230 R. S. TARR— DRAINAGE FEATURES OF CENTRAL NEW YOR£ 



and Susquehanna drainage systems. Most of the facts were obtained in 

 studies leading to the preparation of the Watkins Glen Folio (see plate 

 37) of the United States Geological Survey, which includes the Ithaca, 

 Watkins, Elmira, and Waverly topographic sheets ; but some of the 

 facts were discovered in the studies on the quadrangle east of the Wat- 

 kins Glen. 



General topography* — The area under discussion is a part of the dis- 

 sected Allegheny plateau, with uplands of mature form, deeply trenched 

 by valleys of less mature character, whose sides are often too steep for 

 farming and in some cases even precipices. In ruggedness of topography 

 there is a difference from south to north, the northern portion being both 

 evener and smoother than the southern. The uplands reach elevations 

 of from 1,800 to 2,000 feet in a number of places, and even the smaller 

 streams are in valleys whose bottoms are several hundred feet deep. The 

 lowest known point in the region is the rock floor of the Seneca valley, 

 which at Watkins is at least 63 7 feet below sealevel. 



South of the divide, for the most part near the Pennsylvania 3tate line, 

 there is the long, deep Chemung-Susquehanna valley, extending east and 

 west, with the united drainage from the two directions turning south- 

 ward below Waverly. This is the largest valley in the area. North 

 of the divide are north-south valleys, two of the largest of which are 

 occupied by Cayuga and Seneca lakes. There are numerous smaller 

 valleys tributary to one of these three major valleys, the largest having 

 a general north-south direction, and most of them tributary to the 

 Susquehanna system. 



HANGING VALLEYS 



Hanging valleys in Cayuga and Seneca troughs.^ — In both the Cayuga 

 and Seneca valleys there is a change in valley slope at about the 900- 

 foot contour, the lower slope being much steeper than the upper (see 

 plate 39, figure 2). This steepened slope extends to the bottom of the 

 valley — that is, at least 850 feet in the Cayuga valley and from 1,400 

 to 1,500 feet in the Seneca valley. The region near Watkins may be 

 taken as an illustration of this change in slope. From the 900-foot 

 contour just west of Watkins there is a slope down to the valley bottom 

 of 1,400 feet in a little over a mile, while west of the 900-foot contour 

 the valley side rises only 700 feet in a distance of 5 miles. 



Down to approximately this same level a series of valleys descend 

 with moderate grade from the uplands; then the valleys change to gorges 



♦The text of the forthcoming Watkins Glen Folio contains a fuller and more complete discus- 

 sion of the topography of this region, 

 f R. S. Tarr : American Geologist, vol. xxxiii, 1904, pp. 271-291. 



