2 T. S. Hunt on Alpine Geology. 
its pages to present a condensed summary of our present know- | 
ledge of the structure of Mont Blanc and the adjacent regions. — 
The crystalline rocks of the Alps, as first shown by Studer, 
do not form a continuous chain, but appear as distinct masses, 
separated from each other by uncrystalline sedimentary de- 
oa generally fossiliferous. According to Desor, there are 
etween Nice and the plains of Hungary not less than ah 
four such areas, standing up like islands from out of the sedi 
mentary rocks, and presenting for the most part a fan-like 
structure (en eventail). these masses of crystalline rock, 
Mont Blanc is the most remarkable, and is described by Elie 
de Beaumont as “rising through a solution of continuity in the — 
secondary strata, which may be compared to a great button- 
hole.” The length of this area of crystalline rock, measured 
from the Col du Bonhomme on the S. W. to Saxon in the 
Valais on the N. E., is fifty-nine kilometers, while its breadth, 
from Chamonix on the N. W. to Entréves near Courmayeur 
on the S. E., is fourteen kilometers. The length of the central — 
mass of protogine is, however, only twenty-seven kilometers. Of 4 
the numerous peaks in this area the highest attains an elevation 
of 4810 meters above the level of the sea, being 8760 meters 
above the valley of Chamonix and 3520 meters above the val- 
ley of Entréves. This great mass is described by Favre as sup- — 
ported at the four corners by as many buttresses rising from 
the surrounding valleys, and known as the Cols de Balme, de 
Voza, dela Seigne and de Ferret. The distance between the 
two valleys just named is only 18,500 meters, and the bold- 
ness with which the mountain rises from them is strikingly 
apparent if we take the Col de l’Aiguille du Midi and the Col 
du Géant, which are about 3460 meters above the sea, and dis- 
tant from each other 5,000 meters, giving a slope of about 30°. 
A still greater inclination is obtained if we choose, instead of 
these, the summits of the Aiguilles which bear the same names, 
and, although now isolated, represent portions of the former 
mass of Mont Blanc. 
at the Grands Mulets (4666 meters), the rocks are taleose and 
quartzose schists with graphite, hornblende, epidote, talc, and 
asbestus, and similar rocks and minera found 
to the summit. The protogines themselves, according to the 
evidence of nearly all who have studied them, are stratified 
gneissic in structure, and pass in places into more schis- 
tose varieties, though Favre regards the distinction between 
these and the erystalline schists proper as one clearly marked. 
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