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Show CHAPTEE V. SPECULATIONS CONCEKNING THE CAUSES OF VOLCANIC ACTION. The cause of the succession of rocks apparently a single phase of the more general cause of volcanism.â€" The probable subterranean locus of volcanic activity.â€"Notion of an all-liquid interior.â€"Not associated with volcanicity, and gives no explanation.â€"Large vesicles not tenable.â€"Localization of volcanic phenomena.â€"Independence of vents.â€"Growth and decay of action.â€"Lavas not primordial liquids.â€"Comparison of lavas with metamorphic rocks: First, with reference to chemical constitution; second, mineral components; third, texture.â€"Possibility that lavas are remelted metamorphic rocks.â€"All lavas cannot so originate.â€"Average composition of eruptive and sedimentary rocks compared.â€"Agreement in composition between basalts and sedimentary rocks.â€" Mr. King's hypothesis of segregation of crystals.â€"Primitive magma.â€"Conjectured source of lavas.â€"Dynamical cause of eruptions.â€"Cyclical character of volcanism.â€"Elastic energy of eruptions.â€"Eeal nature of the dynamical problem.â€"The origin of the energy.â€"Increase of local subterranean temperaturesâ€"Eelief of pressure.â€"Access of water.â€"Linear arrangement.â€"Mechanics of eruptions.â€"Penetrating power of lavas.â€"Expelling power.â€"Not effervescence, but pressure of denser rocks overlying their reservoirs.â€"A simple application of hydrostatic laws.â€"Explanation of the sequence of eruptions.â€"A compound function of density and fusibilty.â€"Graphical representation.â€"Discussion of the hypothesis and objections to it.â€"Exceptions and anomalies. I have doubted the propriety of embodying in a work devoted to a statement of observed facts any views of a speculative nature. But the representations of my director and associates have encouraged me to do so, inasmuch as the subject is quite germane to the observations, and the observations are such as have stimulated great curiosity as to their causes. I shall, therefore, present a trial hypothesis, which seems to me to explain the sequence in the eruptive rocks now testified to prevail generally throughout the Rocky Mountain Region. It seems as if the explanation of such an order of facts could only be a phase of the more general cause of volcanism itself. But the origin of volcanic energy is one of the blankest mysteries of science, and it is strange indeed, that a class of phenomena so long familiar to the human race and so zealously studied through all the ages should be so utterly without explanation. Nothing could be further from my intention than propounding 8 h p us |