The Cumberland mountain, which forms a part of this dividing line, is itself a singular formation. It belongs to the class called "Table mountains." Its width varies from a few miles, to more than fifty. Its height is not perceptibly different from that of the Blue Ridge. It forms a circuit, in a shape somewhat resembling a half moon. Winding to the southwest, it keeps a course north of the Tennessee river, in some places nearly parallel with it; passes a few miles to the southeast of Huntsville in the Alabama Territory, and not long after terminates. At one part, over which I crossed, the mountain is eighteen miles wide. This is about 150 miles southwest of Knoxville, a little north of the 35th degree of N. Lat. I had not ascended the mountain more than halfway, before I found sandstone begin to intermingle with limestone strata. As I drew near the summit, the limestone disappeared entirely, and sandstone prevailed in abundance, with no other mineral associated until I reached the western descent, where I met bold precipices of horizontal limestone, reaching from the base to the summit. I examined several sandstone rocks while crossing the mountain, found them usually imbedded in the earth, generally with flat surfaces, of a fine grain, and strong texture. The colour is usually a reddish brown, or grayish red. The specimen which you have received is a good example. I crossed this mountain in the vicinity of Huntsville, not less than one hundred miles southwest of the place above-mentioned, and found it not wider than mountains commonly are. Its height had also become less, and horizontal limestone in regular strata prevailed in every part. Although this mountain forms a part of the dividing line which has been mentioned, it does not exclusively so: for the Rackoon mountain, which crosses the Tennessee river, at the place so well known by the name of "the Suck," and the Look-Out mountain, which terminates abruptly about 6 miles to the left of "the Suck," form an acute angle with the Cumberland, and are composed of horizontal strata of limestone. Thus it would appear the line which divides the two kingdoms of this rock, is nearly north and south, inclining perhaps a few points to the east and west. _Scenery_.