10
THE ERUPTION OF
PELﾃ右
channel of exit, and the curving over of the mass to one side would seem to point to extrusion from beneath a somewhat vaulted or curved casing. One could well compare the structure and its method of escape to a core of paint issuing by pressure from an oil-tube. The general surface-covering was in color ruddy gray, brown and purplish in part, but on the smooth face it was nearly white, a condition probably in some way associated with the rubbing on that side and with the presence of sublimation products on the surface. As to the fundamental and inner construction of this remarkable volcanic appendage, our knowledge until the beginning of 1906 was largely conjectural. Seen with a powerful glass from a point of nearest approach, perhaps 700 feet, the rock appeared "burnt-out," like a furnace-product; and the noise given out by the falling particles and boulders was generally like that of falling clinkers, which led to the supposition that the mass might on the whole be cavernous. But its rigid adherence and resistance to a prodigious crushing strain lent little countenance to this view. The noise from the more imposing discharges of dejecta was like that of rolling thunder, at times barely distinguishable from the roar of the volcano itself, and could only have been produced by the avalanching of compact rock. In a fifth ascent of the volcano, which I made on Feb. 17, 1906,* when, by reason of the dying down of the activities of the mountain, it was made possible to descend into the crater and reach the wilderness of boulder-debris which resulted from the breaking apart of the obelisk, I determined the constitﾂｭ uent rock of the obelisk to be a wholly compact, fine-grained hyperstheneandesite, wholly free from either a vesicular (or scoriaceous) or obsidian-like structure, and giving no indication of having undergone recent fusion, and there was nothing in this examination to give countenance to the surmise that the interior of the obelisk might possibly have been hollow, with fluidal lava, hidden from view by the massive outer walls, contained within. Had such an enclosed flowing magma really existed, there would certainly have been lava overflows at one time or another. On the other hand, that the obelisk was rifted and had irregular passages through it or through parts of it, into which lava was at times injected, is certain; and the members of the Lacroix mission on more than one occasion noticed areas and lines of incandescence in the basal portion of the core, which they associated with flowing lava-masses. Indeed, it can hardly be doubted that the fall or disruption of the giant monolith was brought about in great or greater part as a result of steam expansions in the interior. On the night preceding my fourth ascent of the volcano, June 12, 1903, the southwest base of the rock-core was resplendently luminous, made so either by actually rising lava or by a partial remelting of that portion of the structure. From a distance of a few miles, whence this magnificent spectacle was seen, * An account of this ascent is published in the National Geographic Magazine, for August, 1906.