THE ROSS BARRIER 133 



the snow roofs of the tunnels, approximately two-thirds of the volume of this berg 

 was below water, one-third above. Obviously, therefore, the berg from the water- 

 line to its base must have been composed of material far less dense than typical 

 glacier ice. 



Some further light on the intimate structure of the Barrier is thrown by the 

 section obtained by Messrs. Macintosh, Day, Joyce, and Marston at the site of 

 Scott's Depot " A." Having re-located this old depot and re-aligned it, the party 

 dug down in order to find what depth of snow had been deposited on the depot 

 during the 6^ years that had elapsed since its erection. They came upon the 

 original snow surface on which the depot was formed at a depth of 8 feet 2 inches 

 (2'5 metres). In order to determine the density of this snow they melted down 

 a considerable quantity of it, and measured the volume of the thaw-water resulting. 

 This showed that the annual accumulation of snow on this part of the Ross Barrier 

 is about 15 inches (380 millimetres) of dense snow, almost neve, equal to about 7\ 

 inches (190 millimetres) of rain. This depot is in the latitude of Minna Bluff" about 

 78° 40' S. 



Before proceeding to consider the probable origin of the Barrier, it is necessary 

 to glance at its past history. Throughout almost all the Antarctic regions yet 

 explored, there is abundant evidence of a recent and prolonged shrinkage of the 

 ice masses and neve fields. The Ross Ice Barrier is no exception to this rule. 

 Captain Scott's survey on the Discovery shows the position of the Barrier edge as 

 he found it in 1902, and on his chart he gives the position of the Barrier edge as 

 originally outlined by Ross as the result of the explorations conducted on the Erehus 

 and Terror in 1841-2. These two outlines are shown on the map at the beginning 

 of this chapter (Fig. 46), and prove that the face of the Ross Barrier has 

 retreated southwards no less than about 45 miles from 1842 to 1902 at its eastern 

 end. The mean amount of retreat during the above sixty years aggregates perhaps 

 about 20 miles along the whole front of the Barrier. So much for horizontal 

 shrinkage. 



The following facts refer to vertical shrinkage. The Discovery Expedition 

 proved, from the evidence of stranded moraines 800 feet above sea-level, near Cape 

 Crozier, that the surface of the Barrier at its western end has recently decreased 

 in altitude by about 700 feet. Our observations at Cajae Royds, upon the western 

 slopes of Mount Erebus, showed that large lateral moraines, crowded with blocks 

 of granite and other crystalline rocks, transported from the mainland to the south, 

 were continuous for considerable distances at altitudes of at least 1000 feet above 

 sea-level. It may therefore be concluded that, in late geological time, in the 

 neighbourhood of Ross Island and McMurdo Sound, the Barrier has shrunk, 

 vertically, by no less an amount than about 900 feet. At the time of maximum 

 glaciation, there is also evidence that the outlet glaciers from the inland ice, such 



as the Ferrar Glacier — which formerly fed the Barrier — and the Beardmore Glacier 



s 



