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XV. On the Veined Structure of Glaciers; with observations wpon White Ice-seams^ 
Air-bubbles and Dirt-bands^ and remarks upon Glacier Theories. By John Tyndall, 
F.B.S., Professor of Natural Philosophy, Boyal Institution. 
Eeceived February 24, — Eead February 24, 1859. 
§ 1. Introduction. 
On the 20th of May, 1858, I communicated a paper to the Royal Society, containing an 
account of observations made upon the Mer de Glace of Chamouni. In addition to the 
questions there discussed, another of great importance occupied my attention during 
my sojourn at the Montanvert, and that was the veined structure of the ice. To 
obtain information on this head, I visited almost every portion of the Mer de Glace and 
its tributaries ; I examined the Talefre and Lechaud glaciers, and spent several day& 
amid the seracs of the Glacier du Geant. To investigate the connexion, if any, between 
the structure of the glacier and the stratification of its neve I ascended the Col du 
Geant, and aftei-wards inspected the magnificent ice-sections exhibited in the dislocations 
of the Grand Plateau and other portions of Mont Blanc. 
During this investigation my convictions were by no means fixed; cases strongly 
suggestive of the influence of pressure, in producing the structure, came before me, and 
again other cases appeared which suggested, with almost equal force, the influence of 
stratification. The result, however, of the observations on the Mer de Glace was a 
strong opinion Wot pressure was the true cause of the phenomenon. 
But I could not help feeling that the facts and arguments which I was in a position 
to bring forward would still leave the question an open one. They might influence the 
, opinions of others, as they had influenced mine ; but 1 had nothing to advance on which 
I the mind could rest with perfect certainty. In short, neither the Mer de Glace nor its 
I tributaries furnished facts capable of completely deciding the question. The subject 
; being one on which a great deal had been written and retracted, I was unwilling to 
swell the bulk of the literature connected with it, while a possibility remained that 
what I had to say upon the subject might also require withdrawal, I therefore thought 
it better to wait another year ; to extend the range of my observations, to visit glaciers 
in which the mechanical conditions of strain and pressure were different from those of 
the Mer de Glace. Thus by varying the circumstances, and observing Nature at work 
under different conditions, I hoped to confer upon the investigation the character and 
precision of an experimental inquiry. 
The course of the inquiry in 1858 was as follows: — I first examined the glaciers of 
Grindelwald; crossing the Strahleck, I ascended the lower glacier of the Aar to the 
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