ANTARCTIC ADVENTURE AND RESEARCH 



small degree controlled by the train of events in distant 

 Antarctica." 



Mawson has pointed out that soundings are espe- 

 cially valuable in connection with the possibility of 

 islands in Antarctic v^^aters. Where sea and land are 

 covered with ice it is very easy to miss an island, but 

 soundings should show where such land-forms are 

 probable. (I have already referred to the shallow 

 soundings near the site of Wilkes' doubtful landfalls.) 

 Sonic depth-finders, using electrical signals and the 

 time of return of their echoes, are especially suited for 

 such work. Moreover, the delineation of the sub- 

 merged continental shelf gives a real indication of 

 the boundary of the rock areas beneath the great con- 

 tinental ice cap, and this again can be ascertained with 

 some accuracy by careful soundings. 



The soundings in East Antarctica reveal some curi- 

 ous features. I have based the diagrams in Figure 22 

 on that invaluable map published in 1928 by the Ameri- 

 can Geographical Society. The shelf around Antarctica 

 seems to be submerged distinctly deeper than those 

 around most other continents. Off the Weddell Sea 

 the sharp angle betw^een the gentle continental slope 

 and the steep dip to the abyss lies between six hundred 

 and one thousand meters below the surface of the sea. 

 In the diagram the submarine contour for five hundred 

 meters is charted, so far as our data permit, for three 

 especially interesting regions. In general this contour 



1 See my discussion, "Climatic Relations Between Antarctica and 

 Australia." Problems of Polar Research (Amer. Geog. Soc, New 

 York, 1928). 



