﻿128 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  DYNAMIC 
  GEOLOGY 
  

  

  Under 
  this 
  head 
  there 
  is 
  only 
  enough 
  space 
  to 
  enumerate 
  the 
  

   different 
  agencies 
  which 
  are 
  productive 
  of 
  geologic 
  change 
  or 
  are 
  

   associated 
  with 
  it. 
  For 
  a 
  detailed 
  discussion 
  the 
  student 
  is 
  re- 
  

   ferred 
  to 
  the 
  text-books. 
  

  

  The 
  dynamic 
  agencies 
  of 
  geology 
  may 
  be 
  roughly 
  classified 
  

   into 
  two 
  groups 
  : 
  hypogene 
  or 
  subterranean 
  and 
  epigene 
  or 
  super- 
  

   ficial. 
  Under 
  the 
  first 
  head 
  the 
  principal 
  agencies 
  are 
  volcanoes, 
  

   earthquakes, 
  secular 
  changes 
  of 
  level 
  and 
  metamorphism. 
  

   These, 
  as 
  their 
  group 
  name 
  indicates, 
  are 
  chiefly 
  controlled 
  by 
  

   forces 
  that 
  work 
  beneath 
  the 
  surface 
  of 
  the 
  earth; 
  the 
  second 
  

   or 
  epigene 
  group 
  comprises 
  those 
  which 
  are 
  chiefly 
  manifest 
  upon 
  

   the 
  earth's 
  surface. 
  First 
  among 
  these 
  is 
  the 
  air. 
  Air 
  in 
  motion 
  

   or 
  wind, 
  is 
  of 
  marked 
  importance 
  as 
  an 
  agent 
  of 
  transportation 
  

   as 
  manifested 
  in 
  sand 
  dunes, 
  at 
  places 
  where 
  deposits 
  of 
  fine 
  

   sand 
  occur, 
  chiefly 
  on 
  the 
  sea 
  shore 
  and 
  in 
  deserts. 
  

  

  A 
  more 
  active 
  agent 
  than 
  air 
  is 
  water. 
  By 
  the 
  action 
  of 
  its 
  

   terrestrial 
  forms, 
  rain, 
  snow 
  and 
  ice 
  and 
  by 
  the 
  cumulative 
  forms 
  

   of 
  these, 
  rivers 
  and 
  glaciers, 
  the 
  highlands 
  are 
  reduced 
  and 
  vast 
  

   amounts 
  of 
  material 
  are 
  transported 
  by 
  the 
  aid 
  of 
  gravity. 
  

  

  The 
  oceanic 
  waters 
  are 
  agents 
  of 
  destruction, 
  transportation 
  

   and 
  formation. 
  Waves 
  beat 
  upon 
  the 
  land 
  and 
  loosen 
  fragments 
  

   from 
  the 
  rocks 
  upon 
  which 
  they 
  beat. 
  These 
  fragments, 
  carried 
  

   out 
  within 
  reach 
  of 
  the 
  oceanic 
  currents, 
  are 
  borne 
  along 
  and 
  

   drop 
  to 
  the 
  bottom 
  forming 
  sand 
  bars 
  and 
  other 
  sub-aqueous 
  

   deposits. 
  Lastly, 
  animal 
  and 
  plant 
  life, 
  both 
  terrestrial 
  and 
  

   aquatic, 
  are 
  formidable 
  agents 
  of 
  change, 
  both 
  destructive 
  and 
  

   constructive. 
  

  

  Resume 
  

  

  Hypogene 
  or 
  subterranean 
  agencies 
  

   Volcanoes 
  

  

  Earthquakes 
  

  

  Secular 
  change 
  of 
  level 
  

  

  Metamorphism 
  

  

  