ICEBERGS AND SNOW BERGS 173 



Drygalski Ice Barrier as against many snow bergs. This seems strange when one 

 considers that an immense proportion of the west coast of Eoss Sea and McMurdo 

 Sound is occupied by piedmont ice. At the same time it must not be forgotten that 

 this piedmont ice or shelf ice closely approximates in places to the structure of the 

 snow bergs formed by accumulations of old snow on sea ice of many seasons' growth. 

 Such bergs as were formed of blue ice, and were more or less charged with rock dust 

 and other rock debris, had probably been derived from the snouts of some of the 

 outlet glaciers of the Antarctic, or from the foot of the piedmont. Near the final 

 stage of their history, before they disappear, the snow bergs with their foundation 

 of old sea ice are gradually eroded away by the mechanical force of the breaking 

 waves, and at the same time become thawed in the rays of the sun, until at last 

 nothing is left but what appears to be a perched block of old snow resting on a small 

 ice island, the buoyancy of the latter being sufiicient to keep the old snow of the 

 berg still above the level of high water. Obviously the last part of such a berg 

 to survive would be the substratum of old sea ice on which the snow mass was 

 originally built. 



From what has been said, it is apparent that it might be possible to divide the 

 ice bergs of the Antarctic regions into three classes, viz. : — 



1. Snow bergs formed on a base of old sea ice. 



2. Bergs formed of shelf ice. These may grow as a piedmont resting on a rock 

 foundation forming a wide fringe of the Antarctic shore-line, or may develop like 

 the Great Ice Barrier as a mass of glacier ice formed of the expanded fans of 

 numerous outlet and alpine glaciers with the sea ice between them, held fast for 

 a vast number of years, and then added to by many hundreds of years of snowfall. 

 This latter variety of shelf ice presented by the Great Ice Barrier thus unites 

 some of the attributes of the snow berg ice with that of the piedmont ice. Thus 

 the shelf ice may be said to have two types, (a) the piedmont, (6) the barrier. 



3. The third class of bergs are the blue bergs, with their englacial or supra- 

 glacial morainic freight launched from the snouts of outlet or alpine glaciers. 



In regard to the flotation of these dift'erent types of bei'gs, the buoyancy of class 

 3 is already so well known as not to call for comment here. 



In regard to class 1, we observed at Cape Royds that when the sea ice was 

 breaking out up to the tidal crack, the rectangular bergs so formed had a covering 

 of fi'om 6 to 8 feet of packed tough snow resting on a substratum of sea ice of one 

 season's growth ; the latter originally did not exceed about 7 feet in thickness, and 

 at the time the disruption occurred had been considerably thinned and honey- 

 combed by the thawing action of sea water. As far as we could ascertain, from 

 3 to 4 feet at the base was formed of honeycombed sea ice, the remaining 6 to 8 feet 

 being hard compressed snow. About 1 mile south of our winter quarters at Cape 

 Royds there were four stranded bergs, but it was not clear as to which of the above 

 classes 1 and 2 they might be referred. The portion of these bergs above sea- 



