66 DRY-FARMING 
pure water could do. A study of the composition 
of the drainage waters from soils and the waters of 
the great rivers shows that immense quantities of 
soluble soil constituents are taken out of the soil 
in countries of abundant rainfall. These materials 
ultimately reach the ocean, where they are and have 
been concentrated throughout the ages. In short, 
the saltiness of the ocean is due to the substances 
that have been washed from the soils in countries 
of abundant rainfall. 
In arid regions, on the other hand, the rainfall 
penetrates the soil only a few feet. In time, it is 
returned to the surface by the action of plants or 
sunshine and evaporated into the air. It is true 
that under proper methods of tillage even the light 
rainfall of arid and semiarid regions may be made to 
pass to considerable soil depths, yet there is little 
if any drainage of water through the soil into the 
standing ground water. The arid regions of the 
world, therefore, contribute proportionately a small 
amount of the substances which make up the salt 
of the sea. 
Alkali soils.— Under favorable conditions it 
sometimes happens that the soluble materials, which 
would normally be washed out of humid soils, accu- 
mulate to so large a degree in arid soils as to make 
the lands unfitted for agricultural purposes. Such 
lands are called alkali lands. Unwise irrigation in 
arid climates frequently produces alkali spots, but 
