THE 



NATIONAL GEOGRAPHIC MAGAZINE. 



Vol. I. 1889. No. 3. 



THE RIVERS AND VALLEYS OF PENNSYLVANIA.* 



By William Moeris Davis. 



' ' In Faltensystemen von sehr hohem Alter wurde die urspriingliche 

 Anordnung der Langenthaler durch das Ueberhandnehmen der trans - 

 versalen Erosionsfurchen oft ganz und gar verwischt." 



LOWL. Petermann's Mittheilungen, xxviii, 1882, 411. 



CONTENTS. 



Part first. Introductory. 



1. Plan of work here proposed. 



2. General description of the topography of Pennsylvania. 



3. The drainage of Pennsylvania. 



4. Previous studies of Appalachian drainage. 



Part second. Outline of the geological history of the region. 



5. Conditions of formation. 



6. Foi'nier extension of strata to the southeast. 



7. Cambro-Silurian and Permian deformations. 



8. Perm Triassic denudation. 



9. Newark deposition. 



10. Jurassic tilting. 



11. Jura-Cretaceous denudation. 



12. Tertiary elevation and denudation. 



13. Later changes of level. 



14. Illustrations of Pennsylvanian topography. 



* The substance of this essay was presented to the Society in a lecture 

 on February 8th, 1889, but since then it has been much expanded. 



VOL. I. 15 



