In the mountains of Levotaiah and Miniss, the salt is of a grey bluish colour, and very agreeable to the palate. The salt from the lake of St. Mark is of the same quality, and the principal stratum of it resembles a tesselated pavement, composed of various small cubes of common salt.
On both sides of the Atlas mountains it occurs in great quantities. M. Hornemann discovered a plain on a limestone range, which consisted of a mass of rock salt, extending so far in length that no eye could reach its termination, and at the same time several miles in width. In Ayssinia, there is a plain of salt four clays journey across.
The American salt formation, according to Dr. Van Rensselaer, extends over the continent from the Alle gheny mountains to the North Pacific, between 31° and 45° of north latitude. In this immense tract rock salt has been occasionally found; but the extent of the formation is inferred from the brine springs.
In California, rock salt is found in large quantities.
On the plains east of the Rocky Mountains, it is found in incrustations covering lands of some extent.
The immediate valley of the Canadian river is bounded by precipices of red sand rock, forming the river Bluffs. In the valley between these, incrustations of nearly pure salt is found covering the surface to a great extent like thin ice, and giving it the appearance of a coating of snow when seen at a distance.
In South America the salt mines are numerous. There are many in Peru situated at the height of 10,000 feet, and some of them are near Potosi, where the salt is usually of a violet colour, and occurring in hard, solid, and continuous rocks. It also occurs in Mexico, Chili, New Granada, Ste. It is found in im mense blocks in the muriatiferous clay, lying above sandstone, at Punta Araya, on the Cordilleras; and at the bottom of the lake Pennon Blanco, in Mexico, there is a bed of clay containing about thirteen per cent. of rock salt. The salt lake of Pennon Blanco yields annu ally 250,000 fanegas of unpurified salt of 400 lbs. each.
In North America, salt does not seem to have been found in the state of rock. It is found, however, in incrustations of considerable thickness and solidity on the soil of plains and prairies near the sources of the Arkansas river; and at Fort Osage, there is an exten sive plain 280 miles south-west from the fort, which, in dry and hot weather, is covered with an incrustation of clear white salt, from two to six inches thick. This saline is about thirty miles in circumference, and is in many places covered with drift wood.
Having thus given an account of the principal loca lities of rock salt, we shall conclude this part of the subject with some observations on the origin of this mineral, for which we have been indebted to Dr. Van
Rensselaer.
" As to the origin of rock salt, the most satisfactory hypothesis is the supposition of its being deposited from sea; or by the desiccation of salt lakes formerly covering our present continents. The objection that the composition of rock salt is more pure than that from the sea water, which contains also sulphate and muriate of magnesia, sulphate and muriate of lime, and sulphate of soda, is invalidated by the recollection that whatever impurities may exist in sea water, still, if the process of evaporation be conducted very slowly, the crystals are nearly pure. In some places the pro cess is conducted so well, as at Lymington, in Eng land, where it takes twelve days, that from the most impure or mother water, it still contains only twelve parts in the 1000, or little more than one per cent. of impurities. If, then, the desiccation ol' lakes, or basins filled with salt water, be very slow, as it must be when the process is to be finished by natural evap oration, the muriate of soda would be crystallized be fore the other salts, which being more deliquescent, might be separated and washed, away. In the same way, the gypsum that usually accompanies salt might be deposited, and being nearly insoluble would remain.
That lakes of salt and fresh water have once covered much land, is not to be doubted in the face of so many incontrovertible facts as can be brought forward. Our own day offers proofs of the changes that are constant ly taking place on the earth's surface, by the desicca tion of the lakes, in whatever manner accomplished. Our own country,•with our immense lakes or inland seas, will one day exhibit a different picture to the eye of the geographer, the painter, and the geologist, from what it offers at present. If, as may readily be sup posed, a vast lake once covered that portion of our country to the west of the Alleghany mountains, and which was eventually drawn off by the outlets cut by the St. Lawrence and the Hudson, through the High lands of Montreal and New York, we have an idea upon a grand scale of what will, at some future day, be the effect of draining our northern lakes. The falls of Niagara, gradually receding to the outlet of Erie, will eventually discharge the waters of the great lake and its tributary streams into Ontario, to dash rapidly down the St. Lawrence to the Atlantic, or to be distri buted slowly as from a reservoir.