Page:Popular Science Monthly Volume 20.djvu/59

Rh from the examination of sections of them. This was first attempted at the suggestion of Goethe, in the case of the Kammerbühl, a small hill in Bohemia, concerning which it was disputed whether its materials had been derived from the combustion of coal or from aqueous precipitation, or whether they were of volcanic origin. An excavation to the core of the hill, finished in 1837, showed that the center of the mass was filled with a plug of basalt, which was connected with a small lava-stream flowing down the side of the hill; while the bulk of the hill was composed of volcanic scoriæ and lapilli (Fig. 4). Natural

 a a, metamorphic rocks; b, basaltic scoriæ; c, solid plug of basalt rising through the center of the volcanic pile; d d, lava-stream composed of the same rock; e e, alluvial matter surrounding the old volcano. (The dotted lines indicate the probable former outline of the volcano.

sections are not rare. A very fine one is afforded by the peninsula of Vulcanello, in the Island of Vulcano (Fig. 5). The peninsula consists of three volcanic cones, united at their base, with the lava-streams



which have flowed from them. One half the cone on the left side of the picture has been completely washed away by the sea, so that a perfect section of the internal structure is exposed, as in the accompanying figure (Fig. 6). This section shows—1. The loose scoriæ and lapilli, d, which, in falling through the air, have arranged themselves in tolerably regular layers on the sides of the cone; 2.