148 ELEMENTARY AGRICULTURE 
freezes, thaws and bursts its object into many small 
fragments. Ice also forms into great glaciers or ava¬ 
lanches. The movement and pressure breaks, grinds, 
and transports soil particles. Wind is another one 
of our soil builders. It carries on its work by picking 
up fine sand and blowing it against giant boulders and 
gradually cutting them away. Plants send their roots 
into the crevices of rocks and pry the material apart. 
Animals burrow into the ground and open up channels 
where water and elements of the air enter and cause 
changes in the soil. 
Fig. 113.—Types of soil, clay, sand, loam. 
Soils Classified as to Formation.—The two principal 
classes of soils according to the method of formation 
are the sedentary and transported. The sedentary soil 
is further divided for convenience of study into what 
is known as residual and cumulose soil. The residual 
soil is soil that remains where it is formed by weath¬ 
ering forces. This type of soil represents some of our 
poorer soils as well as some of our better farm lands. 
The limestone and sandy soils that are found in some 
of our Southern states are good examples of this class 
of soils. Cumulose soil is formed by the accumulation 
of waste materials in shallow lakes, or other low places. 
