Shenandoah is the longest branch of Potomac, having a comparative length of 130 miles, and brings down a volume of water but little inferior to that of the main stream. It has its most remote sources in Augusta county, Virginia, interlocks sources with those of Great Calf Pasture branch of James river, and by Blue Ridge, is separated from those of Rivanna, as far south as lat. 37° 55', almost exactly due west of the eutrance of Potomac into Chesapeake bay. The elongated valley of Shenandoah is part of the great mountain valley of Kittatinny, and comprises nearly all the counties of Augusta, Rockingham, Page and Shenandoah, with the eastern sections of Frederick and Jefferson. The upper valley of Potomac, including that of Shenandoah is in length from S. W. to N. E. 160 miles, where broadest 75 miles, but has a mean breadth of 50 miles, area 8,000 square miles. The water level of Potomac at Harper's Ferry is 288 feet above tide water; therefore we may assume at 350 feet the lowest arable land in the valley above the Blue Ridge. This is equivalent to a degree of latitude on the aerial temperature at the lowest point of depression. So rapid is the rise, however, in crossing the valley to the foot of Alleghany mountain, that an allowance of 1,200 feet is rather too moderate an estimate for the extremes of cultivated soil.

Passing the Blue Ridge, with partial windings, the Potomac continues S. E. by comparative courses 50 miles to the lower falls and head of ocean tides at Georgetown. Having in the intermediate distance received the Monocacy river, from the north, and some minor creeks from the south; like the Delaware, below Trenton, and the higher part of Chesapeake bay, below the mouth of Susquehannah the Potomac, meeting the tide, bends along the outer margin of the primitive rock. It is indeed very remarkable that the three bends, in the three consecutive rivers, follow almost exactly the same geographical line: or flow from head of tide water, S. W.— the Delaware 60, Chesapeake 40, and Potomac 45 miles,-the latter a few miles below the place at which it retires from the primitive rocks, reaches within six miles of the Rappahannock, below Fradericksburg. The two Hatter rivers not far from parallel to each other, assume a comparative course 75 miles to the N. E., the intermediate peninsula being no where above 22 miles wide, and the distance from the south side of the mouth of the Potomac, to the north side of that of the Rappahannock, is only 20 miles.

Combining the two sections above and below the Blue Ridge, the whole basin of the Potomac embraces an area of 12,950 square miles, extending from lat. 37° 50' to 40°, and in long. 0° 45' E. to 2° 45' W. of Washington city. The winding of its tide water channel renders the navigation of the Potomac bay (for such it is below George Town,) tedious though not dangerous. The channel has sufficient depth to admit ships of the line of 74 guns to the navy yard at Washington.

With its defects and advantages as an agricultural and commercial section, the basin of the Potomac is a very interesting object in physical and political geography;-deriving its sources from the main Appalachian spine, the Potomac has worn its channel through the intervening chains to their bases; and performed an immense disproportion of the necessary task to effect a water rout into the valley of the Ohio,—such a rout has been commenced under the name of Chesapeake and Ohio canal, and is yet in progress. The Potomac is eight miles wide at its mouth, four and a half at Nomony bay, three at Acquia, one and a half at Hollooing point, and one and a half at Alexandria.

