Disequilibrium profile of the Potomac River near Washington, D.C.; a result of lowered base level or Quaternary tectonics along the Fall Line?

The long profiles of several major rivers in Maryland and Virginia are studied, and explanations for discontinuities near the Fall Line are sought. It is postulated that changes in base level during sea-level fluctuations in the Pleistocene were important contributors to discontinuities. Quarternary downcutting in response to a lowered base level may exlain the process. Strong circumstantial evidence suggests that the discontinuities in river profiles may be due to differential uplife of the Piedmont as well. However, terrace remnants at higher elevations are so dissected that correlations between remnants is impossible. Also, no fossils or radiometrically datable materials have been recovered from terraces above the Fall Line, and attempts to apply paleomagnetic techniques have yielded equivocal results. (Titus-FRC)