436 POLAR ICE. 
their mutual collision. This generally happens early in the 
month of June ; and a few weeks are commonly sufficient to 
disperse and dissolve the floating ice. The sea is at last 
open, for a short and dubious interval, to the pursuits of the 
adventurous mariner. 
While icebergs are thus the slow growth of ages, the fields 
or shoals of saline ice are annually formed and destroyed. 
The ice generated from melted snow is hard, pellucid, and 
often swells to enormous height and dimensions. But the 
concretion of salt water wants solidity, clearness, and strength, 
and never rises to any considerable thickness. It seldom 
floats during more than part of the year ; though, in some 
cold season, the scattered fragments may be surprised by the 
early frost, and preserved till the following summer. 
The whale fishers enumerate several varieties of the salt- 
water ice. A very wide expanse of it they call a field, and 
one of smaller dimensions ^floe. When a field is dissevered 
by a subaqueous or grown swell, it breaks into numerous 
pieces, seldom exceeding forty or fifty yards in diameter, which, 
taken collectively, are termed a pack. This pack again, 
when of a broad shape, is called a patch ; and when much 
elongated, a stream. The packs of ice are crowded and heap- 
ed together by violent winds ; but they again separate and 
spread asunder in calm weather. If a ship can sail freely 
through the floating pieces of ice, it is called drift-ice ; and 
the ice itself is said to loose or open. When, from the effect 
of abrasion, the larger blocks of ice are crumbled into minute 
fragments, this collection is called hrash-ice. A portion of ice 
rising above the common level is termed a hummock, being 
produced by the squeezing of one piece over another. These 
hummocks or protuberances break the uniform surface of the 
ice, and give it a most diversified and fantastic appearance. 
They are numerous in the heavy packs, and along the edges 
of ice-fields, reaching to the height of thirty feet. The term 
sludge is applied by the sailors to the soft and incoherent crys- 
tals which the frost forms when it first attacks the ruffled sur- 
face of the ocean. As these increase, they have some eflfect, 
like oil, to still the secondary waves ; but they are prevented 
from coalescing into a continuous sheet, by the agitation 
which still prevails ; and they form small discs, rounded by 
continual attrition, and scarcely three inches in diameter, call- 
ed pan-cakes. Sometimes these again unite into circular pie- 
ces perhaps a foot thick and many yards in circumference. 
The fields and other collections of floating ice are often 
