of pristine mountain tributaries like the Cacapon
and growing as it goes, cleansing itself of the North Branch's load of
trouble, the river finds its way at last out of the washboard and
meanders among silver maples and great sycamores across the productive
populated expanse of the Great Valley that runs athwart the whole Basin
from north to south. The Potomac is in thickly historic country now as
it flows under the contemplative eyes of fishermen and past old villages
and the relics of generations of human activity going back before
written records, for here and there the funnel shapes of stone Indian
fishing weirs can still be seen at shallow places and the durable
fragments of their way of life can be scratched up along high shores. Of
many Civil War clashes in the valley, Antietam was the most crucial; the
Potomac shaped Lee's strategy there, and still ripples across fords by
which his troops came to that violent place and afterward escaped it.

At Harpers Ferry on the Valley's eastern edge, the river is reinforced
by the waters of its greatest tributary, the Shenandoah, rolling north
out of the limestone country that fed the gray armies till Sheridan put
a stop to that. Then it rams through the high wall of the Blue Ridge
and out of the Valley into the Piedmont, and still gathering strength
from tributaries like the Monocacy, dotted with big islands and
frequented by waterfowl and good fish, moves powerfully downcountry past
further mists and layers of history to Great Falls and the rushing,
crashing descent through the gorge to tidewater at the capital.

From there down it is, as we have seen, a different thing, an arm of the
sea and a sluggish extension of the river, shading from fresh to salt,
called a river still but neither river nor sea in its ways, affected
rhythmically and obscurely by both of them and subject to its own
complex laws as well. In Indian and Colonial times this estuary was the
part of the river that counted most for men, because of the bounty that
came from its waters, the fitness of its shores for farming, and its
navigability for boats and ships in a region where land travel was
laborious and whose colonists depended on commerce with a European
homeland. Its shores and those of the big tributary embayments--"drowned
rivers," they have been called--are thickly sprinkled with traces and
remembrances of three and a half centuries' people and events. Mount
Vernon, old Fort Washington, Gunston