It is to be remarked that nearly all thermal springs which do not owe their high temperature to the vicinity of volcanoes issue forth from faults which open on the surface of masses of a crystalline nature, and principally at the side of modern eruptive rocks which have been thrust up through older strata. The influence of rains and seasons has much less effect upon thermal waters than upon cold springs which proceed from the upper layers of the soil. A great number of warm springs, however, undergo certain changes in their yield of water, which must be without doubt attributable, at least partially, to the same causes as the variations in the discharges of superficial streams. In Auvergne, in the Pyrenees, and in Switzerland, several springs, perfectly protected against any infiltration of rain-water, flow in much greater abundance at the very same period when the adjacent torrents become swollen. At Brig-Baden, in the Valais, the water, the mean temperature of which is in autumn and winter from 71° to 72° (Fahr.), rises to 113° and 122° (Fahr.) when the breath of spring melts the ice on the Jungfrau. Most thermal springs contain mineral substances in solution; there are, however, a certain number which are almost as pure as rain-water--such as, for instance, the celebrated waters of Plombières, also that of Gastein, Pfeffers, Wildbad, and Badenweiler. The springs of Chaudes-Aigues--those in France which have the highest temperature, 158° to 176° (Fahr.)--contain only a small amount of mineral substances. The inhabitants of Chaudes-Aigues use the water to prepare their food, to wash their linen, and to warm their houses. Wooden conduits, erected in all the streets of the town, supply, on the ground floor of each house, a reservoir which serves to heat it during cold weather, and thus dispenses with fires and chimneys. Among the various substances which spring-water brings to the surface, those which are most common proceed from the strata which serve to constitute the very framework of the globe. Chalk, especially, occurs in different proportions in most springs, either under the form of sulphate of lime, or, more often, as carbonate of lime. Water which contains carbonic acid in solution is charged with calcareous matter dissolved away from the sides of the rocks through which it passes; then, by means of evaporation, it redeposits the stony substances which it previously held in solution. Hence arise all those calcareous concretions which form around so many springs; also the stalactites in caverns. [Illustration: The Giant’s Causeway, Antrim, Ireland]