National Geographic : 1889 Jul
The Rivers and Valley8 of Pennsylvania. 253 ture to mature courses in the several cycles of development are so numerous and extensive that, as Lowl truly says, the initial drainage has almost disappeared. The larger westward-flowing streams of the plateau are of earlier, Carboniferous birth, and have suffered little subsequent change beyond a loss of head waters. The lower courses of the Atlantic rivers are younger, having been much shifted from their Permian or pre-Permian courses by Newark and Cretaceous superimposition, as well as by recent downward deformation of the surface in their existing estu aries. No recognizable remnant of rivers antecedent to the Per mian deformation are found in the central part of the State ; and with the exception of parts of the upper Schuylkill and of the Sus quehanna near Wilkes-Barre, there are no large survivors of Per mian consequent streams in the ordinary meaning of the term " consequent." The shifting of courses in the progress of mature adjustment has had more to do with determining the actual loca tion of our rivers and streams than any other process. Harvard College, June, 1889.