CAUSE OF GLACIER MOTION. 253 



descend by its weight into any space which it may 

 find, but capillary attraction will cause it to now into 

 interstices between adjoining crystalline particles; but 

 owing to the principles of regulation, already discussed, 

 the thin film of water would instantly become re- 

 solidified. It would not, however, solidify so as to fit 

 the cavity which it occupied when in the fluid state, 

 for the liquid particle in solidifying assumes the crys- 

 talline form, and of course there will be a definite 

 proportion between the length, breadth, and thickness 

 of the crystal ; consequently it will always happen that 

 the interstice in which it solidifies will be too narrow 

 to contain it. The result will be that the fluid particle, 

 in passing into the crystalline form, will press the two 

 adjoining particles aside in order to make sufficient 

 room for itself between them, and this it will do, no 

 matter what amount of space it may possess in all 

 other directions. The crystal will not form to suit the 

 cavity, the cavity must be made to contain the crystal. 

 And what holds true of one particle, holds true of 

 every particle which melts and re-solidifies. This 

 process is no doubt going on incessantly in every part 

 of the glacier, and in proportion to the amount of heat 

 which the glacier is receiving. This internal pressure, 

 resulting from the solidifying of the fluid particles in 

 the interstices of the ice, acts on the mass of the ice 

 as an expansive force, tending to cause the glacier to 

 widen out laterally in all directions. 



Conceive a mass of ice lying on a flat horizontal 

 surface, and receiving heat on its upper surface, say 

 from the sun; as the heat passes downwards through 

 the mass, particles of the ice melt and re-solidify. 

 Each fluid particle solidifies in an interstice, which has 

 to be widened in order to contain it. The pressure 

 thus exerted by the continual re-solidifying of the 



