308 SCOTT'S: LAST EXPEDITION 
Probably the most interesting of the data collected on gla- 
ciers were connected with their interior structure, the size of the 
individual crystals, the amount of the imprisoned air in the form 
of air bubbles, the occurrence of silt bands and of bands of clear 
blue ice in horizontal layers, and the occurrence and distribution 
of crevasses, and of pressure ridges in the glacier. This field, 
however, is much too large to enter upon in this place. 
THE BARRIER 
By far the most unique feature of the Antarctic is the occur- 
rence of huge masses of floating ice, such as the Great Ross 
Barrier, which fills up the whole of the narrow end of the Ross 
Sea. This great sheet of floating ice has an average depth of 
probably 600 feet and presents an unbroken front to the sea 
400 geographical miles in length with a depth from back to front 
of over 300 miles. The surface of the Barrier is comparatively 
level, and offers little obstruction to sledging. The yearly snow- 
fall from observations by Captain Scott in the Discovery Expe- 
dition and from Sir Ernest Shackleton’s work amounts to about 
eighteen inches of consolidated snow of density about 4%. From 
the same authorities we know that the yearly motion is in an 
east-north-easterly direction (close to Minna Bluff) at the rate 
of about 500 yards a year. 
We have moreover data to show that no great change in the 
position of the seaward edge of the Barrier has taken place since 
the Discovery Expedition (in 1901-04). Thus the Barrier may 
be considered for purposes of calculation as remaining in statu 
quo by virtue of the discharge of icebergs from its seaward face. 
If this is so, we see that the volume of ice due to deposition, 
18% X 42 X% X 400 X 2000 X 300 X 2000 = 12 X 10?° cubic 
yards (taking width as 400 miles, and length 300), should be 
converted into a strip of ice on the seaward side 400 miles long, 
500 yards wide, and 600 feet deep = 8 X 10'° cubic yards. 
This agreement of observation is a remarkably close one and 
proves that our fundamental statement is very close to the truth. 
It should here be pointed out that in the above calculation no 
allowance has been made for the effect of glaciers pushing the 
Barrier before them and so adding to the apparent motion. 
That is, it is assumed the Barrier moves under its own weight 
