Notes on the State of Virginia (1802)/Query 05
QUERY V.
ITS Caſcades and Caverns?
The only remarkable Caſcade in this country, is that of the Falling Spring in Auguſta. It is a water of James' River, where it is called Jackſon's River, riſing in the warm ſpring mountains, about twenty miles ſouth weſt of the warm ſpring, and flowing into that valley. About three quarters of a mile from its ſource, it falls over a rock 200 feet into the valley below. The ſheet of water is broken in its breadth by the rock in two or three places, but not at all in its height. Between the ſheet and rock, at the bottom, you may walk acroſs dry. This cataract will bear no compariſon with that of Niagara, as to the quantity of water compoſing it; the ſheet being only 12 or 15 feet wide above, and ſomewhat more ſpread below; but it is half as high again, the latter being only 156 feet, according to the menſuration made by order of M. Vaudreuil, Governor of Canada, and 130 according to a more recent account.
In the lime-ſtone country, there are many caverns of very conſiderable extent. The moſt noted is called Madiſon's Cave, and is on the north ſide of the Blue ridge, near the interſection of the Rockingham and Auguſta line with the ſouth fork of the ſouthern river of Shenandoah. It is in a hill of about 200 feet perpendicular height, the aſcent of which, on one ſide, is ſo ſteep, that you may pitch a biſcuit from its ſummit into the river 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 generally 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 which yield ſupplies to the fountains of water, diſtinguiſhed from others only by its 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.
An eye draught of Madiſon's Cave, on a ſcale of 75 feet to the inch. The arrows ſhow where it deſcends or aſcends.
Another of theſe caves is near the North mountain, in the county of Frederick, on the lands of Mr. Zane. The entrance into this is on 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 a height of from 5 to 12 feet. After entering this cave a few feet, the mercury, which in the open air was at 50° roſe to 57° of Farenheit's thermometre, 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 ſubterraneous 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 54° 30′ 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 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 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 dryer 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. 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 the reſolution to walk to them, and look over into the abyſs. You involuntarily fall upon 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-ache. 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, 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's River, and ſufficient in the dryeſt ſeaſons to turn a griſt-mill, though its fountain is not more than two miles above.[1]
- ↑ Don Ulloa mentions a break, ſimilar to this, in the province of Angarez, in South America. It is from 16 to 22 feet wide, 111 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 remarkable, and will furniſh ſome light for conjecturing the probable origin of our natural bridge. ‘Eſta caxa, ó cauce eſtá cortada en péna viva con tanta preciſion, que las deſigualdades del un lado entrantes, correſpondan á las del otro lado ſalientes, como ſi aquella altura ſe hubieſe abierto expreſamente, con ſus bueltas y tortuoſidades, para darle tranſito á los aguas por entre los dos murallones que la forman; ſiendo tal ſu igualdad, que ſi illegaſen á juntarſe ſe endentarian uno con otro ſin dexar hueco.’ Not. Amer. II. § 10. Don Illoa 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 worn 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 alſo? 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 having 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 natural bridge of Virginia, conſiſting of a veiny rock which yields to time, the correſpondence between the ſalient and re-entering inequalities, if it exiſted at all, has now diſappeared. This break has the advantage of the one deſcribed by Don Ulloa in its fineſt circumſtance; no portion in that inſtance having held together, during the ſeparation of the other parts, ſo as to form a bridge over the abyſs.