SPRING, a stream of water issuing from the earth. The source of springs is the rain and snow that falls from the clouds. Very little of the water precipitated in any district finds its way immediately by rivers to the sea; the great proportion is either evaporated from the surface of the earth, and, reabsorbed by the atthosphere, is employed by plants and animals, or sinks into the earth. All loose soils and gravels greedily absorb water, which descends until it meets with a stratum through which it cannot penetrate. A pit dug into the water-charged soil would speedily fill itself by draining the water from the soil. All rocks contain water; some retain it by capillary attraction, like a sponge, others hold it merely mechanically, and easily part with it. Chalk will absorb and retain One-third of its bulk of water; and sand, on the other hand, while it will absorb as much, will part with nearly the whole amount to a well dug in it. Argillaceous deposits and compact rocks are barriers to the passage of water, and cause the superincumbent per vious strata to become water-logged, where there is no outlet,. Sometimes the edges of the strata are exposed on the sides of a valley, and permit the free escape of the con tained water, which pours front them over the neighboring land. But rents and fissures, as well as inequalities on the surface of the impervious beds, give the water a circum scribed course, and cause it to issue in springs.
The water, as it percolates through the earth, always or less charged with foreign matter, owing to its solvent property. Carbonate, sulphate, and !titillate of lime. muriate, of soda, and iron, are the most common impurities in spring-waters; magnesia and silica also frequently occur. These substances, from evaporation of part of the water, or the escape of the carbonic acid gas,. by which so large a quantity is often held in solution, are frequently deposik-d on the margins of the springs, or in the courses of the streams flowing front them. Such deposits are found in all so-called petrifying springs; the hot wells of Iceland and the Azores are surround?d ith basins formed of siliceous sinter which has been derived from the water. WI en the
foreign ingredients intV0 medicinal qualities, the springs are known as mineral waters 44 Springs are either associated with the st:perf.cial strata, or rise from a considerable depth. Surface-springs occur where the absorbent surface-deposits rest on an impervious bed, which prevents the further downward progress of the .water, or where the beds through which the water flows are near the sur face, as shown in fig. 1, where C and E are impervious clay-beds, and D is a bed of sand or gravel, which in the upper portion is exposed on the surface, or is only overlaid by loose soil, and after being col ered for some distance by the clay bed C, makes its appearance at B, where the valley cuts it throuLdi ; here the water collected over the.area, A, is discharged. Surface-springs, depending as,they do so directly on the rain for supplies, are very variable in the amount' of water they deliver. They frequently fail entirely in the summer, and always after great droughts.
Their temperature varies with that of the district where they exist,. being warm in sum mer, and cold in winter, as they do not penetrate below that plane in the earth's crust which is affected by the seasonal changes in temperature.
When the bed which forms the reservoir for the' spring is at such a distance from-the -.surface as to be beyond the zone of season changes, and yet within that which is influ enced by the climate, the water has a temperature equal to the mean temperature of the locality where it springs. Such springs have generally a large area for the collection of the superficial water, and are consequently regular in the quantity of water they give out. They are brought to the surface by means of faults. The celebrated well of St. Winifred at Holywell, in Fliutshire, rises through a fault in the coal measures. It dis charges at the rate of about 4,400 gallons per minute, being the most copious spring in Eng land, and the water, in its short course of little more than a mile to the sea, is used to propel 11 mills.