Show i c mob r SOURCE OF VOLCANIC ACTIVITy In a recently published volume on I volcanoes Prof C Ocoltor undertakes to toll why volcanoes havo eruptions Melted rock such ns Is flung from Vesuvius Ve-suvius requires a temperature of 1600 degrees Fahrenheit so that It becomes liquid only far down In the earth perhaps per-haps 60 or 100 mires Below the outer crust of cooled and solidified rocks thero must be a larger zone of rock which still remains solid because Its temperature Is less than that of the melting point corresponding to the pressure under which It rests and below that again there must bo rock or magma in n state of fusion it Is to this magma that Prof Dooltor looks for the primary source of all volcanic activity At the saran tlmo tire depth at which this primary reservoir of inn Km a lies and tin pressure under which It Is confined are so groat that ti direct eruption from It Is Inconceivable Inconceiv-able but when by irovoments In tho overlying crust or otherwise a channel chan-nel Is opened the mntjmn may rise ton to-n depth whoro It In 1 surrounded by rock at a lower temperature than tho molting point In tlioso circumstances solidification begins From all volcanoes largo quantities of steam of carbonic ncld and other gases nro evolved and the course of every lava stream is marked by clouds of steam ovolvod from the cooling lava At one tlmo and the Idea la still common this steam was supposed sup-posed to have been derived from seawater Sea-water which had obtnlndd access to the molten lava whilo still underground under-ground but this explanation is now generally rejected being impossible In some cases and Inadequate In all and tho greater part of the steam and other oth-er emanations from n volcano are now regarded as directly derived from an original store In the interior of the earth However this may be It Is COP tnln that tho magma from which volcanic vol-canic lava Is derived Is not merely in a state of Igneous fusion but Is combined com-bined with water and gases which am I given off as It solidifies and by their h escape frequently form miniature volcanoes vol-canoes on the surface of lava streams If the solidification takes place underground un-derground tho steam and gases are expelled and If there la no free escape es-cape pressure may Increase llll II becomes great enough to overcome the resistance of the overlying rock mud so lend to an eruption and the formation of n volcano whoso character charac-ter will depend on the nature of the I reservoir from which tho eruption took place |