REPORT OF THE DIRECTOR, 1922 167 
northern divide of that system was crossed, for the crossing may 
have been over ice. As has been noted above, there is reason to 
believe that the ice in the Mohawk valley had been overthickened 
and, if that was the case, it is possible that all the drainage from 
the north was deflected westward beyond Utica. We are con- 
cerned here with the origin and significance of the region of prob- 
able overthickening. 
This region is characterized everywhere by heavily drumlin- 
ized topography remarkably free from any subsequent accumu- 
lations of recessional drift. The drumlins and the associated 
flutings and striae evidently mark the last movement of the gla- 
cial ice in this district which has left a record. If the movement 
be thought of as due to pressure transmitted from a great distance 
it may be said to have entered the Hudson and Mohawk valleys 
by way of the Champlain portal,® to have reached and climbed 
the Helderberg escarpment, crossed the dissected plateau to the 
lower slopes of the Catskills and there stopped. It is possible 
that some movement down the Hudson valley belongs to this 
episode and also some southeastward movement away from that 
valley but, if so, the effects of these late movements cannot be 
differentiated from those of the general advance of the glacier. 
But that there was more resistance offered to southward motion 
than can be accounted for by the land topography alone 
would seem to be obvious, for after spreading southwestward 
over most of the Schoharie basin, the principal line along which 
the relief of pressure took place was westward, up the valley of 
the Mohawk, nearly to Utica. This would seem to indicate that 
the ice ‘was not advancing into unoccupied territory. The high 
altitudes reached by this drumlin-forming ice over the Helder- 
berg (it climbed from the 300 foot level to over 2,000 feet) do 
not favor the idea that “drumlins are a product of the sliding 
movement of a thinning ice edge when under efficient thrustal 
motion of thick ice in the rear”? advanced by Professor Fairchild. 
° The writer is of the opinion that the pressure head which moved the ice 
was not all derived from some limited area in the Labrador near the 
geographic center of the glaciated territory; atmospheric conditions are 
are not likely to be so selective in the distribution of precipitation. Every- 
where over the ice sheet and perhaps beyond it, snows accumulated from 
year to year and the ice was being thickened locally by greater average 
snowfall over some parts of the glacier than over others. An attempt to 
trace this Mohawk thrust back to what might be called its root was not 
successful; it may well represent the effects of a movement occasioned by 
overthickening of the ice in a region no further distant than the St 
Lawrence. 
