ALLEGANY RIVER, in Pennsylvania, rises on the western side of the Allegany Mountains, and after running about 300 miles in a south-west direction, meets the Monongahela at Pittsburg, and both united form the Ohio. The lands on each side of this river, for 150 miles above Pittsburg, consist of white oak and chesnut ridges, and in many places of poor pitch pines, interspersed with tracts of good land and low meadows. It is navigable for boats of ten tons for 260 miles above Pittsburg.