The Missouri River is formed in southwestern Montana, by the union of the Jefferson, Madison and Gallatin Rivers. Its length from the source of the Madison River in the Yellowstone National Park to its confluence with the Mississippi above St. Louis is about three thousand miles. The first exploration of the headwaters of the Missouri was by the famous expedition of Captains Lewis and Clark in 1805, who ascended to its sources, and crossing the Rockies descended the Snake and Columbia Rivers into Oregon. They found the confluence of the three rivers making the Missouri, in July, and called it "the Three Forks," at the same time naming the rivers after President Jefferson and his Secretaries of State and the Treasury. The Missouri, from the junction, first flows northward through the defiles of the Rockies, and breaks out of the mountain wall in Prickly Pear Canyon, at the Gate of the Mountains, where the rocky cliffs rise twelve hundred feet. Forty miles northeast it goes down its Great Falls to a lower plateau, having a total descent of nearly five hundred feet, the stream contracting in the gorge to a width of three hundred yards, and tumbling over repeated cascades, with intervening rapids. The Black Eagle descends fifty feet, Colter's Falls twelve feet, the Crooked Falls twenty feet, the Rainbow forty-eight feet, and the Great Falls ninety-two feet, this series of rapids and cascades covering a distance of sixteen miles. Lewis and Clark were the first white men who saw these magnificent cataracts of the Upper Missouri, and they named the different falls. The Black Eagle was named from the fact that on an island at its foot an eagle had fixed her nest on a cottonwood tree. It is recorded by a United States Engineer officer who was there in 1860, that the eagle's nest then still remained in the cottonwood tree on the island, being occupied by a bald eagle of large size. Again in 1872 the nest and the old eagle were still there, and from the longevity of these birds, it was then believed to be the same eagle seen in 1805. The old eagle nest and cottonwood tree are all gone now, and in their place are a big dam, power-house and huge ore-smelter, worked by the ample water-power of the fall. The flourishing town of Great Falls gets its prosperity from these cataracts and is a prominent locality for copper-smelting, having fifteen thousand people. At the head of river navigation, some distance farther down, is the military post of Fort Benton. The river then flows eastward through Montana, receives the Yellowstone at Fort Buford and turns southeast in North Dakota, passing Bismarck, the capital, and flowing south and southeast it becomes the boundary between Nebraska and Kansas on the west, and South Dakota, Iowa and Missouri on the northeast. Its course is through an alluvial valley of great fertility, from which it gathers the sediment with which its waters are so highly charged. Much of the adjacent territory in Dakota