The second great division of the limestone country extends, on the route which I took, two hundred miles from the Cumberland mountain, and others associated with it southwest, as far as the Dividing Ridge, which separates the waters flowing into the Tennessee from those which proceed direct to the gulf of Mexico. The grand circumstance which distinguishes the limestone of this division from that already described, is this, ITS STRATA ARE HORIZONTAL. Frequently immense piles may be seen forming bold precipices, but always in horizontal layers, differing in thickness, from a few inches to many feet. How far this arrangement extends to the west and north, I have not yet been able to learn. Travellers always speak of the limestone rocks in West Tennessee and Kentucky as flat, from which circumstance I conclude that the Cumberland mountain forms for a considerable distance at least, the eastern boundary. I have observed but three other particulars in which the strata of the horizontal differ from those of the inclined limestone.
1. Its colour is not so strongly marked with the bluish tinge.
2. It is not so commonly penetrated with white veins of a semicrystallized carbonate of lime; nor is it so frequently associated with the uneven fractured species.
3. Petrifactions are oftener found in it.
I will here take the liberty to suggest, whether in our maps of geology, some notice should not be taken of this very important division in the limestone country. Such a division exists in fact; nature has made it; and if geology depends on nature for its only legitimate inductions, there can be no reason why a feature so prominent as this, should be overlooked. I shall not undertake to account for their difference: but would not every geological theorist consider them as distinct formations?[31]
Cumberland Mountain.
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.