492 ISLAND OF JAVA. [Ch. XXIX. 



would be still greater, the whole top of the mountain, or a large part of 

 it, might fall in. 



Instances of such truncations, however caused, have occurred in Java 

 and in the Andes within the times of history, and to such events we may 

 perhaps refer a very common feature in the configuration of volcanic 

 mountains, — namely, that the present active cone of eruption is sur- 

 rounded by the ruins of a larger and older cone, usually presenting a 

 crescent-shaped precipice towards the newer cone. In volcanoes long since 

 extinct, the erosive power of running water, or, in certain cases, of the 

 sea, may have greatly modified the shape of the " atrium," or space be- 

 tween the older and newer cone, and the cavity may thereby be pro- 

 longed downwards, and end in a ravine. In such cases it may be impos- 

 sible to determine how much of the missing rocks has been removed by 

 explosion at the time when the original crater was active, or how much 

 by subsequent engulfment and denudation. 



Java. — One of the latest contributions to cur knowledge of volcanoes 

 will be found in Dr. Junghuhn's work on Java, where forty-six conical 

 eminences of volcanic origin, varying in elevation from 4000 to nearly 

 12,000 feet above the sea, constitute the highest peaks of a mountain 

 range, running through the island from east to west. All of them, 

 with one exception, did this indefatigable traveller survey and map. In 

 none of them could he discover any marine remains, whether adhering to 

 their flanks or entering into their internal structure, although strata 

 of marine origin are met with nearer the sea at lower levels. Dr. 

 Junghuhn ascribes the origin of each volcano to a succession of sub- 

 aerial eruptions from one or more central vents, whence scoriae, pumice, 

 and fragments of rock were thrown out, and whence have flowed streams 

 of trachytic or basaltic lava. Such overflowings have been witnessed in 

 modern times from the highest summits of several of the peaks. The 

 external slope of each cone is generally greatest near its apex, where 

 the volcanic strata have also the steepest dip, sometimes attaining 

 angles of 20, 30, and 35 degrees, but becoming less and less inclined 

 as they recede from the summit, until, near their base, the dip is re- 

 duced to 10 and often 4 or 5 degrees* The interference of the lavas 

 of adjoining volcanoes sometimes produces elevated platforms, or " sad- 

 dles," in which the layers of rock may be very slightly inclined. At 

 the top of many of the loftiest mountains the active cone and crater 

 are of small size, and surrounded by a plain of ashes and sand, this 

 plain being encircled in its turn by what Dr. Junghuhn calls " the 

 old crater- wall," which is often 1000 feet and more in vertical height. 

 There is sometimes a terrace of intermediate height (as in the moun- 

 tain called Tengger), comparable to the " black ledge" of Kilauea (fig. 

 641). Most of the spaces thus bounded by semicircular or more 

 than semicircular ranges of cliffs are vastly superior in dimensions to 



* Java, deszelfs gedaante, bekleeding en invendige structuur, door F. Jung- 

 huhn. (German translation of 2d edit, by Hasskarl, Leipzic, 1852.) 



