about 900 square miles, lying between the vallies of Roanoke and Nottaway. MONONGAHELA river, in Virginia, Maryland and Pennsylvania, is formed by Monongahela proper, Tygart's Valley river, Cheat river, and the Youghioghany. The Cheat is in fact the main stream, having its remote source in the southern part of Randolph county, Virginia, at lat. 38° 27', interlocking sources with those of Green river, and Jackson's branch of James river. The remote sources of Tygart's Valley river, are nearly as far south as those of Cheat, and also in Randolph county. The mountain ridge from which both streams rise is known locally as Greenbrier mountain, and the valleys from which the higher sources are derived, must be at least 2,500 feet elevated above tide water in Chesapeake bay.

Monongahela proper, is the western branch, rising in Lewis county, Virginia, with interlocking sources with those of Tygart's Valley and little Kanawha. The three branches near their sources, pursue a general northern course, but the two western, gradually approach each other, and unite at lat. 39° 28', where they form a point of seperation between Harrison and Monongalia counties. Thence assuming a northern course over the latter county, finally leave Virginia, and form a junction with Cheat on the boundary between Fayette and Green counties, Pennsylvania.

The Cheat in the highest part of its course, flows along a mountain valley, in a northern direction, but gradually inclining to northwestward, as already noticed under the head of Cheat river. Below the junction of the main branches, the Monongahela, by a rather circuitous channel, pursues a general northern course over Pennsylvania, about 50 miles, comparative length to its junction with Youghioghany, 11 miles S. E. of Pittsburg.

The Youghioghany is a considerable branch, having its remote sources in the western part of Alleghany county, Maryland. Flowing thence northwardly, enters Pennsylvania, and separating for some few miles, Somerset, from Fayette county, receives a large tributary from the eastward, Casselman's river, and turning to N. N. W. about 50 miles, comparative course, is lost in the Monongahela at MacKeesport. Augmented by the Youghioghany, the Monongahela below the junction, assumes the course of the former, 18 miles by the channel, but only 11 direct distance to Pittsburg, where it unites with the Alleghany to form the Ohio. The general course of the Monongahela is almost exactly north, and almost as exactly along long. 3° W. Washington, 150 miles by comparative distance. The widest part of its valley lies nearly along the line between Pennsylvania and Virginia, 80 miles; the mean width 40, and area 6,000 square miles.

If we allow only 1,500 feet elevation to the arable country on the head branches of Cheat, Pittsburg being elevated 678 feet, will give a descent of 822 feet to the valley of Monongahela. The extremes of lat. are thus almost exactly compensated by declivity, and explain why the seasons near Pittsburg and in Randolph county, Virginia, differ but slightly.

Though the two eastern branches, Cheat and Youghioghany, rise in mountain vallies, and the whole country drained by all the tributaries of Monongahela is very broken and rocky, direct falls are rare and of no great elevation when they occur. Cheat river, is navigable through Monongalia and Preston, into Randolph county; both branches of Monongahela proper, above their junction, and Youghioghany to Ohio, have falls. The whole valley has gained recent increase of importance as being part of the route or routes of proposed lines of canal improvement.

Monongahela river is 400 yards wide at its mouth; at the mouth of the

Youghioghaney 12 or 15 miles higher up, it is 300 yards wide; and continues of that width to the mouth of Cheat river, a distance of 90 miles by water, but only 58 by land. In this space the navigation is frequently interrupted by rapids, but are passable by boats when the river rises a few feet. From that point it admits light boats, except in dry seasons 65 miles further, to the head of Tygart's valley,-presenting only some falls of a few feet, and lessening in width to 20 yards. The western fork is navigable in winter 10 or 15 miles, towards the northern branch of the Little Kanawha, to which a good wagon road might be made. The Youghioghany is the principal branch of this river. This branch passes through the Laurel mountain about 300 miles from its mouth, and is that far, from 300 to 150 yards wide, and the navigation much obstructed in dry weather by rapids and shoals. In its passage through the mountain the fall is very great, admitting no navigation for ten miles to the Turkey Foot. Thence to the great crossing, about 20 miles, it is again navigable, except in dry seasons, and is at that place 20 yards wide. The sources of this river are divided from those of the Potomac by the Alleghany mountain. From the falls at which it intercepts the Laurel mountian to Fort Cumberland, the head of navigation on the Potomac, is 40 miles of very mountaneous road. Willis' creek, at the mouth of which was Fort Cumberland, is 30 or 40 yards wide, but beyond that, there is no navigation.

NANSEMOND river rises in Isle of Wight and Nansemond counties, but chiefly in the latter. It opens by a comparatively wide bay into Hampton Roads, and is navigable for vessels of 250 tons to Sleepy Hole, for those of 100, to Suffolk, the county town of Nansemond, and for those of 25 tons to Milner's.

