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Show 140 GEOLOGY OF THE HIGH PLATEAUS. In as they are useful or otherwise in explaining a wider and wider range of facts. This was true of the hypothesis of a luminiferous ether and of gravitation. Neither of these postulates could be proven a priori, and have gained acceptance because they explain all facts to which they stand related. Following these precedents, we may inquire whether a rise of subterranean temperature is consistent with other categories of facts besides a succession in the order of eruptions and explains other phenomena. I have endeavored to show that the whole tenor and purport of the phenomena of volcanicity point to the conclusion that lavas are not primordial liquids but secondary products derived from the liquefaction of solid matter situated below the surface in layers or maculae. Of this statement of the case in its grosser aspect I believe the circumstantial evidence sufficient to convince a scientific and impartial jury. Taking a generalized view of the subject, the objections against primordial liquids are insuperable. If the whole interior of the earth below a crust a few miles in thickness is liquid, the stability of that crust is intelligible only on the assumption that the crust is less dense than the liquid, and if the reverse is true it seems inevitable that the crust would be speedily submerged. The same reasoning would be applicable to residuary vesicles or primordial reservoirs of great extent underlying states and empires. If we adopt the conception of a multitude of small vesicles left by the secular consolidation of the globe gradually squeezed out one after another, other difficulties equally palpable arise. These vesicles should, in the process of ages, become fewer and fewer, and show signs of exhaustion. But observation teaches us that the eruptions of Tertiary time are apparently as numerous, as varied, and as grand as any which have occurred in anterior ages. But, above all, the intermittent pulsating character of the eruptions in any volcanic cycle is at variance with such an assumption. If this primordial liquid has lain in its receptacle, possessing, from the beginning of the world, all the essential requisites of eruptibility except that it is waiting for some accident to open a vent for it, yet, when the vent is once opened, why does it not pour forth at one mighty belch all its lavas and then close up forever? Why should it require some hundreds or even thousands of eructations with intervals of years to completely exhaust it? Why, in the course of the cycle covering |