172 
ELEMENTS OF GEOLOGY. 
rocks. I also learn from Dr. Torell that there are large 
areas in the outskirts, now no longer covered with perma¬ 
nent snow or glaciers, which exhibit on their surface un¬ 
mistakable signs of ancient ice-action, so that, vast as is the 
power now exerted by ice in Greenland, it must once have 
operated on a still grander scale. The land, though now 
very elevated, may perhaps have been formerly much higher. 
It is well known that the south coast of Greenland, from lati¬ 
tude 60° to about 70° N., has for the last four centuries been 
sinking at the rate of several feet in a century. By this 
means a surface of rock, well scored and polished by ice, is 
now slowly subsiding beneath the sea, and is becoming 
strewed over, as the icebergs melt, with impalpable mud 
and smoothed and scratched stones. It is not precisely 
known how far north this downward movement extends. 
Drift carried by Icebergs.^ —An account was given so long 
ago as the year 1822, by Scoresby, of icebergs seen by him 
in the Arctic seas drifting along in latitudes 69° and 70° N., 
which rose above the surface from 100 to 200 feet, and some 
of which measured a mile in circumference. Many of them 
were loaded with beds of earth and rock, of such thickness 
that the weight was conjectured to be from 50,000 to 100,000 
tons. A similar transportation of rocks is known to be in 
progress in the southern hemisphere, where boulders included 
in ice are far more frequent than in the north. One of these 
icebergs was encountered in 1839, in mid-ocean, in the ant¬ 
arctic regions, many hundred miles from any known land, 
sailing northward, with a large erratic block firmly frozen 
into it. Many of them, carefully measured by the officers of 
the French exploring expedition of the Astrolabe, were be¬ 
tween 100 and 225 feet high above.water, and from two to 
five miles in length. Captain d’Urville ascertained one of 
them which he saw floating in the Southern Ocean to be 13 
miles long and 100 feet high, with walls perfectly vertical. 
The submerged portions of such islands must, according to 
the weight of ice relatively to sea-water, be from six to eight 
times more considerable than the part which is visible, so 
that when they are once fairly set in motion, the mechanical 
force which they might exert against any obstacle standing 
in their way would be prodigious. 
We learn, therefore, from a study both of the arctic and 
antarctic regions, that a great extent of land may be entire¬ 
ly covered throughout the whole year by snow and ice, from 
the summits of the loftiest mountains to the sea-coast, and 
may yet send down angular erratics to the ocean. We may 
also conclude that such land will become in the course of 
