Chap. X.] DISCOLOURED BANDS IN ICE. 21 1 



On three occasions we saw discolourations of bergs. In one 

 case there was a light yellow band on one surface of a cliff 

 high up, possibly the result of birds' dung which had fallen on 

 the snow when the layer was formed ; it was too high up to be 

 due to Diatoms. 



On another occasion two bergs were passed at a distance, 

 which showed conspicuous black-looking bands, apparently 

 dirt bands. In one of the bergs there were two or there such 

 bands, very broad, parallel to the blue bands, and separated 

 by considerable intervals, in which the berg showed the usual 

 stratification. In another, two black bands existed at one end 

 of the berg and one at the other. Both were parallel in 

 direction to the blue bands, but the stratification at the end 

 where the two black bands were, was inclined at an angle 

 to that of the remainder of the berg, as if a dislocation of a 

 part of the berg had taken place. These bergs were too far 

 distant to allow of the exact nature of the black oands being 

 determined. 



In none of the numerous bergs did I see any bending or 

 curved vertical bands, giving evidence of a former differential 

 motion in the mass, such as are to be seen on every land 

 glacier. How far the absence of these characteristic lines of 

 motion may 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 the water, when 

 floating, must, if it were of symmetrical form and equal density 

 throughout, have an actual height of about 2000 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 rock 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 con- 

 centrated at all. The crevasses seen in the upper parts 

 might be produced after a berg is set free by the greater 



