320 Voyages of Discovery and Survey. 



well over any portions of the icy barrier within rench, as over the 

 snows of the land. The uniform, or nearly uniform height of the 

 barrier, when covering various depths of water, and not aground, 

 would apparently indicate some countei'acting cause, preventing such 

 an accumulation of laysrs of ice, as by giving a total increased thick- 

 ness should enable a greater height to rise above M'ator in the deeper 

 situations. It is here assumed, that the thickness of the barrier is 

 not increasing, and remains generally the same, a fact which may per- 

 haps be thought not as yet sufficiently proved. Nevertheless, when 

 we consider that the sea-water beneath the icy barrier is not exposed 

 to that great depression of temperature, to which, when directly in 

 contact with the atmosphere, it is subject, and that beneath the lower 

 part of the barrier, deep as that lower part is, it would be only water 

 of greater specific gravity than that above, which could there find 

 its way, the experiments of Sir James Ross lead us to suppose that 

 after a certain depth the ice would cease, the temperature being too 

 high for its continuance. Upon this hypothesis, the general thick- 

 ness of the barrier would be the same as long as there was a suffi- 

 cient depth of water to secure the needful temperature, the accu- 

 mulation of snow and ice above being met by the melting of the ice 

 beneath. 



We should expect the rise and fall of the tide to act upon the bar- 

 rier, tending to break off portions at its outer edge, where, if the 

 lower part plunge into water of sufficiently high temperature, a melt- 

 ing beneath would assist in detaching fragments. The needful sup- 

 port, by the proper amount of submersion, being thus to a certain 

 extent withdrawn, tlie masses would strive to rend themselves off and 

 adjust themselves in the water, relatively to the floatation-line now 

 become proper to them. It is evident, by the upsetting of the ice- 

 bergs, so often observed, that their centres of gravity become changed, 

 so that the masses take a new floating position relatively to them. 

 In regions where the cold of the atmosphere is so great that little 

 general change is produced upon the upper part of the icebergs com- 

 pared with that which is experienced beneath by plunging into water 

 above the ireezing point, we should expect such changes in position 

 frequently to happen, any load of mud or stones of the remaining 

 portion beneath being comparatively of little importance. 



Great tabular masses, varying in size, some even several cubic miles 

 in volume, float away from the parent barrier, the tidal streams and 

 ocean currents sweeping them onwards. And it should be borne in 

 mind, that the solid barrier presents a submarine cliiF of ice, by the 

 side of which a large volume of water would readily pass without the 

 interruptions usually produced by land. According to the seasons 

 so must the icebergs float, little altered in general form, to different 

 distances from the barriei's, many of them capsized, with their load 

 of mud, sand, gravel, and blocks uppermost. A lai-ge tabular mass 

 of ice, about three-quarters of a mile in circumference, was seen float- 



