A Manual of Elementary Geology: or, The Ancient Changes of the Earth and its Inhabitants as Illustrated by Geological MonumentsLyell, Charles, Sir
Science
A Manual of Elementary Geology: or, The Ancient Changes of the Earth and its Inhabitants as Illustrated by Geological Monuments
Lyell, Charles, Sir
Geology
There are also numerous instances in Sicily of terraces of denudation. One
of these occurs on the east coast to the north of Syracuse, and the same is
resumed to the south beyond the town of Noto, where it may be traced
forming a continuous and lofty precipice, _a b_, fig. 94., facing towards
the sea, and constituting the abrupt termination of a calcareous formation,
which extends in horizontal strata far inland. This precipice varies in
height from 500 to 700 feet, and between its base and the sea is an
inferior platform, _c b_, consisting of similar white limestone. All the
beds dip towards the sea, but are usually inclined at a very slight angle:
they are seen to extend uninterruptedly from the base of the escarpment
into the platform, showing distinctly that the lofty cliff was not produced
by a fault or vertical shift of the beds, but by the removal of a
considerable mass of rock. Hence we may conclude that the sea, which is now
undermining the cliffs of the Sicilian coast, reached at some former
period the base of the precipice _a b_, at which time the surface of the
terrace _c b_ must have been covered by the Mediterranean. There was a
pause, therefore, in the upward movement, when the waves of the sea had
time to carve out the platform _c b_; but there may have been many other
stationary periods of minor duration. Suppose, for example, that a series
of escarpments _e_, _f_, _g_, _h_, once existed, and that the sea, during a
long interval free from subterranean movements, advances along the line _c
b_, all preceding cliffs must have been swept away one after the other, and
reduced to the single precipice _a b_.
[Illustration: Fig. 94. Cross section.]
[Illustration: Fig. 95. Valley called Gozzo degli Martiri, below
Melilli, Val di Noto.]
That such a series of smaller cliffs, as those represented at _e_, _f_,
_g_, _h_, fig. 94., did really once exist at intermediate heights in place
of the single precipice _a b_, is rendered highly probable by the fact,
that in certain bays and inland valleys opening towards the east coast of
Sicily, and not far from the section given in fig. 94., the solid limestone
is shaped out into a great succession of ledges, separated from each other
by small vertical cliffs. These are sometimes so numerous, one above the
other, that where there is a bend at the head of a valley, they produce an
effect singularly resembling the seats of a Roman amphitheatre. A good
example of this configuration occurs near the town of Melilli, as seen in
the annexed view (fig. 95.). In the south of the island, near Spaccaforno,
Scicli, and Modica, precipitous rocks of white limestone, ascending to the
height of 500 feet, have been carved out into similar forms.
[Illustration: Fig. 96. Cross section.]
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