ARKANSAS, a vast affluent of the Mississippi. It rises in the Rocky Mountains near Lat. 42. N. Long. 109. W., and after a winding course of 2170 miles, joins that river in Lat. 33. 56. N. Long. 91. 20. W., flowing generally in an eastward direction from its source as far as Long. 99., when it inclines to the south-east during the rest of its course. It flows through a well-wooded country for 100 miles from the Rocky Mountains; but in its farther progress it traverses a long tract devoid of wood, in which it expands into a wide stream, sometimes a mile in breadth, and interspersed with islands. It passes through the Ozark Mountains, and entering the state to which it gives its name, continues its course through a rich alluvial soil. It receives several considerable tributary rivers, the principal of which are the White River and the Great Canadian. Its annual inundations commence in March, and are at their height in June. It is navigable for steamboats as far as Fort Gibson, and, when in full flood, even so far as 2000 miles from its mouth.