 
  circumscribed 
  by 
  

   the 
  200 
  foot 
  contour 
  line. 
  

  

  At 
  its 
  eastern 
  base, 
  the 
  hill 
  is 
  separated 
  from 
  the 
  extension 
  of 
  

   the 
  morainal 
  wall 
  in 
  that 
  direction 
  by 
  a 
  distinct 
  depression, 
  or 
  

   trough, 
  one 
  of 
  those 
  numerous 
  channels 
  which 
  gave 
  exit 
  to 
  the 
  

   intraglacial 
  waters 
  on 
  to 
  the 
  outwash 
  plain. 
  On 
  the 
  west, 
  its 
  slopes 
  

   fall 
  off 
  to 
  sealevel 
  at 
  the 
  head 
  of 
  Hempstead 
  harbor. 
  The 
  high 
  

  

  