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THE OCEAN WORLD. 
of ico is one of tlie dangers of polar navigation. Captain Scoresby ^ 
given a very detailed description of the different kinds of ice met ^ 
in the Arctic Seas. The ice-fields of this writer form extensive 
of solid water, of which the eye cannot trace the limits, some of 
being thirty-five leagues in length and ten broad, with a thickness pl 
seven to eight fathoms ; but generally these ice-fields rise only four H 
six feet above the water, and reach from three to four fathoms bene 11 * 
the surface. Scoresby has seen these ice-fields forming in the 
sea. When the first crystals appear, the surface of the ocean is c °j 
enough to prevent snow from melting as it falls. On the approach * 
congelation the surface solidifies, and seems as if covered with ' 
small circles are formed, which press against each other, and are fin&w. 
soldered together until they form a vast field of ice, the thickness ? 
which increases from the lower surface. 
The water produced from melted ice is perfectly fresh — the result _ 
a well-known physical cause. When a saline solution like sea water 18 
congealed by cold, pure water alone passes into the solid state, ^ 
saline solution becomes more concentrated, increases in density, ao 1 - 
sinking to the bottom, remains liquid. Blocks of ice, therefore, in ^ 
Polar Seas, are always available for domestic use. There are, howe^f ' 
salt blocks of ice which are distinguished from fresh-water ice by tlu ’’ 8 
opaqueness and their dazzling white colour : this saltness is due to $ ' 
sea water retained in its interstices. Scoresby amused himself SO$m 
times by shaping lenses of ice, with which he is said to have set ^ 
to gunpowder, much to the astonishment of his crew. 
The ice-fields, which are formed in higher latitudes, are driven i0 ‘ 
wards the south by winds and currents, but sooner or later the act 1011 
of the waves breaks them up into fragments. The edges of ^ 
broken icebergs are thus often rising and continually changing : tlP’f 
asperities and protuberances are called hummocks by English n»' r 
gators; they give to the polar ice an odd, irregular appearaP^'j 
Hummocks form themselves of the stray, broken icebergs which coP * 8 
in contact with each other at their edges, and thus form vast rafts, 
pieces of which may exceed a hundred yards in length. 
When these icebergs arc separated by open spaces, through wb*^ I 
vessels can be navigated, the pack ice is said to be open. But it off 6 ' 11 
happens that mountains of ice occur partly submerged, where one e<ft n 
is retained under the principal mass, while the other is above 
