The principal mineral productions of Cheshire are salt and coal. The former is more abundant in this county than in any other part of England ; and the im mense trade carried on in it, with the vast revenue which it affords, render it an object not only of local, but even of national importance. The places which have been most noted for their salt-works are Nantwich, Middle wich, \Viusford, and Northwich. The salt-work at Nant wich was once very considerable ; but, in consequence of the superior advantages in respect to situation belong ing to other towns, it has now been deprived of a great portion of its former trade. It was expected that that trade would have been renovated in some degree, from the termination of the Chester canal in a bason near to this town; but the expectation does not appear to have been yet realised. Mr Pennant conjectures, that it was here that the native Britons first saw white salt, whence they gave to the place the name of IIeldd Wen, or the White Brine Pits. NIiddlewich derives its name from its central situation between the Wiches or Salt-towns. The salt manufactured there is prepared from brine springs, well saturated. The quantity at this time is not great ; but were a demand to offer, it might easily be increased. The great seat of t:ac salt trade in Che shire at present is Northwich. Here the salt is made from brine springs, and also from tl e natural rock. This, as it is the chief of the salt towns, is Lie only one indeed, which, in addition to its brine springs, possesses mines of rock-salt at least there seem strong grounds for believing, that the beds of rock-salt .:ere are perfectly clistinct from any others in the salt district, forming what the Germans would call liegende storke, lying bodies, or masses of the mineral. It is to be runarked at the same tundithat the brines met with in this district are very generally formed by the penetration of spring or rain waters to thc upper surface of rock-sait. The average strength of these !mines appears to be much greater here than in any of the springs that occur in Hungary, Ger many, or France. In the places where all the principal salt-works are situated, they contain between 25 and 26, and in some instances even more, of the pure muriate of soda. The earthy salts held in solution together with this muriate, are principally muriate of magnesia and sulphate of lime, the quantity of which varies in different springs, from to 2 or 21 per cent. The springs of Cheshire were known to the Romans, and had the com mon name of Salina. The mode in which they turned them to account was very similar to the process now employed, and this process, it is supposed, they com municated to the natives. There is a tradition more over, that the rock, as well as the brincpits, were wrought in the tirne of the Romans. In modern times, however, the discovery of this valuable mineral does not appear to have been prior to the year 1670, since which time it has been found in various places in the vicinity of this town.
The rock-salt occurs from 28 to 48 yards beneath the surface of the earth. The first stratum or mine is from 15 to 21 yards in thickness. It very much resembles in appearance brown sugar candy, is perfectly solid, and so hard as not to be broken, but with great difficulty, by iron picks and wedges. Of late, the workmen have been accustomed to blast it with gunpowder, by which means they loosen and remove many tons of it together. Beneath this stratum there is a bed of hard stone, con sisting of large veins of flag, intermixed with some rock salt, the whole from 25 to 25 yards in thickness. Under
this bed is a second stratum or mint of salt, from five to six yards thick, many parts of it perfectly white and clear as crystal, others browner ; but all purer than the upper stratum, yet reckoned not quite so strong. Only these two distinct beds of the fossil salt have been net with at Northwich ; but it has been ascertained, that the same limitations do not exist throughout the whole of the salt district, three distinct beds at least being found in some situations, separated in like manner from each other by intervening strata. The great body of the rock salt, both in the upper and thc lower beds, is composed of crystals of muriate of soda, intimately mixed with cer tain proportions of clay and oxide of iron, containing like wise small proportions of certain earthy salts.—Through out, at the same time, particularly in the lower strata of the rock, there are found separate crystalline concretions of muriate of soda in a purer state, variously disposed, sometimes occurring distinctly in the cubical form, in other places in masses of larger size, and irregularly shaped. Above the whole mass of salt lies a bed of whitish clay, which has been used in the Liverpool earthen-ware ; and in the same situation there is found also a quantity of gypsum.
Rock-salt pits are sunk at great expence, and are very uncertain in their duration, being frequently destroyed by the brine springs bursting into them, and dissolving the pillars that support the roof; through which, then, the whole work falls in, leaving vast chasms in the sur face of the earth. In forming a pit, a shaft or eye is sunk, similar to that of a cool-pit, but MOM extensive. When the workmen have penetrated to the salt rock, and made a proper cavity, they leave a sufficient sub stance of the rock (generally about seven yards in thick ness) to form a solid roof ; and as they proceed, they hew pillars out of the rock, also, to sustain the roof. Gunpowder is then employed to separate what it is meant to raise, which is conveyed to the surface in huge craggy lumps, and is drawn up above ground in capaci ous baskets made for the purpose. When well illumi nated, the crystalline surface of the roof, pillars, and sides of a large pit, make a glittering and magnificent appearance, which seldom fails to very impressive effect on the mind of a stranger. Fresh air is conveyed from the mouth of the pit by means of a tube, with it pair of forge-bellows fixed to it ; and thus a perpetual current is preserved between the outer and inner air. The pits, at the greatest depth, are dry, and of an agreea ble temperature.
The largest rock-salt pit that is now worked in Che shire, is one in the township of Wilton. This has been excavated in a circular form to 108 yards in diameter ; its roof is supported by 25 pillars, each three yards wide at the front, four at the baca, and six yards in the sides. Each of these pillars contains 294 solid yards of rock salt, and the whole area of the pit, which is 14 yards hollow, includes 9160 superficial yards, or little less than two acres of land. The quantity of rock-salt delivered an nually from the pits, in the neighbourhood of North wich, is from 50,000 to 60,000 tons. Hardly more than ith of this is refined in England, the remainder being exported to various parts of the continent. The salt is conveyed down the Mersey, in vessels from 50 to 80 tons burthen, to Liverpool, where it is reshipped for foreign countries, or kept to be refilled.