9 
Pre-Wisconsin Drift in Finger Lake Region 
Erosion of drift. With this distribution of drift there must have 
been differential erosional effects produced by a second invasion 
of ice. Rather slight modifications would be effected under con- 
dition (i). The work of another ice-sheet passing over such an 
area is compressive quite as much as erosive; the more evenly the 
original drift is distributed, the less obstruction it offers to the 
progress of later ice; whereas, the weight of the overriding ice 
tends to compact this drift. 
During the interval of deglaciation, stream-channeling, in the 
featureless topography of condition (i), proceeded slowly, since, 
to some extent at least, the streams were consequent. But with a 
larger lapse of time between the periods of glaciation this surface 
may have attained the relief of mature dissection, when it would 
present to the ice of the next invasion an opportunity for more 
effective corrasive work. 
Each succeeding invasion would remove less of the previously 
deposited drift; it seems very probable that the resultant of several 
glacial invasions of such featureless topography is somewhat 
aggradational. And the final form given this drift depends upon 
the width and spacing of the moraine belts, if the ice were subject 
to varying relations of feeding and melting; or upon the thickness 
of drift deposited in an extensive sheet in case the feeding and melt- 
ing factors were about balanced, the melting being slightly the 
stronger of the two. That the resulting forms due to the aggra- 
dational action of an ice-sheet overriding these two types of drift 
arrangement would not be identical seems reasonable. 
'The drift as described under condition (2) would suffer much 
less from a second invasion. The deposits in the major valleys — 
i.e., the valleys transverse to the direction in which the ice is mov- 
ing — ^would be somewhat protected from erosion; the weight of 
the overriding ice would tend to indurate this drift. But the drift 
in valleys tributary to these, since they trend more in unison with 
the moving ice, must suffer much more from erosion. When such 
accumulations are rather thick, it is probable that a drumlinoid 
form is the resultant of degradation by a second invasion of ice, 
particularly in these tributary valleys. 
The most marked erosional effects, however, are observed in 
