The river, at this point, enters a valley which is defined by rocky cliffs, which attain various elevations from one to three hundred feet, presenting a succession of picturesque or sublime views. In some places these cliffs present a precipitous and abrupt façade, washed by the current. In far the greatest number of cases, the eminence has lost its sharp angles through the effects of frosts, rains, and elemental action, leaving a slope of debris at the foot. As the river descends, it increases in volume and in the extent of its alluvions. These form, in an especial manner, its characteristic features from St. Anthony's Falls to the junction of the Missouri, a distance of not less than eight hundred miles. The principal tributaries which it receives in this distance, are, on the right, the St. Peter's, Upper and Lower Iowa, Turkey River, Desmoines, and Salt Rivers; and, on the left, the St. Croix, Chippewa, Wisconsin, Rock River, and the Illinois. One hundred miles below St. Anthony, it expands for a distance of twenty-four miles into the sylvan sheet of Lake Pepin, at the foot of which it receives the large volume of the Chippewa River, which originates on the sandy tracts at the sources of the Wisconsin, Montreal, and Ontonagon; and it is from this point that its continually widening channel exhibits those innumerable and changing sand-bars, which so embarrass the navigation. But in all this distance, it is only at the Desmoines and Rock River rapids that any permanent serious impediment is found in its navigation, with the larger craft. The fourth change in the physical aspect of this river, is at the junction of the Missouri, and this is an almost total and complete one; for this river brings down such a vast and turbid flood of commingled earths and floating matter, that it characterizes this stream to its entrance into the Gulf of Mexico. If its length of channel, velocity, and other leading phenomena had been accurately known at an early day, it should also have carried its name from this point to the ocean. Down to this point, the Mississippi, at its summer phases, carries the character of a comparatively clear stream. But the Missouri, which, from its great length and remote latitude, has a summer freshet, flows in with a flood so turbid and opaque, that it immediately communicates its qualities and hue to the milder Mississippi. At certain seasons, the struggle between the clear and turbid waters of the two streams can be seen, at opposite sides of the river, at the distance of twenty or thirty miles. Entire trees, sometimes ninety feet long, with their giant arms, are swept down the current; and it is not unusual, at its highest flood, to observe large, spongy masses of a species of pseudo pumice carried into its channel, from some of its higher western tributaries.