48 
Frank Carney 
let past Penn Yan into the Seneca valley. Obviously this cross- 
section, W-like in shape, is made at the junction of the old sauth- 
flowing river and a tributary. 
The general topography of the Finger Lake region, so frequently 
alluded to in geological articles, is a systematic assemblage of 
trough-like valleys opening into the Ontario lowland. Presum- 
ably the bed rock of these troughs slopes northward, as do also 
the divides between them. The Penn Yan quadrangle extends 
almost to the edge of this Ontario lowland. The Drumlin region 
reaches its maximum southern extension north of the Penn Yan 
sheet, and a few miles southwest of Geneva, which lies within the j 
flaring walls of the Seneca valley. f 
I 
if 
ICE-FRONT AND DRIFT AS AFFECTED BY TOPOGRAPHY. i 
The Ontario lobe, as the ice which occupied this lowland is j 
designated, maintained along its southern margin, during the | 
advance and retreat of the ice sheet, valley dependencies, the 
development of which was directly in proportion to the depth of 
the troughs above alluded to. Of these troughs those of the Seneca 
and Cayuga valleys are the deepest and therefore probably were 
occupied longest by tongue-like projections of ice. Contiguous to 
these troughs are upland valleys which were also occupied by ice 
showing more or less dependence upon the lobes lying in the Seneca 
and Cayuga valleys. But as the general border of the ice retreated, 
the divide ridges separating these trough-like valleys were revealed 
farther and farther to the north between the converging lines of 
ice; and in an analogous manner the lesser divides marking and 
forming the valleys contiguous to the Cayuga and Seneca troughs 
became reentrant angles between converging walls of ice. It is 
the work of two such lesser valley dependencies that is supposed 
to have given rise to the peculiar drift accumulation with which 
we are concerned. 
A study of the drift about Penn Yan reveals a massive accumula- 
tion of debris which begins southward a mile or so from Milo 
Center and continues a mile or more north of Penn Yan. This 
moraine, approximately three miles wide, suggests a very slow 
