The _natural bridge_ is celebrated as one of the greatest curiosities of the world. Viewed by a geologist, it would probably be considered as a cave (so to speak) _unroofed_ in all but one place. It seems improbable that if the ravine had been made by a convulsion, which had split and separated the rock to the distance of fifty or sixty feet, any part of it, and particularly so large a mass as that which forms the bridge, should have been left, without exhibiting any marks of violence. The rock is limestone. It is known that this rock wears away rapidly under the attrition of water; and the supposition does not appear improbable, that, in the lapse of ages, so large a creek as that which flows below the bridge, may have worn as deep a ravine as that which now strikes us with so much surprise, In short, may not a cave have been originally formed where the ravine is now, and the pending portion of it have fallen in at every place except that which now forms this celebrated natural curiosity? _Mineral Springs._--The mineral springs of this region are numerous and diversified. Chalybeate springs are promiscuously scattered over the whole of it; and springs impregnated with sulphuretted hydrogen are quite common. Salt springs and licks are found more in the western than the eastern range of mountains. That which was first wrought by William King, is well known. The salt here is associated with gypsum. In the same range of mountains, farther to the southwest, there are now several other salt-works, and also one to the west, on Goose Creek, in Kentucky, which has been very productive. _The Warm Springs._--These springs are situated in a country which presents many attractions to the travelling geologist; and much light, it is hoped, will yet be thrown on the geology of our country, by a more minute and accurate examination of it than has yet been made. The warm springs ooze through the sand on the south bank of the French Broad river, in the mountains which divide the state of Tennessee from her parent state, about the 36th parallel of latitude. The temperature of the water is about 95° of Fahrenheit. On the opposite side of the river from the springs is a geological curiosity. A limestone rock is seen dipping under the sandstone which forms the country. Limestone is nowhere else to be seen within six miles of this place. In this limestone rock is a cave similar to others already described. _Paint Rock_, in the vicinity of the Warm Springs, is interesting on many accounts. It is a bold precipice on the bank of French Broad river. At this place the river passes with a very rapid current directly across the course of a mountain, which terminates abruptly, and forms the precipice on the north bank of the river. On looking at the rock, the opposite end of the mountain, and the ruins around it, the mind is insensibly carried back to the contemplation of some dreadful commotion in nature, which probably shook these mountains to their bases.