ICE-PERIOD IN AMERICA. 
97 
have at this moment a wide expanse of land 
unbroken by mountains, over which a uniform 
sheet of ice moves southward, with occasional 
variations of its trend, according to the undu¬ 
lations of the surface. The interesting ac¬ 
counts of Dr. Rink show that in reality Green¬ 
land is a miniature picture of the ice-period. 
The immense number of icebergs breaking off 
and floating southward every summer gives us 
some idea of the annual waste and renewal 
of the ice. How can we doubt, that, when, 
under the same latitude, Norway, Sweden, 
Scotland, England, and Ireland were covered 
by sheets of ice many thousand feet in height, 
the ice-flelds of Greenland must have shared 
in the same climatic influences, and have been 
much thicker and far more extensive than 
they are at present ? 
Notwithstanding the absence of lofty moun¬ 
tain-chains in America, we are not wholly 
without the means of measuring the thickness 
of the ice-sheet, by comparing it, as in Europe, 
with some of our highest elevations. The 
slopes of the Alleghany range, wherever they 
have been examined, are glacier-worn to the 
very top, with the exception of a few points; 
5 a 
