II.—On the Character and Composition of Lavas

Extract

I Have been gratified by observing of late the appearance among geologists of a more general appreciation of the study of volcanic phenomena,—using that word in its broadest sense, as comprehending not merely the occasional outbursts of vapour, ashes, and lava, but also the action of those subterranean forces, to which alone we are indebted for the existence, now or in former times, of any dry land whatever above the dead sea-level at which the agents of denudation would otherwise maintain the surface of the globe.