through all these natural obstacles, may therefore justly be considered as a masterpiece of mechanical skill. As the pipes must often ascend mountains, the highest elevation above the pit being 1,218 feet, and then again slant down into ravines; as in many parts rocks had to be levelled and forests cut down for the purpose of laying them, and as they are subject to frequent damage in a severe climate, it may easily be imagined that the greatest engineering power was required for the execution of so grand a work.

Hydraulic machines serve to raise the brine over the mountains, and the water-power of the rivulets descending from the heights is used for forcing it upwards. The contrivance is so admirable that the small machine at Berchtesgaden raises 270 cwt. of brine to a height of 311 feet by means of an equal weight of water descending from a height of 375 feet. In some parts the tubes of this colossal duct run along the high road, in others tunnels have been pierced to shorten the distance.

Thus the Alpine rock-salt requires much ingenuity to be rendered productive, while in other parts we find rock-salt cropping out on the surface of the earth, so as to be very easily worked. The soil of many extensive wastes in Asia and Africa is covered and impregnated with salt, which has never been inclosed by superimposed deposits. Near Lake Oroomiah, in Persia, it forms hills and extensive plains, and it abounds in the neighbourhood of the Caspian Sea.

In the valley of Cardona in the Pyrenees two thick masses of rock-salt, apparently united at their bases, make their appearance on one of the slopes of the hill. One of the beds, or rather masses, has been worked, and measures about 130 yards by 250, but its depth has not been determined. It consists of salt in a laminated condition and with confused crystallisation. That part which is exposed is composed of eight beds, nearly horizontal, and having a total thickness of fifteen feet, but the beds are separated from one another by red and variegated marls and gypsum. The second mass not worked appears to be unstratified, but in other respects resembles the former; and this portion, where it has been exposed to the action of the weather, is steeply scarped and

bristles with needlelike points, so that its appearance has been compared to that of a glacier.

The rock-salt deposit of Ilezk, about fifty miles to the south of Orenburg, in Russia, is still more remarkable. On the sides of a crater-like pit, which has been dug into the mass where it most nearly approaches the surface, the rocksalt is seen standing in perpendicular walls. On the west side of the gap a convenient staircase leads to the bottom. The salt is hewn in large square blocks, which are afterwards sawn into smaller pieces of eighty-five pounds. The regular annual produce is fixed by Government at 700,000 pud, or about 10,000 tons, of which part is furnished gratuitously to the neighbouring Kirghise hordes, who no doubt are made to pay dearly for their salt in some other manner.

The labours in the mine are only carried on during the summer, and begin by pumping out the water which has settled at the bottom of the pit from the melting snow; while the transport to the next river by means of sledges takes place during the winter. Were this mine situated in a less barbarous or more accessible country, it might easily rival, or even surpass, the produce of Cheshire. To the south of the pit, where the regular mining operations, such as they are, take place, a great number of old pits or holes may be seen, in which the Cossacks, Baschkirs, and Kirghise used to provide themselves with salt before Government undertook the regular working of the mine in 1754. These pits, some of which are sixty feet square, and from six to eight feet deep, are generally full of a saturated brine of a brownish colour, and are made use of for bathing by the Kirghise, who justly consider them as an excellent remedy for many diseases.

Before 1856 all the salt produced in Prussia was obtained from brine springs, but since that time enormous beds of rock-salt have been discovered in various parts of the kingdom. Those of Stassfurt, near Magdeburg, produced 2,256,000 cwt. in 1866, part of which was exported into foreign countries, through the ports of Lubeck and Hamburg. But the mines of Stassfurt, besides rock-salt, contain also an inexhaustible quantity of highly valuable potash salts, which are largely used for agricultural purposes, and supply the

METHOD OF WORKING ROCK-SALT.

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wants of the numerous chemical manufactories which have rapidly converted an obscure hamlet into a flourishing seat of industry. At Speerenberg, about twenty miles to the south of Berlin, the earth-borer has pierced through an enormous deposit of rock-salt, more than two thousand feet thick, and at Segeberg, in the province of Sleswig-Holstein, a shaft is now being sunk into a rich bed of rock-salt, recently discovered.

