Pleistocene Geology of Moravia Quadrangle 437 
probability of multiple glaciation. '‘Through valleys offer 
equally pertinent hints of repeated ice-invasions. 
Possible evidence of an earlier invasion is indicated also by the 
scattered hints of ice-dammed lakes older than the lakes held up 
in front of the retreating Wisconsin sheet. No data is available 
for a more accurate time-definition; the lakes may have skirted 
the front of the advancing Wisconsin ice; they may mark the 
advance or retreat of an earlier invasion. The shore lines of 
these older lakes so far as traced show discrepancy in attitude 
when compared with the shore lines of the more recent ice-front 
lakes. It is obvious, furthermore, that every ice-invasion of this 
Finger lake region witnessed the growth and decadence of such 
lakes. The strength of shore phenomena developed by the static 
water bodies characterizing the progress or retreat of any ice-sheet 
has a direct connection with the duration of the halt which occa- 
sioned the static body of water. If, therefore, the ice-dammed 
lakes in this region held up, for example, by the Illinoian ice- 
invasion had a duration comparable with the Wisconsin Lake 
Warren, it is probable that shore lines would have been developed 
that might locally 'withstand even one or more later ice-invasions 
and be observed today. Such phenomena have been tentatively 
studied in the valley of Lake Keuka;^^ if found in other of the 
Finger lake valleys, correlating data may aid in arriving more 
closely at the time of their origin. 
On the supposition that this area has been glaciated previous 
to the Wisconsin invasion, we may consider the effects produced 
on an older drift sheet by another incursion of ice. These effects 
would be controlled somewhat by the topography, and to a much 
less degree by the length of the interglacial period. The drift 
which accumulated in transverse valleys obviously would suffer 
less through a second invasion of ice than would the glacial de- 
posits made in longitudinal valleys. For this reason, then, older 
drift sheets should be better preserved in valleys transverse to 
the line of movement of the later ice-invasion. The bearing that 
the length of the interglacial period has on the question arises 
through the amount of soil that would be developed in the lapse 
of glaciation, and also in time through which the till already 
The designation used by Tarr, Bull. Geol. Soc. Am., vol. 16 (1905), p. 233. 
F. Carney: The Am. Jour, of Sc., vol. xxiii (1907), pp. 325-335. 
