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http://geology.19thcenturyscience.org/books/1902-Geikie-Geology/README.htm DYNAMICAL where lava is GEOLOGY 395 directly exposed to the atmosphere, without receiving protection from occasional showers of volcanic ash, or where liable to be washed bare by heavy torrents of rain, its surface decays in a few years sufficiently to afford soil for stray plants in the crevices. When these have taken root they help to increase the disintegration; is the overspread, from its surface. traces of at last, as the rock its volcanic origin fade away Some of the Vesuvian lavas of the pres ent century already support vineyards. Elevation and Subsidence.-P roofs of elevation are fre quent among volcanic vents which, lying near the' sea and containing marine sediments among their older erupted ma terials, supply, in the inclosed marine organisms, of the movement. vius, submarine vents, dimensions not rials, In this way, it is known that Etna, Vesu and other Mediterranean tory as evidence only to and the volcanoes, that they began owe their his their present accumulation of ejected mate but also, to some extent, to an elevation of the sea bottom. Proof of subsidence is less easily traced, but indications have been observed of a sinking of the ground volcanic vent. very decided beneath a During the eruption of Santorin in 1866-67,, but extremely local subsidence near the vent in the centre of the old crater. took place The discharge of such prodigious quantities of material may tend to pro duce cavernous spaces in the terrestrial crust, and the weight of the ejected lavas and tuffs may still further contribute to a general settlement of the ground around a volcanic focus. If we consider the records of volcanic action in past geo. logical time we meet with many proofs that it took place in areas where the predominant terrestrial movement was one of subsidence. Thus among the Pahoozoic systems of Brit.