92 



ROOTS AND THETR WORK 



Later, it cooled into solid rock. Soil making began when the ice and 

 frost, working with the heat, chipped off pieces of rock. These pieces in 



time became ground into 

 fragments by action of ice, 

 glaciers, running water, 

 or the atmosphere. This 

 process is called weather- 

 ing. Weathering is largely 

 a process of oxidation. 

 A glance at almost any 

 crumbling stones will con- 

 vince you of this, because 

 of the yellow oxide of iron 

 (rust) disclosed. So by 

 slow degrees this earth 

 became covered with a 

 coating of what we call 

 inorganic soil. Later, gen- 

 eration after generation of 

 tiny plants and animals 

 which lived in the soil 

 died, and their remains 

 formed the first organic 

 materials of the soil. 



You are all familiar 

 This picture shows how the forests help to cover the witn tne difference be- 

 inorganic soil with an organic coating. tween the so-called rich 



soil and poor soil. The 



dark soil simply contains more dead plant and animal life, which forms 

 the portion called humus. 



Humus contains Organic Matter. It is an easy matter to prove that 

 black soil contains organic matter, for if an equal weight of carefully 

 dried humus and soil from a sandy road is heated red-hot for some time 

 and then re weighed, the hu- 

 mus will be found to have 

 lost considerably in weight, 

 and the sandy soil to have lost 

 very little. The material left 

 after heating is inorganic 

 material, the organic matter 

 having been burned out. 



Organic soil holds water A B C D E F 



much more readily than in- Experiment to illustrate the kind of soil which best 

 organic soil, as a glance at retains water : A, gravel; B, sand; C, barren 

 the accompanying Figure soil ; D, rich soil ; E, leaf mold ; F, dry leaves. 



