CONDITIONS OF CONTINENTAL ICE. 229 



mined by the thickness of the sheet. It was shown 

 that, if 1400 feet be the thickness of the sheet, 700 

 foot-pounds per pound of the sheet is the greatest 

 amount of work that gravity can perform. It follows 

 therefore that, supposing the whole of the work is 

 employed in heating the ice by compression and fric- 

 tion, the heat thus generated would amount to only 

 - 9 of a thermal unit per pound of ice. It must be 

 obvious that, in the case of a flat and tolerably uniform 

 sheet like the Antarctic, in which the pressure must 

 of course be pretty evenly distributed, little or no 

 melting can take place from this cause, as it requires 

 not 0*9 of a thermal unit, but 142 thermal units, to 

 melt a pound of ice already at the melting-point. 

 The total work of 158 pounds of ice would need to be 

 concentrated upon one pound in order to melt it. But 

 such an unequal distribution of force in a sheet so 

 uniform is at least extremely improbable. The tabular 

 form of the southern icebergs, with their stratification 

 parallel to their upper surface, shows the flat character 

 of the ground on which they have been formed. This 

 circumstance appears to have particularly struck Sir 

 Wyville Thomson, as well as all who have visited the 

 Antarctic regions. "The stratification," says Sir 

 Wyville, " in all the icebergs which we saw, was, I 

 believe, originally horizontal and conformable, or very 

 nearly so. I never saw a single instance of deviation 

 from the horizontal and symmetrical stratification 

 which could in any way be referred to original 



structure As I have already said," he 



continues, " there was not, so far as we could see, in 

 any iceberg, the slightest trace of structure stamped 

 upon the ice in passing down a valley, or during its 

 progress over roches montonntfes, or any other form 

 of uneven land ; the only structure, except the parallel 



