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of floating ice, which, as ah-eady mentioned, may be slowly growing 

 through the freezing of fresh water derived from melting of the upper 

 side. In the winter, the ice grows more rapidly, and diatoms are ab- 

 sent owing to the lack of sunlight. Thus yellow strata of frozen 

 diatoms mark the interval between two winter freezings and may be an 

 index to the age of the floe. 



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