Drainage evolution in the southern Appalachians
Following the Appalachian revolution and the Palisades disturbance the main drainage divide between the Atlantic Ocean and the interior was not far from the Blue Ridge. How the drainage was reversed and the divide shifted to its present position has long been a major question of Appalachian geomorphology commonly answered by regional superposition. Difficulties involved in assuming widespread perfect peneplanation or an extended coastal plain cover of the Appalachian Highlands invite an alternative interpretation without recourse to regional superposition. Headwater piracy along the asymmetrical watershed resulting from eastward tilting of the Atlantic border region is believed competent to account for the westward migration of the main drainage divide. Thus the process of drainage reversal has been slow and long-continued rather than abrupt. In the northern part of the Southern Appalachians the relations of streams to rock resistance and structure, the characteristics of dry gaps, the drainage of canoe-shaped valleys, examples of recent and imminent piracy, and the present asymmetrical position of the drainage divide support this interpretation.