NOTTOWAY river, of Virginia and North Carolina, has its most remote source in Prince Edward county. Flowing thence S. S. E. between Nottaway and Lunenburg counties, between Dinwiddie and Brunswick, turns to eastward between Greensville and the western part of Sussex. Entering the latter, and first curving northward winds to S. E., and traversing Sussex and Southampton counties, receives Blackwater river from the north, and entering Gates county, North Carolina, bends to S. W. 10 miles to its junction with Meherin, to form Chowan river. The entire length of Nottaway by comparative courses is 110 miles. The Nottoway valley is about 100 miles, by 20 mean width, comprising great part of Nottaway, Dinwiddie, Sussex, Surry, and Southampton counties, and a smaller part of Lunenburg, Brunswick, Greensville, Prince George, Isle of Wight, and Nansemond counties, and a minor part of Gates county, North Carolina.

OCCOQUAN river rises in Loudon, Fairfax, and Fauquier counties, traverses and drains the western part of Prince William county, and thence forming the boundary between Prince William and Fairfax counties, falls into the Potomac, about 25 miles below Washington City, and nearly opposite Indian Point. [See Prince William county.]

OHIO forms the boundary of Virginia for 355 miles. It is in some respects the most remarkable river upon earth. The physical section of the earth drained by it lies between lat. 34° 12′ and 42° 27', and long. 1o and 12° west of Washington City. The course of the Ohio proper, from the sources of Alleghany to its junction with the Mississippi, is by calculation. 59° 30' west, 680 statute miles.

The form of the valley of the Ohio approaches, in a very remarkable manner, that of a regular ellipse, of which a line drawn from its most north

ern to its most southern sources, from Orleans creek, Cataraugus county, New York, to Bear Grass creek, Marion county, Alabama, 750 statute miles,—would be the transverse diameter, and another line extending from the Blue Ridge, where the sources of the Great Kanawha and those of Watauga branch of Tennessee rise, to the northwestern sources of the Wabash, 450 miles, would be the congugate axis. Measured by the rhombs following the elements in the following table, the area comes out more than 200,000 square miles:

Table of the extent in square miles of the valley of Ohio river:

Between lat. 34° and 35° 24 Rhombs,

square miles.

8,986

Aggregate extent in square miles,

Allowing the greatest length to be 750 miles, the mean width will be 267 very nearly, or the mean breadth amounts to within a rifling fraction of one-third of the greatest length, a compactness seldom equalled in rivers.

If the Alleghany is regarded as the primary and remote constituent of Ohio, this great stream rises by numerous creeks in McKean and Potter counties, Pennsylvania, and Alleghany and Cataraugus coumies, New York. Becoming navigable near the line of demarcation between the two states, the stream, with partial windings, pursues the general course already stated, to its junction with the Mississippi, affording a natural navigable channel of between 1,200 and 1,300 miles. The opposing inclined plains of Ohio valley are of unequal extent, nearly in the proportion of two to three, the larger falling from the Appalachian system of mountains, and containing 120,000 square miles.

In their features also the two Ohio plains differ essentially. The southeastern, declining from a mountainous outline, has a comparatively rapid slope. The most elevated table land from which the eastern tributaries flow, is that where rise the sources of Clinch, Holston, and Great Kanawha, about 2,500 feet. The Appalachian table land declines in relative elevation both to north and south of this nucleus, but there is no one part from the sources of Alleghany and Genesee to those of Tennessee and Coosa, through 7° of lat. but which exceeds 1,000 feet.

The elevation of Ohio at Pittsburg, where the Alleghany and Monongahela unite, is 678 feet, and that of the low water at the confluence of Ohio and Mississippi 283 feet; of course the Ohio below Pittsburg, has a fall of 395 feet in 948 miles, the length of the intermediate channel. The left tributaries must have, from the preceding data, a descent of from 1,000 to 2,200 feet. Down this rapid declivity, advancing from north to south, are found the streams of Clarion, Kiskiminitas, Monongahela, Great Kanawha, Sandy, Kentucky, Cumberland and Tennessee, and several of lesser length of course, whose sources do not reach the Appalachian vallies.

It may well excite surprise, that along this steep plain, direct falls are not frequent, and where they do occur are of moderate direct pitch.

To an eye sufficiently elevated, and powers of vision sufficiently enlarged, the whole valley of Ohio would appear one immense declivity, falling very nearly at right angles to the general range of the Appalachian system, and the rivers would appear to have cut deep channels seldom in a direction corresponding to the plane of general descent.

Of these channels that of Ohio would appear as the principal. Persons competent have carefully measured the height of the hills, in the vicinity of Pittsburg, and found them about 460 feet above the low water level of the rivers, or 1,138 feet above the level of the Atlantic tides. Above Pittsburg to the hills, which rise like mountains from lake Erie, the ascent is at least 400 feet, and below Pittsburg the fall to the Mississippi has been shown to be 395 feet. Without therefore estimating mountain ridges, the great inclined plain of Ohio has a descent of upwards of a foot to the statute mile, but what is something remarkable, the rivers, and particularly the Ohio itself, do not fall gradually with the planes of their courses. The actual channel from Pittsburg to the mouth is 948 statute miles, and the fall 4,716 inches, or not quite five inches per mile.

