178 TWELFTH LETTER ON GLACIERS. [1846. 



1842, " is now about 300 feet ;" in August 1846 it was scarcely 

 more than 100 ! and as the glacier towered up to a great 

 height bej^ond, it had all the appearance of menacing the path- 

 way, and once more tearing up the limestone rock. But this 

 will be still more distinctly conceived by referring to Plate VII., 

 figures 1 and 2, which shew the size of the glacier in 1846, 

 contrasted with the view of 1842. Both these sketches were 

 taken from the same spot (marked A on the ground-plan), and 

 as I had not on the latter occasion my former drawing for 

 comparison, the evidence of the increase is the more striking, 

 and the accuracy of outline of the fixed parts of the landscape 

 is confirmed. The increase of height and length of the glacier, 

 as well as its breadth, is here well marked. In consequence 

 of this great accumulation of ice (accompanied, probably, by 

 an increased velocity of motion), the surface of the glacier is 

 exceedingly crevassed, in some places even divided into pin- 

 nacles, and, generally, incapable of being traversed without 

 great difficulty, although, in 1842, I could have walked over it 

 in almost every direction. 



The cause of this very surprising increase is a general 

 one, since most of the glaciers which have been recently ex- 

 amined, present it in a more or less striking degree ; for 

 instance, the Glaciers des Bois and Bossons, in the valley of 

 Chamouni.* The cause is no doubt to be sought partly in the 

 great fall of snow of the two winters 1843-4 and 1844-5, and 

 the cold wet summers which followed them. The immediate 

 effect of the snow is to protect the ice and diminish the annual 

 ablation. Hence the glacier shoots farther into the valley 

 before the waste suffices to equalize the supply. In the cold 

 spring and summer of 1845, this effect appears to have been 

 most conspicuous, as appears from the decisive observations 

 of Balmat, which I have elsewhere published.! The swollen 



* A very striking evidence of this change has occurred at Chamouni. The 

 torrent Arveiron, instead of issuing from heneath the bed of the Glacier des Bois, 

 at its termination, escapes chiefly at a much higher level, and formed, in 1846, a 

 striking cascade on the west side of the glacier, nearly opposite to the Chapeau. 

 A similar occurrence is said to have happened about 30 years ago. 



f Philosophical Transactions, 1846, [pp. 189, 190J, [and pp. 134, 136, of this 

 volume.] 



