riiigcr Lake Rci:^io}i of Central A'. )'. — Tarr. 289 
in han£i:ins" valleys, there is a discorclance, especially well 
marked in two cases, both of which, however, may possibly 
be explained in harmnnx with the s^'lacial erosion theory; (2) 
the supposed ice-eroded valleys have the cross-section of 
oorges ; (3) the ])resence of many angular, jirecipitous clififs in 
the zone of supposed ice erosion below the hanging valley 
level; (4) the j^resence, in two places, of evidences of pregla- 
cial decay, in situations where such vigorous ice erosion as is 
postulated should have removed them; (5) the presence of a 
cavern in similar position ; (6) the existence of an island in 
lake Cayuga in the line of glacial erosion; (7) the fact that 
the ice erosion could have been accomplished only during those 
periods when the ice was thin enough to be deflected from 
its main course by the valleys which lie transverse to the 
main ice movement, thus limiting ice erosion in time, and to 
those periods when its depth, and hence effectiveness, was 
diminished. The argument that sufficient material to refill 
the basins is not in evidence is not considered of great weight. 
An Alternate Hypothesis: Throughout this investigation 
an eftort has been made to consider all alternate hypotheses 
that could be suggested, and all but one of these are easily 
eliminated. It scarcely seems worth the while to take the 
space to consider three of these hypotheses, which, though 
advanced for, and possibly applicabl-e to other regions, are cen- 
tainly not the explanation of condititons here. Reference is 
made to (T) faulting, (2) folding, and (3) the occupation 
of the lateral hanging valleys by glaciers while the main valleys 
were being deepened by running water. Evidence is clear 
that there is no extensive faulting or folding in this region, 
and that there are no gathering grounds for valley glaciers 
and, indeed. ]:)Ositive evidence that no such glaciers existed. 
It is doubtful if an\-one will call for the proof of these asser- 
tions, which could easilv be substantiated. 
A fourth hvpotliesis. however, that of rejuvenation, has 
not been so easy to set aside, and the difficulty of eliminating 
it has been greatly increased by the recognition of the wide 
distribution of the older gorges, which has been accomplished 
since the publication of my earlier paper on the origin of the 
Lake Cayuga basin. While this hypothesis long seemed im- 
probable, the necessity of considering it has increased with the 
