Q2 TLL OWT AN AE | OF G1RO TE OCA 
area of the ice cap of Greenland is, therefore, much greater than 
that between the latter and the drift-covered area of our conti- 
nent. From the standpoint of ratios, it is an enormously greater 
jump from an alpine glacier to the ice cap of Greenland, than 
from the ice cap of Greenland to such an ice sheet as must have 
covered the northeastern part of our continent, if the drift be the 
product of glacier ice. If the comparison of the three areas be 
made without resort to ratios, their relative sizes are expressed 
approximately by the following numbers: 1, 422 and 5634. 
But even Greenland does not possess the greatest ice sheet 
known. The Antarctic continent—for this land and ice mass 
seems to merit the name of continent —is almost completely cov- 
ered with/jice, So fan as’known. While. its ‘area has) notelbeen 
determined with accuracy, it has been recently estimated to con- 
tain at least 4,000,000 square miles,’ that is, an area equal to the 
great sheet of drift of North America, an area twice as great as that 
of the drift which mantles northwestern Europe. The existence of 
so great an ice sheet today makes it easier to think of the exist- 
ence of an equally extensive ice sheet elsewhere in the este,» ltt 
removes the element of incredibility which, at first thought, seems 
to attach to so striking a theory as that of the glacial origin of 
the drift. From the standpoint of knowledge concerning ice 
sheets, the glacier theory is a possible theory, but it is not to be 
understood that the existence of an Antarctic ice sheet, equal in 
size to the area of North American drift, is any argument for 
the glacier origin of our drift. It is more difficult to account for 
the existence of an ice sheet in temperate than in frigid zones. 
But in spite of the difficulty, our study of the drift has led us to 
the conclusion that glacier ice was the principal agent concerned 
in its production. 
GLACIERS AND ICEBERGS CO-OPERATING. 
Granting that glacier ice was the principal agent of the drift, 
may it not still be true that other agents were concerned in its 
production? Ifso, to what extent? It is well known that the 
*MuRRAY. Proceedings of the Royal Geographic Society. 1894. 
