W. J. McGee—Thickness of Ice-sheet at any Latitude. 265 
ten degrees farther from the pole would be about 400 feet. 
These estimates enable us to institute a comparison with the 
antarctic ice-sheet. 
nly about one-seventh of the seventieth parallel of north 
latitude is so free from land as to present no obstruction to the 
carrying in of vapor from more southerly regions. In the south- 
ern hemisphere, on the other hand, the whole parallel is prac- 
tically open to the introduction of vapor from the adjacent tem- 
perate zone. The accumulation here ought accordingly to 
the margin. It will probably not be objected that these esti- 
mates are too low, as they have purposely been made as large 
as seems at all consistent with the present condition of polar 
regions. It has already been shown that the present accu- 
mulation in these regions is probably about as great as ever can 
have existed. 
Accepting the largest of these estimates as representing the 
greatest possible thickness of the ice-cap at lat. 70°, and com- 
puting the thickness at other latitudes as in table XVII, the 
respective values are found to be as follows :— 
Lat. 40° 14217 feet, = 2°693 miles. 
meen 821g fe Php 
60 6226) 80 
40 2800 ee 880 
hee «5, 1836). 8s os “abs 
eo 1408 eS 
The approximate correspondence between the two estimates is 
apparent. 
nearer the poles than where it is formed. ‘T'wo factors (perhaps 
the ratio of p:p-+ 2°, where p denotes normal precipitation, o 
n 
