26 Thickness of the Antarctic Ice , and its [January, 
the form of icebergs would be 82,446,000,000,000 cubic feet, 
an amount equal to the layer of ice 6 inches in thickness 
covering the area. Consequently, if 6 inches of ice be 
carried annually off the Antarctic continent, the edge of the 
cap must be moving outwards at the rate of about a quarter 
of a mile annually. Even supposing there were only 
2 inches of ice discharged, the rate of motion would require 
to be between 400 and 500 feet per annum. 
A quarter of a mile per annum cannot be regarded as an 
improbable rate of motion for continental ice, when we 
reflect that the Greenland ice has in some places a velocity 
ten times greater. Mr. Amund Helland, for example, found 
that the glacier of Jakobshaven has a velocity of about 
20 metres per diem , which is upwards of 4 miles annually. 
The exceptional high velocity of the Greenland glaciers is 
no doubt owing to the fadt that the ice-sheet covering that 
continent has to force its way through comparatively narrow 
outlets. If the sheet moved off the land in one unbroken 
mass, like the Antarctic sheet, its rate of motion would be 
much less. 
It is the immense extent of the Antarctic continent which 
demands such a high velocity to get rid of the ice. To enable 
it to discharge the annual amount of ice, either the sheet 
must be excessively thick or its rate of motion excessively 
great. If, for example, the ice were only 700 feet instead of 
1400 feet thick, its motion would require to be half a mile 
annually in order that the 6 inches of ice should be got rid 
of ; while, if it were only 100 feet in thickness the rate of 
motion would need to be miles per annum. 
It is this difficulty in getting away which is the chief 
cause of the enormous accumulation of ice on the Antarctic 
continent. And it is just this great thickness in the interior 
that enables the sheet to get rid of its superabundant ice. 
This is effedled in two ways : — 1st. The greater the thick- 
ness of the ice in the interior, the greater is the force by 
which it is impelled outwards, and, other things being equal, 
the greater is the velocity of the ice. 2nd. The thicker the 
sheet becomes, the greater is the quantity discharged cor- 
responding to a given velocity. The velocity being the 
same, the quantity discharged is in proportion to the thick- 
ness of the sheet. 
With the present rate of snowfall on the Antarctic conti- 
nent it is physically impossible that the ice can be otherwise 
than of great thickness. Were not the sheet enormously 
thick the quantity of ice annually discharged would not 
equal that being formed, and consequently the ice would 
