1879*] Relations to that of the Glacial Epoch . 25 
possession of only one-tenth part of their original store of 
moisture, — still, as the area between lat. 8o° and the Pole 
is but one-eighth of that between lat. 6o° and 8o°, this 
would notwithstanding give 24 feet as the annual amount of 
snowfall between lat. 8o° and the Pole. 
Rate of Motion of the Antarctic Ice . — If we knew the rate 
at which the edge of the Antarctic ice-cap is advancing out- 
wards, we could form a rough estimate of the amount of 
snowfall on the continent. Or, conversely, knowing the 
amount of snowfall, we could tell approximately the rate at 
which the ice is moving outwards. 
Dr. Rink calculates that the yearly precipitation on 
Greenland in the form of snow and rain amounts to about 
12 inches. About 2 inches he considers is carried off by ice 
into the sea, and the remaining 10 inches is carried to the 
sea in the form of sub-glacial rivers. He believes that the 
quantity disposed of by evaporation is trifling. 
The amount of precipitation on the Antarctic continent 
is probably much greater than on Greenland. On the 
Antarctic continent it is all in the form of snow or hoar- 
frost, whereas in Greenland a considerable portion of it — 
in summer at least — is in the form of rain. For reasons 
already stated the proportionate amount carried off the 
Antarctic continent in the form of water to that of ice 
must be much less than on Greenland. The quantity of 
ice melted in the Antarctic regions from all causes, we 
have seen, cannot be great ; and of that quantity the 
greater part must be re-solidified long before it can reach 
the sea. I can hardly think that it will be regarded as an 
over-estimate to affirm that at least one-half the precipita- 
tion must reach the sea in the form of ice. Assuming the 
annual precipitation to be no greater than that of Green- 
land, viz., 1 foot per annum, the quantity carried off in the 
form of ice would in this case be 6 inches. At what rate, 
then, would the edge of the cap require to be advancing 
outwards in order to discharge this 6 inches of ice ? If we 
assume the cap to extend on an average down to lati- 
tude 70°, its area will be about 5,940,000 square miles, or 
165,611,000,000,000 square feet. A layer 6 inches thick 
covering that area would contain 82,805,500,000,000 cubic 
feet of ice. The circumference of the cap is 45,300,000 feet, 
and its thickness at the edge is assumed of course to be 
1400 feet. Were the ice, therefore, to move outwards at 
the rate of 1300 feet per annum, and to break up into bergs 
as it advanced, the quantity of ice discharged annually in 
