412 SCOTT'S LAST EXPEDITION 
the breaking front about the same position is 117 cubic 
miles. 
Let us consider the snow deposition. It is stated that 
about 4 inches of compressed snow falls per year. The 
blizzards evidently build up shallow flat hummocks here 
and there, and may cover the whole surface at the fourth 
effort. 
The old Discovery Depot was covered in 13 inches 
of old snow or 9 inches of ice. 
If we assume the Barrier area is 350 X 350 miles, then 
we get a mass of i6'5 cubic miles. 
The difference in these two interesting figures — 16'5 
cubic miles and 117 cubic miles — may be due to an abla- 
tion of the under surface of the sheet by warm water. 
However, we may assume that there is sufficient snow- 
fall on the Barrier to account for the movement, which is a 
fact of the first importance. 
At the edge of the Barrier there is a curved ascent, and 
' doming ' is common in bergs. May not this curving be 
a result of the outward expansion ? 
The movement of the northern glaciers seems to be 
much greater than that of the Beardmore and southern 
glaciers. Perhaps it is six times as great. But the slow 
movement in the south may still be sufficient to account 
for the ice sheet's advance. 
The fact that the great lateral trench keeps open looks 
as if rival motions were at work. 
As far as 170° W., Campbell says that the 191 1 survey 
showed the western edge of the Barrier face to be stable, 
and with no change like that since Ross's time. Of 
