Reports & Proceedings — Geological Society of London. 553 



are of merely local value, and the succession is really continuous 

 througliout. 



5. On the Age of the Waikonaiti Sandstone, Otago. By 

 J. Allan Thomson. Trans. New Zealand Inst., vol. 1, pp. 196-7, 

 1918. 



MOST geologists have correlated this sandstone vpith the Otatara 

 limestone, but the discovery in it of Pachymagas abnormis 

 leads the author to conclude that the sandstone belongs to the Upper 

 Oamaruian, possibly to the Awamoan. 



I. — Geological Society of London. 

 November 6, 1918.— G. W. Lamplugh, F.R.S., President, in the Chair. 



The President read a communication that he had received from 

 Professor Charles Barrels, D.Sc, F.M.G.S., in reply to congratulations 

 sent on the occasion of the evacuation of Lille by the enemy forces. 



A discussion on the Antarctic Ice-cap and its Borders was 

 introduced by Sir Douglas Mawson, D.Sc, BE., F.G.S. 



Sir Douglas Mawson said that at the last meeting of the Societj- ^ 

 the subject of the Antarctic Ice-cap was reviewed in its broader 

 aspects, 'chiefly with the view of promoting a discussion among 

 those specially interested in Glaciology. The present occasion had 

 been reserved for the discussion, and he proposed to show certain 

 lantern-slides in order to bring the salient features freshly to mind. 



Though much of the foundation of the Antarctic Ice-cap is 

 certainly elevated land, it is quite possible that elsewhere the dome 

 rests upon a floor actually below sea-level. In any case it is most 

 probable that the smooth ice-surface masks a very irregular rock- 

 basement. The thickness of the ice may, therefore, be expected to 

 be extremely variable, no doubt reaching a maximum of several 

 thousands of feet. 



An ice-formation of such magnitude introduces questions relating 

 to the flow of its substance and the abrasion of its foundations which 

 do not enter into the physics of ice-masses of smaller dimensions. 

 Here the static pressure on the lower zones of the ice may reach 

 1 ton per square inch. At the same time, the temperature may 

 be so increased by ground heat as to be much higher than that 

 prevailing above. As a consequence, when the ice-formation is 

 very thick, a more plastic base must be admitted. 



The outflow of the inland ice is principally deflected at the coastal 

 margin into depressed areas outlining the heads of gulfs and bays. 

 In such localities the rate of movement and the volume of ice 

 entering the sea are both great. So great indeed, that extensive 



^ See Eeports and Proceedings Geol, Sec, June 19, 1918, Geol. Mag,, 

 August, 1918, pp. 379-80. 



