CONDITIONS OF CONTINENTAL ICE. 225 



ice, Sir Wyville Thomson's conclusion, that the sheet 

 cannot be more than 1400 feet in thickness, would 

 follow as a matter of course. 



But his supposition that, owing to internal heat 

 coming through the earth's crust, the bottom of the 

 Antarctic ice-sheet is kept at the temperature of 32°, 

 cannot be sustained. It is this fundamental error, as 

 I conceive it to be, which has led Sir Wyville astray, 

 and induced him to believe that the ice cannot be of 

 excessive thickness. 



" The normal temperature of the crust of the earth," 

 says Sir Wyville, "at any point when it is uninfluenced 

 by cyclical changes, is, at all events, above the freezing- 

 point, so that the temperature of the floor of the ice- 

 sheet would certainly have no tendency to fall below 

 that of the stream which was passing over it. . . . 

 In fact, ice at the temperature at which it is in contact 

 with the surface of the earth's crust within the 

 Antarctic regions, cannot support a column of itself 

 more than 1400 feet without melting." 



In the question under consideration we are directly 

 concerned with the temperature of the surface of the 

 earth's crust only, — the floor on which the ice-sheet 

 rests, — and not with the temperature below the sur- 

 face. It is perfectly true that at considerable depths 

 below the surface internal heat maintains a tempera- 

 ture above the freezing-point ; but it is not true that 

 it determines the heat of the surface. Underground 

 heat produces scarcely any sensible influence on the 

 temperature of the surface, which is determined almost 

 wholly by that of the air and other external agencies. 

 The temperature, in short, is determined from above, 

 and not from beneath. In warm countries, where the 

 temperature of the air is high, that of the surface is 

 high also. And so likewise in cold climates, the low 



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