VI PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [vol. llXV, 



The President supplemented the questions by asking whether 

 the lecturer could express any opinion as to (1) whether, if the 

 great table of shelf-ice continued to grow by accretion, it would 

 eventually become merged into the main ice-sheet; (2) how much 

 of the remarkable seaward extension of the huge ice-tongues was 

 due to forward flow, and how much to growth-in-place by snow- 

 drift ; and (3) what happened when an advancing ice-front over- 

 rode a rocky island well separated from the mainland ? 



Sir Douglas Mawson, in replying, said that he would take the 

 President's questions first. As to the origin of the land-features — 

 he did not want to commit himself on this difficult point at 

 present, but was inclined to think that the physiography, so far as 

 one sees it, might all have been produced by ice if no other agency 

 had been available; but it was most likely that the ice started upon 

 a surface already sculptured to some extent. He felt sure, how- 

 ever, that the Antarctic ice could and did cut deep channels, not 

 only above but also below sea-level. Where the ice was thickest 

 it burrowed fastest, and tended, therefore, always to accentuate 

 any existing hollow. 



As to the growth of the shelf-ice — although there was a large 

 accretion at the top by snow swept off the land, there was also 

 probably much dissolution below by the action of the sea-water ; 

 so that the net increase of the mass was not so rapid as appeared 

 at first sight. 



That there was forward movement of the ice-tongues was proved 

 by the way in which they ploughed through the fixed shelf- 

 ice and by their upward bulging where they struck bottom ; but 

 most of their movement was over sea-water, and therefore easy and 

 almost frictionless. 



Where the ice-sheet abutted upon an island, it depended upon 

 the relative proportions of ice and land whether the land was 

 entirely overridden or the ice-flow split and diverted. Examples 

 of both phenomena were observed. 



As to the rate of wastage by melting, the great ice-plateau by 

 causing an outflow of cold air kept the temperature at the ice- 

 margin too low for much melting. What melting there was 

 depended mainly upon the lie of the ice-slope in relation to the sun. 

 There was also a good deal of wastage, both of snow and of ice, 

 by direct evaporation, depending upon the season. But the main 

 wastage was due to the descending winds, which fiercely and almost 

 continuously swept the outer slopes. 



With regard to the thickness of the ice. there was perhaps no 

 direct evidence, but a great amount of indirect evidence all indi- 

 cating that it must in places be very thick — probably several 

 thousands of feet. Boring had been thought of, but would be- 

 impracticable because of the movement of the mass at differential 

 rates, so that the borehole could not be kept plumb or open. There- 

 were some new instruments, however, invented for marine pur- 

 poses, which might eventually yield positive information. 



The banding of the ice was not due to dirt or dust, which was 



