542 T. C. CHAMBERLIN — CHRONOLOGIC CARTOGRAPHY. 



Page. 



Tertiary Excavations in the Cretaceous Peneplain 567 



Tertiary Work in New England: the Connecticut Kiver 568 



Tertiary Work in New York : the Hudson River =., _— 570 



Tertiary Work in New Jersey and Pennsylvania : the Delaware and 



Susquehanna Rivers 571 



Tertiary Work in Virginia and beyond 576 



Tertiary Baseleveling of the Cretaceous Overlap 577 



Summary of Cretaceous and Tertiary Topography 578 



Post-Tertiary Topography 579 



Representation of the Dates of Topographic Forms by colored Maps 582 



Index of Localities and Abbreviations 585 



A PROPOSED SYSTEM OF CHRONOLOGIC CARTOGRAPHY 

 ON A PHYSIOGRAPHIC BASIS. 



BY T. C. CHAMBERLIN. 



[Rend by title before the Society December 31, 1890, in connection loith the meynoir by 

 Professor Williani Morris Davis on tJie Origin of certain Topographic Forms.) 



The determination of time-relations has been based chiefly upon aqueous 

 deposits. Attention is now turning more than heretofore to the study of 

 topographic forms as time indices and as means of correlation. The doc- 

 trine of baselevels opened the way to specific studies of land sculpture as a 

 means of determining successfully the varying attitudes of the land and 

 their accompanying time-relations. A considerable body of discriminating 

 geologists have become enthusiastic workers in this new field, and are bring- 

 ing forth results of great interest and value. It becomes evident, upon 

 consideration, that if it is possible to correlate fragments of topography dis- 

 tributed over the face of the continent, we may connect formations at great 

 distances by a physiographic chain, where sedimentary connection is entirely 

 wanting. Many unsolved problems in correlation will yield to the applica- 

 tion of the new method, and many tentative correlations will be overthrown 

 by it. 



The method has been applied in certain districts sufficiently widely and 

 successfully to render it desirable to devise some satisfactory method of car- 

 tographic representation. To illustrate. Professor W. M. Davis^ has deter- 

 mined, as he believes, that the remarkably horizontal crest-lines of the 

 Appalachian ranges in Pennsylvania and New Jersey are remnants of a base 

 plain formed in Cretaceous times. He has also determined that a later 

 plain of much wider extent represents a base plain formed in Tertiary times. 



