32 
The American Geologist. ^"'y- i^^^. 
the trough of the Boston basin had deflected the basal portion 
'of the ice decidedly to the eastward. This was the period of 
drumlin formation, which was, probably, closely followed by 
the esker and sand-plain period. 
The absence of basal water during" all but the latest stages 
of glaciation is easier to understand when we consider how low, 
probably, were the initial temperatures throughout the entire 
thickness of the ice-sheet, and the great depth of frost pene- 
tration into the ground beneath the ice. Nowhere, probably, 
within the range of observation at the present time are the con- 
ditions of the Pleistocene ice-sheet more nearly realized than in 
the interior of Greenland ; and in this connection Nansen's ex- 
perience in his memorable transit over the ice from the eastern 
to the western coast is of special interest. He says,* "Some of 
the temperatures which we experienced were far lower than 
the establiished meteorological laws would have led us to expect. 
The temperature on certain nights, September 12 and 14, prob- 
ably fell, according to the calculations of professor Mohn, to 
— 45" Cent. ( — 49" Fahr.), while the mean temperature of cer- 
tain days, September 11-16, when we were about in the middle 
of the country, or a little to the west of the highest ridge, varied 
from — 30° Cent, to — 34" Cent. ( — 22" to — 29° Fahr.). This is 
at least 20° Cent. (36" Fahr.) lower than anyone would have 
been justified in expecting, if he had based his calculations on 
accepted laws, taking for his data elevation above and dis- 
tance from the sea, as well as the mean temperature of the 
neighboring coasts." Now, supposing similar climatic condi- 
tions to have prevailed during the entire period of the accumu- 
lation of the ice-sheet, and considering that the glaciation of 
Greenland is long past its maximum and the climate, there- 
fore, probably somewhat ameliorated, we have indicated a de- 
gree of refrigeratign in and under the ice which the slow up- 
ward flow of the terrestrial heat would require a long time to 
overcome. The low temperature of the ice is seen not to be 
necessarily inconsistent with flow through the medium of a 
granular structure, in accordance with the views of Klocke, 
Deeley, Fletcher, and others, as summarized by Upham, t 
when we consider that the progressive melting of a granule at 
one point and its growth at another point demand differential 
* The first crossing of Greenland, vol. ii, p. 480. • 
t Amkk. Geol., 17. pp. 16-29. 
