POLAR ICE-CAPS AND SEA LEVELS. 331 



placed upon the top of these islands. I took the 

 actual proportion of the area of land to water, 

 roughly estimated, as being one-third land and 

 two-thirds water. To bring my result into com- 

 parison with the others quoted, you must therefore 

 treble it, because I took only one-third area as 

 covered with ice. Three times 380 =1140, which is 

 my number on a certain supposition ; while Heath's 

 is 650 on a supposition not quite the same as mine. 

 Pratt's estimates is still greater something like 

 2,000 feet. 



Now, if I could say anything to throw light upon 

 the real question of extensions of ice in the southern 

 or northern polar regions, and the effect of such 

 extensions upon the sea level and upon the climate 

 in past times, I should feel my attempt was cer- 

 tainly not insignificant. But I cannot even look 

 upon such an attempt ; I can merely point out cer- 

 tain fallacies and set certain limits to former sup- 

 positions. We cannot have an ice-cap on the 

 Antarctic continent 12 \ miles thick, as Mr. Croll 

 has calculated. I can bring substantial evidence 

 against this. But Mr. Croll's argument does not 



