Page:The National geographic magazine, volume 1.djvu/239



Vol. I.

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.

. Outline of the geological history of the region. Conditions of formation. Former extension of strata to the southeast. Cambro-Silurian and Permian deformations. Perm Triassic denudation. Newark deposition. Jurassic tilting. Jura-Cretaceous denudation. Tertiary elevation and denudation. Later changes of level. Illustrations of Pennsylvanian topography.