Oil the Stratification of the Antarctic Ice. 387 



however, be recollected that the outward movement of the ice 

 is not caused entirely by a horizontal pressure arising from a 

 vis a 'tergo, but that at every place there is a tendency to flow 

 outwards towards the unsupported free edge. In ordinary 

 glaciers the strain thus produced occasionally gives rise to 

 crevasses. It seems improbable, therefore, that the horizontal 

 pressure should ever exceed the vertical ; so that if the latter 

 cannot induce melting, neither can the former do so. 



It is, however, more likely that what Sir Wyville Thomson 

 contemplated was that the pressure of one layer upon the next 

 is not evenly distributed, owing to the layers being in contact 

 in some places but not in others. In this case the pressures 

 upon the areas in contact might increase to a great amount, 

 provided the areas of contact were sufficiently small. And it 

 is quite likely to be partly in this way that neve is converted 

 into solid ice ; for the contact along any horizontal plane is 

 confined to those areas in the neve which are occupied by ice 

 and not by air, so that the pressure on these surfaces is much 

 greater than if the ice were uniformly solid. In fact, the mean 

 pressure upon the portion of any area which is occupied by 

 ice is to the pressure due to the depth alone as the whole of 

 that area is to the area occupied by ice. When the conversion 

 of neve' into ice has taken place, it is not easy to understand 

 how the process of melting and regelation can go further. 



But Dr. Croll has pointed out that the diminution of the 

 thickness of the annual strata of ice from the top downwards 

 may be accounted for by the fact that the ice radiates from a 

 centre of dispersion. Although I am fully aware of the very 

 slight practical value of any addition I can make to what Dr. 

 Croll has said upon this part of the subject (for we are too 

 ignorant of the physical properties of ice to arrive at any cer- 

 tain results), I propose nevertheless to offer a few further 

 remarks upon the mode of origination of the stratified structure, 

 and the consequences which follow as affecting the thickness 

 of the strata. 



The snowfall of each year is deposited upon that of the pre- 

 vious year; and there is no internal cause to alter this order of 

 " conformable " arrangement of the strata. It is conceivable 

 that the movement of the ice over a rough rocky surface might 

 dislocate the strata, or that the liquefaction of the upper surface 

 over partial areas might cause the snowfall of certain periods 

 to be removed before the deposition of some later strata took 

 place, and so render the strata unconformable. But these dis- 

 turbing causes are supposed not to be present. It follows that, 

 in any vertical column, the snowfall of every year intermediate 

 between the earliest represented in it (which will be at the 



