AMELIORATIONS OF PRESENT ARCTIC CLIMATES 393 



some large part of it, when put in motion by winds or tides or both 

 combined. He gives the thickness of the old floes traversed by the 

 "leads" as ranging from less than 20 to more than 100 feet. On the 

 important point of the relative proportion of the ice-field exposed 

 by the lanes to rapid freezing, he writes : 



At least nine-tenths of the surface of the Polar Sea between Cape Colum- 

 bus and the Pole is made up of these floes. The other one-tenth, the ice be- 

 tween the floes, is formed by the direct freezing of the water each autumn and 

 winter. This ice never exceeds eight or ten feet in thickness.^ 



It thus appears that in the course of the cold season of each year 

 about 10 per cent of the surface of the Polar Basin may freeze in the 

 way subsequently described, or in the course of ten years the whole 

 surface or its equivalent may so freeze. 



Peary's narrative shows that even in March and April these 

 leads form suddenly, and that the temperature of the air at the time 

 is often 40° below zero; it shows further that high winds are then 

 frequent and strong. The offsets of the trails recently made by 

 the explorers indicated that differential movements of the ice- 

 mantle were taking place and were considerable in amount. 



Putting the significant items together, it appears that the water- 

 lanes formed in the old ice-floes must be bordered by ice-walls on 

 either side whose vertical faces range as high as 100 feet. The larger 

 part of these vertical faces are below the surface of the water and 

 form bounding walls to the water that arises into the chasm as it 

 opens. Thus the water that fills the lane stands above the common 

 mass below as a raised block or prism. It is the surface of this 

 raised prism of water that is exposed suddenly to very low tempera- 

 ture and often to wind action at the same time. The surface must 

 therefore freeze very promptly, whether it is still or is agitated. 

 More or less agitation is apparently the more common case. If 

 agitated by wind, the surface water should form a sludge of mixed 

 forming ice and residual water. This residual water should be 

 charged with the salts forced out of the frozen portion of the water. 

 This is added to the previous content of salt, giving rise to a brine. 

 The sludge thus formed when the wind is blowing will be driven 

 edgewise over the surface until it encounters the vertical ice-face 



' Op. cit., pp. 195-96. 



