630 president's addkess. 



into the ocean set up a huge wave of disphicement which would 

 sweep to its furthest limits. Happily, however, for the stability 

 of the eartli, there is a property of ice which renders this impos- 

 aible. If we take a piece of ice and submit it to pressure it 

 becomes plastic and moulds itself exactly to the shape of the 

 vessel in which it is contained, and if the pressure is sufficiently 

 great the ice becomes liquefied. When ice is piled on ice until a 

 sufficient pressure is attained, the bottom ice spreads out like so 

 much pitch, and even the pressure of a very moderate height is 

 ample to produce this effect on unrestrained ice. Lord Kelvin 

 has shown that, under the conditions ruling in the great south 

 polar continent, it is improbable that ice can be so restrained as to 

 attain a greater thickness than 2,000 or 3,000 feet. This when 

 melted is equivalent to a depth of 1,600 to 2,400 feet of water. 

 Free or unrestrained ice, whether resting on land or floating on 

 water cannot permanently retain any given thickness; owing to 

 its plasticity it will slowly but surely spread out until stopped 

 by barriers or melted. It is to this plasticit}'^ that are due the 

 enormous ice cliffs so graphically illustrated in the account of the 

 recent National Antarctic Expedition,* for the great ice mass 

 merely flows under the pressure of its own weight until it reaches 

 the sea where it floats, while portions are broken off and drift 

 away as icebergs. The ice barrier is, in fact, the continually 

 renewed face of the ice mass which is ceaselessly moving 

 outwards in obedience to the pressure of the constant accumula- 

 tion behind. 



It iij quite possible that there may at various periods in 

 geological time have been considerable fluctuations in the quantity 

 of ice accumulated at the poles, and it will be interesting to 

 consider very briefly what would be the effect on the ocean level 

 of the withdrawal of definite quantities of water to be stored at 

 the poles as ice, or conversely what would be the result of the 

 addition to the sea of the masses of water set free by the melting 

 of given heights of polar ice. 



The Voyage of the Discovery: Capt. R. F. Scott, 1905. 



