SCOIT'S LAST EXPEDITION 
Consider only the simple case of an ocean current 
washing a natural ice barrier strctclicd across a strait and 
gradually eating its way through. How far-reaching 
will be tlic effect when the barrier is down! The whole 
history of the world might easily be changed by some 
such simple catastrophe. 
Sea Ice 
Possibly foremost among the difl'ercnt forms of ice to 
be studied was that of sea ice — being fast ice * formed 
in autumn on the surface of the sea by the action of the 
cold air above it. The process of freezing is a very 
interesting one to watcli in cold, calm weather. As the 
temperature falls the sea becomes covered with small 
scale-like plate crystals up to one inch across of a delicate 
fern-like structure. They generally float flat upon the 
surface, but many are imprisoned in an approximately 
vertical position. After the surface becomes covered, the 
ice tlicn grows in tlie ordinary way by accretion from 
below. In the initial stages, when the ice is only an inch 
in thickness, the felt-like mass on the surface has little 
rigidity, and even up to 3 inches thick moves freely up 
and down under the influence of a swell without losing 
its colicrence in any way. 
Sea ice is quite different in its properties from the 
ice formed on a pond or lake of fresh water, owing to the 
fact that some of the salt in solution in sea water is always 
imprisoned between the individual crystals in the sea 
ice. This imprisoned salt between the crystals does not 
* Icc iiol ill movoiucnt. 
