SPRING ( AS. spring, spryng, Oil G. spring, sprung, Ger. Spring, spring, from AS. springan, sprinean, OI1G. springan, Ger. springcn, to spring, leap; probably connected with Gk. v74yetlBac, sperehcsthai, Lith. sprugti, to spring away, es cape). A subterranean stream which discharges at the earth's surface. Most springs are fed by meteoric waters in the form of rain and snow that percolate into the soil and accumulate at some depth in the strata. This accumulation is known as ground water, and its upper surface, which is called the water-level, coincides more or less closely with the surface of the ground, receding from it, however, under the hill crests and approaching it closely under the valleys. When the side of a valley is steep or its floor is much depressed the ground water may come to the surface and escape as a spring. Springs may also be formed by the percolating waters encountering an impervions layer of clay or cemented sand which retards their further de scent, causing them to follow this dense stratum until they emerge on some hill slope. Springs of this character are more or less dependent on rainfall. All water in penetrating the soil and rocks, even if at no great depth, becomes more or less charged with dissolved mineral and or ganic matter, as by reason of its carbonic acid it possesses marked solvent powers. Spring waters therefore commonly contain various solid substances in solution, such as the carbonate, sulphate, or muriate of lime, salts of soda, pot ash, magnesia, and iron, or more rarely silica. When the quantity of dissolved solids is un usually large the spring is termed a mineral spring, and is often utilized for medicinal pur poses. See MINERAL WATERS.
Underground waters may collect above an im pervious stratum which does not appear at the surface, and they escape by slow percolation through the overlying strata. forming a marsh or swale. To such marshy tracts occurring in the arid regions of California, Arizona, and Mexico, the name cienega has been given.
Thermal springs, whose temperatures are nota bly higher than that of ordinary springs, usually have a deep-seated origin. In regions where the rocks have been greatly disturbed and fractured the surface waters penetrate to great depths, and thus become warmed by the interior heat of the earth, or they may he heated from contact with uncooled masses of lava. it is also known that igneous rocks of all kinds give off a great quan tity of vapor during the process of cooling, and some springs thus may he fed by waters whose source lies deep within the earth, and which for the first time appear at the surface. Ther mal springs are mostly limited to mountainous regions: in the United States they occur in great numbers along the Appalachians and the Rocky Mountains. In company with geysers they are found in the Yellowstone National Park, Iceland, and New Zealand. Consult Schneider, The Motion of Underground Water, Water Sup ply and Irrigation Papers, No. 67, United States Geological Survey (Washington, 1902). See