﻿8 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  effects. 
  The 
  terms 
  geography 
  and 
  geology 
  are 
  thus 
  here 
  used 
  in 
  

   the 
  sense 
  that 
  the 
  latter 
  includes 
  the 
  former, 
  as 
  the 
  cause 
  includes 
  

   the 
  effect. 
  Paleogeography 
  has 
  reference 
  to 
  the 
  geography 
  of 
  the 
  

   past 
  epochs 
  in 
  the 
  history 
  of 
  the 
  earth. 
  

  

  Physiography, 
  or 
  physical 
  geography, 
  deals 
  with 
  the 
  configuration 
  

   (relief) 
  of 
  the 
  earth's 
  surface 
  and 
  how 
  it 
  was 
  produced. 
  

  

  As 
  a 
  result 
  of 
  the 
  work 
  of 
  many 
  able 
  students 
  of 
  earth 
  science 
  

   during 
  the 
  past 
  hundred 
  years, 
  it 
  is 
  now 
  well 
  established 
  that 
  our 
  

   planet 
  has 
  a 
  clearly 
  recorded 
  history 
  of 
  many 
  millions 
  of 
  years, 
  and 
  

   that 
  during 
  the 
  lapse 
  of 
  those 
  eons 
  revolutionary 
  changes 
  in 
  geog- 
  

   raphy 
  have 
  occurred 
  ; 
  that 
  there 
  has 
  also 
  been 
  from 
  an 
  early 
  stage 
  

   of 
  the 
  earth's 
  history 
  a 
  vast 
  succession 
  of 
  living 
  beings 
  which 
  have 
  

   gradually 
  passed 
  from 
  simple 
  into 
  more 
  complex 
  forms 
  and 
  have, 
  

   in 
  some 
  particulars, 
  reached 
  their 
  highest 
  expression 
  in 
  the 
  organ- 
  

   isms 
  of 
  the 
  present 
  time. 
  The 
  geographic 
  changes 
  and 
  the 
  organisms 
  

   of 
  the 
  ages 
  gone 
  by 
  have 
  left 
  us 
  no 
  abundant 
  evidence 
  of 
  their 
  char- 
  

   acter 
  and 
  the 
  study 
  of 
  the 
  rock 
  formations 
  has 
  shown 
  that 
  within 
  

   them 
  we 
  have 
  a 
  fairly 
  complete 
  record 
  of 
  the 
  earth's 
  history. 
  

  

  In 
  the 
  time 
  of 
  Alexander 
  von 
  Humboldt, 
  less 
  than 
  one 
  hundred 
  

   years 
  ago, 
  the 
  keen 
  student 
  of 
  natural 
  phenomena 
  could 
  carry 
  in 
  

   his 
  own 
  mind 
  most 
  of 
  what 
  was 
  definitely 
  known 
  of 
  earth 
  history. 
  

   Today, 
  because 
  of 
  the 
  tremendous 
  growth 
  of 
  the 
  science, 
  it 
  would 
  

   be 
  a 
  presumption 
  for 
  any 
  man 
  to 
  claim 
  that 
  he 
  knows 
  all 
  of 
  what 
  

   has 
  been 
  learned 
  about 
  the 
  geological 
  history 
  of 
  even 
  the 
  single 
  

   State 
  of 
  New 
  York. 
  While 
  it 
  is 
  true 
  that 
  much 
  yet 
  remains 
  to 
  be 
  

   learned 
  of 
  this 
  old 
  earth, 
  it 
  is 
  a 
  real 
  source 
  of 
  wonderment 
  that 
  

   man, 
  through 
  the 
  exercise 
  of 
  his 
  highest 
  faculty, 
  has 
  come 
  to 
  know 
  

   so 
  much 
  about 
  it. 
  

  

  All 
  the 
  rocks 
  of 
  the 
  earth's 
  crust 
  may 
  be 
  divided 
  into 
  three 
  great 
  

   classes 
  : 
  igneous, 
  sedimentary, 
  and 
  metamorphic. 
  

  

  Igneous 
  rocks 
  comprise 
  all 
  those 
  which 
  have 
  ever 
  been 
  in 
  a 
  

   molten 
  condition, 
  and 
  of 
  these- 
  we 
  have 
  the 
  volcanic 
  rocks 
  (for 
  

   example, 
  lavas) 
  which 
  have 
  cooled 
  at 
  or 
  near 
  the 
  surface; 
  plutonic 
  

   rocks 
  (e. 
  g., 
  granites) 
  which 
  have 
  cooled 
  in 
  great 
  masses 
  at 
  con- 
  

   siderable 
  depths 
  below 
  the 
  surface 
  ; 
  and 
  the 
  dike 
  rocks, 
  which 
  when 
  

   molten 
  have 
  been 
  forced 
  into 
  fissures 
  of 
  the 
  earth's 
  crust 
  and 
  there 
  

   cooled. 
  

  

  Sedimentary 
  rocks 
  comprise 
  all 
  those 
  which 
  have 
  been 
  deposited 
  

   under 
  water 
  (except 
  for 
  some 
  wind-blown 
  deposits) 
  and 
  are 
  nearly 
  

   always 
  arranged 
  in 
  layers 
  (stratified). 
  These 
  rocks 
  may 
  be 
  of 
  

   mechanical 
  origin, 
  such 
  as 
  clay 
  or 
  mud 
  which 
  hardens 
  to 
  shale; 
  

   sand, 
  which 
  consolidates 
  to 
  sandstone; 
  and 
  gravel, 
  which 
  when 
  

   cemented 
  becomes 
  conglomerate. 
  Or 
  they 
  may 
  be 
  of 
  organic 
  origin, 
  

  

  