CHAPTEE XII. 



THE SUBSOIL. 



In the South raw prairie usually has a shallow 

 top soil. By soil we mean that layer of ground 

 into which grass roots have penetrated, and by 

 their decomposition little channels for air and wa- 

 ter have been left, resulting in its darker color; 

 humus has formed from the roots and tops of vege- 

 tation, and oxidation has taken place as far as they 

 have penetrated beneath the surface, thus modify- 

 ing the original color and texture of the turf. 

 Some of the muck lands of Southern California 

 have more than twenty feet of top soil ; in the Mis- 

 sissippi Delta the alluvial deposits are not shallow, 

 and in many parts of Louisiana humus exists sev- 

 eral feet from the surface ; but the ordinary prairie 

 lands along the G-ulf often contain less than six 

 inches of top soil. In the North Central States, 

 where land freezes several feet deep, water pulver- 

 izes it when changing to ice, the particles becoming 

 finely divided by alternate cold and warm weather, 

 and is pervious as deep as freezing ordinarily oc- 

 curs. In the far North, however, seasons are too 

 short for plants to occupy the ground as far as it 

 freezes. Roots gradually enter porous soils, and, 

 if supplied with sufficient moisture, they continue 

 to whatever depths are found comfortable. If top 



