The Flow of Glaciers .— Upliam. 
21 
ginal veins, extending along the sides and turning forward 
into the central part of the glacier, developed by pressure due 
to the faster motion of the center; second, longitudinal veins, 
produced by mutual pressure between tributary glaciers; and 
third, transverse veins, resulting from pressure due to the 
change of inclination, and to the longitudinal thrust endured 
by the glacier, at. the base of an ice-fall. In all these methods 
of its production, the ice lamination, like slaty cleavage and 
schistose foliation, arises from a shearing motion or rearrange¬ 
ment of the ice particles or molecules upon each other in some 
way which, through all the elaborate studies of Forbes and 
Tyndall, eluded their discovery. They each refer incidentally 
to the granulation of glacier ice, but seem to have given no 
attention to it as a possible key to the mysteries of the glacial 
lamination and flow. 
Granular Structure. 
F. Klocke,* summing up the results of his own and others’ 
observations, states that glacier ice is a granular aggregate of 
ice crystals, in the same way as marble is such an aggregate 
of calcite crystals. The optical axes of the separate crystal¬ 
line grains usually have no order, but the utmost irregularity, 
in their orientation; and the diameter of the grains varies, 
according to Klocke, from one to ten centimeters (from two- 
fifths of an inch to four inches). In the Aletsch glacier Forel 
observed that some of the ice grains become two to three 
inches in diameter. Drygalski, in Greenland, finds their max¬ 
imum growth like the size of walnuts. 
How the snow crystals of the firn are transformed into the 
glacier grains is not yet definitely traced. Deeley and Fletcher 
examined the ice beneath the firn snow (neve) near the sum¬ 
mit of Mont Blanc, of which they write if 
The fragments of this ice were formed of the usual glacier grains, 
many of considerable size. On the average they were, as near as can 
be remembered, as large as peas or even beans. Indeed, in many in¬ 
stances where the neve was examined the ice was coarsely granular. 
Regarded from a distance the neve appears to be very finely stratified, 
layers of comparatively pure blue ice alternating with white ones. On 
close examination this stratified appearance is seen to be practically 
wholly due to the distribution in layers of countless imprisoned air- 
*Neues Jahrbuch, 1881. Band i, pp. 23-30, written Nov., 1879, and 
Aug. 1880. 
tGeol. Magazine, IV, vol. ii, pp. 153, 151, April, 1895. 
