﻿634 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  ing 
  content 
  of 
  the 
  gravels 
  ; 
  and, 
  2) 
  the 
  erosion 
  of 
  valleys 
  and 
  

   harbors 
  in 
  its 
  mass 
  prior 
  to 
  at 
  least 
  the 
  last 
  till 
  deposits 
  on 
  the 
  

   island. 
  The 
  latter 
  phenomena 
  are 
  so 
  extensive 
  as 
  to 
  indicate 
  a 
  con- 
  

   siderable 
  lapse 
  of 
  time 
  for 
  their 
  production. 
  

  

  Discoloration 
  of 
  the 
  gravels 
  by 
  the 
  yellow 
  or 
  hydrous 
  sesquioxid 
  

   of 
  iron 
  has 
  taken 
  place 
  to 
  a 
  variable 
  extent, 
  sometimes 
  affecting 
  less 
  

   than 
  a 
  cubic 
  foot 
  of 
  the 
  materials 
  and 
  in 
  other 
  places, 
  particularly 
  

   beneath 
  the 
  moraine, 
  changing 
  the 
  entire 
  appearance 
  of 
  the 
  section 
  

   there 
  exposed. 
  

  

  Local 
  discoloring 
  by 
  the 
  yellow 
  oxid 
  is 
  frequently 
  seen 
  in 
  the 
  

   gravel 
  pits 
  on 
  the 
  west 
  shore 
  of 
  Hempstead 
  bay, 
  wherever 
  some 
  

   iron-bearing 
  pebble 
  has 
  oxidized 
  and 
  hydrated, 
  the 
  iron 
  salts 
  spread- 
  

   ing 
  outward 
  and 
  mainly 
  downward 
  through 
  the 
  action 
  of 
  infiltrating 
  

   rain 
  water. 
  The 
  sands 
  and 
  gravels 
  above 
  the 
  till 
  bed 
  mainly 
  exhibit 
  

   this 
  change. 
  

  

  Widespread 
  discoloration 
  of 
  the 
  gravels 
  to 
  a 
  deep 
  yellow 
  occurs 
  

   in 
  Roslyn 
  in 
  the 
  bluffs 
  on 
  the 
  east 
  side 
  of 
  the 
  town 
  below 
  the 
  base 
  

   of 
  the 
  moraine. 
  This 
  deeper 
  and 
  more 
  thorough 
  coating 
  of 
  the 
  

   gravels 
  in 
  this 
  locality 
  is 
  a 
  natural 
  result 
  of 
  the 
  lixiviation 
  of 
  the 
  

   ferruginous 
  rocks 
  in 
  the 
  overlying 
  moraine, 
  the 
  products 
  of 
  whose 
  

   oxidation 
  and 
  hydration 
  have 
  worked 
  downward 
  into 
  the 
  porous 
  

   gravels 
  beneath. 
  

  

  The 
  discoloration 
  is 
  therefore 
  a 
  change 
  which 
  is 
  probably 
  secular 
  

   and 
  in 
  progress. 
  That 
  it 
  had 
  already 
  advanced 
  very 
  far 
  before 
  the 
  

   moraines 
  were 
  formed 
  is 
  indicated 
  by 
  the 
  abundant 
  occurrence 
  in 
  

   the 
  moraine 
  of 
  yellow, 
  stained 
  quartz 
  pebbles 
  ; 
  but 
  these 
  pebbles 
  in 
  

   the 
  moraine 
  are 
  usually 
  not 
  in 
  the 
  place 
  in 
  which 
  they 
  were 
  originally 
  

   stained, 
  for 
  they 
  have 
  water- 
  washed 
  surfaces. 
  The 
  staining 
  was 
  

   accomplished 
  while 
  the 
  pebbles 
  lay 
  in 
  an 
  earlier 
  deposit, 
  either 
  the 
  

   Columbia 
  or 
  some 
  unexposed 
  member 
  of 
  the 
  ancient 
  coastal 
  plain. 
  

  

  Erosion 
  interval. 
  The 
  evidence 
  of 
  late 
  dislocation 
  on 
  a 
  small 
  

   scale 
  commensurate 
  with 
  the 
  pushing 
  and 
  dragging 
  action 
  of 
  a 
  

   great 
  ice 
  sheet, 
  the 
  spreading 
  of 
  till 
  and 
  boulders 
  over 
  the 
  surface 
  

   of 
  the 
  Columbia, 
  and 
  the 
  amassment 
  of 
  heaps 
  of 
  drift 
  evidently 
  in 
  

   part 
  derived 
  from 
  the 
  surface 
  of 
  the 
  deposit, 
  afford 
  indubitable 
  evi- 
  

   dence 
  of 
  the 
  degradation 
  of 
  the 
  formation 
  to 
  some 
  extent 
  by 
  ice 
  

   action 
  subsequent 
  to 
  the 
  completion 
  of 
  the 
  series 
  of 
  deposits. 
  But 
  

  

  