204 DISCUSSIONS IN CLIMATOLOGY. 



About 60 or 80 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 therefore 

 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 submerged. 



" I should think it probable that this process, or some 

 modification of it, may be the provision by which the 

 indefinite accumulation of ice over the vast nearly level 

 regions of the ' Antarctic Continent ' is prevented, and the 



