This Wind-gap is about a mile broad, and the stones in it such as seem to have been washed for ages by water running over them.  Should this have been the case, there must have been a lake behind that mountain; and, by some uncommon swell in the waters, or by some convulsion of nature, the river must have opened its way through a different part of the mountain, and meeting there with less obstruction, carried away with it the opposing mounds of earth, and deluged the country below with the immense collection of waters to which this new passage gave vent.  There are still remaining, and daily discovered, innumerable instances of such a deluge on both sides of the river, after it passed the hills above the falls of Trenton, and reached the champaign.  On the New Jersey side, which is flatter than the Pennsylvania side, all the country below Croswick hills seems to have been overflowed to the distance of from ten to fifteen miles back from the river, and to have acquired a new soil, by the earth and clay brought down and mixed with the native sand.  The spot on which Philadelphia stands evidently appears to be made ground.  The different strata through which they pass in digging for water, the acorns, leaves, and sometimes branches which are found above twenty feet below the surface, all seem to demonstrate this.”

How little reason there is to ascribe to extraordinary convulsions the excavations which are made by water upon the surface of the earth, will appear most evidently from the examination of that natural bridge of which mention is made above, and which is situated in the same ridge of mountains, far to the south, upon a branch of James’s River.  Mr Jefferson gives the following account of it.

“The natural bridge, the most sublime of nature’s works, 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 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 its 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 cord of the arch, is many times longer than the transverse.  Though the sides of the bridge are provided in some parts with a parapet of fixed rock, yet few men have resolution to walk to them, and look over into the abyss.  You involuntarily fall on your hands and feet, and creep to the parapet, and look over it.  Looking down from this height about a minute gave me a violent headache.  If the view from the top be painful and intolerable, that from below is delightful