What is more remarkable than all, it forms for the whole distance it has yet been explored, a walled and vaulted passage, for a stream of cool and limpid water, which, where it leaves the cave, is six feet deep and sixty feet wide. A few years since, Col. James Ore of Tennessee, commencing early in the morning, followed the course of this creek in a canoe, for three miles. He then came to a fall of water, and was obliged to return, without making any further discovery. Whether he penetrated three miles up the cave or not, it is a fact he did not return till the evening, having been busily engaged in his subterranean voyage for twelve hours. He stated that the course of the cave after proceeding some way to the southwest became south; and southeast by south, the remaining distance. _Natural Nitre._ The sides of the principal excavation present a few apartments which are interesting, principally because they furnish large quantities of the earth from which the nitrate of potash is obtained. This is a circumstance very common to the caves of the western country. In that at Nicojack, it abounds, and is found covering the surfaces of fallen rocks, but in more abundance beneath them. There are two kinds, one is called the "clay dirt," the other the "black dirt;" the last is much more strongly impregnated than the first. For several years there has been a considerable manufacture of saltpetre from this earth. The process is by lixiviation and crystallization, and is very simple. The earth is thrown into a hopper, and the fluid obtained, passed through another of ashes, the alkali of which decomposes the earthy nitrate, and uniting with its acid, which contains chiefly nitrate of lime, turns it into nitrate of potash. The precipitated lime gives the mass a whitish colour, and the consistence of curdled milk. By allowing it to stand in a large trough, the precipitate, which is principally lime, subsides, and the superincumbent fluid, now an alkaline, instead of an earthy nitrate, is carefully removed and boiled for some time in iron kettles, till it is ready to crystallize. It is then removed again to a large trough, in which it shoots into crystals. It is now called "rough shot-petre." In this state it is sent to market, and sells usually for sixteen dollars per hundred weight. Sometimes it is dissolved in water, reboiled, and recrystallized, when it is called refined, and sells for twenty dollars per hundred. One bushel of the clay dirt yields from 3 to 5lbs. and the black dirt from 7 to 10lbs. of the rough shot-petre. The same dirt, if returned to the cave, and scattered on the rocks, or mingled with the new earth, becomes impregnated with the nitrate again, and in a few months may be thrown into the hopper, and be subjected to a new process. The causes which have produced the nitric salts of these caves, may not yet have been fully developed. But it is highly probable, they are to be ascribed to the decomposition of animal substances.