It is highly probable that, between the oldest trachytes of Tuscany
and the newest rocks in the neighbourhood of Naples, a series of volcanic
products might be detected of every age from the Older Pliocene to the
historical epoch.
PLIOCENE VOLCANOES OF THE EIFEL.
Some of the most perfect cones and craters in Europe, not even excepting those
of the district round Vesuvius, may be seen on the left or west bank of the
Rhine, near Bonn and Andernach. They exhibit characters distinct from any which
I have observed elsewhere, owing to the large part which the escape of aqueous
vapour has played in the eruptions and the small quantities of lava emitted. The
fundamental rocks of the district are grey and red sandstones and shales, with
some associated limestones, replete with fossils of the Devonian or Old Red
Sandstone group. The volcanoes broke out in the midst of these inclined strata,
and when the present systems of hills and valleys had already been formed. The
eruptions occurred sometimes at the bottom of deep valleys, sometimes on the
summit of hills, and frequently on intervening platforms.
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