244 A NATURALIST ON THE " CHALLENGER 



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be explained by the fact, that only about the uppermost tenth of 

 the entire height of the bergs is seen, I do not know. A berg 

 200 feet in height above water, when floating, must, if it were of 

 symmetrical form and equal density throughout, have an actual 

 height of about 2,000 feet. 



A mass detached from the edge of the barrier, and then 

 showing lines of motion might, whilst floating, receive a sufficient 

 addition of weight by successive falls of snow to sink it entirely 

 below water in supporting the new structure. 



Moraines and large rock masses would become hidden by 

 such snow accumulations, both towards the free margins of the 

 continuous glaciers, and also after the bergs containing them 

 were detached ; and a berg laden with rock need not expose it 

 to view until after long thawing or capsizing. 



The accumulation of rocks and stones in the form of definite 

 moraines is, of course, a phenomenon which can only be pro- 

 duced by the accompaniment of thawing or evaporation of ice 

 in combination with its motion. If both these processes occur 

 to very small extent in the ice of the glaciers, whose free edge 

 forms the Great Barrier, the rocks and stones received from the 

 overhanging cliffs inland, or supporting beds, will be distributed 

 evenly throughout the mass, and never be concentrated at all. 

 The crevasses seen in the upper parts of the bergs might be pro- 

 duced after a berg is set free by the greater expansion, through 

 increase of temperature, of the denser ice at the base of the mass. 



I may be allowed here to make a remark with regard to the 

 movements of glaciers, a subject to which my late father, the 

 Eev. Canon Moseley, devoted much time and research. The 

 theory propounded by him to account for the descent of glaciers, 

 which, as he proved most conclusively, cannot take place by 

 means of their weight alone, was that the motion was due to the 

 expansion and contraction of the mass. A heavy body lying on 

 a slope, inclined ever so little, and subject to expansion and 

 contraction, must necessarily crawl down the slope, every change 

 of dimensions tending to push the mass in the direction of least 

 resistance.* This theory has been considered inadequate, and 



* Rev. H. Moseley, F.RS., " On the Descent of Glaciers," Proc. Roy. 

 Soc, April 19, 1855. "On the Mechanical Impossibility of the Descent of 



