Ice Al 
the continent, and its ice may extend for many miles out to 
sea, floating along the surface. Eventually, because of wave 
and tidal action, large blocks of ice are broken from the 
parent body and float away. This process, called calving, ‘is 
accompanied by loud reports and roars as the ice cracks. 
ICEBERGS WEIGHT OF ICE ICEBERGS 
CONTINENT 
Charles Darwin, the father of the Theory of Evolution, 
gathered his evidence for the theory on a scientific expedi- 
tion in the British ship Beagle. Once, upon sighting a glacier, 
he put off in a small boat to examine it more closely and 
almost met an untimely end when suddenly a large piece 
split off nearby with a loud crash and dangerous waves. 
Ice fragments broken from glaciers are called glacier ice, 
and many ordinary icebergs fall under this general heading. 
Because glacier ice is composed of compacted snow it is 
essentially free from salt and when melted supplies fresh 
water. Thirsty sailors of bygone days filled empty water casks 
with water obtained on icebergs. 
Ice formed in rivers may be swept into the ocean, and is 
called river ice. This kind of ice is not very dangerous or very 
important. Besides glacier ice and river ice, we have another 
kind of ice, formed in the sea itself. Thus we distinguish three 
kinds of ice according to origin: glacier ice, river ice, and 
sea ice. 
