THE ICE. 251 



estimate. The greatest heights observed of perfectly 

 new bergs with horizontal upper surfaces and vertical 

 flanks do not exceed 200 feet above the water ; 250 feet 

 has, in fact, never been observed with any reliable degree 

 of certainty. On the usual basis of calculation, this mass 

 visible above water would correspond to a nine-fold 

 thickness below, i.e., to 1,800 feet under the surface of 

 the sea, and from this it would result that the total 

 thickness of the iceberg would be about 2,000 feet. But 

 even this calculation is an overestimate, because the 

 fact is ignored that the mass above the water is speci- 

 fically lighter than that below, and is therefore borne by 

 a less volume of the denser mass. The submerged part 

 may possibly be no more than six-sevenths of the total 

 height, which would give to a freshly-formed berg of an 

 average maximum height above water a total thickness of 

 1,400 to 1,500 feet. If it is further taken into considera- 

 tion that it is just the submerged part which generally 

 is the chief carrier of the rock and rubble brought away 

 imbedded in the ice from the birthplace of the glacier, 

 one might under circumstances assume a thickness even 

 less than that just named. The theoretical calculation 

 of Sir Wyville Thomson leads to the conclusion that 

 1,400 feet is the maximum thickness that the inland ice 

 can attain, for a greater superincumbent volume would 

 by its pressure liquefy the lowest stratum ; this, however, 

 assumes that the temperature of the lower surface was 

 at 32 F., which according to Drygalski's observations in 

 Greenland need not necessarily be the case. 



If Sir W. Thomson's conjecture is correct, then it 

 might further be expected that the Antarctic inland ice 

 is melting underneath — at least slowly — the whole year 

 round- precisely the same as Nansen has shown to be 

 happening with the ice of Greenland. If this be not 

 so, then icebergs would be the only means for removing 



the Antarctic inland ice — a mode which brings the 



17 



