286 The American Geologist. ^^^y, 1904. 
Presence of Angular Cliffs : In such a deep, narrow valley 
it would seem as if ice motion would be so interfered with by 
friction on the sides as to lose rather than gain erosive power. 
The presence of cliits, sometimes with moraine banked up 
against the angular joint plane corners, points toward the 
accuracy of this conclusion. These cliffs occur in places where 
post-Glacial stream erosion is altogether out of the question. 
It is certainly a point difficult to explain that actual precipices, 
with angular joint plane corners, should form part of the wall 
of a valle\' due to ice erosion. River-deepening would cause 
just such rock outlines; but ice erosion should leave rounded, 
smoothed surfaces. The presence of these cliffs is considered 
to be a very important evidence against the glacial erosion 
theory. 
Presence of Products of Residl^al Decay : That ice ero- 
sion can hardly be appealed to in explanation of the Cayuga val- 
ley is strongly indicated by the presence, in at least two places, 
of evidence of pre-Glacial decay. One of these places is in the 
gypsum quarries between Union Springs and Cayuga, near the 
northern end of the lake. Here is still preserved the irregular 
surface of pure gypsum, with decayed material above, overlain 
bv till. The other locality is at the Portland Cement Works, 
about five miles north of Ithaca on the east side of the lake, 
where Tully limestone is being removed for making cement. 
The upper Tully layer is ice-smoothed on the top and covered 
with a thin veneer of till ; but beneath it. and separating it from 
the next layer below, is a red clay of residual decay. It seems 
evident, therefore, that ice erosion was, unable to wear down be- 
neath the zone of rock decay. This locality is well below the 
edge of the hanging valleys, and in a part of the lake valley 
where ice erosion must have been as vigorous as in most por- 
tions. 
Presence of a Cave : In this same limestone, near by, 
there is a small cave which must have been formed after 
the valley was lowered enough to permit the free passage 
of ground water. Post-Glacial time seems too short for this ; 
if inter-Glacial, later ice erosion should have removed it. The 
presence of this cave seems to testify to pre-Glacial deepening 
of the main valley, and to oppose the glacial erosion theory. 
