FACTS AND CONSIDERATIONS ON THE STRATA OF MONT BLANC, AND ON SOME
INSTANCES OF TWISTED STRATA OBSERVABLE IN SWITZERLAND.[27]

270. The granite ranges of Mont Blanc are as interesting to the
geologist as they are to the painter. The granite is dark red, often
inclosing veins of quartz, crystallized and compact, and likewise
well-formed crystals of schorl. The average elevation of its range of
peaks, which extends from Mont Blanc to the Tete Noire, is about 12,000
English feet above the level of the sea. [The highest culminating point
is 15,744 feet.] The Aiguille de Servoz, and that of Dru, are excellent
examples of the pyramidal and spiratory formation which these granite
ranges in general assume. They rise out of immense fields of snow, but,
being themselves too steep for snow to rest upon, form red, bare, and
inaccessible peaks, which even the chamois scarcely dares to climb.
Their bases appear sometimes abutted (if I may so speak) by mica slate,
which forms the southeast side of the Valley of Chamonix, whose flanks,
if intersected, might appear as (in _fig._ 72), _a_, granite, forming on
the one side (B) the Mont Blanc, on the other (C) the Mont Breven; _b_,
mica slate resting on the base of Mont Blanc, and which contains
amianthus and quartz, in which capillary crystals of titanium occur;
_c_, calcareous rock; _d_, alluvium, forming the Valley of Chamonix. I
should have mentioned that the granite appears to contain a small
quantity of gold, as that metal is found among the granite debris and
siliceous sand of the river Arve [_Bakewell_, i. 375]; and I have two
or three specimens in which chlorite (both compact and in minute
crystals) occupies the place of mica.

J. R.

_March_, 1834.

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With this paper were printed some observations on it by the Rev. W. B.
Clarke, after which (p. 648) appears the following note by J. R.

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271. "TWISTED STRATA.--The contortions of the limestone at the
fall of the Nant d'Arpenaz, on the road from Geneva to Chamonix, are
somewhat remarkable. The rock is a hard dark brown limestone, forming
part of a range of secondary cliffs, which rise from 500 feet to 1000
feet above the defile which they border. The base itself is about 800
feet high. The strata bend very regularly except at _e_ and _f_,[28]
where they appear to have been fractured.

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_To what