Rk. M. Deeley—Striations on Glacier Granules. 113 
a still further enlargement of a portion of Fig. 2 to show more clearly 
the details of the surface-structure. It will be seen that both the 
ridges and the furrows frequently bifurcate, and that whilst main- 
taining their general direction across the granules they curve about 
considerably. Fig. 1 shows several granules abutting against each 
other. ‘Che most marked feature is that some of the surfaces of the 
granules occupy depressions, whilst others project above the general 
level of the surface. The surface was originally quite level, and 
evaporation and melting have taken place on the surfaces of some of 
the granules more rapidly than upon others. The coarseness of the 
grooving on different granules varies somewhat. In Fig. 1 all the 
granules differ in this respect. Compare the fineness of the grooving 
on the larger granule with the coarse incipient grooving on the 
top one. 
The rubbings I had previously obtained seemed to show that 
even when protected from the sun, as in a cave, each granule 
was separated from its neighbour by a canal of more or less 
width. These actual impressions, however, make it clear that this 
appearance was produced by the pencil passing from raised to depressed 
granule surfaces and vice versa. Sometimes the grooving of the 
surface of the lower crystal is not well marked near its junction with 
other granules. This is probably the result of capillary forces 
causing water to collect along the line of junction. Evaporation 
rather than melting appears to be the main cause of the appearance of 
the surface-structure we are considering. It occurs at all points in 
caves both in the light and in the dark. Ventilation appears to have 
the most marked effect on its appearance; for the surface-markings 
were very well developed in many of the crevasses intersecting the 
ice cave. 
I have never seen the structure on lake ice, pieces of which have 
been exposed in a freezing atmosphere. Shear planes in the granules, 
produced by the differential motion of the glacier might produce the 
ridges and furrows. O. Mugg! says ‘“‘ broken surfaces, especially those 
of bent bars of ice, almost always show a fine striation’’. With regard 
to McConnell’s work on the bending of ice Mugg’ says, ‘‘ As 
McConnell died during these experiments I decided to take them up 
again, and especially to make the experiment to produce in the ice 
the pure translation without curvature and also if possible to ascertain 
the direction of the translation.” ‘‘The result was a complete con- 
firmation of McConnell’s experiments.” Mugg’s investigation was 
a very exhaustive one from the point of view of the chemist and 
erystallographer. 
The microscopical examination of polished surfaces of alloys which 
have been sheared shows that the distortion takes place along definite 
shear planes in the crystals and not equally throughout the mass, as 
in amorphous liquids. Crystalline ice, it would appear, also shears 
along definite planes, and the distortion in the crystalline structure 
along such planes results in differences of surface evaporation, which 
give rise to the surface ridges and furrows. 
1 Jahrb. fiir Min., 1895, p. 217. 2 Tbid., pp. 213, 214. 
DECADE Y.—YOL. VII.—NO. III. 8 
