488 My. J. Ball on the Structure of Glaciers. 
glacier rather high up on the north-north-east side of the Téde, 
above the Upper Sand Alp, and I have since seen it elsewhere, 
e. g. on the glacier of La Brenva. 
I next proceed to ask whether, supposing it possible that 
pressure alone can produce in beds of névé alternate layers of 
denser and of less compact ice perpendicular to the direction of 
pressure, the form and position of the veined structure as we 
find it in nature is consistent with the new hypothesis? It is 
well known that if, by a comparison of the dip and strike of the 
veined structure in different parts of a glacier, we construct sur- 
faces to pass through the apparently continuous layers of blue 
or white ice, such surfaces, at the lower end of great glaciers, 
usually assume the form of a scallop shell, or flattened spoon, 
with its concave side turned up, and dipping outwards towards 
the lower end of the glacier. In the middle region of glaciers 
whose length is great compared to their breadth, this spoon- 
shaped structure becomes much elongated, and it seems to be 
distinetly traceable only near the sides, while in the central part 
the veined structure is arranged in parallel planes nearly vertical, 
and directed towards the lower end of the glacier. In smaller 
glaciers, which, instead of flowing in deep valleys, occupy depres- 
sions on the slopes of the higher Alps, the spoon-shaped arrange- 
ment is usually traceable more clearly throughout their whole 
breadth, and the dip towards the centre is nearly conformable to 
the form of the solid bed of the glacier. 
It will readily be admitted that there are cases where large 
masses of ice are forced in their onward course into channels 
with steep sides, where the greatest pressure is probably that 
due to the lateral constriction of the ice-stream between the 
containing walls, and where we might accordingly expect that 
the veined structure, if produced by pressure alone, should be 
developed in planes parallel to the direction of motion. The 
Mer de Glace of Chamouni, and the great glacier of the Aar, 
are familar instances of this class. But I can scarcely admit that 
this holds true of many other glaciers in which the direction 
of the veins is the same. Let us take for instance the Aletsch 
glacier, the greatest, I believe, of all known ice-streams. Omit- 
ting many small affluents which cannot produce much effect, it 
is nourished by three main branches, proceeding respectively 
from the north side of the Aletschhorn, from the col connecting 
the Monch and the Jungfrau, and from the valley leading by the 
north side of the Viescherhérner to the Finster Aarhorn. After 
the junction of these separate streams, the great glacier flows on 
with remarkable uniform slope and breadth, with no projecting 
promontories of rock to disturb its course, for a distance of eight 
or nine English miles, until opposite to that singular and beau- 
