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Show LOCAL CHARACTER OF VOLCANIC PHENOMENA. 115 than the crust. If the liquid were lighter an eruption would be inevitable, and once started would continue until the lighter liquid had all found its way to the surface. If the liquid were heavier, it could no more be erupted than a frozen lake could erupt its waters and pour them over its icy covering. Lest these considerations should seem too purely speculative to authorize us to conclude that lavas cannot be emanations from a general liquid interior or from vesicles holding primordial liquid magma, we may turn to other considerations more concrete and bearing more directly upon the point. Volcanic eruptions are very local phenomena. At any given epoch they are confined to a few localities of very small relative extent. They have no general distribution in the sense of a widely-extended and connected system. Each volcano is an independent machineâ€"nay, each vent and monticule is for the time being engaged in its own peculiar business, cooking as it were its special dish, which in due time is to be separately served We have instances of vents within hailing distance of each other pouring out totally different kinds of lava, neither sympathizing with the other in any discernible manner nor influencing the other in any appreciable degree. Again, we find vents at high levels and at low levels in close proximity with each other, and both delivering the same kind of lava. The great craters of the Sandwich Islands are remarkable instances of this kind, and indicate that each crater derives its lavas from a distinct reservoir. It is inconceivable that a liquid from a common reservoir could rise and outflow from the loftier vent while the lower vent remained open. The same phenomenon is exhibited at JEtna and in Iceland and other active volcanoes. Then, too, we have the outpouring of widely distinct kinds of lava from the same orifice at successive epochs, and as a general rule the grander volcanoes present a succession of eruptions marked by different kinds of lava; and it should be noted that these varieties of ejecta are not intermixed nor formed by the commingling of two or more magmas, nor do they present intermediate and transition types, but each coulee has a well-defined character, which serves to distinguish it and assign it to its proper place in the classification. All these subordinate phenomena, and many others which it is needless to mention here, are apparently incon- |