290 The Aviencaii Geologist. ^'^'^- ^^'^^■ 
accumulation of evidence opposed to the glacial erosion theory. 
Stated in general terms this hypothesis is as follows : — 
the region of the Finger lakes, having attained a condition of 
topographic maturity, represented by the hanging valleys, and 
by the gentle slopes of the main walls above the 800 foot 
contour, was subjected to rejuvenation. The main valleys, 
with their elevation above sea level decidedly increased, and the 
power of their streams possibly further increased by tilting, were 
transformed, below the 800 foot contour, to broad, deep gorges, 
whose bottoms were cut to levels below present sea level. The 
side valleys, always behind the main valleys in stage of de- 
velopment, were, moreover, occupied by smaller and weaker 
streams, which, in the majority of cases were either only 
slightly or even adversely affected by the tilting. These \yeaker 
members of the stream systems were unable to do more than 
cut the gorges which are so generally present in the bottoms 
of the hanging valleys. On this theory a moderate amount of 
glacial erosion is of course allowed, possibly deepening the 
valleys somewhat, and certainly broadening them by erosion 
on the sides, and, in favorable situations, even partially erasing 
the older gorges. 
If the tilting were from the northeast it might account for 
the discordance of Salmon creek. If it were accompanied by 
headwater erosion and stream capture near the present divide, 
it would account for many ]jeculiar conditions of drainage in 
that region. 
Further studies are necessary to settle this problem. The 
glacial erosion theory is opposed by various facts ; the re- 
juvenation theory must at present be considered a possible 
explanation of the phenomena. Distinct progress toward so- 
lution might be made if it were possible to establish the grades 
of the buried gorges. If they can be shown to have such 
steep grades as to carry them down to the main vallev bottoms 
the theory of rejuvenation will be greatly strengthened. To 
gain this proof it seems necessary to have a series of borings, 
since the older gorges are deeply drift-filled. 
If rejuvenation by uplift is the explanation of the condi- 
tions in the Finger Lake valleys it is but a jiart of a wider in- 
terference with drainage. Studies now in progress outside 
the basins of the I'^inger lakes have discovered certain ev- 
