THE BARRIER'S FLOATING ICE-FRONT 
Even if it is 7 to i, then the Barrier is afloat at its edge, 
and the same is of course the case if the ratio be taken as 
4 to I. Professor David quotes an example of i to i, but 
that is certainly exceptional. 
It seems certain that there is a layer of water under 
the great Ice Barrier, which has five times the extent of 
the North Sea. 
II. Limits. — ^We have several observations of the 
ice front, notably Ross in 1840, and the Discovery in 
1902. The latter showed a recession in general of from 
15 to 20 miles, with a maximum of 45 miles. In 1911, 
however, Pennell reported that the conditions appeared 
to have changed little during the last ten years. 
This means that 45 miles at any rate must have been 
afloat. The Ross Sea does not get shallower so far as 
we know. 
We must remember that the wall near Balloon Bight 
varies greatly in height. If the ratio of the edge of the 
Barrier above and below water line be taken as i to 4, 
then the ice sheet seems to vary in thickness from 70 to 
700 feet, with an average of about 400 feet. 
But it is quite conceivable that this sheet is extremely 
thin in places. 
III. Crevasses, — These natural breaks in the con- 
tinuity of the ice have been studied in some detail. We 
observe that they are radial near the Bluff and White 
Island. They have parallel sides, both in plan and 
section. No crevasses seem to occur more than 15 miles 
from the land. Curiously enough, none of these seem 
to have any great depth, for I saw platforms about 
