oe 
R. MW. Deeley—The Structure of Glaciers. 435 
Except in ice caves, the very deep portions of crevasses, or beneath 
the moraines or large stones on the surfaces of the lower glaciers the 
ice is seldom seen in its blue compact condition. The effect of the 
sun upon the surface of a glacier is to break up the compact ice into 
loose crystalline granules. The principal effect of the sun is therefore 
to separate the granules by melting them at their interfaces. It is 
not necessary to postulate the presence of sodium salts in the ice to 
account for the rapid melting at the interfaces. At the interfaces the 
molecules are in an abnormal condition of strain, and are more easily 
set free (melted) than are those in the interior of the granules. Many 
of the interfaces are the result of slow shear without fracture bringing 
part of one grain against another, and in such cases there is surely no 
likelihood of the presence of foreign salts. 
When not subjected to severe strains the larger ice granules grow 
in size at the expense of the small granules, which disappear. Where 
the strains are great, however, the large granules are broken up into 
smaller ones again. This breaking up of the granules occurs in layers 
of more or less considerable thickness in directions parallel with the 
motion of the glacier, which thus becomes composed of layers -of 
granules of varying coarseness. ‘The heat of the sun shining on the 
glacier disintegrates the grains, and the smaller these are the whiter 
the glacier surface appears, and the larger they are the bluer the 
surface appears. A large transparent bluish crystal, for instance, if 
broken up will form a white powder. The blue and white veins 
seen on the surface of a glacier and passing near the sides of the 
glacier stream almost vertically down the walls of the crevasses, are 
due to the disintegration of layers of granular ice of varying coarse- 
ness. That this is the case I have proved by cutting away the 
disintegrated white surface until firm blue ice was reached, and by 
examining the granules below blue and white veins. 
Ribboned. structure.—TYhe veined and the ribboned structures are 
generally so closely associated that they were dealt with by Forbes as 
one structure. We will leave Forbes to describe this feature in his 
own words. ‘‘I noticed in some parts of the ice an appearance which 
I cannot more accurately describe than by calling it ribboned 
structure, formed by them and delicate blue and bluish-white bands 
or strata, which appeared to traverse the ice in a vertical direction, or 
rather which by their opposition formed the entire mass of the ice. 
The direction of these bands was parallel to the length of the glacier, 
and of course being vertical they cropped out at the surface .. . 
Not only did we trace them down the walls of the crevasses by which 
the glacier is intersected, as far as we could distinctly see, but, 
coming to a great excavation in the ice, at least 20 feet deep, formed 
by running water, we found the vertical strata or bands perfectly 
well defined throughout the whole mass of ice to that depth.” It is 
these vertical strata or bands which run mainly in or near the white 
veins which I regard as the ribboned structure. Neither these 
ribbons nor the white and blue veins should be confounded with the 
stratification of the névé due to air bubbles. The ribboned structure, 
and also the veining when seen near the sides of the glacier, is 
generally more or less vertical, but in the Mer de Glace, etc., the 
