554 Reports & Proceedings — Geological Society of London. 



floating "glacier tongues" are a feature of such situations, often 

 extending 40 to 50 miles from the shore. 



Along other stretches of the coast less well placed for receiving 

 contributions from the interior of the Continent, the outflow is so 

 much less that the destructive influences at work on reaching the sea 

 easily maintain its boundaries at approximately the true coastline. 



As exceptions to this latter prevailing condition, however, there 

 are known already two notable localities where the general overflow 

 from the land maintains itself as an immensely thick floating 

 structure extending far out over the sea — a veritable oceanic ice- 

 cap. To this type of formation we apply Professor Nordenskj old's 

 term "shelf-ice". The formations referred to are the Great Ross 

 Barrier at the head of the Ross Sea and the Shackleton Shelf off 

 the coast of Queen Marj' Land. 



The former occupies what is really the head of the Ross Sea — 

 a somewhat triangular area. From apex to base it measures 

 500 miles, with a base-length of about 400 miles. This great raft 

 of ice presses forward to the open sea at the rate of a few hundred 

 yards per annum. The available figures, quoted by David and 

 Priestly, show that, at the present rate of advance, the ice now 

 appearing at the sea-face must have left the inner extremity of the 

 floating sheet at some time during the seventh century. A survey of 

 the ice-cliff forming the sea-face indicates by its changing height 

 that the Ross Barrier is of varying thickness. This has been 

 explained by the presence, in localities Avhere it is thickest, of the 

 remnants of the massive ice contribution received during its course 

 from certain of the large tributary glaciers. The ice from these 

 glaciers, in fact, constitutes a strong framework which stiffens and 

 contains the more crumbling structure derived from the consolidation 

 of the annual snowfall. 



To a great extent this must certainly be so ; but the influence of 

 a varying snowfall, and the effect of violent periodic winds — a 

 feature of the region — in sweeping the loose snow from certain 

 areas and depositing it in other favoured localities, must be reckoned 

 with. The snowfall is lighter on the eastern side than on the 

 west. Furthermore, the snow tends to accumulate on the western 

 side owing to the fact that the winds regularly blow from the 

 quarter south to east, and not from the west. 



In the case of the Shackleton Shelf, this is the more remarkable 

 because it maintains itself as a pontoon stretching into the open 

 sea, even across the drift of the prevailing ocean-current. 



The deluge of ice, after descending to the sea, presses northwards 

 as an integral whole, at first touching bottom at intervals, then 

 forcing its way past several islands, eventually reaching an extreme 

 distance of 180 miles from the land before it is mastered by the 

 swell and currents of the Southern Ocean. It is somewhat 

 ti'iangular in form, with the apex out to sea. The base against 

 the land, though not completely charted, extends in all probability 

 for a distance of about 200 miles. 



The main body of the shelf-ice advances rather slowly, but the 

 Denman Glacier, which contributes to it, has a much more rapid 



