67S ' MARIUS R. CAMPBELL 



Chattahoochee system, it seems probable that they have persisted 

 in the course then determined up to the present time. This 

 interpretation also presupposes the existence of a peneplain at 

 the time the depression occurred, for with the present rugged 

 topography along this line almost no amount of tilting could 

 produce such a radical rearrangement of large streams as that 

 which inaugurated Triassic deposition. This conclusion is per- 

 haps the most important result of the present study, for it 

 appears to verify the statement of Davis '^ that the Atlantic slope 

 was reduced to a peneplain before the deposition of the Triassic 

 sediments. In order to permit the formation of such longitudinal 

 streams, the peneplain must have been practically continuous 

 along the axis of the western fold, and hence today must be at 

 an altitude at least equal to that of the main summits which 

 cross the line. 



(6) UTILITY OF THE STUDY OF DRAINAGE FEATURES. 



It now remains but to add a word concerning the utility of 

 this study. If the writer has succeeded in establishing the prop- 

 osition that streams suffer modifications during crustal move- 

 ments, no one can deny that a careful study of such modifica- 

 tions is extremely important in determining the principal move- 

 ments in recent geologic ages. If it will do that, it is practi- 

 cally as efficient as the study of physiographic forms. The 

 writer does not wish to be understood as advocating the replace- 

 ment of the study of physiographic forms by the study of drain- 

 age forms, but rather to use the two in conjunction ; in other 

 words, to study the forms assumed by the instruments of erosion 

 at the same time that we are studying the land forms produced 

 by these same instruments — the streams. The results cannot be 

 at variance and the studies will be a mutual advantage, one to 



the other. 



Marius R. Campbell. 

 United States Geological Survey. 



^ The Geological Dates of Origin of Certain Topographic Forms on the Atlantic 

 Slope of the United States, by W. M. Davis, Bulletin Geological Soc. Am., Vol. II. p. 



549- 



