98 Hayes and Campbell—Appalachian Geomorphology. 
of the sediments derived from the waste of the land during the 
interval and deposited as a fringe around its margin. 
That the conclusions reached by these three methods of in- 
vestigation should agree is manifest, and our confidence in them 
may be in proportion to their concordance. It remains to be 
seen whether the conclusions already reached can be verified by 
the study of the drainage and by the sediments deposited in the 
surrounding seas. 
CYCLES OF DRAINAGE DEVELOPMENT. 
The evolution of the drainage of this region began with the 
earliest emergence of Paleozoic sediments from the sea and the 
consequent increase of the eastern continental area toward the 
west. This process of emergence is believed to have begun in 
Cambrian time and to have continued at intervals to the close of 
the Carboniferous. ‘The character of the drainage is much better 
known since the final emergence of the entire province than 
during Paleozoic time. Its modifications can be traced much 
more definitely because the surrounding conditions are better 
understood, and hence the history of the drainage development 
which can be read with any degree of certainty may be consid- 
ered as beginning with the close of Paleozoic time. This de- 
velopment has not been a continuous process, but has been at 
times rapid, and then again for long periods almost stationary. 
This recurrence of similar conditions in the life history of a 
river may be termed cycles of drainage development. First 
comes a general elevation of its drainage basin, by which the 
stream is rejuvenated. The elevation ceasing, the stream in the 
course of long ages accomplishes its life-work and sinks into the 
sluggish-inactivity of old age. This is followed by an uphft and 
the cycle of events is repeated. 
Two such cycles are represented on the accompanying diagram, 
figure 1. The heavy line represents the position of the surface 
with reference to present sealevel, and hence its changes in alti- 
tude, by the slow process of degradation and the more rapid 
process of orogenic movement. The horizontal spaces are roughly 
proportional to the duration of the periods which constitute a 
cycle. The first of these cycles was extremely long, reaching 
from the final emergence of the western half of the province to 
near the close of the Cretaceous period. It includes the most 
extensive period of baseleveling known to have affected this 
