Compact limestone, and sandstone of several varieties, are the rocks which invariably occur along that portion of the Ohio we are now considering. Sandstone of a light gray or ashen colour, of a compact {38} texture, an argillaceous cement, and a slaty or lamellated structure, is the most abundant, and occupies the lowest points which we have hitherto been able to examine. This rock frequently contains alternating beds of coal, bituminous shale, and its accompanying minerals. The beds of compact limestone, which occur in this region, usually rest upon the sandstone just mentioned. Considered as a stratum, its distribution is the reverse of that of the sandstone. It occupies the central and least elevated portions of the formation; and on the borders where the sandstone is most abundant, the limestone is of less extent and of more uncommon occurrence. These remarks are applicable to the hilly district on the upper portion of the Ohio river. From Pittsburgh to Cincinnati, the prospect from the river is that of hills of moderate elevation, sometimes rocky and abrupt, but often sufficiently gradual in their ascent to admit of cultivation to their summits. Their character, as to extent, direction, &c. seems to be determined by the number, direction, and magnitude of the streams which traverse them. They are the remains of what was formerly a continuous and nearly horizontal stratum, with a large deposit of superincumbent soil, which the flowing of water, during the lapse of ages, has channelled and excavated to its present form. These hills diminish in altitude as you approach the falls from above; there they again rise to a height nearly equal to what they attain at the head of the river, and from thence gradually diminish, until they disappear, a little above the confluence of the Ohio and Green[055] rivers. Here commences the low country, which extends west to the Mississippi. It is characterized by the great extent of the river alluvion, the increased width and diminished velocity of the stream. The river banks are low, but thickly wooded with sycamore, cotton-wood, river maple, the planera aquatica, cypress, &c. The river hills, which terminate the alluvial district, {39} are distant and low; and it often happens that the surface descends on both sides, from the immediate banks of the river to these hills. Hence, when the waters of the river are sufficiently swollen to flow over its banks, they inundate extensive tracts; from which they cannot return to the channel of the river, and are left stagnant during the summer months, poisoning the atmosphere with noxious exhalations. Many of these inundated tracts have a soil of uncommon fertility, which it is probable will hereafter be recovered from the dominion of the river by dikes or levees.