388 
Frank Carney 
{g) Including some six miles along the western side of the sheet, 
from North Lansing as far north as the headwater area of Hollow 
Brook, the moraine is so strong as to suggest a permanent position 
of ice-front. But its development may be completely interpreted 
only in connection with the adjacent drift of the Genoa quadrangle. 
It is probable that by the time this moraine was being deposited, 
the eastern side of the Cayuga lobe had commenced to develop 
an irregularity due to Salmon Creek valley. The southern por- 
tion of this drift area is alluded to in the preceding section as 
continuous with morainal development about Goose Tree. The 
abundance of washed deposits over an area a mile square, north 
and east of North Lansing, is in keeping with the topography and 
the relations that the ice-front evidently maintained to this general 
southward rock slope. 
( 3 ) Nunatak Drift. The maximum thickness of the great ice 
sheet was attained far from its outer margin. Various estimates^^ 
have been made of its depth at several points in northeastern 
North America. Whatever may have been the depth of ice in 
any particular locality, it is evident that towards the outer edge 
the ice sheet tapered to the uncovered region. The condition 
must have been analagous to the relations of the ice noted now 
in Greenland where there is a seaward thinning. 
The irregular topography, the result of a complex drainage 
history, would give the decaying ice a more or less patchy surface 
condition. As the ice grew thinner the highest land areas, if 
limited in extent, evidently would show through the sheet, pre- 
senting bare surfaces designated nunataks, or limited ice-free 
areas sometimes surrounded entirely, and again partly surrounded 
by the glacier. It is obvious that when such a point of land has 
appeared above the sheet, melting in its immediate neighborhood 
Would be increased because of the heat reflected from the bare 
rock or soil. 
So long then as the ice continued in this position in reference to 
the nunatak, a quantity of glacial debris would be accumulated. 
The decay of the ice evidently was more rapid on the southern 
exposure of the nunatak; the fact that the glacier in general fed 
from the north would accentuate this difference in the height of 
the ice about the exposed hill. There would be a tendency for 
drainage to carry more or less drift, other things being equal, to 
Chamberlin is’ Salisbury: Geol.^ vol. iii (IQ06), pp. 355-58. 
