THE WORK OF SNOW AND ICE 



279 



much like a cube cut from the pile of cards. If it is so placed that 

 its plates are horizontal (Fig. 235) , and if it is rested on supports at 

 two edges and heavily weighted in the middle, it will sag, the plates 

 sliding slightly over one another. In this case the cube offers con- 

 siderable resistance to deformation. If the cube is so placed that 

 the plates are on edge, each reaching from support to support (Fig. 

 236), it will offer very great resistance to deformation. But if the 

 plates are vertical and transverse to the line joining the supports, 

 as in Fig. 237, the middle portion will sag under moderate weighting 

 by the sliding of the' plates on one another, and in a comparatively 





Fig. 235. Fig. 236. Fig. 237. 



Figs. 235, 236, and 237. Figures to illustrate the method of deformation 



of ice crystals. 



short time the middle portion may be pushed entirely out, dividing 

 the cube. 1 These properties have been made the basis for the 

 hypothesis that glacier motion is primarily the result of the slipping 

 of the plates of the crystal on one another. This hypothesis might 

 have much in its favor if the crystals of ice in the glacier were all 

 oriented so that the plates were parallel with the bed of the glacier; 

 but this is not the case. The crystals, starting from snowflakes, 

 have their axes turned in various directions according to the acci- 

 dents of their fall; and as the snow develops into ice, the principal 

 axes of the granules continue to lie in all directions. 



There does appear to be a tendency, however, for the crystals 

 of ice to approach parallelism in the basal, terminal part of a glacier. 

 From such observations on this point as are available, it is probable 

 that the parallel orientation is due (1) partly to the vertical pressure 



1 McConnel and Miigge. On the Plasticity of Glaciers and Other Ice. 

 Proc. Roy. Soc., Vol. XLIV, 1888, pp. 331-67 (with D. A. Kidd); Vol. XLVIII, 

 1890, pp. 259, 260; Vol. XLIX, 1891, pp. 323-43. 