The method of preparing the rock-salt, and the processes employed in manufacturing salt from brine springs, are nearly the same in all salt-works. The first process is to obtain a proper strength of brine, either by saturating fresh water with the salt that has been brought up from the mine, or pumping up the salt water from springs that have become saturated by passing through saliferous beds. The brine obtained in a clear state is put into evaporating pans and brought as quickly as possible to a boiling heat (in the case of strong brine 226° F.), when a skin is formed on the surface, consisting chiefly of impurities. This is taken off, and either thrown away or used for agricultural purposes, and the first crystals which form are likewise raked away and thrown aside as of little value. The heat is then kept up to the boiling point for about eight hours, during which time evaporation goes on steadily, the liquid gradually diminishing, and the salt being deposited; it is then raked out, put into moulds, and placed in a drying stove, to render it perfectly dry and ready for sale.

When salt is to be prepared from the weak brines which are of common occurrence in France and Germany, the brine is concentrated by natural evaporation previous to the more costly application of artificial heat. Having been first raised by pumps, it is then allowed to trickle in a continuous stream down the surface of bundles of thorns exposed to the sun and wind, and built up in regular walls between parallel wooden frames. These evaporating works (Gradirwerke or graduation-houses) are frequently of an immense extent. At Salza, near Schönebeck, for instance, the graduationhouse is 5,817 feet long, the thorn walls are from 33 to 52 feet high in different parts, and present a total surface of 25,000 feet. According to the weakness of the brine it

must be the more frequently pumped up and made to flow down repeatedly over the thorns in different compartments of the building. An immense quantity of fuel is saved by this economical mode of evaporation.

The origin of rock-salt deposits is one of the most interesting geological questions. According to some authorities, they were the result of igneous agency, while others are of opinion that in every case they have been deposited from solution in water. Their usual occurrence in lenticular or irregularly-shaped beds, having a great horizontal extension, favours the aqueous theory, for masses protruded upwards, or sublimated by volcanic power, are generally found to occupy vertical fissures. To account for their formation we must suppose a sea such as the Mediterranean cut off by an elevation of the land at its mouth from its previous communication with the ocean, and gradually losing more water by evaporation than it receives by rain and rivers. As thus the amount of salt which it holds dissolved increases, deposits of rock-salt will ultimately form at the bottom of its deepest parts, and subsequent changes in the earth's surface may then either conceal them under superincumbent strata, as at Northwich, or leave them exposed, as in many of the African or Asiatic wastes.

CHAPTER XXXV.

SULPHUR.

Sulphur Mines of Sicily-Conflagration of a Sulphur Mine-The Solfataras of Krisuvick-Iwogasima in Japan-Solfatara of Puzzuoli-Crater of Teneriffe -Alaghez-Büdöshegy in Transylvania-Sulphur from the Throat of Popocatepetl Sulphurous Springs-Pyrites-Mines of San Domingos in PortugalThe Baron of Pommorão.

THOU

ПHOUGH in every volcanic region of the globe sulphurous exhalations arise from a great number of craters or solfataras, yet sulphur is but rarely found in sufficient quantities to remunerate the miner's toil. In this respect the island of Sicily is unrivalled, for no other country possesses such masses of this valuable, and in many cases indispensable, mineral.

The numerous sulphur pits of Sicily, which occur in crevices or hollows over a space of 150 geographical miles, are situated chiefly in the southern part of the island, in the districts between the sea-border of the province of Girgenti and the mountains of Etna, Mannaro, Castro Giovanni, and Catolica. They are no doubt the produce of a vast volcanic action which took place about the beginning of the tertiary period, when the sulphurous fumes, rising through countless clefts or fumaroles from the mysterious furnaces of the deep, condensed in the chalk and clay grounds of the superficial strata.

In former times, as long as the chief use of sulphur was confined to the fabrication of gunpowder, its production was comparatively insignificant; but since the manufacture of sulphuric acid has become a branch of industry of continually increasing importance, sulphur, the ingredient necessary to its formation, has considerably risen in value, and now constitutes the chief article of Sicilian exportation.