Not infrequently the beds of tuff composing the flanks of the volcano, upon dissection by the same process, bring to light walls of cooled lava standing in relief (Fig. 147)—the filling of the fissure which gave outlet to the flanks of the mountain at the time of the eruption. Study of exposed dikes formed in connection with recent eruptions of Vesuvius has shown that in many instances they are still hollow, the lava having drained from them before complete consolidation. Another agent which is effective in uncovering the buried structures of volcanoes is the action of waves on shores. Always a relatively vigorous erosive agency, the softer structures of volcanic cones are removed with especial facility by this agent. On the shores of the island of Volcano, the little cone of Vulcanello has been nearly half carried away by the waves, so as to reveal with especial perfection the structure of the cinder beds as well as the internal rock skeleton of the mass. Here the characteristic dips of lava streams, intercalated as they now are between tuff deposits and the lava which consolidated in fissures, are both revealed. [Illustration: FIG. 148.—Map and general view of St. Paul’s Rocks, a volcanic cone dissected by waves.] In mid-Atlantic a quite perfect crater, the St. Paul’s Rocks, has been cut nearly in half so as to produce a natural harbor (Fig. 148). In still other instances we may thank the volcano itself for opening up the interior of the mountain for our inspection. The eruption in 1888 of the Japanese volcano of Bandai-san, by removing a considerable part of the ancient cone, has afforded us a section completely through the mountain. The summit and one side of the small Bandai was carried completely away, and there was substituted a yawning crater eccentric to the former mountain and having its highest wall no less than 1500 feet in height (Fig. 149). In two hours from the first warning of the explosion the catastrophe was complete and the eruption over. [Illustration: FIG. 149.—Dissection by explosion of Little Bandai-san in 1888 (after Sekiya).] The eruption of Krakatoa in 1883, probably the grandest observed volcanic explosion in historic times, left a volcanic cone divided almost in half and open to inspection (Fig. 150). Rakata, Danan, and Perbuatan had before constituted a line of cones built up round individual craters subsequent to the partial destruction of an earlier caldera, portions of which were still existent in the islands Verlaten and Lang. By the eruption of 1883 all the exposed parts and considerable submerged portions of the two smaller cones were entirely destroyed, and the larger one, known as Rakata, was divided just outside the plug so as to leave a precipitous wall rising directly from the sea and showing lava streams in alternation with somewhat thicker tuff layers, the whole knit together by numerous lava dikes. [Illustration: