72 



JOHN LYON RICH AND EDWIN A. FILMER 



on the rock bottom of the old gorge, to plot its profile to scale (see 

 Fig. 6) . Points were taken at intervals through a distance of over 

 a mile along the gorge. It was found that, when these points were 

 plotted, the line connecting the first and last passed very close to 

 all the others. This would show that the gorge bottom was well 

 graded. When this profile of the gorge is projected out over the 

 Cayuga valley it is found that at the edge of the Cayuga trough the 

 bottom of the gorge must have been hanging 80 feet above the 

 present lake level. Projecting this line still farther to the axis of 

 the trough, we find it 28 feet above the present lake level. This 



P r of lies 



bottom of COO Faat Gortti 



Upp&r/onfite onscah of- J-u^.i, loyrer on icalt o/ f'^-l- 

 X- Sieraiicn of projected line It-W at eciae cj- flat 

 >l-£levaiicn of prejecictl line H-IV at ami of CayucaTfouftt 

 fioures re/>ye ie/ii eleyottons above leirei afCauLWa take. 



Horizontal iScait - Ait ies 



Fig. 6. — Profiles of the rock bottom of the 600-foot gorge. Elevations, taken 

 from the Ithaca water survey map, represent height above Cayuga Lake level. For 

 height above sea add 381 feet. 



would indicate that during the first interglacial interval the base 

 level in the main valley stood approximately 80 feet above the 

 present lake level. This base may have been a stream in the main 

 valley or it may have been a lake similar to the one now occupying 

 the basin. We shall discuss later the evidence bearing on this point. 

 4. Second glacial epoch. — -A second glacial epoch followed and so 

 lowered the base level in the main valley that the tributary stream 

 again found itself hanging. The ice, during this glacial invasion, 

 seems to have considerably modified the lower part of the 600-foot 

 gorge. The sides and bottom were smoothed and striated and the 

 walls of the gorge at the lower end appear to have been much eroded 



