THE 
GEOLOGICAL MAGAZINE. 
NEV SERIES: “DECADE Ve = VOE™ Vii: 
No. X.— OCTOBER, 1910. 
ORIGINAL ARTICLHS. 
pL Se Se 
I.—Tue Srructure oF GLACIERS. 
By R. M, Dezztzy, F.G.S. 
li August, 1841, Professor J. D. Forbes, in company with Professor 
Agassiz and Mr. Heath, spent some time upon the Lower Glacier 
of the Aar, and Forbes states that it was then for the first time that 
he noticed the veined or ribboned structure of glaciers. Although the 
description given in the communication he made to the Royal Society 
of Edinburgh in December of the same year is most interesting, he 
does not state clearly how the structure is related to the glacier grains 
of which the ice streams are built up. 
During the several visits I have paid to Switzerland for the purpose 
of studying the structure of glacier ice the relationship between the 
form and size of the ice grains and the superficial effects produced by 
their weathering have been carefully noted. 
Except at high altitudes the granular structure of the ice can only 
be properly studied in the ice caves which have been excavated for 
the attraction of tourists. At low levels the glacier surface is much 
disintegrated by the warm air and sun, and its appearance will be 
found to depend upon the size and shape of the glacier grains or the 
inclusion of air bubbles. Although Forbes frequently speaks of the 
veined or ribboned structure as though they were one and the same 
thing, the ribboning is rather a feature of the glacier surface when 
the veining is well developed. 
Stratification.—In cases where the vertical unweathered faces of 
glaciers are exposed, such as those which are formed by the breaking 
away of the ice of hanging glaciers, the ice is seen to be horizontally 
stratified, the white layers being those portions of the ice which 
contain an excess of air bubbles imprisoned in the mass. 
If the surface of the névé were always in a powdery loose condition 
at the surface it is likely that, as the mass became consolidated, the 
air would be almost wholly expressed and very blue clear ice would 
be formed. Glaciers, where clean vertical surfaces are exposed, vary 
much as regards blueness, the air bubbles where they are numerous 
making the ice appear more or less white in appearance. 
The transformation of the snow into ice is the result of the slow 
growth of some crystals and the disappearance of others, and to the 
viscosity of the crystals in a direction at right angles to their optic 
DECADE Y.—VOL,. VII.—NO. X. 28 
