Considerations on Volcanos: The Probable Causes of Their Phenomena, the Laws which Determine Their March, the Disposition of Their Products and Their Connexion with the Present State and Past History of the Globe; Leading to the Establishment of a New Theory of the Earth |
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Common terms and phrases
accumulation active volcanos aeriform fluids aperture appear aqueous vapour atmosphere augite augmentation Auvergne basalt beds caloric Cantal cavity ceteris paribus circumstances clinkstone column comminution compact condensation consequently considerable consolidation continually crust crystalline particles crystals current of lava degree dilatation diminished direction distance ebullition effect ejected elastic fluids elevated erup escape exist expansive force explosions external felspar felspathic fissure fluidity fragmentary matters fragments frequently globe gneiss grain granite greater habitual heat increase interior intumescence irregular island Isles lava currents lava rock less liquid lava manner mass of lava Mezen mineral Mont Dor numerous observed occasioned occur orifice overlying parasitical cones paroxysmal phonolitic Ponza pressure produced proportion proportionately quantity ratio remarkable repressive force rise scoriæ sides Solfatara solid specific gravity steam strata Stromboli structure substances subterranean expansion superficial surface take place temperature tion trachytic tufa Vesuvius violence volcanic cone volcanic mountain volcanic phenomena volcanic vent weight
Popular passages
Page 153 - ... felt, and a stream of lava broke out from the side of the cone, at no great distance from its apex. Shortly after this had ceased to flow, a second stream burst forth at another opening, considerably below the first; then a third still lower, and so on till seven different issues had been thus successively formed, all lying upon the same straight line, prolonged from the summit nearly to the base of the mountain.
Page 264 - ... Fresh supplies were probably emitted successively during the course of an eruption which lasted a year; and some of these, resting on those first emitted, might only spread to a small distance from the foot of the cone, where they would necessarily accumulate to a great height. " The showers, also, of loose and pulverulent matter from the six craters, and principally from Jorullo, would be composed of heavier and more bulky particles near the cones, and would raise the ground at their base, where,...
Page 229 - ... its axis and the liquefaction of its outer envelope, would necessarily occasion its actual figure of an oblate spheroid. As the process of expansion proceeded in depth, the original granitic beds were first partially disaggregated, next disintegrated, and more or less liquefied, the crystals being merged in the elastic vehicle produced by the vaporization of the water contained between the laminae. "Where this fluid was produced in abundance by great dilatation — that is, in the outer and highly...
Page 214 - The vallies of either kind have been subsequently enlarged and otherwise modified; and many others, perhaps indeed a far greater number were wholly and entirely excavated by the slow but constant and powerful action of the same causes which are still continually in force ; amongst which the fall of water from the sky, and its abrasive power as it flows over the surface of the land from a higher to a lower level, is the principal.
Page 234 - ... spots, wherever accidental circumstances in the texture or composition of the oceanic deposits led them to yield more readily; and in this manner were produced those original fissures in the primeval crust of the earth through some of which (fissures of elevation) were intruded portions of interior crystalline zones in a solid or nearly solid state, together with more or less of the intumescent granite, in the manner above described; while others (fissures of eruption) gave rise to extravasations...
Page 18 - There unquestionably exists within and below volcanic vents, a body of lava of unknown dimensions, permanently liquid at an intense temperature, and continually traversed by successive volumes of some aeriform fluid, which escape from its surface — thus presenting all the appearance of a liquid in constant ebullition.
Page 163 - Such a catastrophe destroyed, in the year 1638, a colossal cone called the Peak, in the Isle of Timor, one of the Moluccas. The whole mountain, which was before this continually active, and so high that its light was visible, it is said, three hundred miles off, was blown up and replaced by a concavity now containing a lake.
Page 102 - the current had all the appearance of a huge heap of rough and large cinders rolling over and over upon itself by the effect of an extremely slow propulsion from behind. The contraction of the crust as it solidified, and the friction of the scoriform cakes against one another, produced a crackling sound. Within the crevices a dull red heat might be seen by night, and vapour issuing in considerable quantity was visible by day.
Page iv - Geology has for its business a knowledge of the processes which are in continual or occasional operation within the limits of our planet, and the application of these laws to explain the appearances discovered by our Geognostical researches, so as from these materials to deduce conclusions as to the past history of the globe.
Page 17 - ... at a brilliant white heat, may be seen alternately rising and falling within the chasm which forms the vent of the volcano. At its maximum of elevation one or more immense bubbles seem to form on the surface of the lava, and*rapidly swelling, explode with a loud detonation.