In deciding upon the physical character of the Mississippi River, it may be advantageously considered under four natural divisions, as indicated by permanent differences in its geological and physical character--its vegetable productions, and its velocity and general hydrographical character. Originating in a region of lakes upon the table-lands which throw their waters north into Hudson's Bay, south into the Gulf of Mexico, and east into the Gulf of St. Lawrence, it pursues its course south to the Falls of Pakagama, a distance of two hundred and thirty miles, through natural meadows or savannas covered with wild rice, rushes, reeds and coarse grasses, and aquatic plants. During the distance, it is extremely devious in its course and width, often expanding into lakes which connect themselves through a vast system of reticulated channels. Leech Lake, Cass Lake, and Lake Andrúsia would themselves be regarded as small interior seas, were they on any other part of the continent but that which develops Superior, Michigan, Huron, Erie, and Ontario. Its velocity through the upper plateau is but little, and it affords every facility for the breeding of water fowl and the small furred quadrupeds, the favorite reliance of a nomadic population. At the Falls of Pakagama, the first rock stratum and the first wooded island is seen. Here the river has an aggregate fall of twenty feet, and from this point to St. Anthony's Falls, a distance of six hundred miles, it exhibits its second characteristic division. The granitical and metamorphic rocks, which support the vast plateaux and beds of draft of its sources, are only apparent above this point, in boulders. The permanent strata are but barely concealed at several rapids below the Pakagama, but appear plainly below the influx of the De Corbeau, at Elk River, Little Falls, and near Sac River. And this system of rock is succeeded, before reaching the Falls of St. Anthony, by the horizonal white sand rock and its superior limestone series of the carboniferous formation. Vegetation is developed as the river descends towards the south. A forest of maples, elm, oak, ash, and birch, is interspersed with spruce, birch, poplar, and pine above the Pakagama, and continues, in favorable positions, throughout this division. The black walnut is first seen below Sandy Lake, and the sycamore below the River De Corbeau. The river in this division has numerous well-wooded islands; its velocity is a striking feature; it abounds with rapids, none of which, however, oppose serious obstacles to its navigation. Agreeably to memoranda kept,[76] it has fifty-six distinct rapids, including the Little and Big Falls, in all of which the river has an aggregate estimated descent of two hundred and twenty-four feet, within a distance of fourteen thousand six hundred and forty yards, or about eight miles. The mean fall of the current, exclusive of these rapids, may be computed at nearly six inches per mile. [76] _Vide_ Appendix.