22 
The American Geologist . 
January, 1896 
bubbles... .After a fall of snow, surface melting leads to the production 
of a mass of more or less spherical granules of ice, the interstices be¬ 
tween which are occupied by air. Further accumulations of snow lead 
to pressure, the granules are compressed, and much of the air may be 
expelled. But under certain conditions of weather a surface layer of 
snow may be melted, and, freezing again, may form an impervious 
layer, and the adjacent air-bubbles be unable to escape, even under the 
pressure resulting from further falls of snow. Thus we have bands of 
air-bubbles parallel with the surface and alternating with strata of blue 
ice which are comparatively free from air... .The small granular par¬ 
ticles of ice referred to undergo a rapid metamorphosis. They grow, 
some of them increasing in size at the expense of others, until they 
may exceed one or two inches in diameter, and would probably increase 
indefinitely but for the stresses existing in the glacier which cause 
their fracture. The mode of growth, and also the effects of fracturing, 
are discussed later. It is remarkable that these changes in the shape 
and size of the ice-grains do not appear to affect the arrangement of 
the air-bubbles, the layers of which are extremely regular, the trans¬ 
ference of water in a molecular condition from grain to grain failing to 
affect the position, in space, of the air-bubbles, which are seen to tra¬ 
verse the crystalline grains. 
Seven figures of the glacier grains, drawn as seen in thin 
slices with a polariscope by these authors, which they present 
in the paper cited, are reproduced on a somewhat smaller 
scale in Plate II. Figure 1 exhibits the striations on the sur¬ 
face of ice crystals in the ice-cave of the Rhone glacier. Here 
the largest crystals are nearly two inches long. Figure 2 
shows the granular structure of the ice in the grotto at the 
foot of the Obergrindelwald glacier. The section is vertical 
and at right angles to the direction of flow. Attention is 
directed to it as revealing a lamination which on weathering 
produces blue and white veins. It also well displays the re¬ 
markable difference in size of contiguous grains. Figure 3 
is a section in the ice-cave of the Rhone glacier, taken in a 
vertical plane parallel with the flow. As in the preceding- 
figure, it is seen that most of the grains have a greater hori¬ 
zontal than vertical extension, and that they are roughly 
arranged in layers with approximately horizontal shear 
planes. “ In many cases,” say the authors, “ where the shear 
planes are best marked the grains are smallest. Indeed, we 
have layers an inch or more thick, in which the crystals are 
large as in Figure 6, and the bounding surfaces utterly 
irregular. Between them are layers composed of smaller 
