THE WORK OF SNOW AND ICE 287 



regarded. 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 Agassi z 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 hypothe- 

 sis 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 tem- 

 peratures 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 com- 

 pression 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 re-frozen 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 the ice 

 movement. 



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

 ice crystals serve an important function in glacial movement. 



