182 



TWELFTH LETTER ON GLACIERS. 



[1846. 



Veined Structure. Glacier of La Brenva. 



I must now proceed to notice an observation of a very 

 interesting kind which my visit of 1846 to this glacier enabled 

 me to make, and which seems perfectly conclusive as to the 

 truth of the explanation which I have elsewhere given of the 

 origin of the veined structure, so important to the correct theory 

 of glacier motion. The present appears to me to be an experi- 

 mentum crucis ; I can only hope that it [the peculiarity in 

 question] may remain in existence long enough to convince all 

 those who have any remaining doubts on the subject. 



The glacier of La Brenva is distinguished by the beauty of 

 its structure. I have described it in my Travels, p. 202, and 

 endeavoured to represent it in Plate V. of that work. This 

 was as it existed in 1842. But now that the ice has risen up 

 against the promontory B, Plate VIII. fig. 1 [of the present 

 volume], and has filled up the bay C, the structure opposite to 

 B has become developed in the most remarkable and beautiful 

 manner. The plates of green and white ice alternating in the 

 direction of the lines E D, not close to the foot of the rock at 



Fig. 21. 



B, but at a little distance, the veins E D running in the direc- 

 tion of the declivity of the glacier, and beginning to be deve- 

 loped at E, becoming more and more so towards D, where they 

 form a tangent to a swelling surface of rock, whose resistance 

 evidently gives rise to them. It seems clear that all the ice 

 within the line F E D, or between it and the shore i C B D is 

 embayed, as it were, and has but little motion, in consequence 



