Page:Popular Science Monthly Volume 32.djvu/635

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615
UNDERGROUND WATERS AS SOCIAL FACTORS.

bottom not far from the shore. The limestone around Mont Ventoux is riddled in a zone of seventy kilometres by natural wells and unfathomable pits, many of which bear names well known in the local legends. The waters which these rocks have stored up are poured out at their lowest point, and give rise, in a picturesque grotto, to the copious fountain of Vaucluse, which was formerly regarded as a beneficent divinity. Compared with the depth of the rains at different stations in the basin, the mean outflow of the fountain indicates a volume of infiltration equal to about six tenths of the quantity of rain-water. The limestone under the valley of the Loire, at Orleans, is plowed by interior currents from which the water-supply of the city is directly taken. The waters begin to be lost at a point some forty kilometres above the city, and return to the river about thirty kilometres below. The Iton, in the department of the Eure, fails to flow over the surface for several kilometres, and is called the Sec-Iton, or dry Iton; but its waters are reached in their subterranean course by excavations of twenty metres. Similar facts may be observed in all parts of the globe. By a similar kind of drainage the cavernous limestone of the Apennines gives rise to the Aqua Martia, which was brought to Rome b. c. 608 by the consul Quintus Marcius, and which still continues to be of prime importance to the city; "the most celebrated water in the universe," enthusiastically says Pliny, "a franchise of salubrity, one of the benefits granted to Rome by the favor of the gods."

A grain of truth sometimes lies at the bottom of the ancient fictions. Was not the observation of water-courses which are ingulfed and appear again the origin of the fable of the fountain of Arethusa, which the Greeks regarded as the reappearance of the river Alpheus? After a pursuit from Peloponnesus across the Ionian Sea, it was supposed to overtake the nymph personified in this fountain at the moment when it gushed out near Syracuse.

Besides moving through the interstices, fissures, and cavities of the crust of the globe, water exists everywhere in another state, in which, although quite invisible, it is of hardly less importance. All rocks, including the most compact ones, inclose water within their pores, however minute they may be, where it is held by capillary attraction, and is not apparent to our instruments of highest magnifying power. But it may be disengaged by desiccation, when the rock will be found to have lost a sensible fraction, some ten thousandths at least, of its weight. At the same time some of the qualities of the rock are modified; for workers in slate, sandstone, and other rocks find it a matter of great difference, in the facility of their tasks, whether these stones still hold their quarry-water or have been dried in the air. The Romans availed themselves of the porosity of the onyx to soak it in certain liquids which would enliven the color of the stones that they used in their cameos. Under this form of intimate latent impregnation,