166 SCIENCE IK SHOUT CHAPTERS. 



The ordinary course of glaciers affords abundant illustrations 

 of the plasticity of such masses of ice. They spread out where 

 the valley widens, contract where the valley narrows, and follow 

 all the convexities or concavities of the axial line of its bed. 

 If the bending thus enforced exceeds a certain degree of 

 abruptness crevasses are formed, but a considerable bending 

 occurs before the rupture is effected, and crevasses of consid- 

 erable magnitude are commonly formed without severing one 

 part of a glacier from another. They are usually V-shaped, in 

 vertical section, and in many the rupture does not reach the 

 bottom of the glacier. Very rarely indeed does a crevasse 

 cross the whole breadth of a glacier in such a manner as to 

 completely separate, even temporarily, the lower from the 

 upper part of the glacier. 



If a glacier can thus bend downward without * ' sundering 

 its connection with the frozen mass behind," surely it may 

 bend upward in a corresponding degree, either with or without 

 the formation of crevasses, according to the thickness of the 

 ice and the degree of curvature. 



A glacier reaching the sea by a very steep incline would 

 probably break off, in accordance with Mr. Geikie's descrip- 

 tion, just as an Alpine glacier is ruptured fairly across when it 

 makes a cascade over a suddenly precipitous bend of its path. 

 One entering the sea at an inclination somewhat less precipitous 

 than the minor limit of the effective rupture gradient would be 

 crevassed in a contrary manner to the crevassing of Alpine 

 glaciers. Its crevasses would gape downward instead of up- 

 ward have a A-shaped instead of a V-shaped section. 



With a still more moderate slope, the up- floating of the ter- 

 mination of the glacier, and a concurrent general uplifting or 

 upbending of the whole of its submerged portion might occur 

 without even a partial rupture or crevasse formation occurring. 



Let us now follow out some of the necessary results of these 

 conditions of glacier existence and glacial prolongation. The 

 first and most notable, by its contrast with ordinary glaciers, is 

 the absence of lateral, medial, or terminal moraines. The 

 larger masses of debris, the chippings that may have fallen 

 from the exposed escarpments of the mountains upon the sur- 

 face of the upper regions of the glacier, instead of remaining 

 on the surface of the ice and standing above its general level 

 by protecting the ice on which they rest from the general 

 snow-thaw, would become buried by the upward accretion of 

 the ice due to the unthawed stratum of each year's snowfall. 



