28 



THE PRINCIPLES OF SOIL MANAGEMENT 



change, or the removal of constituents, which fact is 

 shown in the tables of soil-composition on pages 32-57. 

 Their influence on surface topography is profound, and 

 of great importance to the pursuit of agriculture because 

 of the leveling which results. 



Fir. 11. Lichen growing on a granite boulder. These low forms of 

 plants disintegrate the rock and assist in the decomposition of its constituent 

 minerals. 



10. Plants and animals. Plants and animals unite 

 with the other agencies mentioned to effect the breaking 

 down of minerals and rocks. Like the other processes, 

 they have both their mechanical and their chemical 

 side. The development of plant roots in crevices of rock 



