Veined Structure. 99 



To fix the position of the lowest point of the glacier in the 

 valley, a line joining the vault of ice from which the river 

 Doire issues, and the door of the chapel of Notre Dame (ob- 

 served from below), runs S. 42° W. magnetic. 



On the whole, the observations of this year on the sur- 

 prising extension of this glacier during the short space of 

 four years under the influence of meteorological circum- 

 stances, peculiar no doubt, but scarcely anomalous, confirm 

 amply the remarks which I formerly made (Travels, p. 205), 

 on the great extension which it underwent in 1818. Were 

 the climate of the years 1844 and 1845 to become perma- 

 nent, the increase of all glaciers would evidently be enor- 

 mous. In fact, a more turbid and cloudy atmosphere, with 

 an increase of the usual precipitations, would suffice to in- 

 crease glaciers to almost any extent; a great degree oi dry 

 cold would not produce the desired effect (viz., an exten- 

 sion which would account for the erratic phenomenon), a 

 temperate climate being most favourable to the growth, 

 especially the progression, of glaciers. 



Veined Structure. Glacier of La Brenva. 



I must now proceed to notice an observation of a very in- 

 teresting 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 cor- 

 rect theory of glacier motion. The present appears to me 

 to be an experimentum crucis ; I can only hope that it 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 II., fig. 1), and 

 has filled up the bay C, the structure opposite to B has be- 

 come developed in the most remarkable and beautiful man- 

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



