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418 S T R A T I F I C A T I O N .
in the Alps, and that the upper earthy
limestones of the English, acquire the hardness
and other mineral characters of marble.
This fact, which has hitherto been little
known or regarded, taken in conjunction
with the fossil remains, furnish the tru e
key to the comparative geology of these
vast ranges of mountains. It is true, we
can seldom trace an exact similarity in the
geological characters of rocks of distant
countries, but we may find a near approximation.
Thus the strata in th e Swiss
Alps, which contain gypsum and rock-salt,
agree more with our lias and lias clay, than
with any of the lower formations; and as
our lias clay is eminently saliferous, the
agreement is still so far preserved.* The
limestones that are associated with gypsum
and salt in the Tarentaise, at least, those
which 1 examined, may, perhaps, more
properly be classed with the magnesian
limestone in the red marie in England ;
they have no resemblance to lias.
But if the limestones in the Alps, that
* It is true the muriat of soda, or common salt, in
our lias, is generally more or less intermixed with other
salts, but this cannot affect the question. The strata
in contact with gypsum in the Vallois, I observed, bore
a strong resemblance to lias limestone.
S T R A T I F I C A T I O N . 419
correspond to our upper limestones in their
geological characters, difier from them
greatly in their mineralogical characters,
they do not differ less in their stratification.
In England these limestones generally
occur nearly flat and horizontal ; whereas
in the Alps they are most frequently bent
into deep curves, or are highly inclined.
This curved or arched stratification commences
with the Jura, and is extended far
into Savoy ; it produces a variety of remarkable
appearances of irregular and contorted,
or waved strata, according as the
escarpements which cut into the mountains
change their direction, or are more
or less irregular. The strata at the summits
of the mountains are often flat, but dip
down rapidly on each side. In the calcareous
mountains, at a distance from the
central range of the Alps, the escarpements
generally face the north or north-west;
but nearer tbe central range, they face
to the south or south-west. Where the
mountain is not broken by escarpements,
the strata on the opposite sides dip in different
directions.
That this curved stratification has been
produced by a force directed from beneath,
must appear evident to the unprejudiced
E E 2
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