258 POLAR PROBLEMS 



discovery of the island. The very complete method of ascertaining 

 the depths of the sea now supplied by echo sounding instruments 

 such as the sonic depth finder will furnish future expeditions with a 

 powerful aid in their search for such minute specks in the wide oceans. 



Delineation of the Antarctic Continental Shelf 



This leads on to the consideration of the invaluable work that 

 only sounding can accomplish, namely the delineation of the limit of 

 the continental shelf of the Antarctic crustal bulge. Whether the 

 rocky basement under the polar ice dome is continuously above sea 

 level over almost its entire area or whether it exists merely as a number 

 of isolated, island-like units, we are certain, from the nature of the 

 sediments composing those portions already examined and the story 

 unfolded in the strata, that we are dealing with a convexity of the 

 earth's crust of continental proportions, which, in the vicissitudes of 

 time, has been at some periods above and at others below the sea. 

 Such soundings as are available thus far further support this conten- 

 tion, for they indicate a general shoaling of the oceans in proximity to 

 the present known and conjectured coast line. Thus it is that we are 

 satisfied that there does exist an Antarctic continental bulge of the 

 crust. Hence, more basic than the question as to how much at this 

 epoch lies above sea level — the actual charting of the coast line — ^is 

 the delineation of the continental shelf, a geographic feature of fun- 

 damental importance. 



In the conduct of all these operations at sea the distribution and 

 movements of the pack ice should be carefully noted. With the ac- 

 cumulation of such information in time, communication with the 

 continent will eventually be much simplified. 



Form of Antarctic Land Relief under the Ice and Structural 

 Contrast between West and East Antarctica 



From what has already been said of the possible disposition of the 

 rock basement of the icy continent, it will be appreciated that it 

 is of the greatest possible interest and value to ascertain the true 

 nature of such foundation. Is it one continuous rocky land above 

 sea level, merely veneered by ice? Is it a number of isolated epicon- 

 tinental islands which have been overwhelmed and united by a flood 

 of glacier ice and between which the sea would flow were the ice to 

 melt? In the latter case, are the inter-island channels choked to the 

 very bottom with glacier ice so that the ice rides on a rock bottom 

 beloW' sea level? Or does the sea water, in some at least of these, 

 maintain a through-flow deep down under the capping ice so that the 

 inter-island ice caps, though very thick and of land origin, are yet 

 afloat on sea water? 



