SPRINGS. Rain and snow fall in quantities so unequal in different districts, and on soils which exercise upon them such various influ ences, that the phenomena of springs, which are primarily dependent on the penetration to some depth in the earth of water which was absorbed at the surface, are extremely complicated and curious. It is very interesting to geologists to classify and determine the causes of these phenomena, and very important in agriculture and the arts to acquire a power of directing the water currents in and below the soil and strata. The art of draining consists essentially in giving to the diffused and injurious springiness of particular soils and situations a concentrated, perhaps beneficial, current ; while artesian wells relieve the hydrostatic pressure prevalent at great depths, and yield copious streams in dry lands and deserts.
As a general rule, springs are permanent in proportion to the depth to which the water which supplies them has descended from the surface; they are perennial and almost invariably constant in temperature and volume, whether hot or cold, copious or full, in situations where, from the arrangement of the mineral masses of the globe, deep subterranean channels exist for the reception of rain, and particular impediments direct and contract the passages of reflux to the surface. Such cases are common in stratified countries where jointed limestones or sandstones receive water at elevated points on the surface, and conduct it downwards below strata of clay, which are only pervious at a few points, and there permit natural discharges at lower levels than the recipient surfaces. Frequently these argillaceous strata are so nearly impervious, that artificial perforations relieve the pressure of the subterranean columns of water better than the few natural points of efflux, and thus pits and levels excavated for mines may drain springs at some distance.
On the contrary, in a country which contains narrow and frecTuently mixed masses of clay and gravel, or clay and sand, which cover the solid rocks, concentrated springs are almost absent, but there is a prevalent humidity and diffused springiness along the limit of the gravelly or sandy tracts. After a continuance of dry weather such springs and wetness disappear, to be renewed after the next fall of rain.
The particular points at the surface where springs, or "wells," as they are often called in the districts where somewhat of the Saxon elements of our language remains (quelle, in German, signifying not what is commonly understood by the English word " well," and the French " puit," but a spring), are determined in general by one of three things: 1. They occur at the point of lowest level, on the edge of the impervious clay which dams up the water. This happens in the cretaceous and oolitic districts of England.
2. They are often dependent on the lines of great joints, or fissures of the rocks, produced in the course of the consolidation and shrinking of the mineral masses. Large springs are thus poured out of the
mountain-limestone of England.
3. The waters are directed to the surface by lines of fault, which are often quite impervious to water, and traverse the rocks in vertical or inclined planes. The hot springs of England and Wales are mostly thus circumstanced.
In general, then, the water which issues from the earth in one copious spring has been received by minute absorption on a large surface : as the living tissue of a sponge receives water by absorption through the numerous pores, collects it internally in a few channels, and rejects it by a very limited number of orifices, or as the capillaries collect blood for the veins, and these supply the heart, so the porous texture and channelled structures of rocks permit that continual circulation of water below the earth's surface, on which, in a great degree, its habitable character depends.
Between perennial or constant springs, and those which are merely dependent on the last shower of rain, the gradations are insensible, and the explanation is entirely obvious upon the general principles stated. One of the most interesting cases of this intermediate series, is that of the " intermitting " springs. It is a common circumstance on the chalk downs of the South of England (Wiltshire, Dorsetshire) for the valleys to be quite dry in one part of the year (autumn or winter), and very fully watered in another (spring, summer); the springs bursting higher up the valley in some years than in others, according to the quantity of rain which fell in some previous season (as the autumn), and the rate of its transmission through the jointed and absorbent chalk.
Another peculiarity of springs flowing out of cavernous limestone rocks is marked by a variable discharge ; the springs now gush with vehemence, now subside, shrink away, and disappear. These ebbing and flowing wells are noticed in many districts, as near Dynevor in Caermarthenshire, at Tideswell in Derbyshire, and near Settle in Yorkshire. The explanation most generally received supposes the water to fill cavities underground, from which the discharging channels are siphon-formed, so that at a particular moment the full cavity begins to be discharged and finally runs out, and the current then ceases till the space be again filled to the vertex of the siphon.formed arch.
In thus descending downwards and rising upwards through various mineral masses, springs become impregnated with gaseous, saline, earthy, or metallic admixtures—as carbonic acid gas, sulphuretted hydrogen gas, nitrogen, muriate of soda, sulphate of lime, carbonate of lime, silica, carbonate of iron, &c. [ARTESIAN WELL; WATERS, 3frx ens L.]