Rappahannoc river rises on the south-eastern slope of the Blue ridge, interlocking with the Rivanna branch of James river and the Shenandoah branch of Potomac ; it is formed by the Rappahannoc, properly so called, and Rapid Ann rivers, which unite about 10 miles above Fredericksburg, after a course respectively of 60 miles. The tides are arrested at Fredericksburg by the gneiss ledge alreatly noticed. Thus far vessels of 140 tons are navigated.
The Potomac next demands our attention. This is a stream of incalculable importance in the interior or in land navigation of the United States. If we turn our eye to a map of Virginia, we perceive the extreme north western sources of Jamcs river flowing to the south west along the mouotain valleys, and extending our view to the head waters of Potomac, we behold them flowing parallel to each other north-east, also down the moun tain valleys ; and in the latter case we are struck with the very remarkable fact, thz-it the Potomac rises west of all the ridges of the Appalachian system, except that denominated Laurel Hill. The south-west angle of Maryland, or extreme western source of the Potomac, having the residue of the collateral ridges to pierce in its progres towards its recipient, the Chesapeake hay. This peculiar structure of the river valleys of the Uni ted States yields an unequalled facility of forming in land water communications through a very broad chain of mountains. Before proce-aling to describe the Poto mac or Susquehanna, it may be remarked, that the Ap palachian, or Allegheny system of mountains, does not form the dividing ridge which separates the waters flow ing into thc Atlantic ocean from those which enter the "Mississippi ba.-in ; but that the separating liver line cuts the mountains obliquely. But to return to our survey.
The Potomac, draining the valleys of the Appalachian mountains from North Lat. 389 25'. to 40°, unites its various branches before piercing the Blue Ridge, which it finally effects at Harpor's Ferry, 60 oiiles north-weet from Washington city. B.–ow its passage through the Blue Ridge to its egress into Ch-sapeake bay is about 200 miles, following the ..vindings of the stream. The tide ascends to Georgetown, 3 miles above the capital in 'Washington, where it is arrested by the gneiss range of rocks. Ships of the largest class are navigated to the Navy yard, one mile below the capitol. Like ail other trihutaries of Chesapeake bay, the Potomac, below the head of tide water, opens gradually into a long nar low bay. By a singular caprice of custom, the Susque
hanna is considered as terminating at the head or tide water, whilst in nature, what is known by the name of Chesapeake bay is merely the continuation of that noble river ; and in strictness, James liver, York river, Rap pahannoc liver, and Potomac, are tributaries to the SIIS quelianna.
The sources of Cheat river branch of the Mononga hela rise in Randolph county in Virginia. in the sarne valley with the Potomac, and those of the Youghiogany, with a single intervening ridge, separating them from those of Potomac, partly in Randolph and M-onongaliela counties in Virginia, and partly in Allegany county in Maryland. Thus, here again occurs the second in stance of advancing from the south to north of the origin of waters, flowing into the two opposite systems of the Mexican Gulf and Atlantic Ocean, without an interven ing mountain, and yet amidst the Appalachian ridges. The peculiar features we have noticed in this section of country has drawn the attention of persons inquiring into the subject of canal connexion between the two river systems. The facilities afforded to such designs by the connecting waters of the Potomac and Monongahela will be more particularly noticed in its proper place.
The south-east and niain source of the Potomac rises in Pendleton county in Virginia, at North Lat. 38? 25', and the next considerable stream of the valley, the Shenandoah, rises in Augusta county, as far south as North Lat. 38°. The latter overheads the sources of York and Rappahannoc rivers, and interlocks with the sources of James river : the middle ridge of the Appa lachian, or the mountain properly called the Kittatinny, ranges between the Potomac proper, and the Shenan doah. Both rivers and all their branches flow to the north-east down the mountain vallies, The Potomac continues in that direction as far as North Lat. 39° 41f, Ivithin two miles of the south boundary of Pennsylvania, whence it turns at right angles, pierces the Kittatinny mountain, and flows to the south-east. Foity miles by comparative courses, below its passage through the Kit tatinny, the Potomac receives thc Shenandoah from the south-west, and the united waters here pierce the Blue Ridge. This latter passage of the Potomac through another of the Appalachian ridges is known as the cele brated Harper's Ferry. At their junction, the Potomac has flowed by comparative courses 160, and the Shenan doah 120 miles.