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  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  of 
  grooves 
  and 
  polished 
  surfaces 
  and 
  the 
  material 
  transported 
  

   by 
  it. 
  

  

  The 
  glacial 
  phenomena 
  are 
  well 
  marked. 
  Ice 
  worked 
  blocks 
  

   of 
  stone 
  have 
  a 
  peculiar 
  angular 
  form, 
  which 
  does 
  not 
  occur 
  on 
  

   water 
  worn 
  boulders. 
  

  

  The 
  theory 
  of 
  continental 
  glaciation 
  was 
  first 
  worked 
  out 
  in 
  

   Europe 
  from 
  studies 
  of 
  the 
  glaciers 
  of 
  the 
  Alps. 
  These 
  are 
  the 
  

   result 
  of 
  a 
  copious 
  precipitation 
  of 
  moisture 
  on 
  the 
  mountains 
  

   in 
  the 
  form 
  of 
  snow 
  and 
  the 
  formation 
  of 
  snow 
  ice. 
  Large 
  masses 
  

   of 
  this 
  consolidate 
  and 
  form 
  ice 
  rivers 
  or 
  glaciers, 
  which 
  slowly 
  

   move 
  toward 
  the 
  valleys 
  grooving 
  and 
  polishing 
  the 
  rocks 
  over 
  

   which 
  they 
  pass 
  and 
  tearing 
  off 
  rock 
  fragments, 
  which 
  in 
  turn 
  are 
  

   polished 
  and 
  scratched 
  as 
  they 
  are 
  dragged 
  along 
  in 
  the 
  base 
  of 
  

   the 
  ice. 
  

  

  Glaciers 
  now 
  exist 
  in 
  Iceland, 
  Greenland 
  and 
  Alaska 
  and 
  in 
  

   other 
  Arctic 
  countries, 
  also 
  on 
  some 
  of 
  the 
  mountains 
  of 
  Wash- 
  

   ington, 
  South 
  America, 
  Asia 
  and 
  Africa. 
  They 
  also 
  abound 
  

   within 
  the 
  Antarctic 
  Circle. 
  

  

  Evidences 
  of 
  former 
  continental 
  glaciation 
  occur 
  in 
  both 
  hem- 
  

   ispheres. 
  

  

  In 
  New 
  York 
  state 
  the 
  continental 
  glacier 
  extended 
  as 
  far 
  south 
  

   as 
  Long 
  Island 
  and 
  Staten 
  Island 
  and 
  formed 
  at 
  its 
  front 
  a 
  great 
  

   ridge 
  of 
  transported 
  rock 
  debris, 
  sand, 
  gravel, 
  boulders 
  and 
  clay, 
  

   at 
  some 
  points 
  over 
  360 
  feet 
  in 
  height, 
  which 
  is 
  called 
  the 
  ' 
  ter- 
  

   minal 
  moraine 
  ' 
  and 
  is 
  known 
  locally 
  as 
  the 
  back 
  bone 
  of 
  Long 
  

   Island. 
  

  

  After 
  reaching 
  its 
  point 
  of 
  maximum 
  extension 
  and 
  resting 
  

   there, 
  perhaps 
  for 
  a 
  long 
  time, 
  the 
  ice 
  sheet 
  with 
  a 
  recurrence 
  of 
  a 
  

   warmer 
  climate 
  began 
  to 
  retreat. 
  This 
  retreat 
  was 
  not 
  at 
  an 
  

   even 
  rate. 
  There 
  were 
  periods 
  of 
  arrested 
  motion 
  and 
  probably 
  

   of 
  temporary 
  advance 
  as 
  shown 
  by 
  the 
  moraines 
  of 
  recession. 
  

   These 
  are 
  masses 
  of 
  earth, 
  gravel 
  and 
  boulders 
  which 
  form 
  small 
  

   hills 
  and 
  ridges. 
  

  

  As 
  the 
  ice 
  melted, 
  great 
  volumes 
  of 
  water 
  were 
  poured 
  over 
  

   the 
  land 
  and 
  the 
  valleys 
  were 
  flooded. 
  The 
  streams 
  thus 
  formed 
  

   were 
  loaded 
  with 
  sand 
  and 
  gravel 
  which 
  they 
  carried 
  for 
  a 
  dis- 
  

  

  