Glacier IVork. — Scott. 225 
between 1° and 10°. With the sandstone poHshed the move- 
ment was observed at an angle of forty minutes. The laws 
of friction between solids are found to be inapplicable to the 
conditions of a glacier on its bed, though the angle of slope 
of the bed obviously is an important factor in glacier motion, 
and particularly so in the matter of erosion, which will be con- 
sidered later. 
The Rev. Coutts Trotter has described ^experiments * 
showing that glacier ice will shear under small forces if al- 
lowed sufficient time, and more recent experiments by 
Miigge t appear to prove that the apparent viscosity of 
glaciers is partly the result of shearing along the cleavage 
planes of the crystalline granules of the glacier ice. 
A study of some of the larger Swis5 glaciers, by Deeley 
and Fletcher $ concerning glacier structure, and its bearing 
upon glacier motion, is interesting because it involves meth- 
ods somewhat different from those of their predecessors. A 
Ix)lariscope was used and sketches made purporting to show 
the character of the crystalline particles in a satisfactory way, 
just as they found them in the glaciers. Glacier ice had, of 
course, previously been regarded as a crystalline aggregate, 
by Heim, McConnell, Bertin, Grad, and others, the individual 
crystals fitting closely without the presence of a matrix. This 
conception is verified by Deeley and Fletcher, who further 
show that the optical structure of each grain is uniform, as 
indicated by the polariscope, but the bounding surfaces are 
very irregular and usually curved. The optic axes of neigh- 
boring grains appear to be arranged at random, and the sur- 
faces of the majority of the granules are seamed with exceed- 
ingly small furrows. The relation between these furrows or 
, striae and the optic axis, however, is not noted. It is believed 
that the stride are analogous to those seen on other crystals, 
and are due to the alternation of two faces of crystallization. 
A sketch of such striated crystals from the ice-cave of the 
Rhone glacier, § shows no definite direction of the striae 
with reference to the crystal mass, or to the neighboring crys- 
tals. 
*Proc. Roy. Soc. 1885, Vol XXXVIII, pp. 92-108. 
tJour. of Geol. 189.'). 
f'Stiucture of Glacier Ice and its bearing upon Glacier Motion." 
Geol. Mas. 1895. pp. 152-162. 
SGeol. Mag:. (1895), Plate 156. 
