Upham.] 14 [Nov. i6, 
as higli as the tops of the most prominent druinliiis. C'urrents 
ascending at tliis rate, or even two or three degrees or more, may 
very probably have existed in the lowest part of the ice-sheet, on 
account of the acceleration of its upper currents, within distances 
from 20 to 50 miles or more back from its boundary. By these 
currents much drift eroded from the land surface would be grad- 
uall}^ incorporated in the comparatively sluggish lower part of the 
ice, reaching altitudes from 100 to 1,000 feet above the ground 
within a few miles from its sources. 
When the boundary receded, the upper currents of the outer 
belt of the ice, upon a width of ])robably ten miles, would pour 
down toward the open land, causing the deposition of much sub- 
glacial till ; and whenever a stratum of the etiglacial drift became 
covered with much new ice, it would probably be aggregated 
englacially or altogether subglacially in drumlins. The drift that 
had been eroded and lifted into the lower part of the ice during 
many centuries might thus be rapidly accumulated in tlie drum- 
lins during only a very small fraction of the time that had been 
required for its being stored up in the ice. Through such pro- 
cesses I can better understand the origin of these prominent 
drift hills, than by any method that I am able to imagine for 
nearly contemporaneous erosion, subglacial transportation, and 
deposition of their till. Moreover, I find great difficulty in form- 
ing a conception of convergent basal currents powerful enough, 
in spite of their friction on the land, to amass these hills ; but 
the inequalities of contour of the outer belt of the ice, as irregu- 
larly thinned by ablation, may well have produced upper and 
central currents of sufficient energy to sweep the englacial drift 
stratum into irregularly grouped and scattered or even solitary 
drumlins, when new ice and snowfields added a considerable 
depth over all the previous drift-covered surface of the ice-sheet. 
The second objection alluded to arises from the abundance or 
frequenc}^ of glaciated stones and boulders in the till of the drum- 
lins, and from its compactness, flaky lamination, and other feat- 
ures which prove it to be subglacial till or ground moraine. If 
this drift was englacial during a considerable time and became 
amassed in these hills beneath only a few hundreds of feet of ice, 
could it present so impressive characteristics of subglacial accum- 
ulation under heavy pressure? To this question we must reply 
that the stratum of englacial drift would be subjected to much 
