257 
Chemical Composition. 
Moisture 3. 300 
Organic matter and combined water 8.000 
Oxide of iron and manganese 7.400 
Oxide of alumina 8.200 
Lime 0.060 
Magnesia 0.054 
Potash . 0.085 
Phosphoric acid 0.010 
Soda 0.074 
Sulphuric acid 0.008 
Chlorine 0.003 
Sand and silicates 72.806 
100.000 
Containing nitrogen 0.128 
Equal to ammonia 0.156 
Lower oxide of iron Trace 
Acidity Much 
Citric soluble potash 0.006 
Critic soluble phosphoric acid Nil 
Alluvial Soil. — For physical properties these soils are usually 
good, and the amount of sediment periodically deposited during 
floods adds considerably to the chemical richness of the soil. 
They are largely composed of the lighter materials carried 
down in suspension by moving water. The particles are very 
fine, most of them passing a 60 mesh. The fineness of such soils 
partly depends on the speed of the moving water ; the swifter the 
flow the coarser the particles. 
The particles are arrested and precipitated all along the banks 
of the river during flood time. During heavy floods very large 
quantities of matter are often deposited along the banks, but they 
are often of a coarser nature due to the higher speed. 
The particles which go to make up all alluvial soil may have 
been brought from considerable distances ; they constitute the fine 
parts of soils liable to wash within the drainage area of the river. 
Attempts have been made in some countries to regain this sus- 
pended soil by the process called "warping," which is only prac- 
ticable in the neighborhood of tidal estuaries. This is accom- 
plished by letting the water run over the land, and then cutting it 
off from the main supply by sluices ; after some time, by repeatedly 
going through this process, a soil is built up. This artificial allu- 
vial soil is usually rich in organic matter and other plant food, 
but usually poor in soluble food such as potash. 
