section_path: Principal works/The Book of Healing/Earth sciences
section_name: Earth sciences
paragraph_text: Earth sciences
  
  Avicenna wrote on Earth sciences such as geology in The Book of Healing. While discussing the formation of mountains, he explained:
  
  Either they are the effects of upheavals of the crust of the earth, such as might occur during a violent earthquake, or they are the effect of water, which, cutting itself a new route, has denuded the valleys, the strata being of different kinds, some soft, some hard... It would require a long period of time for all such changes to be accomplished, during which the mountains themselves might be somewhat diminished in size.