﻿THE 
  GEOLOGICAL 
  HISTORY 
  OF 
  NEW 
  YORK 
  STATE 
  9 
  

  

  such 
  as 
  limestone 
  which 
  is 
  formed 
  by 
  the 
  accumulation 
  of 
  calcareous 
  

   shells 
  ; 
  flint 
  and 
  chert, 
  which 
  are 
  accumulations 
  of 
  silicious 
  shells 
  ; 
  

   coal, 
  which 
  is 
  formed 
  by 
  the 
  accumulation 
  of 
  partly 
  decayed 
  

   vegetable 
  matter. 
  Or, 
  finally, 
  they 
  may 
  be 
  formed 
  by 
  chemical 
  

   precipitation, 
  as 
  beds 
  of 
  salt, 
  gypsum, 
  bog 
  iron 
  ore, 
  etc. 
  

  

  Metamorphic 
  rocks 
  comprise 
  both 
  sedimentary 
  and 
  igneous 
  

   masses 
  which 
  have 
  been 
  greatly 
  changed 
  from 
  their 
  original 
  con- 
  

   dition. 
  Thus, 
  under 
  conditions 
  of 
  great 
  pressure 
  and 
  heat, 
  with 
  

   superheated 
  moisture, 
  sedimentary 
  rocks 
  may 
  ibecome 
  crystalline, 
  

   as 
  when 
  shale 
  is 
  changed 
  to 
  schist, 
  sandstone 
  to 
  quartzite, 
  or 
  lime- 
  

   stone 
  to 
  marble 
  ; 
  or 
  an 
  igneous 
  rock 
  may 
  take 
  on 
  a 
  banded 
  structure, 
  

   due 
  to 
  a 
  rearrangement 
  of 
  its 
  component 
  minerals, 
  and 
  thus 
  become 
  

   a 
  gneiss. 
  

  

  To 
  the 
  modern 
  student 
  of 
  earth 
  science, 
  the 
  old 
  notion 
  of 
  a 
  " 
  terra 
  

   firma 
  " 
  is 
  outworn. 
  That 
  idea 
  of 
  a 
  solid, 
  immovable 
  earth 
  could 
  

   never 
  have 
  emanated 
  from 
  the 
  inhabitants 
  of 
  an 
  earthquake 
  country. 
  

   In 
  the 
  recent 
  San 
  Francisco 
  earthquake, 
  along 
  a 
  line 
  of 
  several 
  

   hundred 
  miles, 
  one 
  portion 
  of 
  the 
  Coast 
  Range 
  mountains 
  slipped 
  

   from 
  two 
  to 
  twenty 
  feet 
  past 
  the 
  other. 
  In 
  Alaska, 
  in 
  1899, 
  a 
  por- 
  

   tion 
  of 
  the 
  coast 
  was 
  bodily 
  elevated 
  forty-seven 
  feet. 
  In 
  Japan 
  

   in 
  1891, 
  for 
  a 
  distance 
  of 
  forty 
  miles 
  along 
  a 
  rift 
  in 
  the 
  earth's 
  

   crust, 
  there 
  was 
  a 
  sudden 
  movement 
  of 
  from 
  two 
  to 
  twenty 
  feet. 
  

   These 
  are 
  merely 
  striking 
  instances 
  of 
  many 
  of 
  the 
  sudden 
  earth 
  

   movements 
  of 
  recent 
  years. 
  Hundreds 
  of 
  earthquakes 
  occur 
  yearly 
  

   in 
  the 
  islands 
  of 
  Japan 
  alone, 
  and 
  it 
  is 
  probably 
  true 
  that 
  the 
  

   earth 
  is 
  shaking 
  all 
  the 
  time. 
  

  

  There 
  are 
  still 
  other 
  movements 
  which 
  are 
  taking 
  place 
  more 
  

   slowly 
  and 
  quietly, 
  but 
  which 
  are 
  more 
  significant 
  for 
  our 
  interpre- 
  

   tation 
  of 
  the 
  profound 
  geographic 
  changes 
  which 
  have 
  occurred 
  

   during 
  the 
  millions 
  of 
  years 
  of 
  known 
  earth 
  history. 
  Thus 
  the 
  

   coast 
  of 
  Norway 
  is 
  rising 
  while 
  that 
  of 
  northern 
  France 
  is 
  sinking. 
  

   Distinct 
  beaches 
  at 
  different 
  elevations 
  far 
  above 
  the 
  ocean 
  level 
  

   on 
  the 
  western 
  slope 
  of 
  the 
  southern 
  Andes 
  testify 
  to 
  important 
  

   changes 
  of 
  level 
  in 
  comparatively 
  recent 
  time. 
  A 
  fine 
  illustration 
  

   of 
  notable 
  sinking 
  of 
  the 
  land 
  is 
  proved 
  by 
  the 
  drowned 
  character 
  

   of 
  the 
  lower 
  Hudson 
  valley, 
  and 
  by 
  the 
  fact 
  that 
  the 
  old 
  Hudson 
  

   channel 
  has 
  been 
  definitely 
  traced, 
  as 
  a 
  distinct 
  trench 
  in 
  the 
  ocean 
  

   bottom, 
  for 
  one 
  hundred 
  miles 
  eastward 
  from 
  Sandy 
  Hook. 
  That 
  

   this 
  same 
  region 
  has 
  still 
  more 
  recently 
  been 
  partially 
  re-elevated 
  

   is 
  indicated 
  by 
  the 
  presence 
  of 
  very 
  young 
  stratified 
  beds 
  of 
  clay 
  

   and 
  sand 
  which 
  are 
  now 
  raised 
  from 
  seventy 
  to 
  three 
  hundred 
  feet 
  

   above 
  the 
  river, 
  the 
  elevation 
  increasing 
  northward 
  toward 
  Albany. 
  

   Actual 
  surveys 
  show 
  that, 
  in 
  the 
  Great 
  Lakes 
  region, 
  a 
  differential 
  

  

  