" The facts that have been enumerated, and to which sufficient
attention has not been bestowed, render it probable that the vicinity of the
sea, and the penetration of sea water to the foci of volcanoes, are not
absolutely necessary to the eruption of
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subterranean fire, and that littoral situations only favor the eruption by
forming the margin of a deep sea basin, which, covered by strata of water,
and lying many thousand feet lower than the interior continent, can offer
but an inconsiderable degree of resistance.
The present active volcanoes, which communicate by permanent craters
simultaneously with the interior of the earth and with the atmosphere, must
have been formed at a subsequent period, when the upper chalk strta and all
the tertiary formations were already present: this is shown to be the fact
by the trachytic and basaltic eruptions which frequently form the walls of
the crater of elevation. Melaphyres extend to the middle tertiary
formations, but are found already in the Jura limestone, where they break
through the variegated sandstone.*
[footnote] *Dufrenoy et Elie de Beaumont, 'Explication de la Carte
Geologique de la France', t. i., p. 89.
We must not confound the earlier outpourings of granite, quartzose porphyry,
and euphotide from temporary fissures in the old transition rocks with the
present active volcanic craters.
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