E. H. L. Schwarz — The Thickness of the Ice-Cap. 121 



thicknesses of 120,000 feet, yet see no reason why there could not 

 have been ice-sheets 5,000 feet thick. The publication of Captain 

 Scott's narrative of the voyage of the " Discovery " has given us 

 certain definite data from the Antarctic which enable the case for the 

 1,600 feet maximum to be put with more confidence, and I will 

 endeavour in the present paper to state the main lines of the 

 argument. The question is of importance not only to us in South 

 Africa with our two Palseozoic ice-ages, but to all geologists, as it 

 affects the problem of the earth's equilibrium. To give a recent 

 example, Professor Penck, in describing the Bodensee, discusses 

 whether the weight of ice pouring down from the Alps in a sheet 

 3,600 feet thick may not have had some effect in producing a 

 sinking in the earth's crust.^ 



To begin with, it is necessary to enquire into the thickness of the 

 ■ice-sheet at the present day, and in no case where there has been 

 direct measurement has the ice been found to exist in sheets 

 surpassing the 1,600 feet limit. The estimates of the thickness of the 

 Greenland ice-cap rest on assumptions which it is impossible to prove 

 or disprove, but if they are examined closely they will be found to be 

 as favourable to the lesser limit as to the greater one of 6,000 feet. 

 Dr. Nansen's argument is that the coastline of Greenland is very 

 like that of Scandinavia, and therefore it is permissible to assume 

 that the internal relief of the island continent is the same as that of 

 Norway and Sweden ; if the latter were covered with an ice-sheet 

 up to the tops of the mountains the valleys would be filled with ice 

 to depths of 6,000 to 7,000 feet; consequently, in Greenland, 

 allowing for the land surface being somewhat higher than in 

 Scandinavia, the valleys would have accumulations of ice 5,000 to 

 6,000 feet thick. As confirmatory evidence Dr. Nansen quotes 

 instances of the enormous erosion which has gone on along the 

 coast of Greenland, which he states was produced by glaciers 

 excavating their valleys while filled with ice and giving at the foot 

 pressures of not less than 160 atmospheres.- 



Von Drygalski, as the result of two expeditions to Greenland, has 

 given elaborate measurements of the glaciers that now end in the 

 sea, and concludes that an iceberg rises higher than the glacier 

 front from which it has calved only when it turns over on its side ; ^ 

 as the glacier front, where it is floating, rarely rises to 300 feet, 

 icebergs of more than 300 feet high must be ones that have turned 

 over, and are consequently of no use in measuring the height of the 

 original ice -sheet from which they have issued. If we take 

 Steenstrup's figures for the proportion of the parts of an iceberg 

 above and below water, namely, 1 : 7-4 to 1 : 8-2,* a height of 

 300 feet would make an iceberg have a base over 2,000 feet deep. 

 Von Drygalski, however, found that soundings off the edge of 



^ Vortrage d. Vereius z. Verbr. Naturwiss. Keunt., xlii (Vienna, 1902), Heft 6, 

 p. 11. 



2 " The First Crossing of Greenland," Appendix, p. 472 ; London, 1890. 



3 "Gronland Expedition," p. 387; Berlin, 1897. 



* " Meddeleser om Gronland," p. 97 ; Copenhagen, 1879. 



