There is, therefore, in humid countries, a continuous drainage
through the soil after every rain, and in general there is a steady
downward movement of soil-water throughout the year. As is clearly
shown by the appearance, taste, and chemical composition of drainage
waters, this process leaches out considerable quantities of the
soluble constituents of the soil.
When the soil contains decomposing organic matter, such as roots,
leaves, stalks, the gas carbon dioxid is formed, which, when
dissolved in water, forms a solution of great solvent power. Water
passing through well-cultivated soils containing much humus leaches
out very much more material than 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.
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