Upon emerging from the foothills of the mountains, both streams begin to assume that peculiar character which distinguishes them throughout the rest of their course to the sea. They flow through alluvial bottoms, built up of the detritus from the highlands and mountains, until the present bed of the river is in most places fifty to a hundred feet above the original bed in the solid rock. The usual characteristics of an alluvial river are here found in their highest development—a muddy current, freshly formed islands, sandbars innumerable, an unstable channel, and a shifting bed which is never in the same place for two years in succession.
Among the most striking phenomena of a river like the Missouri is the constant change that is going on in the location of its channel. This seems to be in some places a periodical matter. The forces of the river get to working on particular lines and push their devastations for many years in one general direction. Being finally arrested by some insurmountable obstacle, or turned, it may be, by trifling causes, they work in another direction, and invade lands which have enjoyed long immunity, and upon which the cottonwood, walnut, and cedar have attained mature growth.
A NEW “CUT OFF”
Old course of river
toward background
Old course of river
from background
A WINDING WATERWAY.
The river, in its unrestrained rambles from bluff to bluff, performs some curious freaks. It develops the most remarkable bends, varying in length from one to thirty miles, with distances across the necks but a small fraction of those around. In time these narrow necks are cut in two, and the river abandons its old course, which soon fills up near the extremities of the bends and leaves crescent-shaped lakes in the middle. This process is a never-ending one, and the channel distances along the river are in a state of never-ending change. There is one bend in the upper river, known from the earliest times as the Great Bend, which was not formed in the way just described. The course of the river here is comparatively permanent, and is evidently the same as that of the original stream bed. The distance around is nearly thirty miles, while that across is only a mile and a half. It was a regular custom with travelers, when the Indians were not too dangerous, to leave the boats at the beginning of this bend and walk across, going on board on the other side.
The existence of so many bends increased the length of the channel, but this drawback was more than offset by the reduction of the slope which made the current less strong and enabled steamboats to overcome it with greater ease. The river is like a great spiral stairway leading from the ocean to the mountains. A steamboat at Fort Benton is 2565 feet—two and one-half times the height of the Eiffel tower in Paris—above the level of the sea; yet so gentle is the slope nearly all the way that, in placid weather, the water surface resembles that of a lake. This wonderful evening-up of the slope of the river by the extreme sinuosity of its course is a fact not only interesting as a natural phenomenon, but of the utmost importance in the behavior and use of the stream.
