SALT 741 



1 ,200 feet deep), it occurs in tertiary strata. But in addition to these concealed deposits, 

 this substance presents itself in vast masses upon many parts of the earth's surface : 

 in the high lands of Asia and Africa are often extensive wastes, the soil of -which is 

 covered and impregnated with salt, which has never been enclosed by superimposed 

 deposits ; near Lake Oroomiah, in the N.W. of Persia, it forms hills and* extended 

 plains ; it abounds in the neighbourhood of the Caspian Sea, and penetrates the entire 

 soil of the steppes of the south of Russia. 



The beds of rock-salt arc sometimes so thick, as at Wieliczka and Northwich, that 

 they have not yet been sunk through, although mined for many centuries ; but in 

 ordinary cases the thickness of the layers varies from an inch or two to ten or fifteen 

 yards. When the strata are thin, they are usually numerous, and throughout a 

 certain extent parallel ; but when explored at several points such enlargements and 

 diminutions are observed, as to destroy this appearance of parallelism. 



It has been remarked that the plants which generally grow on the sea-shore, such 

 as the Triylochin maritimum, the Salicornia, the Salsola Kali, the Aster trifolium, or 

 'farewell-to-summer,' the Glaux maritima, &c., occur also in the neighbourhood of salt- 

 mines and salt springs, even of those which are most deeply buried beneath the surface. 

 It is also generally found that the interior of salt-mines is extremely dry, so that the 

 dust produced in the workings becomes an annoyance to the miners, though in other 

 respects the excavations are not insalubrious. 



Much discussion has been raised concerning the origin of these rock-salt deposits ; 

 some asserting that they were the result of igneous agency, and others that they have 

 been in every case deposited from solution in water. The great argument in favour of 

 the former view appears to rest upon the fact, that chloride of sodium and Hydrochloric 

 acid gas are among the substances erupted by volcanoes ; whilst, on the other hand, it 

 is urged that the specimens of erupted chloride of sodium which have been analysed 

 always differ much from rock-salt, since they contain a large amount of chloride of 

 potassium ; and in addition to this, the frequent occurrence of bodies such as bitumen 

 and organic remains, and of cavities containing liquids, and in some cases gases, in 

 almost all varieties of rock-salt, are held to furnish indisputable proof of the deposi- 

 tion of this substance from its aqueous solution. The occurrence of sandstone pseu- 

 domorphs in the cubical form of rock-salt, also favours this opinion ; and so also does 

 the general character of these deposits ; they are usually lenticular, or irregularly- 

 shaped beds, having a great horizontal extension, and but rarely occur in the form 

 of dykes, or masses filling vertical fissures, which is the usual form assumed by a 

 molten mass projected upwards from the interior of the earth. The method of its 

 formation was, according to those who hold the aqueous theory, somewhat as follows: 

 A sea, such as the Mediterranean, is, by an elevation of the land at Gibraltar, cut off 

 from communication with the ocean ; the rate of evaporation from its surface is 

 greater than the supply of water by rain and rivers, consequently the amount of salts 

 which it holds dissolved, increases; now chloride of sodium is the principal saline 

 constituent of sea-water, and Bischof s experiments have shown that wheji a solution 

 of this salt is allowed to be at rest, the particles of salt sink, so that the lower 

 layers soon become more saturated than the upper ; concentration is then supposed to 

 go on until at the undisturbed bottom of this inland sea a saturated solution of chloride 

 of sodium exists, from which masses of rock-salt are slowly deposited. Its great 

 purity is accounted for by the fact, that the other salts existing in sea- water are either 

 far less or far more soluble than chloride of sodium ; thus the carbonate and sulphate 

 of lime would be almost wholly precipitated before the solution became sufficiently 

 concentrated to deposit rock-salt, whilst at that degree of concentration the sulphate 

 and chloride of magnesium would still remain for the most part in solution. 



The principal European mines of rock-salt are those of Wieliczka in Galicia, 

 excavated at a depth of 860 feet below the soil ; at Hall in the Tyrol, and along the, 

 mountain range through Aussee, in Styria, Ebensee, Ischl, and Hallstadt. in Upper 

 Austria ; Hallein in Salzburg, 3,300 feet above the sea. level, and Reichenthal in 

 Bavaria ; in Hungary, at Marmoros ; in Transylvania and Wallachia ; at Vic and 

 Dieuze in France ; at Bex, in Switzerland ; in the Valley of Cardonna, and elsewhere, 

 in Spain ; and in the region around Northwich, in Cheshire, in our own country. 

 Some of these deposits, as at Wieliczka and Northwich, are almost pure chloride of 

 sodium ; others, again, as many of the Austrian beds, are only saliferous clay ; whilst 

 others, as at Arbonne in Savoy, elevated 7,200. feet above the level of the sea, and in 

 the region of perpetual snow, are masses of saccharoid gypsum and anhydrite, which 

 are imbued with chloride of sodium, and which become quite light and porous when 

 the salt has been removed by water. 



Of late years valuable saline deposits have been discovered and are actively worked 

 in the neighbourhood of Stassfurt, in Prussian Saxony, and in tho adjoining duchy of 

 Anhalt. The rock-salt which occxirs at a considerable depth from tho surface, is hero 



