The width of the tunnel varies from fifty to one hundred and fifty feet.  Its course is that of a continuous curve, resembling the letter S; first winding to the right as we enter on the upper side, then to the left, again to the right, and then again to the left on arriving at the entrance on the lower side.  Such is its peculiar form, that an observer, standing at a point about midway of its subterranean course, is completely excluded from a view of either entrance, and is left to grope in the dark through a distance of about twenty yards, occupying an intermediate portion of the tunnel.  When the sun is near the meridian, and his rays fall upon both entrances, the light reflected from both extremities of the tunnel contributes to mollify the darkness of this interior portion into a dusky twilight.

“The extent of the tunnel, from its upper to its lower extremity, following its meanders, is about 150 yards; in which distance the stream falls about ten feet, emitting, in its passage over a rocky bed, an agreeable murmur, which is rendered more grateful by its reverberations upon the roof and sides of the grotto.  The discharge of a musket produces a crash-like report, succeeded by a roar in the tunnel; which has a deafening effect upon the ear.

“The hill through which this singular perforation leads, descends in a direction from east to west, across the line of the creek, and affords a very convenient passage for a road which traverses it at this place, having a descent in the direction just mentioned of about four degrees.

“The rocks found in this part of the country are principally sandstone and limestone, in stratifications nearly horizontal, with occasional beds of clay slate.  A mixture of the two former frequently occurs among the alternations presented by these rocks.  A variety of rock resembling the French burr occurs in abundance on Butcher’s-fork of Powell’s river, about twenty miles northwardly of the Natural Tunnel.  Fossils are more or less abundant, in these and other rocks.  Fossil bones, of an interesting character, have been found in several places.  Saltpetre caves are numerous.  Coves, sinks, and subterranean caverns, are strikingly characteristic, not only of the country circumjacent to the Natural Tunnel, but of the region generally situated between the Cumberland mountain, and the Blue ridge or Apalachian mountain.  Bituminous coal, with its usual accompaniments, abounds in the northerly parts of this region; and in the intermediate and southerly portions, iron, variously combined, often magnetic, together with talcose rocks, &c. &c. are to be met with in great abundance.

“The mountains in this vicinity—­long. 82 deg. to 84 deg.  W. from Greenwich, lat. 35 deg. to 36 deg.  N.—­are among the most lofty of the Allegheny range.  Several knobs[3] in this part of the range, among which may be enumerated the Roan, the Unaka, the Bald, the Black, and Powell’s mountains, rise to the height of at least four thousand five hundred feet above tide.”