. Bulletin. Forests and forestry -- United States. 154 FOREST INFLUENCES. Springs.—A spring is water which has penetrated the soil and reappears collected on the snrface. Springs are in most cases the heginnings-of brooks and rivers. Accord- ing to the manner in whicli tlie percolated water reaches the surface, springs may be classed as standing or running springs. The standing or ground-water s])riugs are such as collect water in some depression of the soil and overflow only as long as the water reaches the lower level of the out- let. Their formation is easily understood from the acccompauyi
. Bulletin. Forests and forestry -- United States. 154 FOREST INFLUENCES. Springs.—A spring is water which has penetrated the soil and reappears collected on the snrface. Springs are in most cases the heginnings-of brooks and rivers. Accord- ing to the manner in whicli tlie percolated water reaches the surface, springs may be classed as standing or running springs. The standing or ground-water s])riugs are such as collect water in some depression of the soil and overflow only as long as the water reaches the lower level of the out- let. Their formation is easily understood from the acccompauying figure (61), in which (1) represents a hillside of massive rock, continuing under the overlying strata at a. The latter consists of impermeable 8trata/2, 2) clay, loam, marl); above this a layer of gravel or coarse sand und rock material (3), and above this a stratum of soil (4), whicli at X is absent, leaving an open bowl where the gravel layer becomes visible. All the rain water falling on the plateau op and on the slope o a running down, when arriving at the impenetrable strata near h, will be diverted into the gravel bed and spread in this, being prevented l>y the underlying impermealjle strata from ?iinking. When sufficient water is supidied the water level rises until it appears at X, and if there is an outlet over the rim of the bowl and sufficient slope of the ground the spring begins to flow, forming, it may be, the beginning of a Such a standing or ground-water spring ceases to run if precipitation ceases for a length of time sufficient to reduce the water level lielow the outlet. Similar condi- tions can occur alongside of rivers when the seepage of the river supplies the water to a spring Ijelow the river level, and the level of these seepage waters rises and falls, of course, with the rise and fall of the river level. Of running springs, there may be distinguished, according to the manner of their formation, three —soil or surface springs, t
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