The navigation, however, of these great rivers was for many years attended with almost endless difficulties and dangers. In the Ohio and other western waters of the United States, though the current does not average more than three miles an hour, there were rapids where, in some instances, it attains a velocity of from seven to eight miles. There were also numerous sandbanks, most of which have now been removed, whereon the boats frequently took the ground and were detained until the next rise of water, sometimes for even three and four months. In the upper waters, too, the floating ice during the spring of the year occasioned many disasters, and is still a danger not to be prevented. But the greatest danger arose from what was known as “snags,” stumps of trees which, from the falling in of the banks, are carried down the river until they lodge, with one end resting in the mud or sand, and the other rising to the surface sometimes so concealed as to baffle the utmost precaution in avoiding it. Among the sixty-six boats lost in the navigation of these western rivers during the years 1831-2-3, while seven were wrecked by ice, fifteen stranded and abandoned, fifteen destroyed by fire, and five wrecked by collision with other boats, no less than twenty-four were “_snagged_.” But, besides the “snags,” there are dangers, though of somewhat less importance, arising from other falling trees, known by the name of “sawyers,” trees which have sunk with an inclination down the stream, the action of the current upon them causing a continual vertical vibration, whence their name. Generally, when a boat going down stream strikes a sawyer, she will pass over it with little or no injury as its inclination is in the direction of the boat’s movement. But the danger, here, differs from that of the “snags.” Their inclination is up the river, their ends sometimes projecting above the surface at low water, or when the river is at a higher stage, remaining just sufficiently beneath the surface to be still more dangerous. Boats going down stream, therefore, encounter very great peril, and it has frequently occurred that, when the “snag” lies at a great inclination, the end rises when struck and not only pierces the hull but passes up through all the decks. These dangers are increased by the remarkable fluctuation in the depth of the water in the rivers, which is sometimes so great, as to admit the navigation of the largest vessel, and again so small, as to render it impossible to construct vessels with draught of sufficient lightness to float upon them.