The ac,companying nomenclature of the strata traversed by the sinking for rock-salt at Witton, near Northwich, shows the position of the Cheshire salt, as given by Holland :— The following analysis of the beds of " stone " undc rlying and intercalated between the beds of salt may be of interest, as a matter of comparison with the composition of pan-scale, and of the deposits formed during the evaporation of sca-wster The Wieliczka salt-mine, certainly the most celebrated in the world, is situate 9 miles from Cracow in Galicia, and las been worked for about 600 years. It is excavated in the ridge of hills at the N. extremity of the chain which joins the Carpathians. The salt is stoped out in longitudinal and transverse galleries, and large excavations are made in it, forming vaulted chambers of c,onsiderable height, and leaN ing massive pillars with arches between them for the support of the roof ; but the work is more of the nature of quarrying than of mining. Explosives are not very generally employed in this or in many of the other salt-mines of the Carpathian district, the rock being cut out in square or longitudinal blocks. Grooves are cut about 25i in. deep, forming the face of the rock into rectangular divisions ; lumps are then broken off from the face of the rock by wedging, and these are further broken up into masses of t. for sale. The percentage of lumps to smalls produced by this method is stated to he as 75 to 25, the former selling for about 78. a ton more than the latter. The lumps are generally sold just as they come from the mine, while the smalls are still further ground, and packed in sacks or casks ; the scarcity of fuel precludes tho possibility of dissolving and refining this salt, while its great purity admits of its easy sale in its natural state. The colour of the rock-salt forming the walls of this mine reminds one of a light-grey granite. The mine is divided into 4 levels or " fields," in the uppermost of which, 34 fathoms below the surface, the packing and preparation for transport is proceeded with. In the lower levels, the work of excavation is carried on ; and on the second level, is a lake of fresh water derived from £1 small stream which flows over the top of the bed of salt, and is carried by wooden shoots t,o this spot. Many of the chambers in -this mine are 80-100 ft. in height, and the excavations have been carried to a depth of no less than 783 ft., while many of the galleries are 1000 yd. long, and the total length of these galleries is about 30 English miles. The mines of Bochnia and Wieliczka together are, however, said only to yield 45,000 tons of salt per annum, the latter counting for 34,000. These mines give employment to 800-1000 miners and other persons. Many books of travel are replete with descriptions of this mine, but visitors who had read the acc,ounts must have been frequently disappointed.
To add descriptions of other salt-mines would be mere repetition, the extraction of rock-salt differing in no respect from the getting of stone in any underground quarry, or the working of coal or similar stratified deposits. Foul air or explosive gases are not usually met with in salt-mines. In the Marston mine, however, after a shot had been fired on one occasion, there wa.s a considerable evolution of marsh gas (methyl hydride), which took fire and burnt for some time, issuing from rt blow-holo in the floor. E. Falk also met with a like evolution of inflammable gas in his mine at Winsford. In the strata above the salt in the Dax explorations, a disengagement of marsh gas took place during the sinking of a srnall shaft, and subsequently during some borings executed at about a mile distant. Some highly compressed pent-up gases, proved to he liquefied hydro carbons, have likewise been found in small quantities in the rock-salt of Wieliczka and some other places, giving rise to small explosions when the rock is in c,ourse of being dissolved. Salt
mines aro as a rule perfectly dry, and the miners are usually healthy and subject to no special infirmities or inconveniences, unless it be some occasional slight annoyance from the irritating effects of the saline dust entering the throat, eyes, or nose. It is advisable when working a bed of rock-salt to leave a good thickness of the salt under the floor and in the roof, not trusting to the beds of clay with which rock-salt is usually interstratified, and which often exfoliate and give way. The pillars left for the support of the roof should be as large and massive as possible, in view of the possibility, however remote, of their becoming clisinteg,rated and weakened, composed 118 they are of a soluble, more or less deliquescent material. When a rock-salt working is disposed to give way, cracks and fissures usually appear in the roof, and signs of crushing about the upper part of the pillars.
A process of cutting rock-salt by a stream of water, invented by an engineer named Pletsch, was employed till lately in the mines of Varengeville St. Nicolas, near Nancy. Fresh water, led through a pipe into the galleries of the mine, was there, from nozzles conveniently mounted on playable stands, caused to impinge in fine but forcible jets against the face of the rock. By this means, deep furrows were rapidly cut into the salt by solution, and large blocks could be detached with little manual labour and without blasting. This method, economical though it may appear, seems to havo been the cause of a severe disaster iu the mines in question. The salt was being worked in one of the lower beds (of which there are seven in all) where it was purest and of best quality, the cutting-water being permitted to run away to a still lower level in a channel cut in the underlying bed of clay, on which, in this case, the levels were driven. This water had a sp. gr. of not more than 1.52, and was consequently fax from saturated; the purest portions of rock were therefore selected for sale as rock-salt, and the rest was broken up and used for further saturating the water of the reservoir below. The brine of the reservoir was finally pumped up to be evaporated for white salt. This plan of getting both brine and rock-salt was ingenious, and seemed to work successfully. The workmen, however, had long observed that the galleries of the mine seemed to fill up, by the swelling, as they supposed, of the clay floors, though in reality this was produced by the sinking of the pillars, probably from solution. One day the whole of this part of the mine suddenly fell in, and since then, the getting of rock-salt by this means has been aban doned. Since 1876, a salt-cutting machine has been introduced at Wieliczka with much success. It is constructed somewhat on the principle of Winstanley and Barker's coal-cutting machine. It would appear that in the course of 8 months' working, this nuachine has shown itself capable of cutting rock-salt horizontally at a rate of 59 sq. ft. per hour, or vertically to a height of 5 ft. 9 in. at a rate of 30-10 sq. ft. per hour. The average cost is stated to be about 21s. per cub. yd., as against 27s. for hand work. It is likewise stated that in working out the salt, this machine pro duces less smalls than hand labour, the proportion being only 17 per cent. The machines supplied by Stonek and Reska, of Prague, are made of steel in all their moving parts ; they cost about 430/. e.ach, and work by compressed air.