TRUE VOLCANOES. 



Junghuhn, indeed, remarks " that the vast volcano Gunnng 

 Merapi has not poured forth coherent, compact lava streams 

 within the historical period of its eruptions, but has only 

 thrown out fragments of lava (rubbish), or incoherent blocks 

 of stone, although for nine months in the year 1837 fiery 

 streams were seen at night running down the cone of erup- 

 tion."* But the same observant traveler has distinctly de- 

 scribed, in great detail, three black, basaltic lava streams on 

 three volcanoes Gunung Tcngger, Gunung Idjen, and Sla- 



* Junghuhn, bd. ii., s. 309 and 314. The fiery streaks which were 

 seen on the volcano G. Merapi were formed by closely-approximated 

 streams of scoriae (trainees defragmens\ by non-coherent masses, which 

 roll down during the eruption toward the same side, and strike against 

 each other from their very different weights on the steep declivity. In 

 the eruption of the G. Lamongan on the 26th March, 1847, a moving 

 line of scoria} of this kind divided into two branches several hundred 

 feet below its point of origin. "The fiery streak," we find it express- 

 ly stated (bd. ii., s. 767), "did not consist of true fused lava, but of 

 fragments of lava rolling closely after one another." The G. Lamongan 

 and the G. Semeru are the two volcanoes of the island of Java, which 

 are found to be most similar, by their activity in long periods, to the 

 Stromboli, which is only about 2980 feet high, as they, although so re- 

 markably different in height (the Lamongan being 5340 and the Semeru 

 12,235 feet high), exhibited eruptions of scoriae, the former after pauses 

 of 15 to 20 minutes (eruptions of July, 1838, and March, 1847), and the 

 second of 1J to 3 hours (eruptions of August, 1836, and September, 

 1844) (bd. ii., s. 554 and 765-769). At Stromboli itself, together with 

 numerous eruptions of scoriae, small but rare effusions of lava also 

 occur, which, when detained by obstacles, sometimes harden on the 

 declivities of the cone. I lay great stress upon the various forms of 

 continuity or division, under which completely or partially fused mat- 

 ters are thrown or poured out, whether from the same or different 

 volcanoes. Analogous investigations, undertaken under various zones, 

 and in accordance with guiding ideas, are greatly to be desired, from 

 the poverty and great one-sidedness of the views, to which the four 

 active European volcanoes lead. The question raised by me in 1802 

 and by my friend Boussingault in 1831 whether the Antisana in the 

 Cordilleras of Quito has furnished lava streams ? which we shall touch 

 upon hereafter, may perhaps find its solution in the division of the 

 fluid matter. The essential character of a lava stream is that of a 

 uniform, coherent fluid a band-like stream, from the surface of which 

 scales separate during its cooling and hardening. These scales, be- 

 neath which the nearly homogeneous lava long continues to flow, up- 

 raise themselves in part, obliquely or perpendicularly, by the inequal- 

 ity of the internal movement and the evolution of hot gases ; and when, 

 in this way, several lava streams, flowing together, form a lava lake, as 

 in Iceland, a field of detritus or fragments is produced on their cool- 

 ing. The Spaniards, especially in Mexico, call such a district, which 

 is very disagreeable to pass over, a malpais. Such lava fields, which 

 are often found in the plain at the foot of a volcano, remind one of 

 the frozen surface of a lake, with short, upraised ice-blocks. 



VOL. V. N 



