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 brook. 



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 kiud.s — soil or surface springs, tissure sitrings, and cavern springs. 



A surface spring originates when a more or less imiiermeable soil lorms part of or 

 lies near the upper soil stratum, allowing the water to enter only imperfectly and 

 to an iuconsideralde depth, and, passing through the looser parts of the soil, to col- 

 lect and como to the snrface at some point where the top soil is absent. These 

 shallow- soil springs naturally vary quite 8ensil)ly, according to the physical condi- 

 tions of the surface, and are dependent directly on tlie ])recipitatii)n ; ilry uj) easily 

 if it does not rain or if the soil is exposed to in.solation and is de])rived of shade; 

 they are warm in summer and freeze out in winter. They are usually found in local- 

 ities where the rock consists of easily disintegrated clay slates and sandstones, 

 capped with a shallow layer of decomposed rock, or in the neighborhood of loam 

 hills. An addition of broken rock and stones to the soil facilitates tlie penetration 

 of the water aiid increases the comparative tlow of tliese springs. 



Wlnde districts along the foot of the Alps in Switzerland. Bavaria, Austria, and 

 the Carpathians in Galicia, etc., have hardly any other kind of springs. 



The second class, conveniently called " fissure" si)rings, originate from the waters 

 which have deeply peneti'ated the soil and rock through the fissures, rents, and splits, 

 or numberless cleavage strata of the ujtper rock torniations, and ultimately reach a 

 deeper lying inclined rock formation, which prevents further penetration and causes 



