Following down the great river, its winding and varying channel south of Memphis becomes the boundary between the States of Mississippi and Arkansas. To the westward the Arkansas shore is a lowland and the interior largely swamps, with many bayous and lakes, the tributaries of St. Francis River, which, rising in the Iron Mountain district of Missouri, flows four hundred and fifty miles, generally southward, to fall into the Mississippi just above Helena. This river passes through a continuous swamp after entering Arkansas, spreads into numerous lakes, and its extensive basin is one of the great reservoirs of overflow relieving the Mississippi in time of flood. Its port of Helena has a trade in timber brought out of the neighboring swamps and forests. About one hundred miles below, the White River and the Arkansas River flow in upon the western shore. Very curiously, these rivers, having mouths about fifteen miles apart, join some distance above, their waters commingling in the alluvial bottom land. The White River is nine hundred miles long, rises in the Ozark Mountains of Northern Arkansas, makes a long circuit through Missouri and then comes southward, being navigable some four hundred miles to Batesville, the seat of Arkansas College. The Arkansas River, next to the Missouri, is the greatest Mississippi tributary, being nearly twenty-two hundred miles long and having its sources in the Rockies in Colorado, out of which it flows in a magnificent canyon. It comes for five hundred miles eastward through plains that are largely sterile, enters Kansas, turns southeast in the Indian Territory, and crosses the State of Arkansas to its mouth, being navigable for eight hundred miles. At the western border of the State the river is guarded by Fort Smith, where an active town has grown around the former frontier post on the verge of the Indian Territory, having large trade and a population of fifteen thousand.