After the mud flows have occurred, the Vesuvian cone, like all similar volcanic cones under the same conditions, is found with deep radial corrugations (Fig. 144), such as were long ago described as “barrancoes” and supposed to support the “elevation crater” theory of volcano formation. =The dissection of volcanoes.=—To the uninitiated it might appear a hopeless undertaking to attempt to learn by observation the internal structure of a volcano, and especially of a complex volcano of the composite type. The earliest successful attempt appears to have been made by Count Caspar von Sternberg in order to prove the correctness of the theory of his friend, the poet Goethe. Goethe had claimed that a little hill in the vicinity of Eger, on the borders of Bohemia, was an extinct volcano, though the foremost geologist of the time the famous Werner, had promulgated the doctrine that this hill, in common with others of similar aspect, originated in the combustion of a bed of coal. The elevation in question, which is known as the Kammerbühl, consists mainly of cinder, and Goethe had maintained that if a tunnel were to be driven horizontally into the mountain from one of its slopes, a core or plug of lava would be encountered beneath the summit. The excavations, which were completed in 1837, fully verified the poet’s view, for a lava plug was found to occupy the center of the mass and to connect with a small lava stream upon the side of the hill (Fig. 145). [Illustration: FIG. 145.—The Kammerbühl near Eger, showing the tunnel completed in 1837 which proved the volcanic nature of the mountain (after Judd).] It is not, however, to such expensive projects that reference is here made, but rather to processes which are continually going on in nature, and on a far grander scale. The most important dissecting agent for our purpose is running water, which is continually paring down the earth’s surface and disclosing its buried structures. How much more convincing than any results of artificial excavation, as evidence of the internal structure of a volcano, is the monument represented in Fig. 146, since here the lava plug stands in relief like a gigantic thumb still surrounded by a remnant of cinder deposits. Such exposed chimneys of former volcanoes are found in many regions, and have become known as volcanic _necks_, _pipes_, or _plugs_. [Illustration: FIG. 146.—Volcanic plug exposed by natural dissection of a volcanic cone in Colorado (U. S. G. S.).] [Illustration: FIG. 147.—A dike cutting beds of tuff in a partly dissected volcano of southwestern Colorado (after Howe, U. S. G. S.).]