50 The Sea 
completely smashed their tiny craft. In June 1881, the Jean- 
nette was finally crushed and sunk, and the sick and weary 
crew hauled three boats and what little supplies they had left 
over the ice southward. Finally, upon reaching clear water, 
a storm arose, one of the boats broached to, and all its crew 
were lost. The remaining two boats were separated in the 
same storm and finally landed at different points in the wil- 
derness of the Lena River Delta. One crew reached safety, 
but De Long and those who were in his boat died of starva- 
tion before they could find aid. Sea ice has sent many another 
ship and crew to the bottom. It is no wonder, then, that the 
presence of ice is adequate cause for concern. 
WHERE ALL THE ICE COMES FROM 
The ice that one encounters at sea has been studied in some © 
detail, and a suitable classification of its different forms has 
been devised by Maurstad, a Norwegian oceanographer. For 
the purpose of primary classification we consider the origin 
of the ice; whether it is formed on land or in the sea. In cer- 
tain localities like Greenland and the Antarctic Continent 
snow is the main form of precipitation; and as a result the 
land is covered by a thick layer of compacted snow. As the 
years pass more and more snow is accumulated, forming ex- 
tensive glaciers. Such glaciers differ from ordinary mountain 
glaciers chiefly in size because they may cover an entire 
continent as in Antarctica. They may be several thousands of 
feet thick and cover everything except the highest mountain 
peaks. , 
To relieve the pressures generated by so large an accumu- 
lation of ice, a general movement of the ice toward its outer 
edges arises. The glacier tends to move toward the shores of 
