Cataracts or falls are formed by the descent of rivers over rocks, from a higher to a lower level. That of Niagara, is situated on the river Niagara, between Canada and the United States, which takes its rise in the eastern extremity of Lake Erie, and, after flowing for thirty-five miles, empties itself into Lake Ontario. Its breadth is nine hundred feet, and its depth very considerable; but its current is so exceedingly strong and irregular, and its channel so frequently interspersed with rocks, that it is navigable for small boats only. Proceeding lower, the stream widens, and the rocks gradually recede from the view, and the current though strong, is smooth and regular. At Fort Chippewa, however, situated one league above the cataracts, the scene is again changed, and the river so agitated, that a boat would be inevitably dashed in pieces, were it permitted to pass Fort Niagara, situated on its bank. So impetuously do the waves break among the rocks, that the mere sight of them, from the adjacent shore, is sufficient to strike terror in the spectator. As it approaches the falls, the stream rushes along, with redoubled fury, until it reaches the edge of the stupendous precipice, when it tumbles suddenly to the bottom, without meeting with any obstruction in its descent. Precisely at this place, the river strikes off to the right, and the line of cataracts winds obliquely across, instead of extending, in the shortest direction, from the one bank to the other. It ought to be observed, that the water does not precipitate itself down the vast abyss in one entire sheet, but, being separated by islands, forms three distinct, collateral falls. One of these is called the great or Horseshoe fall, from the similarity of its form to that of a horseshoe. It is situated on the north-west extremity of the river, and is most deserving of the attention of the spectator, as probably seven-eighths of the water passes over it, and as its grandeur is evidently superior to that of the adjacent cataracts, although its hight may be somewhat less. As the extent of this fall can be ascertained by the eye only, it is impossible precisely to describe its limits; but its circumference is generally computed at eighteen hundred feet, somewhat more than one-third of a mile. Beyond the intervening island, the width of which may be equal to one thousand and fifty feet, is the second fall, about fifteen feet wide; and at the distance of ninety feet, occupied by the second island, is the third fall, the dimensions of which may be reckoned equal to those of the large island; so that the entire extent of the precipice, including the intermediate islands, is four thousand and five feet; a computation which certainly does not exceed the truth. The quantity of water precipitated from the falls is prodigious, and it has been estimated, amounts to _six hundred and seventy thousand, two hundred and fifty tuns per minute_.