In the southern part of Pennsylvania, the range called particularly the Alleghany ridge, is near the centre, and is most elevated of the group. Its summit divides the waters of the Susquehannah on the east from those of the Ohio on the west. This mountain consists principally of argillite and the several varieties of grey wacke, grey wacke slate, and the other aggregates, which in transition formations usually intervene between the metalliferous limestone and the inclined sandstone. The strata have less inclination than in the Cove, Sideling, and South mountains, and other ridges east of the Alleghany. The summit is broad, and covered with heavy forests. Something of the fertility of the Mississippi valley seems to extend, in this direction, to the utmost limits of the secondary formation. The western descent of the Alleghany ridge is more gradual than the eastern, and the inclination of the strata in some measure reversed. It is proper to remark, that, {10} throughout this group of mountains, much irregularity prevails in the direction as well as of the dip and inclination of strata. If any remark is generally applicable, it is, perhaps, that the inclination of the rocks is towards the most elevated summits in the vicinity. Laurel ridge, the next in succession, is separated from the Alleghany by a wide valley. Its geological features are, in general, similar to those of the eastern ranges; but about its summit, the sandstones of the coal formation begin to appear alternating with narrow beds of bituminous clay-slate. Near the summit of this ridge, coal beds have been explored, and, at the time of our visit, coals were sold at the pits for ten cents per bushel. In actual elevation, the coal strata at the summit of Laurel-hill, fall but little below the summits of the Alleghany. Thus, in traversing from east to west the state of Pennsylvania, there is a constant but gradual ascent from the gneiss at Philadelphia, the several rocky strata occurring one above another, in the inverse order of their respective ages, the points most elevated being occupied by rocks of recent origin, abounding in the remains of animal and vegetable life. Near the summit of this ridge some change is observed in the aspect of the forest. The deep umbrageous hue of the hemlock spruce, the Weymouth pine, and other trees of the family of the coniferæ, is exchanged for the livelier verdure of the broad-leaved laurel, the rhododendron, and the magnolia acuminata.