i 4 6 WORK OF SNOW AND ICE 



brittleness and rigidity find a ready elucidation under the view that ice is really 

 a solid body at all times, and that its apparent fluency is due to the momentary 

 fluidity of small portions of its mass assumed in succession as compression demands. 



In addition to the considerations already adduced, it may be urged that a 

 glacier does not flow as a stiff liquid because its granules are not habitually drawn 

 out into elongated forms, as are cavities in lavas, and plastic lumps in viscous 

 bodies. Flowage lines comparable to those in lavas are unknown in glaciers. 



All this is strictly consistent with our primary thesis, that a glacier is crystalline 

 rock of the purest and simplest type, and that it never has other than the crystalline 

 state. This strictly crystalline character is incompatible with viscous liquidity. 



Other views of glacier motion. While these views of glacial motion seem 

 to us to accord best with the known facts, they are not to be regarded as established 

 in scientific opinion, or as the views most commonly held. The main alternative 

 interpretations that have been entertained are the following: 



(1) In the early days of glacial studies De Saussure thought that glaciers 

 slid bodily on their beds. 



(2) Charpentier and Agassiz referred the movement to the expansion of 

 descending water freezing within the glacier. 



(3) Rendu and Forbes, followed by many modern writers, believed ice to be 

 viscous, and that in sufficiently large masses it flows under the influence of its own 

 weight, like pitch or asphalt. 



(4) Others, realizing the fundamental difference between crystalline ice and 

 a true viscous body, have fallen back on a vague notion of plasticity, which scarcely 

 amounts to a definite hypothesis at all. 



(5) Tyndall urged that the movement was accomplished by minute repeated 

 fracturing and regelation, appealing to the fact that broken pieces of ice slightly 

 pressed together at melting temperatures freeze together, but neglecting the fact 

 that this would destroy the integrity of the crystals. 



(6) Moseley assigned the movement to a bodily expansion and contraction 

 of the glacier, analogous to the creeping of a mass of lead on a roof. 



(7) James Thompson demonstrated that pressure lowers the melting-point, 

 and while this effect is so small as probably to be ineffectual, it is correlated with 

 the very important fact that compression, by generating heat, may cause melting, 

 which is not the case in most other rocks. He recognized that under pressure 

 partial liquefaction took place, that the water so liberated might be refrozen as 

 it escaped from pressure, and appears to have regarded this as a vital factor. 



(8) Croll held that the movement was due to a consecutive series of molecular 

 changes somewhat like the chain of chemical combinations in electrolysis. 



(9) Hugi, Eli de Beaumont, Bertin, Forel, and others thought that the 

 growth of the granules was the leading factor in ice movement. 



(10) McConnel and Miigge have made the gliding planes of the ice crystals 

 serve an important function in glacial movement. 



It will be seen that the principle of partial liquefaction for which Thompson 

 laid the basis, the crystallization of descending water urged by Charpentier and 

 Agassiz, and the granular growth on which Hugi, Beaumont, Forel, and others 

 founded their hypotheses, are incorporated in the view already presented. Prob- 

 ably the agencies on which some of the other views are based may also be partici- 

 pants in producing glacial motion, in some places as incidental factors, and in others 

 perhaps as important ones. 



