}Y ATKINS GLEN 



389 



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Fig. 4. Cross section OF Seneca Lake, three miles north of Watkins. (Horizontal scale 

 y 2 inch to the mile ; vertical scale, % inch to 1000 leet. Column of figures gives elevations in 

 feet with reference to sea-level. ) 



Fig. 5. Cro;S section of Lake Cayuga Valley, two miles north of Ithaca. (Scale same 

 as Fig. 4.) 



longer present. To state this explanation calls for a preliminary con- 

 sideration of the general topography. 



The Finger Lake valleys extend nearly north and south, long and 

 narrow, like so many fingers, the two longest, Cayuga and Seneca, 

 being about forty miles in length, and at the lake surface from one 

 to three miles in width. Their bottoms are below sea-level. They 

 are excavated in the plateau of southern New York, a dissected plateau 

 of nearly horizontal Devonian shales and sandstones, trenched by many 

 deep valleys (Fig. 2). But among these valleys those of the Finger 

 Lakes stand out prominently because of certain notable peculiarities. 



If one of the upland valleys of the plateau should be damned so as to 

 contain a lake as deep as Cayuga (435 feet) or Seneca Lake (618 feet), 

 or even one a hundred feet in depth, its shore-line would be very 

 irregular, and its waters would extend as bays up the tributary valleys. 

 But in the Finger Lakes this is not the case. The lake shores are 

 smooth and regular (Fig. 3), and this condition extends for several 

 hundred feet above the lake level. The valley walls enclosing the lakes 

 are gullied only by the narrow gorges which are so abundant (Fig. 1). 

 Xot only are they smooth and regular, but they are steepened below 

 the 900-foot contour line (Figs. 2 and 3), so that a profile of the 

 valley slope shows a distinct increase in the steepness of the valley 

 wall below that level (Figs. 4 and 5). 



At the upper level of the steepened slope, upland valleys open out 

 and lead back into the plateau, so that if the lake waters could be 

 raised 500 feet higher than the present, they would enter into these 

 tributary valleys and the lake shore line would become very irregular, 

 as is natural in a stream valley dammed so as to hold a lake. These 

 upland tributary valleys are broad and mature, having evidently re- 

 quired a long period for their formation; and their counterpart ap- 

 pears throughout the plateau region. They are the normal valleys of 

 the region; the Finger Lake valleys the abnormal. 



