492 Mr. J. Ball on the Structure of Glaciers. 
opposite side the mechanical condition must be completely dif- 
ferent ; the feeble moraine can exert little or no lateral pressure, 
while it is probable that a considerable amount of frontal resist- 
ance is encountered in the glacier itself, in consequence of the 
retarded motion of that side towards which the mass of the ice 
is twisted. Contrary, however, to my expectation, | found im 
crossing the glacier from a point immediately below the Chapel 
of Notre Dame, that the arrangement of the surfaces of the 
veined structure is remarkably symmetrical. Measures of dip 
taken with a clmometer near the edge of a glacier are, indeed, 
very fallacious. The ice does not melt uniformly from its upper 
surface; the action of the sun and of radiant heat reflected from 
the shore is most energetic upon the exposed sides, and the 
steep banks of ice which rise terrace-like, one above the other, 
at the edge of the glacier, are formed of beds or layers of ice, 
of which the outermost coming into contact with the rock, must 
have been originally much lower in the interior of the glacier, 
before the processes of movement and ablation had brought it 
into its exposed position. ‘The inward dip of the veined struc- 
ture opposite the Chapel, as I have constantly found it in similar 
positions, increases from the outermost and lower, to the inner 
and higher ridges of the ice. Where in actual contact with 
the rock, at the only point which I was able to attain, it did not 
exceed 30°, which was at that point, as nearly as I could judge, 
the inclination of the underlying rock, while at the opposite 
edge of the glacier, where it forms a steep ridge thinly covered 
with gravel, sometimes more than 80 feet in height, and with 
no retaining wall of rock, the dip towards the centre seems to 
vary from 30° to 40°. Contrary to the experience of Professor 
Forbes in 1846, I found the veined structure better developed 
towards the centre than close to the sides; but I lay no stress 
upon this circumstance, for I believe that the ice varies ex- 
ceedingly in this respect within short distances, and no two 
observers pass over exactly the same course upon the glacier, 
while, as I have already observed, there is a constant source of 
error in the various degree of weathering of the surface of the 
ice. But the fact to which I wish to call particular attention, is 
the regularity of the so-called spoon-shaped arrangement of the 
veined structure on this glacier, subjected as it is, on one side, to 
intense lateral pressure. I was unable to detect any difference in 
this respect between the lower extremity of the Brenva and those 
elaciers which are most free from disturbance from this cause. 
In taking leave of this part of the subject, I would suggest 
that a theory which would explain the structure of glaciers by 
lower end of the glacier, extending from below the Chapel of Notre Dame 
towards Cormayeur, 
