290 CAINOZOIC PAL^OGEOGRAPHY 



is of great importance. If it can be shown that the whole of the western side of 

 Ross Island has been raised, since the time of maximum glaciation, to a height of fully 

 600 feet, the old moraines of the Ross Barrier at 850 feet above the present level of 

 the ice vertically, may imjaly a decrease in the former altitude of the Ross Barrier 

 of 250 feet as compared with 850 feet. But for reasons already adduced in the 

 description of the raised marine muds, it is considered now to be almost certain 

 that the bulk of the Ross Island upraised marine muds owe their present position 

 to upthrust by the tongue of the Ross Barrier formerly occupying McMurdo Sound. 

 Moreover, evidences of deglaciation are so widespread in this region of the Antarctic, 

 extending as they do from 85° S. lat. to at least as far north as Mount Larsen in 

 75° S. lat., that it cannot all be explained away by a recent considerable elevation 

 of the land. It may be safely assumed that the minimum amount of deglaciation 

 from 85° S. to near Mount Nansen amounts to approximately the order of about 

 1000 feet in the case of large ice masses like the Ross Ice Barrier, and to from 

 2000 to 3000 feet in the case of the ice of the outlet glaciers. Fig. 46 of 

 Chapter VI. shows the probable approximate limit of the old Ross Barrier during 

 the maximum glaciation. 



As already stated, the evidence in the American Sector of the Antarctic shows 

 a recent deglaciation amounting to from 600 to 700 feet (18.3-213 metres) near 

 Graham Land and Danco Land, and as much as nearly 1000 feet (305 metres in King 

 Oscar Land). At Gaussberg the decrease in level of the inland ice in Recent 

 Geological time amounts to nearly 1150 feet (350 metres). 



It may be concluded, therefore, that it may be assumed at present that the 

 average amount of deglaciation in recent times, in such parts of the Ross region 

 as have recently been explored, amounts to approximately from 300 to 320 metres 

 (984-1050 feet). 



It will be a matter of great interest to decide whether or not the deglaciation has 

 been differential in different localities. Much more extended observations will be 

 needed in order to throw light on this question. 



As regards the interesting question as to the maximum thickness of glacier ice 

 during an Ice Age, we think that its maximum thickness was attained at the outlet 

 glaciers either at their heads, just west of the Antarctic Horst, or in their lower 

 portions near their junction with Ross Sea. This maximum thickness of ice at the 

 climax of an Ice Age was probably of the order of from 4000 tojSOOO feet (1219-1524 

 metres) at the outlet glaciers, and about 3000 feet to 3500 feet (914-1066 metres) 

 in the case of the Ross Barrier along the latitude of Ross Island. Information is as 

 yet lacking as to the amount of deglaciation of the inland ice since the time of the 

 latest ice flood. 



