326 Ascent of the Jungfrau in 1841. 
become paler as our eyes turned downwards. Unfortunately 
we had neglected to bring a cyanometer with us, which would 
have enabled us to indicate the difference in the degrees of 
intensity. Mr Forbes observed the polarisation of the sky, 
and found it perfectly normal and similar to what he had ob- 
served in the plain at the same hour, although a little less in- 
tense. Now, as the intensity of this phenomenon depends on 
the quantity of reflected light, it is natural that it should be 
less sensible when the sky is of a very deep colour. 
The rock in situ, near the summit, on the edge of the 
ridge which overlooks the Rottthal, is gneiss. Although 
very compact, it easily splits into small fragments; its sur- 
face assumes a coppery appearance from the effects of oxy- 
disation, but the fresh fractures are greenish, with large 
crystals of felspar, having a pearly lustre. The existence of 
this rock, in such a locality, is an important fact for geology, 
for this reason that gneiss being, to all appearance, a meta- 
morphie rock, its presence on one of the highest summits of 
the Alps is sufficient of itself to demonstrate, that the eleva- 
tion has not been effected here by crystalline masses rising 
from the bosom of the earth, and spreading over the summits 
of the crests, as must have been the case with many systems 
of mountains, among others that of Mont Blanc, the centre 
of which is protogene, flanked with gneiss and other stratified 
rocks. It is long since our most skilful geologists have ex- 
pressed the opinion, that true granite does not exist in the 
chain of the central Alps, and that all the crystalline rocks, 
even the most compact, shew marks, more or less distinct, of 
stratification (the demi-granite of MM. Studer and Escher), 
and are, consequently, metamorphosed rocks. Now, assuredly 
there is no granite on the summit of the Jungfrau, and it may 
be presumed that it is likewise wanting on the less elevated 
peaks in its vicinity. 
To our great surprise, we discovered on the surface of the 
exposed rock, as well as on the fragments detached from it, 
many lichens in a very fresh state, some of which occupied a 
surface of many inches in diameter. Our celebrated lichen- 
ologist, the minister M. Scherer, recognised among them 
