The Missouri River has its sources high in the Rocky Mountains, in Lat. 45° N., and Long. 110° 30' W., almost in the regions of British America. Its course is at first nearly N. to the Great Falls, when it bends to the E.N.E. till it joins the White Earth River, whence its course to its confluence with the Mississippi is generally S.E. But little serious impediment to navigation is interposed lower down than the Great Falls, a distance of 2575 miles from the mouth. The Missouri drains a basin of half a million square miles, and its whole length to its junction with the Mississippi is estimated at 3090 miles. Its course throughout is irregular and turbulent, abounding in rapids and bars. The United States engineers, who surveyed its whole extent in 1853-54, arrived at the conclusion that a steamer loaded, and drawing 24 inches, could navigate, from the opening of the season until the 1st of September, as far as Fort Union; and that one drawing 20 inches could go up even beyond Fort Benton. From the very elaborate report of these engineers, employed by the government to survey the several routes for a railroad to the Pacific, we condense the following interesting particulars in regard to the course of the river, its length, characteristics, and tributaries.

The Missouri enters the Mississippi in Lat. 38° 50. 50. N., and Long. 90. 13. 45. W. of Greenwich. Below the mouth of the Kansas its course is nearly E., and lies almost entirely in the state of Missouri. This portion is continuously settled with flourishing cities and towns; and the soil is of surpassing fertility, abounding in coal, iron, and other minerals. Its average velocity in this section is a little over five miles an hour. Concealed snags and sawyers are liable to occur in any part of the river, and its banks are heavily wooded from the mouth of the Kansas to the Mississippi. The principal tributaries between the mouth and Fort Leavenworth are the Osage, Grand, and Kansas Rivers, which are navigable,—the first, for six months in the year, 200 miles; the second at all seasons; and the last 150 or 200 miles, obstructed, however, by two sets of rapids. The valley of the Missouri possesses great resources for future wealth and influence. From the mouth of the Kansas to near the parallel 40. 38. N. Lat., this river separates the state of Missouri from the Indian territory, and from that point to the Big Sioux, separates Iowa from the Indian territory. Before reaching the Platte, the Nodawa, Little Tarkio, Big Nemaha, Nishnabotana, and Little Nemaha, minor streams, enter the Missouri. In uniting with the Missouri the Platte forms a delta, and debouches through three channels varying from 30 yards to 350 yards in width. The delta is composed of sand-bars, and intersected by numberless sloughs. From its mouth to Fort Laramie the Platte is 700 miles long, and is less tortuous than the Missouri. Below the fork the bed of the stream is occupied with vast quantities of drifting sand or quicksand, so that the depth may not be more than 3 feet, and cannot be made available, it is thought, for purposes of navigation. The course of the Missouri from the mouth of the Platte to the Kansas is S.E., and its length 236 miles. Carboniferous limestone and coal measures form the principal geological features of this part of the river. From the mouth of the Platte to Fort Pierre the distance is 638 miles; from Fort Pierre to the Big Sioux the direction of the river is S.E. Council Bluff, situated on the left bank, is the last town now seen on ascending the Missouri, and is the ordinary head of steamboat navigation. The soil of the bottoms on this part of the river is very rich. The Big Sioux is 100 yards wide at its mouth, and navigable for steamers to the rapids; it is susceptible of improvement. Within a few years the channel of the Missouri has changed here several miles from north to south. From the mouth of the Platte to Fort Pierre the Missouri varies in width from 400 to 1000 yards, and its valley becomes less fertile. From the mouth of the Big Sioux to that of the White Earth the Missouri separates Minnesota from the Indian territory. From the mouth of the White Earth to Fort Clark the course of the river is S.E., and then is S. to Fort Pierre,—the whole distance being 715 miles. Here the great northern bend of the river is found. The Yellow Stone enters still further up, and is navigable 200 miles to the rapids. The channel of the Missouri becomes now entirely choked by sand-bars. In 1853 a steamer ascended in forty-two days to Fort Union, and returned to St Louis in seventeen days more; but for the ice, steamers might even ascend to Milk River throughout the year, this being the highest point to which navigation has been carried.

The Missouri is affected by two annual floods, which greatly facilitate navigation by larger steamboats. The first and lesser flood is caused by the melting of snows on the prairies, and generally takes place in May; the second is occasioned by the melting of the mountain snows, and occurs in June. Steamers, heavily laden, and bound for the Yellow Stone, should leave St Louis about the middle of April, in order to have the benefit of the June rise. The river above Council Bluff City is closed by ice from about the middle of November to the 1st of April.