| 1. Uppermost calcareous marl | 15 feet |
| 2. Red and blue clays | 120 ” |
| 3. Bed of rock-salt | 75 ” |
| 4. Clay, with veins of rock-salt | 31 ” |
| 5. Second bed of rock-salt | 110 ” |
Droitwich, in Worcestershire, which is situated nearly in the centre of the county, has been celebrated for the production of salt from its brine-springs from the time of the Romans, who imposed a tax on the Britons, who, it appears, worked the mines; and also made salt a part of the pay of their soldiers’ salarium, or salary.[32] Ever since, this inexhaustible fountain of saline water has continued flowing up, and yielding salt in undiminished quantities. It is very likely that the manufacture is coëval with the town itself; but it was not till the year 1725 that the strong brine for which it is now celebrated was discovered. From one spring, even, the enormous amount of one thousand tons of salt are obtained every week. At the depth of thirty or forty feet is a bed of hard gypsum, about one hundred and fifty feet in thickness; through this a small hole is bored to the stream of brine, which is about twenty-two inches in depth, and beneath this is the rock-salt. The brine rising quickly through the aperture is pumped into a capacious reservoir, whence it is conveyed into iron boilers for evaporation. It is supposed to be much stronger than any other in the kingdom, containing above one-fourth part its weight of salt. “One of the shafts is sunk to a depth of nearly five hundred feet, and passes through four layers of salt, eighty-five feet in aggregate thickness. Some of the beds of salt in Cheshire are from seventy to one hundred and twenty feet in thickness;” and it is sometimes so hard that it requires to be blasted with gunpowder.
In those districts where the marls of the Trias are covered by other beds, and the salt-springs force their way through the superincumbent deposits to the surface, these solutions of the chloride of sodium undergo a chemical change, acquiring other properties, and are then called mineral waters. The Cheltenham waters originate thus.[33] Beneath the town of Cheltenham lie the Triassic deposits, the reservoir of the rock-salt and brine-springs, which generate the mineral waters, and from which they derive their saline ingredients. In their passage to the surface they go through various modifications, by reason of the superincumbent beds of Lias, which are impregnated with iron pyrites and the sulphate of lime. From the analyses of these waters, it appears that their principal constituents are the chloride of sodium (muriate of soda), or sea-salt, and the sulphates of soda and magnesia. Sulphate of lime, oxide of iron, and the chloride of magnesium are present in some wells only, and in much smaller quantities. Besides these ingredients, iodine and bromine have been detected by Dr. Daubeny, who instituted experiments to ascertain whether these two active principles, which the French chemists had recently discovered in modern marine productions, did not exist in mineral waters issuing from strata formed in the ancient seas. As the saline springs of the red marls rise up through the Lias they undergo certain chemical changes. From the decomposition of the sulphate of iron which takes place, a vast quantity of sulphuric acid must be generated, which, reacting on the different bases of magnesia, lime, etc., contained in the strata, forms those sulphates so prevalent in the higher or pyritous beds of the Lias; the oxide of iron being at the same time more or less completely separated. By this means the mineral waters, which are probably mere brine-springs at the greatest depths, acquire additional medicinal qualities as they ascend to the places whence they flow. At the same time, it must be borne in mind that fresh water is continually falling from the atmosphere upon the surface of the Lias clays, and percolating through the uppermost strata.[34]
The medicinal properties which are peculiar to these mineral waters will be considered further on, when we come to discuss the action of salt on the system, in health and disease, and the restorative results which are due solely to its instrumentality.
The salt district is in the line which joins the Severn, the Dee, and the Mersey, and doubtless once consisted of lakes flooded at every tide, which, drying at certain seasons and at low tides, deposited beds of salt, from Droitwich in Worcestershire, through Nantwich, to the Mersey; brine-springs flowing over beds of salt, or rock-salt, being found at different places on the entire line.
In the year 1863 a bed of rock-salt was discovered near the mouth of the Tees, at Middlesborough, and also on the Durham side of the river. The boring at Middlesborough showed that it was about 100 feet in thickness. Of late, borings have been made near Port Clarence, on the Durham side, but with what result I am not informed.
Scotland, as well as Ireland, is deficient in the more recent formation; for salt, as well as chalk, does not occur. Both are entirely absent; but geologists inform us that at one time chalk did exist, judging from the presence of flints in considerable quantities in Aberdeenshire, which they say affords unequivocal evidence of the former presence of cretaceous strata now integrated; and they account for it thus: the soft chalk being exposed to the action of the rain and storms, has been gradually washed away, while the flints which were embedded in it still remain. If this hypothesis is correct, that at one time chalk existed and is now absent, we may by inference, though we possess no evidence, presume that salt likewise, at some period or other, was present in this part of the United Kingdom. Chalk being entirely composed of the accumulation of marine shells ground to impalpable powder, which has been gradually consolidated, and being very rich in organic remains of shells, star-fish, sponges, fishes, and lizards, must have been deposited by sea-water, as its various ingredients indicate; therefore, during its deposition, salt, if originating from sea-water, must of necessity have left some marks characteristic of itself, in conjunction with the chalk; both being, more or less, intimately connected with sea-water, though the formation of one may not have been simultaneous with the formation of the other.[35]
In our lately acquired “gem of the sea,” Cyprus, there have been found extensive lakes of salt near Larnaca, the capital, so that this liberally-abused island possesses at least something which may prove of pecuniary value to its present owners. Being for several centuries under the benighted rule of the Turk, this staple of commerce has been entirely neglected, so as not to have been of the slightest use to the inhabitants or to the greedy pachas.
In the south of Western Australia there are vast salt marshes which only require to be worked so as to become the means of enriching the colonists, and indirectly attracting emigrants to this hitherto unprofitable portion of a dependency of England. The principal, which is called Lake Austen, is 1400 feet above the level of the sea.
Salt is also to be found in our Indian Empire, in Rajpootana and elsewhere, and is of considerable value to that country, especially while it remains in the hands of the enterprising European; according to Mr. Wynne, there is a salt range which extends from Kalabagh to a point north of Tank. After acquainting us with its geographical position, he says: “The coincidence between the physical features and the geological structure of the ground is intimate, the axial lines of the mountains carrying on the Salt Range feature being also axes of anticlinals lying for the most part along the scarped acclivities presented towards the Indus plains. These plains are part of the great quasi-desert flat over which the Indus has in past times capriciously wandered towards the Arabian Sea. Whether they are due in any degree to marine explosion is uncertain, though the sea may very possibly once have covered the low ground in question. The ridges of the Salt Range, as they exist at present, doubtless mark the same great later, or post-tertiary, period of mountain-forming activity, in which originated not only the remainder of the Salt Range, but also the Western Himalaya and the Suliman and Afghan mountains.” When we come to consider the geological bearings of salt, and its presumed origin, and other points in connection with it, I shall again revert to this highly interesting paper of Mr. Wynne’s.