18 



MARION EXPEDITION TO DAVIS STRAIT AND BAFFIN BAY 



A Crack in Pack Ice 



Figure 7. — Winds and currents often open cracks in the pacli ice such as shown 

 here. A crack differs from a lead in respect to its width, a crack not being of 

 sufficient width to permit navigation. A crack i.s the antithesis of a pressure 

 ridge. (Photograph by H. G. I'onting in the Scientific Reports of the British 

 Antarctic Expedition.) 



A LEAD 



Figure 8. — A lead in pack ice. Sliips in tlie pack are conned by the ice navigator 

 from a station aloft. This is tlie best vantage point to study the system of leads 

 and the location of open water. (Photograph by II. (i. I'onling in the Scientific 

 Reports of the British Antarctic Expedition.) 



I 



