160 
PHYSICAL HISTORY OF THE 
tinguished from the more connected traces of 
glaciers, or extensive sheets of ice, resting 
directly upon the face of the country and 
advancing over it. There seems to be an 
inextricable confusion, in the ideas of many 
geologists, as to the respective action of cur¬ 
rents, icebergs, and glaciers. The facts con¬ 
nected with these phenomena are in truth very 
different from each other, and easily recog¬ 
nized after the discrimination has once been 
made. As to the southward movement of an 
immense field of ice extending over the whole 
north, it seems inevitable, the moment we ad¬ 
mit that snow may accumulate around the pole 
in such quantities as to initiate a pressure 
radiating in every direction. Snow alternately 
thawing and freezing must, like water, find 
its level at last. A sheet of snow ten or fif¬ 
teen thousand feet in thickness, extending all 
over the northern and southern portions of the 
globe, must necessarily lead, in the end, to the 
formation of a northern and southern cap of 
ice, moving toward the equator. 
I have spoken of Tijuca and the Pom Pedro 
Railroad as favorable localities for studying 
the peculiar southern drift; but one meets it 
