they are never turbid; because they do not rise and fall in correspondence with that in times of food, or of drought; and because the water is always cool. It is probably one of many reservoirs with which the interior parts of the earth are supposed to abound, and which yield supplies to the fountains of water, distinguished from others only by its being accessible. Th 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 valt generates on that, and on the base below, stalactites of a conical form, some of which have met and formed mas

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sive columns.

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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 ision the top of an extensive ridge. 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 height of from 5 to 12 feet, Af1912 ter entering this cave a few feet, the mercury, which in the open air was at 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 all subterraneous cavities of any depth, where no chemical agents may be supposed to produce a factitious heat, has been found to be 10°. of Reamur,

equal to 541 Farenheit. The temperature of the cave abovementioned so nearly corresponds with this, that the difference may be ascribed to a difference of instruments.

At the Panther gap, in the ridge which di vides 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 fect diameter, and emits constantly a current of air, of such force as to keep the weeds prostrate to the distance of twenty yards 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 Cumber. land 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 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. 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 lime. stone.... The arch approaches the semi-elliptical form; but the larger axis of the ellipsis, which would be the chord 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 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 straight, for a considerable distance above and below the bridge, opens a short but very pleasing view of the North mountain on one side, and 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.*

* Don Ulloa mentions a break, similar to this, in the province of Angaraez, in South-America. It is from 16 to 22 fret wide, 111 feet deep, and of 1-3 mile's continuance, English mea fure. Its breadth at top is not sensibly greater than at bottom. But the following fact is remarkable, and will furnish some light for conje&uring the probable origin of our natural bridge.. • Esta caxa, ó cauch está cortadae n péna viva con tanta precision, que las desigualdades del un lado entrantes, corresponden â las del otro lado salientes, como si aquella altura se hubiese abierto expresameute, con sus bueltas y tortuosidades, paru darle transito á los aguas por entre los dos murallones que la fo: man; fiendo tal su igualdad, que si llegasen á juntarse se endentarian uno con otro sin dexar hueco. Not. Amer. II. § 10. Don Ulloa inclines to the opinion, that this channel has been effected by the wearing of the water which runs through it, rather than that the mountain should have been broken open by any convulsion of nature. But if it had been worn by the running of water, would not the rocks which form the sides, have been wore plane? or if, meeting in some parts with veins of harder stone, the water had left prominences on the one side, would not the same cause have sometimes, or perhaps generally, occasioned prominences on the other side alse? Yet Don Ulloa tells us, that on the other side there are always corresponding cavities, and that these tally with the prominences so perfectly, that, were the two sides to come together they would fit in all their indentures, without leaving any void. I think that this does not resemble the effect of running water, but looks rather as if the two sides had parted asunder. The sides of the break, over which is the n natural bridge of Virginia, consisting of a veiny rock which yields to time, the correspondence between the salient and reentering inequalities, if it existed at all, has now disappeared. This Break has the advantage of the one described by Dan-Ulloa in its finest circumftankesno portion in that instance having held together, during the separation of the other parts, so as to form a bridge over the abyss.

QUERY VI.

A NOTICE of the mines and other subterraneous riches; its trees, plants, fruits, &c.

I knew a single instance of gold found in this. state. It was interspersed in small specks through a lump of ore, of about four pounds weight, which yielded seventeen pennyweight of gold, of extraordinary ductility. This ore was found on the north side of Rappahannoc, about four miles below the falls. I never heard of any other indication of gold in its neighbour hood.

On the great Kanhaway, opposite to the mouth of Cripple creek, and about twenty five miles from our southern boundary, in the county of Montgomery, are mines of lead. The metal is mixed, sometimes with earth, and sometimes with rock, which requires the force of gunpowder to open it; and is accompanied with a portion of silver, too small to be worth separation under any process hitherto attempted there. The proportion yielded is from 50 to 80lb. of pure metal from 100lb. of washed ore. The most common is that of 50 to the 100lb. The veins are at sometimes most flattering; at others they disappear suddenly and totally. They enter the side of the hill, and proceed horizontally. Two of them are wrought. at present by the public, the best of which is 100 yards under the hill. These would employ about 50 labourers to advantage. We.