70 ME. T. DEBEXHAil OX A NEW [vol. lxXV,. 



calculations without wide assumptions. If we take assumed figures. 

 as near as judgment will go, we obtain interesting results, which 

 are here given as an example rather than as a basis for deduction. 



Taking the thickness as 200 feet, the rate of movement as- 

 50 feet per year, and the distance between the submerged ridge and 

 the first exposure of muds as 5 miles, we get the annual decrease 

 of the surface, 



50X200 _10 

 n ~ 5x5280~25 teet ' 



that is, about 5 inches a year. 



Of these quantities the thickness and the rate of movement 

 would be comparatively easy to measure, and the quantity" E not 

 at all impossible. 



The next stage is represented by the deposits near D (fig. 1, p. 52), 

 where the muds have travelled many miles on the surface of the sheet,. 

 and have become sorted hj water so that the organisms are to some 

 extent damaged by exjjosure to atmospheric weathering. The fate 

 of these muds is to be floated aAva} 7 " on small bergs that occasionally 

 break off from here, most of which would melt in more northern 

 latitudes and return the muds to the bottom of the sea. 



The high-level deposits at Cape Royds exhibit a further stage, 

 and are particularly interesting as showing that, even when the 

 McMurdo Sheet was much thicker than its present 100 or 200 

 feet, the same process of picking up sea-floor was going on. I 

 have no doubt that there are other deposits at a still higher level, 

 but the difficulty of finding them is considerable. The remnant of' 

 ice upon which they are still resting will disappear in time, and 

 they will come to the final stage as shown by the Dry Valley case 

 (K, fig. 1, p. 52) where the ice has entirely disappeared, and there 

 is nothing left to show the origin of the shells. 



With regard to the shells and sponges that form the bulk of the 

 organisms in the muds it is interesting to note that they come 

 from all depths down to 80 or 100 fathoms, the zone of the sponges 

 in particular being in the neighbourhood of 80 fathoms. The best 

 ' catch ' of living sponges was made by the ship in 78 fathoms off 

 the mouth of the Ferrar Glacier. Some of the shells belong to 

 shallower depths; but, as the} 7 are all collected on the surface of the 

 sheet, they will ultimately be deposited in the same narrow bed of 

 mud. The occurrence of the deeper forms shows that the process 

 can go on even when the thickness of the ice reaches 600 or 

 700 feet. 



General Summary. 



The results may be recapitulated in a few words, as follows. 



The raised marine beds and bottom deposits are found in this 

 part of the Antarctic at all stages of their evolution, and, whatever 

 may be the process of their elevation, it is quite certain that they 

 do rise through the ice, and so are preserved from shock and dis- 

 integration. The most plausible explanation of the process is that 



