A substance supposed to be Pumice, found floating on the Mississippi, has induced a conjecture that there is a volcano on some of its waters; and as these are mostly known to their sources, except the Missouri, our expectations of verifying the conjecture would of course be led to the mountains which divide the waters of the Mexican Gulf from those of the South Sea; but no volcano having ever yet been known at such a distance from the sea, we must rather suppose that this floating substance has been erroneously deemed Pumice. 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 two hundred 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 the 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 twelve or fifteen feet wide above and somewhat more spread below; but it is half as high again, the latter being only one hundred and fifty-six feet, according to the mensuration made by order of M. Vaudreuil, Governor of Canada, and one hundred and thirty according to a more recent account. [Illustration: An eye draught of Madison's cave on a scale of 67 feet to the inch. The arrows show where it descends or ascends.]