SURFACE SOIL AND SUBSOIL 9 



fine particles of rock there would be little difference between 

 the surface soil and the subsoil. After the rocks were 

 made fine, plants began to grow and by their death and 

 decay they have added to the soil the dark-colored material 

 which we call organic matter or humus. As the stems 

 and leaves of plants fall on the ground and decay they 

 are worked into the soil. Thus the surface soil is made 

 to contain large quantities of decaying plants, while the 

 subsoil contains but little of this material. This is the 

 chief difference between the two. These decaying plants 

 are an important addition to the soil. They add nitrogen 

 and make the soil capable of holding more moisture. 