Its soundings are seven fathoms at its mouth, five at St. Georges island, four and a half at Lower Matchodie, three at Swan's point and up to Alexandria, thence 20 feet of water to the falls, which are 13 miles above Alexandria. These falls are 15 miles in length, and of very great descent, and the navigation above them for batteaux and canoes is so much interrupted as to be little used, It is however used in a small degree up the Cohongoronta branch as far as Cumberland, at the mouth of Wills's creek; and is capable of being made navigable at no grerat expence. The Shenandoah branch interlocks with the sources of James river, near the Blue Ridge. RAPPAHANNOCK river, formed by two branches, Hedgeman's and Thornton's rivers, both deriving their remote sources from Blue Ridge. Hedgeman's river, after a comparative course of 30 miles, between Fauquier and Culpeper counties, receives Thornton's river from the latter, and the united waters continuing the course of the former S. E. 20 miles, join the Rapid Ann. A navigable river at the junction of its two main branches, the Rappahannock, continues to the S. E. 10 miles to its lowest falls, where it traverses the primitive ledge, and meets the ocean tides at Fredericksburg. Similar to the Delaware, and all the large western tributaries of Chesapeake bay, the Rappahannock turns after passing the primitive rock, but after a short curve to the southward, this stream resumes a S. E. course, which with a rather tortuous channel it maintains to Leeds, in Westmoreland county, where it approaches to within five miles of Potomac, at the mouth of Mattox creek. Gradually widening, and with the features of a long, narrow bay of 55 miles, the Rappahannock by a S. S. E. course, is lost in Chesapeake bay between Windmill and Stingray points. The tide ascends this channel to the falls at Fredericksburg, something above 100 miles, admitting vessels of considerable tonnage. In all the distance below the union of its two main branches, it does not receive any accession above the size of a small creek. The entire basin is 140 miles by a mean width of 20; area 2,800 square miles. Extending in lat. from 37° 34' to 38° 44', and in long. from 0° 41' east to 1° 22' west of Washington.

RAPID ANN river, deriving its remote sources from the Blue Ridge, and flowing thence S. E. 20 miles across the valley, between Blue Ridge and South East mountain, turns thence N. E. 15 miles to the influx of Robertson's river from the N. W. Passing South East mountain and inflecting to a general eastern course of 30 miles, it joins the Rappahannock 10 miles above Fredericksburg, after a comparative course of 65 miles. In nearly the whole of its length Rapid Ann separates Orange county first 35 miles from Madison, and thence 25 from Culpeper. At their junction it is superior in volume to Rappahannock; and exceeding also in length, of course, the Rapid Ann is the main stream.

RIVANNA river, a branch of James river, is navigable to its intersection with the South West mountain, which is about 22 miles. The navigation has lately been opened by dams and canals, and it is now navigable to Pireus, within one mile and a quarter of Charlottesville.

Rock creek, a small stream of Maryland, and of the District of Columbia, gains importance only as it separates the city of Washington from Georgetown. This creek has its extreme source about four miles westward of Mechanicsville, Montgomery county, Maryland, heading with the east branch. of Potomac river, at an elevation above tide water at Georgetown of 500 feet. The entire length of the creek, following its valley, is about 28 miles.

The fall being upwards of 17 feet to the mile, and that fall being in many places far above the mean, renders it an excellent mill-stream.

