490 Mr. J. Ball on the Structure of Glaciers. 
steadily forward along the main valley, seems to me to prove 
conclusively that the chief pressure acting upon it in the plane 
of the horizon, must be in the direction of its motion, and that 
surfaces formed perpendicular to the lines of maximum pressure 
should intersect the glacier in flattened curves, slightly convex 
towards its lower extremity. The fact, however, is otherwise. 
The upper portion of what I may call the long reach of the 
glacier, was covered with snow when I traversed it ; but opposite 
to the Marjelen See, and for three or four miles up the stream, 
I found the veined structure quite well developed in the central 
region of the glacier, arranged as usual in vertical planes parallel 
to the direction of motion. If it be said that this structure was 
originally produced by the mutual pressure of the three main 
ice currents which unite in the upper basin already referred 
to, I would reply, that the point of junction is fully eight miles 
from the Marjelen See; that it is probably a considerable over- 
estimate if we allow 200 feet as the average annual advance 
of that part of the glacier; and, consequently, that the veined 
structure at the lower station must, according to this latter 
hypothesis, have been produced more than 200 years before we 
observe it. For the greater part of that time we have proof 
that the ice has been subject to little or no lateral pressure, but 
constantly to a force acting in the direction of motion, and to 
the vertical pressure of the upper on the lower parts of the mass. 
At the most moderate estimate of the superficial waste along the 
intermediate portion of the glacier, we must suppose that a thick- 
ness of 400 or 500 feet of overlying ice has been removed during 
the long interval in question. But if the long-continued action 
of pressure in new directions is incompetent to alter the struc- 
ture impressed upon the ice 200 years before, what becomes of 
the assumed obliteration of the original stratification of the névé 
through the agency of pressure ; and how are we to believe that 
an effect so universal as this must be, if indeed that original 
stratification is everywhere effaced, should not be repeated in a 
field where the same causes must have been in operation with 
remarkable uniformity for a period unusually protracted ? 
Even in those glaciers where it is conceded that lateral com- 
pression has probably been at work to a great extent, such as 
the Mer de Glace of Chamouni, there are many parts of the 
glacier where it appears to me that the hypothesis of Pro- 
fessor Tyndall would require that the veined structure should 
be developed at right angles to the motion of the centre of the 
glacier* ; but I do not venture to urge that view against the 
* Professor Tyndall’s mud experiments illustrate this, by the mae 
of the circular rings impressed on the centre of a stream moving over a be 
of irregular slope. i 
