144 GLACIOI.OGY 



shrunk vertically by about 700 feet, near Cape Crozier, since the maximum glaciation. 

 At this time the Ross Piedmont was obviously aground, but, with diminished snow- 

 fall on the firnfelds of the feeding glaciers, a time must have come when the Ross 

 Piedmont floated off the bottom and its base commenced to thaw. At the rate of 

 thaw of a yard (-914 metre) a year it would have taken the Barrier only about 400 

 years to have floated vertically through the amount of about 200 fathoms, which is 

 near the average amount. 



To this would have to be added the time needed for the lowering of the Barrier 

 surface from 800 feet above sea-level to about 300 feet above sea-level, that is, a 

 lowering of about 500 feet. There are no data known to us for estimating this. 



(b) Ilorizonial Shrinkage of Boss Barrier. On this question the evidence is a 

 little clearer. From 1842 to 1902 the seaward edge of the Ross Barrier has retreated 

 southwards some 20 miles (32 kilometres) on the average in sixty years. Evidence has 

 already been given to show that the Barrier front was formerly at least 200 miles 

 north of its present position. At the above rate of recession the Barrier front may 

 have retreated all the way from the latitude of Cape Washington down to its present 

 position in so short a period of time as 600 years, which seems scarcely credible. 

 Probably the rate of recession at first, when the ice of the Ross Barrier was about 

 2500 feet thick on the average, was far slower than at present, when its average 

 thickness is only about perhaps 720 feet. Even if the rate was formerly three times 

 as slow as at present, it may all have taken place in about 1200 years. Of course 

 a very considerable amount of time may have elapsed during oscillations to and 

 fro of the Barrier front during the latest of its maxima. Accurate soundings of the 

 whole of Ross Sea would no doubt throw mucli light upon the positions of the Ross 

 Barrier front during various maxima of glaciation. Such evidence might be afforded 

 by submarine ridges formed of push moraine or dumped moraine.* 



Future Oh serrations . It appears to us that in addition to detailed soundings 

 future observers might profitably direct attention to the following problems in con- 

 nection with the Ross Barrier : — 



1. The trend of individual glacier ribs or fans. 



2. The trend of the undulations of the nature of gentle pressure ridges and 

 troughs more or less normal to the path of the main glacier streams. 



3. The presence or otherwise of sea ice just south of low-lying portions of the 

 Barrier cliff, and the amount of nt've and ice overlying it derived from old snow. 

 This might be ascertained by boring and recovering the core of ice from the bore 

 from time to time, or by studying the character of the ice In these low-lying portions 

 of the Barrier in the sides of any convenient crevasse situated at some distance south 

 of the Barrier edge. 



* It is understood that Commander E. R. G. R. Evans, R.N., of Captain Scott's expedition, as well 

 as Lieutenant Pennell, R.K., of the same expedition, have lately obtained, when sounding on the 

 Terra Nova, important information on this subject. 



