Reports & Proceedings — Geological Society of London. 379 



at places where the pyrites is absent, to exert only a slight hardening 

 eifect on the shale. In JSTorth Wales pisolitic iron-ore is known to 

 occur in several places at the horizon of ISfemagraptus gracilis. From 

 the mode of origin assigned above to the pyrites it follows that the 

 mineral is of Bala age, since it was formed before the intrusion, 

 itself of Bala age, had cooled. The pisolitic ironstone must have 

 been in existence in Bala times, and this supports the idea that the 

 ironstone is a bedded contemporaneous deposit. 



3. June 19, 1918. — G. W. Lamplugh, F.R.S., President, in the 



Chair. 



A lecture on "Some Features of the Antarctic Ice-cap" was 

 delivered by Major Sir Douglas Mawson, D.Sc, F.G.S. lu the 

 course of liis lecture, Avhich was illustrated by a large series of 

 lantern-slides, Sir Douglas Mawson said that the ice mantle of the 

 south formally involved sub-Antarctic Islands, Patagonia, Southern 

 ISTew Zealand, and the higher mountains of Tasmania and of the 

 neighbouring portions of Australia, but it retreated to its present 

 confines — a circum-Polar Continent — at a time apparently concurrent 

 with the disappearance of the extensive Pleistocene ice-sheets of the 

 ITorthern Hemisphere. 



The existence of a great land mass situated on the face of the 

 globe just where the sun's rays fall most obliquely has the effect of 

 intensifying the Polar conditions. This result is achieved by reason 

 of the elimination of the ameliorating influence of the ocean and as 

 a result of the acceleration of the circulation of the moist atmosphere 

 from the surrounding sea to the land, owing to the wide difference in 

 temperature pertaining over the one and the other. Thus the presence 

 of extensive land at the Pole, in contradistinction to ocean, results, 

 under present cosmical conditions, in increased refrigeration, and 

 consequently in greater extension of the Polar ice-cap. This in 

 turn reflects on the average temperature of other regions of the 

 globe, for an ice surface absorbs but a relatively small proportion of 

 the sun's radiant heat. The existence of the Antarctic Continent 

 must therefore have some bearing on the climate of the Northern 

 Hemisphere and be reckoned with as a factor contributing to the 

 refrigeration thereof. 



The lecturer laid great stress upon the work of the outflowing 

 surface winds in developing the domed form of the ice-cap. Tliese 

 winds, owing to their persistence and violence, strip the surface of 

 much of the newly fallen snow, and otherwise ablate the marginal 

 zone, thereby considerably reducing the volume of ice that would 

 otherwise reach the sea by glacial flow. Crevasses in the ice-cap 

 observed far inland at "The Nodules" indicate that the ice of the 

 hinterland is in motion. 



In the seaward termination of the ice-sheet at Cape Denison, a 

 basal zone, attaining as much as 50 feet in thickness, bearing 

 englacial drift, is a well-marked feature. 



The shelf-ice formations, including the Uoss Barrier and the 

 Shackleton Shelf were specially referred to : mention was made 



