ON THE STRUCTURE AND MOTION OF GLACIERS 19 
known in this country through his important memoirs on the 
Mechanical Theory of Heat :—“I must now,” writes M. Clausius, 
“describe to you another singular coincidence. I had read your 
paper upon the cleavage of rocks ..... and it occurred to me at 
the time that the blue veins of glaciers, which indeed: I had not seen, 
but which had been the subject of repeated conversations between 
Professor Studer of Berne, Professor Escher von der Linth, and 
myself, might be explained in the same manner. When, therefore, I 
reached the Rhone glacier for the first time, I walked along it for a 
considerable extent, and directed my attention particularly to the 
structure. I repeated this on the other glaciers which I visited 
during my excursion. I did not indeed pursue the subject so far 
into detail as to be able in all cases to deduce the blue veins from the 
existing conditions of pressure, but the correctness of the general 
explanation impressed itself upon me more and more. This was 
particularly the case in the glacier of the Rhone, where I saw the blue 
bands most distinctly, and where also their position harmonized with 
the pressure endured by the glacier when it was forced to change the 
direction of its motion. You can therefore imagine how astonished I 
was to learn that at the same time, and on this very glacier among 
others, you had been making the same investigations.” It ought also 
to be remarked, that a similar thought occurred to Mr. Sorby, from 
whom after his return from Switzerland one of us received a note, in 
which pressure was referred to as the possible cause of the veined 
structure of glacier ice. 
A fine example of ice lamination is that produced by the mutual 
thrust of two confluent glaciers. The junction of the Lauter Aar and 
Finster Aar glaciers to form the glaciers of the Unter Aar is a case in 
point, and the results obtained with a model of this glacier were 
highly interesting. Fig. 9 is a sketch of the trough in which the 
experiments were made. The branch terminating at UL is meant to 
represent the Lauter Aar glacier; that ending at FN the Finster Aar 
branch. The point at A represents the “ Abschwung,” so often 
referred to in the works of M. Agassiz. B and B’ are two boxes with 
sluice fronts, from which the mud flows into the trough. The object 
was to observe the mechanical state of the mass along the line of 
junction of the two streams, and along their respective centres, and 
compare the result with the observations upon the glacier itself. The 
mud was first permitted to flow simultaneously from both boxes, and 
after it had covered the bottom of the trough to some distance below 
the line ST, the end of a glass tube was dipped into a fine mixture of 
the red oxide of iron and water, and the two arms of the glacier were 
C2 
