on has undergone within the period
alluded to, some tracts which were previously land having gained in
altitude, others, on the contrary, having sunk below their former level.

That the existing lands were not all upheaved at once into their present
position is proved by the most striking evidence. Several Italian
geologists, even before the time of Brocchi, had justly inferred that
the Apennines were elevated several thousand feet above the level of the
Mediterranean before the deposition of the modern Subapennine beds which
flank them on either side. What now constitutes the central calcareous
chain of the Apennines must for a long time have been a narrow ridgy
peninsula, branching off, at its northern extremity, from the Alps near
Savona. This peninsula has since been raised from one to two thousand
feet, by which movement the ancient shores, and, for a certain extent,
the bed of the contiguous sea, have been laid dry, both on the side of
the Mediterranean and the Adriatic.

[Illustration: Fig. 7.]

The nature of these vicissitudes will be explained by the accompanying
diagram, which represents a transverse section across the Italian
peninsula. The inclined strata A are the disturbed formations of the
Apennines, into which the ancient igneous rocks a are supposed to have
intruded themselves. At a lower level on each flank of the chain are the
more recent shelly beds _b b_, which often contain rounded pebbles
derived from the waste of contiguous parts of the older Apennine
limestone. These, it will be seen, are horizontal, and lie in what is
termed "unconformable stratification" on the more ancient series. They
now constitute a line of hills of moderate elevation between the sea and
the Apennines, but never penetrate to the higher and more ancient
valleys of that chain.

The same phenomena are exhibited in the Alps on a much grander scale;
those mountains being composed in some even of their higher regions of
the newer secondary and oldest tertiary formations, while they are
encircled by a great zone of more modern tertiary rocks both on their
southern flank towards the plains of the Po, and on the side of
Switzerland and Austria, and at their eastern termination towards Styria
and Hungary.[198] This newer tertiary zone marks the position of former
seas or gulfs, like the Adriatic, wherein masses of strata accumulated,
some single groups of which are not inferior in thickness to the most
voluminous of our secondar