INTERPRETATION AND CONCLUSIONS 241 



That before the glacial period stream erosion was vigorous throughout 

 this divide region is evident from the steep slopes of the valley sides both 

 in the small and the large valleys and from the presence of gorges in many 

 of the valleys. Neither glacial erosion nor ice-born stream erosion, even 

 with the maximum possible number of ice advances, can possibly be 

 appealed to in explanation of all these steep valley slopes, and since 

 they harmonize in form with the steep slopes of the lowered divides they 

 lend support to the hypothesis of headwater erosion for the lowered 

 divides. 



On the other hand, as has been suggested to the author by both Doctor 

 Gilbert and Professor Davis, such a condition of '' through valleys/' while 

 not uncommon in regions of faulting or in regions of inclined and varied 

 strata, has not been described in regions of horizontal strata outside the 

 glacial belt. I have examined several hundred sheets of the United 

 States Geological Survey topographic map in regions outside the glaciated 

 area without finding even an approach to the conditions described above. 

 To this difficulty must be added that of understanding just how divide 

 lowering, operating excessively in some valleys, has produced no effect 

 whatsoever in neighboring headwaters. 



DISCORDANCE OF THE CAYUGA AND SENECA VALLEYS 



The lowering of the divides is in no way related to rejuvenation result- 

 ing from the deepening of the Cayuga and Seneca valleys, for it extends 

 outside of their drainage areas, and, even where developed in the head- 

 waters of tributaries to these two valleys, occurs in valleys hanging high 

 above the bottom of the main lake troughs. The upper parts of these 

 hanging valleys are broad, deep, and steep-sided, with the main divides 

 obliterated by erosion and glacial deposit, but with the lower ends ter- 

 minating on the edge of a steepened slope notched only by small gorges. 

 This fact favors the theory of glacial erosion for the basins of these two 

 lakes, although other facts, stated in another paper, oppose it. 



Conclusions 



The one conclusive result of the studies so far made toward the solu- 

 tion of this drainage problem is that, in several typical instances, the 

 phenomenon of lowered divides antedates the last or Wisconsin ice in- 

 vasion. The establishment of this fact is the excuse for the present 

 paper. 



In all other respects this paper must stand as an unfinished study, in 

 which certain observations are recorded and difficulties opposing each 

 of three hypotheses pointed out. 



