134 GLACIOLOGY 



— which still feeds it — have shrunk vertically, the former by 4000 feet, the latter 

 by at least 2000 feet. The shrinkage definitely proved at Mount Erebus may be 

 taken to apply, more or less, to the whole of the Barrier surface. At the time, 

 then, of maximum glaciation, if the sea-level was in its present position, the height 

 of the Barrier at Cape Royds would have been 1000 feet above sea-level, and at 

 Cape Crozier fully 800 feet. The avei'age depth of the soundings along the present 

 face of the Barrier from Cape Crozier eastwards is about .350 fathoms, or 2100 

 feet — i.e. in water of this depth, one-third of the Barrier material would have been 

 above the water and two-thirds submerged. If it be assumed that the Barrier 

 during maximum glaciation averaged 500 feet above sea-level instead of about 

 100 feet as at present, then in water of an average depth of about 2000 feet, one- 

 fifth of the ice would have been above sea-level and four-fifths would have been 

 submerged, on the assumption that the density of this ice as compared with the 

 density of the adjacent sea water was not less than 8 to 1 . Thus it may be concluded 

 that, by far the greater part of the Barrier during the maximum glaciation being ice, 

 this Barrier ice must have rested and pressed heavily on the floor of Boss Sea. 

 This would still be the case even if it be assumed that sea-level, during the maximum 

 glaciation, was 200 feet higher than it is now, and even if the maximum depth as 

 yet sounded along the Barrier be taken instead of the mean depth. The maximum 

 depth recorded is 460 fathoms. If, therefore, during the maximum glaciation and 

 submergence the Barrier surface at this deepest sounding to the east of Mount 

 Erebus were 800 feet above sea-level, as much as a little over a quarter of the 

 Barrier mass would be above sea-level, an amount quite sufiicient to keep the 

 Barrier resting on the bottom, even in this deepest part. 



In considering now the origin of the Barrier, two reasonable alternatives suggest 

 themselves. First, the hypothesis put forward by Captain Scott — that the present 

 Barrier is a direct descendant of the old Barrier formed during maximum glaciation, 

 and that when, as the result of diminishing snow supplies, the old Barrier shrunk in 

 thickness as it retreated Polewards, the weight of ice was no longer sufficient to 

 keep the Barrier on the bottom of Ross Sea, and consequently the Barrier floated up 

 ofl" the sea bottom into its present position. Here it is still nourished by the smaller, 

 but stQl active, glaciers of to-day. Scott, of course, would concede that drift snow 

 contributes to even up its surface, but apparently does not regard this snow as an 

 important contributing factor. The other alternative, to which we Incline, is that 

 there may not necessarily be any of the ice or snow in the present Barrier which 

 belonged originally to the old Barrier during the maximum glaciation. The material 

 of the Barrier at its sides is undoubtedly glacier ice. These ice-streams, when they 

 reach the south-western shores of Boss Sea, fan out, the fans coalescing at their 

 margins. Had there never been a maximum glaciation, each individual glacier 

 might have formed a long ice-jetty projecting into the upper end of Ross Sea now 

 occupied by the Barrier, much in the same way as do the present glaciers of 



