52 The American Geologist. January. 1905 
SOME DRAINAGE FEATURES OF SOUTHERN CENTRAL N. Y.* 
K SJ. Takr, Ithaca, N. Y 
In many instances along fhe divide between the Susque- 
hanna and-St. Lawrence drainage systems there is a condition 
of lowered divides, across some of which, as in the Tiough- 
nioga valley, east of Cortland, and the Cayuta creek valley, 
west and south of Van Etten, the present drainage passes. 
Three theories are discussed to account for these phenomena, 
glacial erosion ; erosion by ice fed stream ; and headwater 
erosion during rejuvenation. Evidence from valley form, 
glacial deposits, and hanging tributary valleys is presented 
to prove that these drainage features are in many cases, if 
not in all, due to changes of earlier date than the advance 
of the Wisconsin ice sheet. While the influence of possible 
earlier ice advances, of which no evidence has been found in 
this region, is not eliminated, the facts so far discovered favor 
the hypothesis of rejuvenation rather than of glacial action 
during earlier ice advance. 
MOUNTAIN GROWTH AND MOUNTAIN STRUCTURE.* 
Bailey Willis, Washington, D. C. 
The study of peneplains at various altitudes with refer- 
ence to sea level in North America and Eurasia, demon- 
strates that elevations of the earth's surface have resulted 
from deformation which occasioned warping of previously 
planed surfaces. Observations of the effects of erosion in 
the elevated masses show that the process has in general been 
a recent one, post-Mesozoic, and has justified Powell's gen- 
eralization that mountains are youthful features of the earth. 
The study of the mechanics, physics, and chemistry of 
rock deformation has shown that the structures discovered 
* Abstract of a paper read at the Philadelphia meeting, u. S. A., 
Dec, 1904. *< 
* Abstract of a paper read at the Philadelphia meeting, G. S. A., 
Dec, 1904. 
