PEOFESSOE TYNDALL ON THE VEINED STETJCTUEE OF OLACIEES. 
287 
§ 5. The Aletsch Glacier. 
Ha\ing made the foregoing observations upon the glacier of the Ehone, I proceeded 
to the Aletsch glacier, and during a residence of eight days at the hotel upon the slope 
of the ^ggischhorn, made frequent excursions upon the ice. I had never previously seen 
this grand ice-stream, and my interest in it, at the time of my visit, -was greatly 
augmented by the arguments which Mr. John Ball had founded upon its deportment 
against the pressure theory of the veined structure. I shall here limit myself to a few 
brief remarks upon this subject. 
I have already stated, and this must be particularly remembered, that the veined struc- 
ture often appears in places which have no share in its production. The longitudinal 
structure in the centre of the stream of the Aletsch, for four miles above the base of the 
iEggischhorn, is not due to the lateral pressure endured by the glacier during these four 
miles. It is due, as Mr. Ball himself suggests, to the mutual thrust of the branch 
glaciers, which unite to form the trunk stream; and, once formed by this thrust, it 
perpetuates itself throughout a great portion of the trunk stream. 
But it is urged against this view, that pressure exerted in new directions — the longi- 
tudinal pressure, for example, endured by the stream in its descent, and acting through 
long periods, ought, — ^if pressure has the power ascribed to it, to obliterate the first struc- 
ture. Now here, again, it must be remembered that it is the portions of the ice near 
the bed of the glacier that yield, and that the upper portions of the ice, in many cases, 
are simply floated upon the moving under 
portions. Were the uniform “ long reach” 
referred to by Mr. Ball strictly examined, 
it would, in all probability, be found that 
the ice near the surface is no more com- 
pressed than a log of timber would be if 
placed upon the glacier, and permitted to 
share its motion downwards. 
I may sum up by saying that a close 
examination of the glacier satisfied me, 
not only that it presented no phenomena 
which were at variance with the pressure 
theory, but also exhibited some which, as 
far as I could see, w^ere perfectly fatal to 
the theory of stratification. The state of 
the ice at the base of the A5ggischhorn, as shown in fig. 6, is certainly quite in harmony 
with the pressure theory ; another fact observed upon the glacier shall be referred to 
at a future page. 
§ 6. Glaciers of Monte Rosa. 
I will next endeavour to describe the phenomena of structure exhibited in the system 
2 Q 2 
