There is one phenomenon which is peculiarly interesting. There are two kinds of ice floating in the Arctic and Antarctic seas—the flat ice and the mountain ice. The one is formed of sea-water, the other of fresh. The flat or driving ice is entirely composed of salt water, which, when dissolved, is found to be salt, and is readily distinguished from the mountain or fresh-water ice by its whiteness and want of transparency. This ice is much more terrible to mariners than that which rises in lumps. A ship generally can avoid the one, as it is seen at a distance; but it frequently gets in amongst the other, which, sometimes closing with resistless force, crushes the doomed vessel to pieces. The surface of that which is congealed from the sea-water is not only flat, but quite even, hard, and opaque, resembling white sugar, and incapable of being slid upon. Salt is found in variable quantities in different countries, and in various conditions; in one part it may be found as a huge mountain, in which there are dark and lofty caverns; in others it is deposited in marshes and lakes, and in others in deep mines, many hundreds of feet beneath the surface of the earth. In some countries there are vast quantities of rock or fossil salt. Salt has been divided into _three_ kinds: native or rock salt; common or sea salt, also called white-salt; and bay-salt. Under the title of bay-salt are ranked all kinds of common salt, extracted from the water, wherever it is dissolved by means of the sun’s heat and the operation of the air. If sea-water is evaporated by means of a gentle heat we also obtain what is known as bay-salt. Common salt, or sea-salt, or white-salt, which is extracted from the sea, is composed of hydrochloric acid, saturated with soda, and is found in salt water and salt-springs, also in coal and gypsum-beds. “The sea itself, if desiccated, would afford a bed of salt five hundred feet thick, one hundred for every mile.” In England, and especially in Cheshire, there are large salt-mines, at Nantwich and Middlewich, which have existed ever since the Roman occupation of Britain; and in the year 1670 the Staffordshire salt-mines were discovered, and accordingly excavated. Those in Cheshire have been renowned for centuries; their great extent is such that the surface has subsided on account of its being undermined for so many miles. “In England, the Trias is the chief repository of salt, or chloride of sodium; and brine-springs, which are subterranean streams of water impregnated with salt from percolating through saliferous strata, are abundant in the great plain of the red marls and sandstones of Cheshire. The salt, however, is not uniform in extent, but occupies limited areas.” The saliferous strata of Northwich present the following series: