2 Thickness of the Antarctic Ice , and its [January, 
of the strata of ice in a berg from the top of the berg down- 
wards. The regularity of this diminution leaves it almost 
without a doubt that the layers observed are in the same 
category, and that therefore the diminution is due to subse- 
quent pressure or other aCtion upon a series of beds which 
were at the time of their deposition pretty nearly equally 
thick. About 60 or So feet from the top of an iceberg the 
strata of ice, a foot or so in thickness, although of a white 
colour, and thus indicating that they contain a quantity of 
air and that the particles of ice are not in close apposition, 
are still very hard, and the specific gravity of the ice is not 
very much lower than that of layers not more than 3 inches 
thick nearer the water-line of the berg. Now it seems to 
me that this reduction cannot be due to compression alone, 
and that a portion of the substance of these lower layers 
must have been removed. 
“ It is not easy to see why the temperature of the earth’s 
crust, under a widely extended and practically permanent 
ice-sheet of great thickness, should ever fall below the 
freezing-point, and it is a matter of observation that at all 
seasons of the year vast rivers of muddy water flow into the 
frozen sea, from beneath the great glaciers which are the 
issues of the ice-sheet of Greenland. Ice is a very bad 
conductor, so that the cold of winter cannot penetrate to 
any great depth into the mass. The normal temperature of 
the crust of the earth at any point where it is uninfluenced 
by cyclical changes is, at all events, above the freezing- 
point, so that the temperature of the floor of the ice-sheet 
would certainly have no tendency to fall below that of the 
stream which was passing over it. The pressure upon the 
deeper beds of the ice must be enormous ; at the bottom of 
an ice-sheet 1400 feet in thickness it cannot be much less 
than a quarter of a ton on the square inch. It seems there- 
fore probable that, under the pressure to which the body of 
ice is subjected, a constant system of melting and regelation 
may be taking place, the water passing down by gravitation 
from layer to layer until it reaches the floor of the ice-sheet, 
and finally working out channels for itself between the ice 
and the land, whether the latter be sub-aerial or sub- 
merged. 
“ I should think it probable that this process, or some 
modification of it, may be the provision by which the inde- 
finite accumulation of ice over the vast nearly level regions 
of the ‘ Antarctic Continent ’ is prevented, and the uni- 
formity in the thickness of the ice-sheet is maintained ; 
that, in faCt, ice at the temperature at which it is in contact 
