ANTARCTIC EXPLORATION AND RESEARCH 263 



connection with anti-submarine warfare, I suggested^^ that a modifica- 

 tion of the same device might be employed in the determination of 

 the thickness of glacier ice. The difference in elasticity between ice 

 and rock should be sufficient to allow of the application of this method. 



Since that time the principle has been developed and perfected 

 in the sonic depth finder for sounding the ocean. It now remains only 

 to extend this further to deal with ice. No doubt there will be certain 

 inherent difificulties, on account of the rigidity of the ice and also 

 on account of the variability of entrapped air in glacier ice, but these 

 should not be insuperable. Other methods of attack that suggest 

 themselves are the employment either of the principle of electrical 

 permeability or of the differential specific gravity between the ice and 

 the rock floor. Instruments based on these principles are already 

 employed in the field as ore finders. 



When an instrument capable of such measurements has been per- 

 fected, it can also be employed to ascertain the thickness of the shelf - 

 ice formations and the depth of the underlying sea water. Then will 

 there be cleared up many of the outstanding problems of the Antarc- 

 tic, and, in addition, the study of glaciology as a whole will benefit 

 immensely. 



Other Desirable Studies Relating to the Ice Cap 



Other studies relative to the land ice of interest to the general 

 geographer may be mentioned. Determinations as to its rate of move- 

 ment are required. To assist in accurately gauging this for the mar- 

 gin of the ice sheet, very detailed and accurate charts of short stretches 

 of the ice-cliff face, each related to some fixed datum point, should 

 be made at intervals along the coast line and resurveyed by later 

 expeditions. 



Also, any information as to the alimentation of the ice cap and 

 its ablation will supply a great need in arriving at conclusions regard- 

 ing the factors operative in determining the present domed contour 

 of the inland ice sheet. Such information can be got only by journeys 

 over the ice cap. To obtain such data, and as an indispensable feature 

 of a meteorological program, stations should be established on the 

 inland ice plateau and continuously occupied for considerable periods. 



The Problem of Previous Glaciations 



Careful soundings taken on the continental shelf will serve a useful 

 purpose in defining submarine moraines and overdeepened rock-floored 

 valleys respectively deposited and carved out during the climax of the 



12 Douglas Mawson: A Discussion on the Antarctic Ice-Cap and Its Borders, Nov. 6, 1918, 

 Quarl. Journ. Geol. Soc. of London, Vol. 75, 1919, pp. i-vii; reference on p. vi. Though the method sug- 

 gested at that meeting for sounding the depth of the ice was verbally explained, the reference to such 

 invention was necessarily left vague in the printed proceedings. 