ROANOKE river, of Virginia and North Carolina. Taken in the utmost extent, Roanoke basin is the same as Albemarle, and includes the sub-basins or vallies of Roanoke proper, and Chowan river. Advancing from south to north, all the rivers beyond the Roanoke, have their most remote fountains on the Atlantic side of Blue Ridge; but with the Roanoke a new feature appears. The Blue Ridge is pierced by that stream, which derives its higher fountains from the main Alleghany chain in Montgomery county, Virginia, and within eight miles of the main channel of New river, and at an elevation without estimating the mountain ridges, of at least 2,000 feet. Issuing by numerous creeks from this elevated tract, and uniting into one stream near the border between Montgomery and Botetourt counties, it is here literally “The Rapid Roanoke," having at Salem, in the latter county, fallen 1,000 feet in little more than 20 miles. At Salem the water level is 1,002 feet by actual admeasurement, above mean Atlantic tide. Below Salem the river inflects 20 miles in an eastern course, to its passage through Blue Ridge, and thence S. E. 25 miles to its passage through South East mountain. Passing South East mountain between Bedford and Pittsylvania counties, the now navigable volume sweeps by an elliptic curve to northward, and round to S. E. 50 miles comparative course, to the influx of Dan river, entering its right side from the west part. Below the junction of these two rivers, the united waters in a course a little south of east 60 miles by comparative distance, reach tide water at Weldon, having fallen by a lengthened cataract over the primitive ledge. About midway between the influx of Dan river and Weldon, Roanoke leaves Virginia and enters North Carolina. Mingling with the tide, the Roanoke by a very tortuous channel, but by comparative course flows South East 50 miles, and thence eastward 25 miles to its junction with Chowan river at the head of Albe marle sound. The entire valley of Roanoke, if measured along the main stream or Dan river is 250 miles, but the rivers wind over this space by channels of much greater length. By comparative courses it is 155 miles from Salem to Weldon, whilst from a report made by the Roanoke compa ny, the intermediate channel is 244 miles. Taking these proportions, the length of this river by its meanders is about 400 miles. Including the whole Albemarle basin, it is 290 miles from its outlet into the Atlantic ocean, to the fountains of Roanoke in Alleghany mountain, but with the Chowan and Dan vallies united to that of the principal river, the basin is comparatively narrow, being only 80 miles where broadest, and not having a mean breadth above 50 miles, or an area exceeding 14,500 square miles. It is not, however, its extent which gives most interest to the Roanoke or Albemarle basin; it is at once a fine physical section and physical limit. The difference of arable level, amounts to at least 2,000 feet, and no two regions of the earth can differ in every feature more than do the truly beautiful hills and vales on each side of the Appalachian chains, from the stagnant marshes and level plains towards the Atlantic ocean. Along the lower Roanoke commences, advancing from the north the profitable cultivation of cotton, the fig tree begins to appear, rice can be produced, and in summer the advance towards the tropics is felt, and very distinctly seen on vegetation. Ascending the basin, the aspect of the northern states gradually appears, both on the features of nature and on cultivated vegetables. Wheat, rye, and other small grain, with meadow grasses, and the apple, flourish. The

summers are cooler, and the winters have the severity suitable to relative elevation. Though the higher part of Roanoke is annually frozen, and for a shorter or longer period rendered unnavigable in winter, with lower Roanoke commences the region on the Atlantic coast where navigation remains open at all seasons. It is true that even Albemarle sound has been occasionally impeded with ice, but this phenomenon is rare. As a navigable channel following either branch, the importance of this basin is lessened by the shallowness of Albemarle sound-an irremovable impediment. At present, however, there is in progress a scheme for connecting, by rail-road, the navigable tide water below Weldon with Chesapeake bay. In its actual state the rivers are navigable for boats to Salem on the Roanoke, and to Danbury in North Carolina by Dan river. This was effected by side canals, sluices and other artificial improvements.

SANDY river, of Virginia and Kentucky, is composed of two branches, called relatively East fork and West fork. East fork, the main constituent of Sandy, rises in the Appalachian valleys, interlocking sources with those of Great Kanawha to the east, and with those of Holston and Clinch branches of Tennessee river to the S. E. Issuing from this elevated region, and draining part of Tazewell and Logan counties, Virginia, the Sandy river pursues a N. W. direction by comparative courses 50 miles, to its passage through Cumberland mountain. Becoming a boundary between Virginia and Kentucky below the Cumberland chain, Sandy assumes a direction of N. N. W. 70 miles, separating Logan and Cabell counties, of Virginia, from Floyd, Lawrence, and Greenup counties, of Kentucky, to its final influx into Ohio river opposite Burlington, Ohio. West Sandy rises in Russell and Tazewell counties, Virginia, and assuming a N. W. direction pierces the Cumberland chain, enters Kentucky, and after traversing Pike and Floyd counties, bends to the northward and joins East Sandy in Lawrence county. The valley of Sandy river has that of Tennessee river S., Kentucky S. W., Licking W., that of Ohio N., Guyandotte E., and Great Kanawha S. E. It is about 100 miles long, mean width 35, and area 3,500 square miles.

SHENANDOAH river, one of the great southern branches of Potomac river, is composed of two branches, called with no great relative correctness, North Branch and South Branch. The southern and main branch rises in Augusta county, as far south as latitude 38°, and long. 2° west of Washington City. Flowing thence northeastward along the northwestern slope of Blue Ridge, over Augusta, Rockingham, and Page counties, receives the North Branch in the southern angle of Federick county, after a comparative course of 90 miles.

