252 J. W. Judd — On Volcanos. 



face of a solid mass of lava, or the agglutinated fragments of 

 similar materials. Several active fumaroles still exist about Mont- 

 agnone, and if we may be permitted to judge from the much less 

 weathered condition of its rocks, almost destitute of soil and vegeta- 

 tion as they are, we should pronounce this cone to be of even more 

 recent date than Monte Eotaro. 



This latter cone is situated on the western side of Montagnone, and 

 is so contiguous to it that in their lower portions the slopes of the 

 two hills blend with one another. The highest point of the beautiful 

 cone of Monte Eotaro is on its S.S.W. side, and is 982 feet above 

 the sea; the lowest point of the crater-ring, on its western side, 

 is 677 feet ; while the floor of the crater is only 570 feet. Nothing 

 can be more striking than the contrast between the appearance 

 of Eotaro and Montagnone, the latter being remarkable for the 

 barrenness of its bristling surface of lava, while the former is 

 completely clothed with the most luxuriant trees and shrubs. The 

 interior of the crater of Eotaro, especially, presents the most 

 picturesque appearance, offering some analogy with the well-known 

 much-larger crater of Astroni, near Naples. The extraordinary 

 fertility of the soil formed by the decomposition of the volcanic 

 rocks, combined with the sheltered situation, and perhaps also the 

 subterranean heat (for hot vapours issue from the rocks at a number 

 of points), have caused the ordinary shrubs of the Mediterranean 

 area to assume a luxuriance unknown to them elsewhere. It is even 

 said that the abnormal development of certain forms growing in 

 this natural hot-house is so great as to make the species in some 

 cases difficult of recognition. 



The cone of Monte Eotaro is made up of an agglomerate con- 

 taining blocks of all sizes of the ordinary sanidine-trachyte, more 

 or less scoriaceous, and sometimes becoming pumiceous. Among the 

 blocks are many composed of sanidine-trachyte with a vitreous base 

 (pitchstone-porphyry), the glass being of a jet black colour, and the 

 brilliant white crystals of sanidine scattered through it giving the 

 rock a most striking appearance. When the glassy base of this 

 " pitchstone-porphyry " or porphyritic obsidian is distended by gases, 

 it passes into pumice, which still contains entangled among its fibres 

 the fine crystals of sanidine, showing clearly that these latter must 

 have been formed within the volcano, and not during the progress 

 of the cooling of the lava. 



It must of course be borne in mind that, as was clearly pointed 

 out by Abich, we have two distinct series of obsidians and pumices, 

 the one corresponding to the quartz-trachytes, and the other to the 

 ordinary trachytes. Of the first of these we have already given 

 many illustrations in describing the Lipari Islands ; of the latter we 

 can perhaps nowhere study more interesting examples than in 

 Ischia. All volcanic rocks may pass into the vitreous condition, but 

 their tendency to do so seems to be directly related to the propor- 

 tion of silica which they contain. Thus by far the most abundant 

 obsidians are those which correspond to the highly acid lavas, the 

 quartz-trachytes or Liparites ; next in order, but far less abundant, 