The waters in effect have abraded their channels, deeper toward their sources than in proportion to length of course. It is this circumstance which has contributed to give to the Ohio proper, the appearance of flowing in a deep and immense ravine. The difference of climate arising from difference of level, frequently exceeding a degree of latitude in less than a mile, and radiated heat, with an exuberant alluvial soil, giving in spring a precocious vegetation along the river bank, have superinduced great misunderstanding respecting the temperature and seasons of this region.

Descending the Ohio, say from Pittsburg, the scenery along the banks and hills, is in an eminent degree picturesque and varied, but these fine features imperceptibly fade away, and long before reaching the Mississippi, totally disappear, and leave a narrow horizontal ring sweeping round the heavens, formed by the trees along the banks.

As a navigable channel, few, if any other rivers of the globe, equal the Ohio. In the higher part of its course, the navigation is annually more or less impeded in winter by ice, and in autumn by a want of water. Impedi ment from ice prevails in all its course, but below the influx of Kanawha, drought is of less injury, and below the rapids at Louisville, in a com mercial point of view, removed by a navigable canal.

The four most important of all mineral productions abound in the Ohio valley, limestone, mineral coal, salt, and iron ore. Of all continuous bodies

of productive soil on earth, if climate and fertility are combined, the valley of Ohio will, it is probable, sustain the most dense population. Not long since there did not exist upon its immense surface 20,000 civilized human beings. In 1831, it sustained about 3,000,000. Can the history of the world afford any parallel to such increase?

PAMUNKEY river, the principal constituent of York river, is formed by Pamunky proper and North Anna. The latter rises in Orange, the northern part of Louisa and in Spottsylvania counties, and flowing thence southeastward unites with the Pamunkey, between Caroline and Hanover counties.

The Pamunky rises in the S. W. mountain, on the border between Albemarle and Louisa; drains the southern and central part of Louisa, and traversing Hanover, joins the North Anna. Below their junction, the united waters, known by the name of Pamunky, preserve the original course

southeastward, about 45 miles comparative course, (but perhaps double that distance by the bends,) to its junction with Mattapony to form York The entire comparative length of Pamunkey, by either branch, is about 90 miles. The broadest part of the valley but little exceeds 30 miles, and is only about 15 mean width, area 1,300 square miles, lying between those of James and Chickahominy on the right, and Mattopony on the left.

PIG river, rises in the southeastern slope of the Blue Ridge, and flowing thence eastward, between Black water and Irvine rivers, traverses and drains the central part of Franklin county, and entering Pittsylvania, turns to E. and falls into Roanoke, after a comparative course of 35 miles.

POCATALICO. This river has its sources near the northern boundary of the county of Kanawha, and flows through a body of forest land finely timbered: much of it fertile, and sufficiently level for advantageous cultivation. The alluvial lands on its borders, are generally rich, and of width sufficient to form good farms. Pocatilico discharges itself into the Great Kanawha, 20 miles below Charleston, and forty miles above the mouth of the latter river; it is navigable by batteaux, which ascend from 20 to 30 miles, and during the winter and spring months, large and heavy loaded boats may descend with safety, as also rafts of timber of various descriptions. Extensive beds of rich bituminous coal, are found near the Pocatalico, and its branches, and iron ores apparently of good quality, are often dug out of the hills.

POTOMAC river, of Virginia, Maryland and Pennsylvania. This river above Blue Ridge, is formed by the north branch, distinctively called Potomac, Patterson's river, South Branch, Cacapon, Back creek, Opequhan and Sheandoah, from the southwestward, and by a series of bold, though comparatively small streams from the northward. The stream to which the name of Potomoc is first applied, rises in the Alleghany chain, opposite to the sources of Cheat and Youghioghany branches of Monongahela, at lat. 39° 10' long. from Washington city, 2° 30' W. Flowing thence N. E. 30 miles, receives from the north, Savage river, and bending to S. E. 10 miles, traverses one or two minor chains of mountains, and returning to N. E. 18 miles to the influx of Will's creek, from the north at Cumberland. Now a considerable stream, by a very tortuous channel, but direct distance 15 miles to S. E., the Potomac below Cumberland, breaks through several chains of mountains to the influx of South Branch. The latter is in length of course, and area drained, the main branch. The various sources of this mountain river originate in Pendleton county, Virginia, lat. 38° 25', between the Alleghany and Kittatinny chains. Assuming a general course of N. E., the branches unite in Hardy county, near Moorfields, below which, in a distance comparative course of 40 miles to its union with the N. Branch, the South Branch receives no considerable tributary. The volume formed by both branches, breaks through a mountain chain immediately below their junction, and bending to N. E. by comparative distance of 25 miles, but by a very winding channel reaches its extreme northern point at Hancock's town, lat. 39° 41', and within less than two miles south of the southern boundary of Pennsylvania. Passing Hancock's town the Potomac again inflects to S. E., and as above winds by a very crooked channel, but by comparative course of 35 miles to the influx of Shenandoah from the southward.