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THE WATERS UNDER THE EARTH

The underground lake in its magnificent setting of dazzling stone columns and stalactites in the Cheddar Caves, England. All these wonderful natural halls, chasms and snowy incrustations were formed by the age-long action of the water on the limestone rocks through which it filtered.

Water is found in Nature in three states or conditions—as ice, vapor or steam, and as simple water. These three forms have the same chemical composition—the substance being a compound of oxygen and hydrogen, represented by the formula H₂O; but the physical condition depends entirely on its temperature. Under ordinary atmospheric conditions water is a solid below 32 degrees Fahrenheit; a gas above 212 degrees Fahrenheit, and a liquid between these temperatures.

The purest form of water which exists in nature is rain water, though this always contains a little oxygen and carbon dioxide dissolved from the air. To obtain pure water artificially, any ordinary water is distilled, when all the solids dissolved in it are left behind. River water and spring water always contain a small quantity of solid matter, the amount and nature of the dissolved solids depending on the nature of the rocks over which the water has flowed.

Geographically it may be considered under the four heads of springs, rivers, lakes, and the ocean, which taken together forms the hydrosphere of the earth.