Combining the two sections above and below the Blue Ridge, the whole basin of Potomac extends over an area of 12,950, say 13,000 square miles.
Extending in Lat. from 37° 50' to 40° North, and in Lon. from 0° 45' E. to 2° 45' W. from W.C.
From its relative position, and from the great distance inland to which its channel admits ships of the heaviest draught, the basin of Potomac is a very interesting object in physical and political ge ography; and it is naturally, and by the erection of the Baltimore and Ohio Rail Road, already artifi-, cially connected with the western shore of Chesa peake Bay, between its own estuary and that of Susquehannah. In a direction very nearly from north to south, and from the southern boundary of Pennsylvania to the lower part of St Mary's county, Maryland, extends a strip of about 110 miles in length, and where broadest, in Harford and Balti more counties, 45 miles wide. The mean width, however, about 25, area 2750 square miles. This slope is drained by Patuxent, Patapsco, and Gun powder rivers.
The western shore of Chesapeake, broken into minor bays by the confluent rivers, is opposed by another slope still more indented. The eastern shore of Chesapeake is, in one respect, very re markable; that circumstance is, that the confluent creeks and rivers rise almost on the margin of the Atlantic Ocean from Cape Henry to Indian river; and again, a similar remark, with some limitation, may be extended to that part lying between Chesa peake and Delaware bays, as, in the latter case, the comparatively large streams of Pocomoke, Nanti koke, Choptank, Chester, Sassafras, and Elk rivers, are opposed by a series of mere creeks, flowing across a strip of about one hundred miles in length, with a mean width of fifteen. The whole elliptic
curve, from Cape Charles to the head of Elk river, following the shores of the .Atlantic Ocean and Delaware Bay, in a distance of two hundred miles, does not exceed an average width of more than ten miles; area 2000 square miles.
The Chesapeake slope of the peninsula we are surveying is also very narrow, not exceeding a mean breadth of five miles for the first seventy miles from Cape Charles to the mouth of Pocomoke river, but thence rapidly widens in the basins of Pocomoke, Nantikoke, and Choptank rivers to a mean breadth of 50 miles, and length of 70 miles. Again, con tracting over the basins of Chester and Elk rivers, to a point towards the source of the latter, the whole eastern slope of Chesapeake Bay presents an elon gated ellipse of 200 miles from south to north, mean width 25, and area 5000 square miles; extending in Lat. from 37° 7' to 40° N., and in Lon. from 0' 40' to 40' E. from W.C. The entire peninsula, by careful measurement, including the space be tween the head fountains of Elk river and Cape Charles, embraces a superficies within a trifling fraction of 7000 square miles; extreme breadth 65, but mean breadth 30, very nearly. From these ele ments, live-sevenths of the peninsula is drained into the Chesapeake Bay.
For specific description of the residue of the Chesapeake basin, see article SUSQUEIIANNAH. The relative extent and elevations of the sections are shown by the subjoined tables.