which washes its base. The entrance of the cave is, in this side, about two-thirds of the way up. It extends into the earth about 300 feet, branching into subordinate caverns, sometimes ascending a little, but more gen -[36] erally descending, and at length terminates, in two different places, at basons of water of unknown extent, and which I should judge to be nearly on a level with the water of the river; however, I do not think they are formed by refluent water from that, because they are never turbid; because they do not rise and fall in correspondence with that in times of flood, or of drought; and because the water is always cool. It is probably one of the many reservoirs with which the interior parts of the earth are supposed to abound, and yield supplies to the fountains of water, distinguished from others only by being accessible. The vault of this cave is of solid lime-stone, from 20 to 40 or 50 feet high; through which water is continually percolating. This, trickling down the sides of the cave, has incrusted them over in the form of elegant drapery; and dripping from the top of the vault, generates on that, and on the base below, stalactites of a conical form, some of which have met and formed massive columns.

Another of these caves is near the North mountain, in the county of Frederic, on the lands of Mr. Zane. The entrance into this is on the top of an extensive ridge [37]. You descend 30 or 40 feet, as into a well, from whence the cave then extends, nearly horizontally, 400 feet into the earth, preserving a breadth of from 20 to 50 feet, and a height of from 5 to 12 feet. After entering this cave a few feet, the mercury, which in the open air was 50°. rose to 57°. of Farenheit's thermometer, answering to 11°. of Reaumur's, and it continued at that to the remotest parts of the cave. The uniform temperature of the cellars of the observatory of Paris, which are 90 feet deep, and of all subterranean cavities of any depth, where no chymical agents may be supposed to produce a factitious heat, has been found to be 10°. of Reaumur, equal to 541°. of Farenheit. The temperature of the cave above-mentioned so nearly corresponds with this, that the difference may be ascribed to a difference of instruments.

At the Panther gap, in the ridge which divides the waters of the Cow and the Calf pasture, is what is called the Blowing cave.

It is in the side of a hill, is of about 100 feet diameter, and emits constantly a current of air of such force as to keep the weeds. prostrate to the distance of twenty yards [38] before it. This current is strongest in dry frosty weather, and in long spells of rain weakest. Regular inspirations and expirations of air, by caverns and fissures, have been probably enough accounted for, by supposing them combined with intermitting fountains; as they must of course inhale air while their reservoirs are emptying themselves, and again emit it while they are filling. But a constant issue of air, only varying in its force as the weather is drier or damper, will require a new hypothesis.' There is another blowing cave in the Cumberland mountain, about a mile from where it crosses the Carolina line. All we know of this is, that it is not constant, and that a fountain of water issues from it.

The Natural bridge, the most sublime of Nature's works, though not comprehended under the present head, must not be pretermitted. It is on the ascent of a hill, which seems to have been cloven through its length by some great convulsion. The fissure, just at the bridge, is, by some admeasurements, 270 feet deep, by others only 205. It is about 45 feet wide at the bottom and 90 feet at the top; this of course determines the length of the bridge, and its height from the water. [39] Its breadth in the middle is about 60 feet, but more at the ends, and the thickness of the mass at the summit of the arch, about 40 feet. A part of this thickness is constituted by a coat of earth, which gives growth to many large trees. The residue, with the hill on both sides, is one solid rock of limestone. The arch approaches the Semi-elliptical form; but the larger axis of the ellipsis, which would be the cord of the arch, is many times longer than the transverse. Though the sides of this bridge are provided in some parts with a parapet of fixed rocks, yet few men have resolution to walk to them, and look over into the abyss. You involuntarily fall on your hands and feet, creep to the parapet, and peep over it. Looking down from this height about a minute,

2

In the edition of 1853 is a footnote reference, "See Musschenbroek, § 2, 604."

Altered in edition of 1853 to read: "than the semi-axis which gives its height."

gave me a violent head ach.' If the view from the top be painful and intolerable, that from below is delightful in an equal extreme. It is impossible for the emotions arising from the sublime to be felt beyond what they are here; so beautiful an arch, so elevated, so light, and springing as it were up to heaven, the rapture of the spectator is really indescribable! The fissure continuing narrow, deep, and streight [40] for a considerable distance above and below the bridge, opens a short but very pleasing view of the North mountain on one side, and the Blue ridge on the other, at the distance each of them of about five miles. This bridge is in the county of Rockbridge, to which it has given name, and affords a public and commodious passage over a valley which cannot be crossed elsewhere for a considerable distance. The stream passing under it is called Cedar creek. It is a water of James river, and sufficient in the driest seasons to turn a grist mill, though its fountain is not more than two miles above.' [41]

1 In the edition of 1853, the text from this point to the end of the paragraph is altered to read: “and descending then to the valley below, the sensation becomes delightful in the extreme. It is impossible for the emotions arising from the sublime to be felt beyond what they are here: so beautiful an arch, so elevated, so light, and springing as it were up to heaven, the rapture of the spectator is really indescribable. The fissure continues deep and narrow, and following the margin of the stream upwards, about three-eighths of a mile, you arrive at a limestone cavern, less remarkable for the height and extent than those before described. Its entrance into the hill is but a few feet above the bed of the stream. This bridge is in the county of Rockbridge, to which it was given name, and affords a public and commodious passage over a valley, which cannot be crossed elsewhere for a considerable distance. The stream passing under it is called Cedar Creek. It is a water of James River, and sufficient in the dryest seasons to turn a grist mill, though its fountain is not more than two miles above.

This description was written after a lapse of several years from the time of my visit to the bridge, and under an error of recollection which requires apology, for it is from the bridge itself that the mountains are visible both ways, and not from the bottom of the fissure, as my impression then was. The statement therefore in the former editions needs the corrections here given to it. August 16, 1817."

2 Don Ulloa mentions a break, similar to this, in the province of Angaraez in South America. It is from sixteen to twenty-two feet wide, one hundred and eleven feet deep, and of 1.3 miles continuance, English measure. Its breadth at top is not sensibly greater than at bottom. But the following fact is