File:The Quarterly journal of the Geological Society of London (12711461403).jpg

18 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. .NoV. 15,
peculiarities of interest ; it exhibits the junction of two beds of gypsum
of very different characters, separated by an irregular waving line,
which is on the whole vertical, striking E. The southern portion is
traversed by well-marked planes of cleavage, dipping S. 70°, along
which are small folia of talc, giving the mass a grey colour. The
northera bed is a pure white gypsum, quite free from cleavage ; the
annexed woodcut, fig. 1, will give a rough idea of this arrangement.
Fig. 1.
S 1/
A /
/ Y / \
/ -'1 / /
1 1 . I
Talcose Gypsum. Pure white Gypsum.
It appears from these sections that there are two deposits of gypsum
of very different ages in the valley of Chamoanix ; the earlier one
laminated, the later deposited after the lamination of the rocks was
completed. In both these cases the detritus concealed the base of
the gypsum.
The lower part of the valley of Chamounix is so much filled up
by detritus that I despaired of finding anywhere the central axis of
the valley exposed ; but since my return I observe that Saussure
mentions at § 656, that at Blaitiere, to the east of the village of
Chamounix, the foliation of the crystalline schists is nearly hori-
zontal, striking N.E., from which spot the inclination gradually in-
creased as he ascended towards Mont Blanc. This observation bears
out what I had inferred, that the foliation of Mont Blanc and the
Aiguilles Rouges forms together a complete arch, the crown of which
runs down the valley of Chamounix.
In Section No. 5, PI. I., I have given a rough sketch of the posi-
tion of the bedding and cleavage of the rocks seen in crossing the Col
du Bonhomme from Nant Bourant to Chapieux. The Bonhomme is
exactly on the southern prolongation of the western line of vertical
foliation of Mont Blanc. The section is a most interesting one, and