556 Reports & Proceedings — Geological Society of London. 



For his own part, he would like to ask at once whether the 

 lecturer had formed any opinion as to the origin of the evidently 

 bold land-features that were buried under the ice — could they have 

 been carved out by the ice itself, or were they the relics of a time 

 when the land was ice-free ? 



In the discussion which followed, Professor P. F. Kendall, Sir 

 Henry Howorth, Dr. J. W. Evans, Mr. G. W. Young, Mr. A. E. 

 Kitson, and Dr. A. Strahan took part. 



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 snowdrift; 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, however, 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 a,t the top by snow swept off thg 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 thej^ 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 

 over-ridden 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 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 indicating 



