ím
68 STRATIFICATION.
STRATIFICATION. 6 9
R
town of Tliones, there is a rock which presents
an appearance of double stratification,
not uncommon in the calcareous mountains
of the Alps, and which has frequently induced
Saussure to suppose that vertical
strata were placed in junction with other
strata nearly horizontal ; an error into
which he has been led, by mistaking very
distinct vertical cleavages for stratification.
On approaching this rock, I had little
doubt that the strata were vertical; but
when I came in front of it, I perceived the
true strata-seams forming curves, which
were intersected at one end by a vertical
cleavage, as in the annexed figure.
It sometimes happens that the strata-seams
are entirely concealed in a perpendicular
escarpement of rock, by a calcareous incrustation
deposited over the face of the
rock, and, in such instanc*es, the cleavages
often project and resemble strata so much
that it requires great care to avoid error
in tracing the true line of dip in the stratification.
This probable cause of error is of
very frequent occurrence in the Alps, and
I shall again have occasion to refer to it.
The air in the valley, which had been
extremely sultry and close during the day,
now became cool and refreshing, and as
the shades of night approached, they threw
an imposing solemnity over the impending
cliffs ; but my enjoyment of the scenery
was disturbed by an unforeseen accident.
The poor donkey on which I rode became
lame, his master having sent him unshod.
This greatly retarded our progress ; and
long before we had descended the mountains,
the sun had set, and it was so dark
that we could with difficulty discover thé
road. As we were proceeding at a very
slow pace, my guide’s foot slipt, and he
fell down a considerable descent into a
vineyard; but fortunately he received no