by the new volcanoes; but we
have scarcely sufficient data to bear out such a conjecture. The older
rocks of the island consist, in a great measure, of that kind of
basaltic lava called dolerite, sometimes columnar, and partly of common
basalt and amygdaloid. Some recent lavas assumed, on entering the sea, a
prismatic form, and so much resembled the older lavas of the Canaries,
that the only geological distinction which Von Buch appears to have been
able to draw between them was, that they did not alternate with
conglomerates, like the ancient basalts. Some modern writers have
endeavored to discover, in the abundance of these conglomerates, a proof
of the dissimilarity of the volcanic action in ancient and modern times;
but this character is more probably attributable to the difference
between submarine operations and those on the land. All the blocks and
imperfectly rounded fragments of lava, transported during the intervals
of eruption, by rivers and torrents, into the adjoining sea, or torn by
the continued action of the waves from cliffs which are undermined, must
accumulate in stratified breccias and conglomerates, and be covered
again and again by other lavas. This is now taking place on the shores
of Sicily, between Catania and Trezza, where the sea breaks down and
covers the shore with blocks and pebbles of the modern lavas of Etna;
and on parts of the coast of Ischia, where numerous currents of trachyte
are in like manner undermined in lofty precipices. So often, then, as an
island is raised in a volcanic archipelago by earthquakes from the deep,
the fundamental and (relatively to all above) the oldest lava will often
be distinguishable from those formed by subsequent eruptions on dry
land, by their alternation with beds of sandstone and fragmentary rocks.

The supposed want of identity, then, between the volcanic phenomena of
different epochs resolves itself partly at least into the marked
difference between the operations simultaneously in progress, above and
below the waters. Such, indeed, is the source, as was before stated in
the First Book (Chap. V.), of many of our strongest theoretical
prejudices in geology. No sooner do we study and endeavor to explain
submarine appearances, than we feel, to use a common expression, out of
our element; and unwilling to concede that our extreme ignorance of
processes now continually going on can be the cause of our perplexity,
we take refuge in a "pre-existent order of