In regions where the strata are pierced with wide and deep caverns, and especially in calcareous countries, the waters sometimes accumulate in sufficient quantities to form perfect streams with long subterranean courses. At their issue from the caverns, these waters form a contrast with the rocks and hills around, all the more striking because the latter are completely devoid of moisture, and fearfully sterile, while on the brink of the limpid stream the fresh verdure of plants and trees is at once developed. Like a captive, joyous at seeing the light once more, the water which shoots forth from the sombre grotto of rocks sparkles in the sun, and careers along with a light murmur between its flowery banks. Among these subterranean streams, the most celebrated, and doubtless one of the most beautiful, is the Sorgues of Vaucluse. The vaulted grotto from which the mighty mass of water escapes opens at the mouth of an amphitheatre of calcareous rocks with perpendicular sides. Above the spring rises a high white cliff, bearing on its summit a ruined tower of the Middle Ages; the rock is everywhere sterile and bare; there is nothing but a miserable fig-tree, clinging to the stone like a parasitical plant to the bark of a tree, which has plunged its roots into the fissure of the cave, and greedily absorbs with its leaves the moisture which floats like a mist above the cascades of the spring. After heavy rains, the liquid mass, which is then estimated at 26 or even 32 cubic yards a second, flows in a wide sheet high above the entrance to the cavern, which is then altogether inaccessible. When the waters are low, they flow bubbling across the barrier of rocky débris which obstructs the entrance; at that time it is quite possible to penetrate under the arch, and to contemplate the vast basin in which the blue waters of the subterranean stream spread out before they leap into the open air. Soon after its issue from the cave and amphitheatre of Vaucluse, the Sorgues is divided into numerous irrigation channels, which spread fertility in the country over an area of more than 77 square miles. The subterranean course of the affluents which form the stream is not ascertained; but it is known that most of them commence 12 or 15 miles to the east, in the plateaus of Saint Christol and Lagarde, which are pierced all over with _avens_ or chasms, into which the rain-water sinks and disappears.