The North Branch of Shenandoah river has its source in Rockingham county, from which it flows by comparative courses N. N. E. 50 miles over Rockingham and Shenandoah counties, enters Frederick, bends to the eastward, and joins the South Branch as already noticed. Below the junction of its two branches, the Shenandoah flows Ñ. E. along the N. W. slope of Blue Ridge 40 miles to its junction with the Potomac at Harper's Ferry.

TENNESSEE river, of the state of the same name, and of the states of Kentucky, Mississippi, Alabama, Georgia, North Carolina, and Virginia, is the great southeastern constituent of the Ohio. The very peculiar features of the valley of Tennessee, demand a general and particular notice. This valley is naturally divided into two physical sections; the higher or mountainous, and the lower or hilly. The most remote sources of Tennessee are

found in those of Clinch, in Tazewell, and of Holston in Wythe counties, of Virginia, interlocking sources with those of Sandy and Great Kanawha. From this elevated origin, the main constituents pursue a southwestern course between the two parallel chains of the Appalachian system, Cumberland, and the main spine, both stretching in a similar direction with the rivers, at a mean distance of about 70 miles asunder. Besides this principal valley, another of less width between the main chain and Blue Ridge, is also drained by the constituents of Tennessee; but this more eastern and more elevated valley slopes to the N. W., at right angles to the mountain chains. The latter mountain valley comprises the North Carolina and Georgia part of the valley of Tennessee. Including both minor vallies, upper Tennessee drains an elongated ellipise of 350 miles longer axis; shorter axis 120 miles from the Blue Ridge at the sources of French Broad, to Cumberland mountain, where it separates the sources of Powell's river from those of Cumberland: mean breadth 80 miles, and area 24,000 square miles. Descending from the extreme fountains in Virginia, the valley widens as the mountain chains recede from each other, and again contracts as the same chains gradually re-approach each other at the northwestern angle of Georgia, and northeastern of Alabama. At the latter point, well known by the name of Nickajack, all the large tributaries have united, and the Blue Ridge and Cumberland chains have inclined to within less than 40 miles of each other. Below Nickajack, the now large volume of Tennessee continues S. W. 60 miles, without receiving a single creek of 20 miles course, the two bounding mountain chains still inclining upon each other, till their approaching bases force the river through the Cumberland chain. To one whose eye first glanced on the volume of Tennessee, below its passage through Cumberland mountain, without previous knowledge of the valley above, no adequate idea would occur, that before it, flowed the accumulated waters of a mountainous region of 24,000 square miles extent. In fact, to an observer, thus placed, the main volume of Tennessee would ap-pear as one of the constituents of a river valley below the Cumberland chain. About 20 miles below the passage of Tennessee river through it, the Cumberland mountain receives the Blue Ridge, if such a term can be correctly applied to the merging of two mountain chains. Here, along the northern sources of Mobile basin, the Appalachian system changes its distinctive character, and the confused masses of hills follow each other westwardly toward the Mississippi. The Tennessee river deflects rather more than does the mountain system, and flows N. W. by W. by comparative courses 120 miles, to the northwestern angle of Alabama, and the northeastern of Mississippi, where this large stream again bends at nearly right angles, and pursues a course of a very little west of north 150 miles, to its entrance into the Ohio, after an entire comparative course of 680 miles.

The second great section of Tennessee, and the lower part of the first, below Nickajack, are comprised in the fine northern valley of Alabama. The main volume flowing along the base of a physical line extending from the Ohio valley in the vicinity of Pittsburg, to the northern part of the basin of Mobile. The very striking coincidence of the river inflections be-tween the extremes of this region, must appear to the most inattentive observer of a good map of that part of the United States. This regularity of structure is evinced by the great inflections of Ohio, Kanawha, Kentucky, Green, Cumberland, and Tennessee rivers. The Tennessee itself literally occupies the base of the physical region indicated, as in all its comparative