Piiii^rr Lake h'ciiioii of Central X. )'. — '/'(//'/'. 285 
and Salnidii creeks. Ijotli lril)Ulai"ies to the Ca\u_sj;'a valley from 
llie east. In the case of Six Mile creek (V\(^. 24) tlierc is a 
chant^c in slope several niiles from its mouth ; Init this change 
occurs much farther hack than in the other valleys, and it is 
not nearly so distinct. It is true that the present stream fol- 
lows approximately the line of the huried gorge, and this fact 
may account for its discordance. Salmon creek (l^g- 25) 
/V 
Fig. 2.5. Profile of Salmon ci'eck, enteiing Cayuga lake six miles north 
of Ithaca. (Scale same as Fig. 7.) 
shows no change of slope throughout its course, and is alto- 
gether out of harmony with the other streams tributary to the 
southern ends of Cayuga and Seneca lakes. It is significant 
that this is a north-south valley, and, on the glacial erosion 
theory, its discordance might be explained as a result of glacial 
erosion. 
Little ])rogress in solving the problem of the significance 
of this discordance seems possil)le until the grade of the gorges 
can be established ; and boring appears to be the only way of 
accomplishing this result. At present, therefore, it must suf- 
fice to point out the fact of discordance and to show that, while 
out of harmony with the other valleys, the discordance ma\- 
possiblv be so explained as to fall in with the glacial erosion 
theory. But this discordance gains importance as evidence 
against glacial erosion when su])ported by other opposing ev- 
idence. 
Gorge Form of \^\lleys : The cross section of both Cay- 
uga and Seneca valleys is opposed to the glacial erosion theory. 
Below the 800 foot contour the slope is gorge-like. If the 
depth is due to glacial erosion, trenches from one to tw(T miles 
wide, and at least 850 feet deep in the case of Cayuga and 1400- 
1500 feet in Seneca, have been cut in the bottoms of broad, ma- 
ture valleys. It does not seem probable that ice could so concen- 
trate its work in a narrow zone r^long the axis of a winding 
valley The valley form below the 800 foot contour is rather 
that of a gorge formed by river cutting. It resembles the val- 
ley of the Susquehanna further south, in the formation of 
which ice erosion certainl\- had no important effect. 
