CONTENTS.

The Rivers and Valleys of Pennsylvania: William Morris Davis
    (Illustrated by one map and twenty-five cuts.)

Topographic Models: Cosmos Mindeleff
    (Illustrated by two plates.)

National Geographic Society—Abstract of Minutes

International Literary Contest to be held at Madrid, Spain

July, 1889.

THE

NATIONAL GEOGRAPHIC MAGAZINE.

THE RIVERS AND VALLEYS OF PENNSYLVANIA.¹

"In Faltensystemen von sehr hohem Alter wurde die ursprünglicheAnordnung der Langenthäler durch das Ueberhandnehmen der transversalenErosionsfurchen oft ganz und gar verwischt."

¹ The substance of this essay was presented to the Societyin a lecture on February 8th, 1889, but since then it has been muchexpanded.

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. Former 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.

PART THIRD. General conception of the history of a river.
    15. The complete cycle of river life: youth, adolescence, maturity and old age.
    16. Mutual adjustment of river courses...