Briefly summarized the Hawaian type of volcanic action is ex pressed by the caldera, by basalt, the most easily fused of all vol canic rocks, by the development of an ascensive column from whose summit lakes of molten lava accumulate and flow away in termittently, by a sympathetic uprising in adjacent calderas, by the building up of domes rather than cones from material forced up from below by subterranean power, by displaying magnificent fountains of fire, and usually by rather quiet eruptions and few earthquakes. By way of contrast Vesuvius possesses a cone with curved sides ; while basaltic it is composed largely of the trachytic element, builds up cinder cones and discharges bombs and stones in an explosive manner. It was the common doctrine at the time of my visit in i866 that the eruptions followed the filling of the crater with debris, on the principle that the free egress of volcanic matter was impeded, and that the obstacle must be removed. In i866 no crater existed, it had been filled up ; and true to the prin ciple stated, an eruption ensued in the following year, The ques tion whether there may be an ascensive column has not been studied at Vesuvius. Mineral chlorids are plentiful, as sug gested by the greater nearness to the sea, four miles, as con trasted with Kilauea nine and Mauna Loa twenty.
There are some minor points of agreement between the types. They both have periods of filling up, discharging and collapsing, or intermittent action. Some of the vents are fissures at the base
of the mountain. The streams of lava form tunnels and show the ropy structure. Both present the spectacle of a dark cloud said to resemble a pine tree, which consists of vapors carrying ashes that are spread over the adjacent country.
Vesuvius is a small volcano compared with Kilauea. The cavity left in Halemaumau in i886, say half a mile across and six hundred feet deep, represents the size of a crater of Vesuvius. At Kilauea this was but a minor discharge.
Possibly it may be better to claim that every volcano has its own type of eruption. Thus, Pelee, in Martinique, was char acterized by the terrible hot blast of steam and vapors directed down the mountain side, with mud flows and the rising of the obelisk ; Krakatoa by a tremendous explosion with wonderful attendant atmospheric phenomena ; Tarawera by the discharge of ashes, mud and scoria from a long rent accompanied by geyser like action ; Baldaisan by the ascent of a dense column of steam and dust with many explosions, a landslide, no flow of lava, and geyser-like action, all accomplished in six hours ; Stromboli, by a constant ebullition of liquid lava, known to be active for 2,000 years, and so easily affected by the weight of the atmosphere that it serves as a barometer to the passing ships.