392 THE WORK OF THE ATMOSPHERE 



rust, slowly crumble and wear away, and their broken bits 

 mingle with the soil and give color to it. 



Any process which causes rock to break up and decay is called 

 weathering. Oxygen, carbon dioxide, and water vapor weather 

 rock. Destruction by weathering is a slow process. Well-built 

 houses last for years in spite of weathering, and rocks exposed to 

 the atmosphere change their character and appearance very 

 slowly. When weathering and transportation go hand in hand, 

 erosion results. Water vapor weathers rock, but does not 

 cause erosion because it is powerless to transport to new regions 

 the products of weathering ; wind not only weathers rock but 

 also erodes it, blowing away with it the products of its work. 



