“Onondaga factory filled salt” is as pure as the rock salt of Cheshire, England, which is one of the purest known. An impurity of 3 per cent. renders salt unfit for domestic purposes, especially if the impurity consist of chlorides of calcium and magnesium, particularly the former. Beds of rock salt and brine springs occur in geological formations of almost every period. The New York springs are in the upper Silurian, and most of those of western Pennsylvania and Virginia, of Michigan, Ohio, Indiana, Illinois, and Kentucky, in the lower coal measures; most of the Russian mines and springs are in the Permian; those of Cheshire in England, Ireland, eastern France, Würtemberg, and many other parts of Germany, in different members of the triassic group; those of the Austrian Alps in oolitic beds; those of the Pyrenees and of Cardona in cretaceous rocks; while those of Wieliczka in Galicia, of Tuscany, Sicily, and Petite Anse belong to tertiary strata. Its most invariable mineral associate is gypsum or hydrated sulphate of lime; in some places, as at Bex in Switzerland, this is replaced by anhydrite, or the same mineral without water; while polyhalite (a mineral consisting of sulphates of lime, magnesia, potash, and soda), bitumen, sulphur, and calc spar also frequently occur with it; and in many places, as in the wells in the coal formation, a copious discharge of carburetted hydrogen gas accompanies the flow of brine, and also jets of rock oil. (See Petroleum, vol. xiii., p. 370.)—Geographically salt is widely distributed. Excepting Norway, Denmark, and Holland, the European countries are all provided with salt to some extent from domestic sources, and even in some of these rock salt is imported and refined. The principal mines of rock salt are those of Wieliczka in Galicia; at Hall in the Tyrol, and along the mountain range through Aussee, in Styria, Ebensee, Ischl, and Hallstadt in Upper Austria, Hallein in Salzburg, and Reichenhall in Bavaria; in Hungary in the county of Mármaros; in Transylvania, Moldavia, and Wallachia; at Vic and Dieuze in German Lorraine; at Bex in Switzerland; in the valley of Cardona and elsewhere in Spain; in the region around Northwich in Cheshire, England; near Carrickfergus, Ireland; and in the government of Perm in Russia. The principal salt springs are in Cheshire, Worcestershire, and Staffordshire, England; in Würtemberg and Prussian Saxony; and in northern Italy. Russia is almost the only country which derives much from salt lakes. France, Spain, Portugal, and Italy, with a number of the islands of the Mediterranean, are the principal producers of sea salt. England, Austria, France, Spain, Portugal, and Italy, with some of the Mediterranean islands, are the principal exporters of salt.—In Russia the supplies from mines, springs, and lakes are inexhaustible. Over the vast area of the Permian group, covering upward of 300,000 sq. m., salt is found, and in numerous localities is extensively and profitably worked. Ancient mines of rock salt have been explored in the Caucasus, supposed to be among the oldest in the world. In Sweden, Carlstad near the N. shore of Lake Wener produces some salt, but both Sweden and Norway import much, principally from England and Sardinia. Denmark is also a large importer. In Holland and Belgium refined salt is made from British rock salt, which is dissolved in fresh or sea water, and crystallized by artificial heat. Among the largest salt mines in the world are those of Stassfurt in Prussia, and the adjoining Anhalt mines.—In the Austrian empire, Upper Austria, Salzburg, Styria, and Tyrol on the west, and Croatia and Dalmatia on the south, have almost inexhaustible stores of rock salt and brine springs; while the province of Istria derives much wealth from the lagoons bordering the Adriatic. The salt mines of Wieliczka, 7 m. S. E. of Cracow, extend over a space of about 2 m. in length by nearly 1 m. in breadth, and are about 1,000 ft. in depth. The salt occurs in great lenticular masses, inclined at a high angle. It varies very much in quality; the so-called “green salt” contains 5 or 6 per cent. of clay, which destroys its transparency; a variety called śpiza is crystalline and mixed with sand; while that known as szybik, principally from the lower levels, is in largely crystallized masses, perfectly pure and transparent. The strata in which it occurs are compact tertiary clays, containing fossils; and the principal associated minerals, besides gypsum, are bitumen, anhydrous sulphate of lime, the sulphates of baryta and strontia, and sulphur. The mines are entered by numerous shafts, with galleries at seven different levels, leading to a labyrinth of passages and immense excavations extending to a total length of upward of 500 m. Some of the chambers formerly excavated were more than 150 ft. high, but those now made are much smaller. One of these is fitted up as a chapel dedicated to St. Anthony, in which the altar, statues, columns, pulpit, &c., are all of salt. In another part is a lake 650 ft. long and 40 ft. deep, formed by the water which trickles through the strata. The annual yield is now about 1,400,000 cwt. It is not known when these mines were discovered. They are believed by recent authorities to have been worked in the early part of the 11th century, when they belonged to Poland, and in the 14th Casimir the Great established regulations for their working, as they had then become very productive. They were pledged to Austria in 1656, but recovered by John Sobieski in 1683. In 1772, when the first dismemberment of Poland took place, Austria again obtained them, and, except from 1809 to 1815, has since held them. The kings of Poland drew considerable revenues from these mines, and depended upon them for the dowries of their queens and the endowments of their convents, to which last purpose their revenues were applied as early as the
