The beds or masses of rock-salt are oc casionally so thick, that they have not been yet bored through, though mined for many centuries. This is the case with the immense mass of Wieliczka, and the lower bed at Northwich. But in ordinary cases, this thickness varies from an inch or two to 12 or-15 yards. When the strata are thin, they are usually numerous ; but the beds, layers, or masses never exhibit throughout a great extent any more than an illusory appear ance of parallelism ; for when they are explored at several points, enlargements arc observed, and such diniinutions as cause the salt to disappear sometimes altogether. This mineral is not deposit ed, therefore, in a geological stratum, but rather in lenticular masses, of very varia ble extent and thickness, placed along side of each other at unequal distances, and interposed between the courses of other formations.
Sometimes the rock salt is disseminat ed in small masses or little veins among the calcareous and argillaceous marls which accompany or overlie the greater deposits. Bitumen, in small particles, hardly visible, hut distinguishable by the smell, occurs in all the minerals of the saliferous system.
It has been remarked, that the plants which grow generally on the sea shores, such as the Triglochinum nuirititnuni, the Salicornia, the Salsola kali, the Aster trifolium, or farewell to summer, the Gaux maritima, &c., occur also in the neighborhood of salt mines and salt springs, even of those which are most deeply buried beneath We surface.
The interior of rock-salt mines, after digging through the strata of clay marl, &c. is extremely dry ; so that the dust produced in the workings becomes an an noyance to the miners, though in other respects the excavations are not at all in salubrious.
Salt springs occur nearly in the same circumstances, and in the same geological formation f1.9 the salt-rock. It has been noticed that salt springs issue, in general, from the upper portion of the saliferous strata, principally from the saline clay marls. Cases however occur, where the salt springs are not accompanied by rock salt, and where the whole saline matter is derived from the marls themselves, which thus constitute the only saliferous beds.
The salt used in the United States, is derived here by importation from Liver pool, or from Turks Island, or obtained from the salines of Onondaga, the waters of which are evaporated to dryness. That of Turks Island is chiefly produced by solar evaporation. In Key West, Florida,
the manufacture of salt by solar evapora tion is carried on on a small scale, that is from 30 to 40 thousand bushels yearly. This salt is of a superior quality for pack ing meat. The manufacture commenced in 1845. The salt made in the State of New York, is from the salines of Onon daga, the waters of which furnish abun dance of salt, as much as from 16 to 25 ozs. to the gallon of water. The State imposes a tax of 121 cents per bushel on all salt made. Besides muriate of soda the waters contain chloride, calcium, sul phates of lime and magnesia, and oxide of iron. Some years back there were an nually produced half a million bushels of salt per year, the price 25 cents per bushel. The salt is obtained by evapo rating the brine down to the point of crystallization and separating the impuri ties.
The State Superintendent of the Sa lines of Onondaga, reports as follows : "We have manufactured this year (1849) very nearly five million bushels of salt already, and shall exceed that figure some what at the close of the year, say 800,000 bushels over last year. (The bushel is reckoned at 26 lbs.) In regard to the consumption of fuel, I cannot say much that will be new to you. No improve ment has been made, perhaps, since you were here." The importance of these Salines may be inferred from the fact, that in the year 1836 the whole import of salt into the ports of the United States amounted to 5,088,666 bushels, of 56 lbs each, being but a trifle more than this year's produc tion of the Salines of Onondaga.
With regard to the use of Anthracite coal, as fuel for making salt, the experi ment is said not to have been successful, and that the gentleman who made the trial has since substituted wood for coal.
Heretofore one cord of wood was used in making forty bushels of salt. At that rate, 125,000 cords of wood are required for the evaporation of brine for 5,000,000 bushels of salt. About forty gallons of brine make a bushel of salt, therefore requiring two hundred millions of gallons of brine to be raised from the wells, to produce the quantity. By the Salometer, the brine tests about 74°-0 being the mark for fresh water, and for brine of full saturation.
"From very minute and extensive ex aminations of the Salines of Onondaga, and from my own experience in the evaporation of fluids by heat, my opinion is clear, that 25,000 cords of wood may be made to do the work heretofore per formed by 125,000 cords."