216 
SECOND BOOK. 
Humus, or vegetable soil, formed by the decay of plants. It is of a dark 
colour, and is even black sometimes. 
Soils composed almost entirely of decayed vegetable matter are known as peat. 
All fertile soils have some humus in them. 
Mixed Soils. — In describing a mixed soil we consider the propor- 
tions of sand and of clay in it. 
Loam has about equal parts of clay and sand. 
In a sandy loam the sand exceeds the clay, and in a clayey loam the clay exceeds 
the sand. 
A marl soil has lime in it. 
A chalky soil is more than one-fifth lime. 
The classification is shown in the diagram. 
SANDY. CLAY. 
More than J sand. | More than f clay. 
LOAM. 
Nearly \ clay and J sand. 
SANDY LOAM. ~ ~ CLAY LOAM. 
About 2 parts sand and 1 part clay. About 2 parts clay and 1 part sand. 
Descriptions Of Soils. — Soils may also be described thus — - 
Alluvial ; if laid down by water. 
Local ; if it has been formed where it is found. 
Transported ; if it has been carried to a distance by wind or water. 
Surface Soil ; top soil. 
Subsoil ; underlying the surface soil. 
Heavy or Stiff; a clayey soil, which is “heavy” or “stiff” to work. 
Light or Free ; a sandy soil, which is “ light ” or “free ” to work. 
MORE ABOUT THE SOIL (p. 87). 
Plant-food. — The plant-food in the soil may be — 
1. Active; being soluble in rain-water ; or 
2. Dormant, i.e. “sleeping”; being insoluble in rain-water, and unable 
to feed the crops. 
Moisture. — All soils hold moisture, though not in the same degree. 
Water drains downwards through the soil ; it also rises as the surface-soil dries. 
TILLAGE (p. 89). 
The object of tillage is to increase the fertility of the soil. This it does 
in the following ways — 
1. It prevents hardening of surface, and lets in air and water. 
