GO 
II. T. FERRAR. 
freeze up soon after they are formed, and no movement in the reverse direction can 
therefore take place. Cracks made in this way seldom open much more than two 
inches at any time, hut during the year have indicated a movement of more than 
20 yards. Sea-ice therefore is removed in three ways: (l) through corrosion by 
sea- water, (2) breaking up and floating away piecemeal, (3) creeping bodily away 
from the land. 
The “ creep ” of sea-ice is very small compared with the movement which takes 
place when an ice-field breaks up at the end of the winter ; but it is important, as it 
prepares the field-ice for the action of the ocean-swell which breaks it up during the 
Pig. 34. — The Relief-ships forcing their way through the barrier of Floe-ice in 1904. 
summer. As the field-ice breaks up, the floes that are formed drift northwards to 
augment the pack-ice. 
Thawing . — Virtually no surface-thawing of the sea-ice takes place, for the 
air-temperature in the open is always far below the freezing point, and the snow 
reflects most of the radiant heat. Locally dust and other extraneous particles sink 
into the ice or snow, but the holes thus formed are filled by the silting action of 
the snow. Mention has already been made of the action of the sea in reducing 
the thickness of the floe-ice, and it is noteworthy that during sunny days the 
sea-temperature itself is slightly raised and then the water melts more quickly the 
ice at its seaward edge. This greater capacity for melting the ice has been observed 
for at least two miles within the margin of the fast-ice of McMurdo Sound. 
