PACK-ICE. 
57 
water-level, and the original freezing surface of the ice had been depressed to four 
feet below water-level. The total thickness of snow accumulated at this spot during 
the two years was more than 20 feet ; as the thickness here when the ice broke up 
was only 15 feet, the whole of the original ice and the earliest deposits of snow 
must have been entirely removed by the melting action of the sea-water previous 
to the final break-up. By this means, water-vapour from low latitudes is condensed 
in high latitudes and transported again to low latitudes, without taking part in the 
glaciation of the polar land-masses. 
Size of floes. Names * such as Pancake-ice, Bay-ice, Field-ice, Pack-ice, 
Stream-ice, are given to sea-ice at certain periods of its short life. Thus Pancake- 
ice is the first product of the frozen sea. It is an aggregation into roughly circular 
masses of the ice-plates which first crystallize. The fiat cakes thus formed are 
about an inch thick and one 
to two feet across, and have 
notably turned-up edges. In 
a sheltered bay where these 
cohere to form a thin sheet, 
the result is called Bay-ice. 
Later, this thickening extends 
to large areas and the ice is 
then called Field- or Fast-ice. 
During the summer Field- or 
Floe-ice breaks up into floes, 
which float out northwards 
from McMurdo Sound and 
join the belt of Pack - ice 
(Drift-ice, Treib-eis ) encircling 
the Antarctic regions (Figs. 
30, 31). As the floes drift north they break up and dissolve away, and they are 
met with at sea in elongate and scattered patches which are termed Stream-ice. 
The size of the floes varies greatly; one may be 100 yards across, another may be 
two miles or more, but the thickness in the Ross Sea is never more than six feet. 
The floes are necessarily larger f on the south side of the belt of pack, as there 
they are protected from the swell by the stream-ice. Outside, the swell is most 
destructive and rapidly breaks up any large ice-field. 
Hummocks are rather exceptional in the sea-ice of South Victoria Land, 
and all that occurred in McMurdo Sound were less than three feet high. These 
seemed to be caused by the ice in the outer part of the bay breaking for a time 
* Markham, ‘The Antarctic Manual’ (Boy. Geogr. Soe.), 1901, p. xiv; H. Bink, ‘Danish Greenland,’ 
1877, p. 73. 
t Colbeck, Geog. Journ., 1905, vol. xxv, p. 403. 
Fig. 31. — The ‘Discovery’ brought to a standstill by Pack-ice. 
VOL. I. 
I 
