Silica 



.. 60-25 



Alumina 



.. 13-09 



Oxide of Iron 



.. 10-55 



Oxide of Manganese 



.. 0-38 



Lime 



.. 11-16 



Magnesia 



.. 9-43 



Soda (with some Potash) 



.. 4-92 



Loss 



— 



J. W. Judd — On Volcanos. 61 



Reserving for a future occasion, when some other volcanic districts 

 have been described, all general remarks upon the classification of 

 the products of volcanic action, we may notice that the modern lavas 

 of the northern fissure (Stromboli and Stromboluzzo) produce rocks 

 of the most typical basic character, namely, basalts and dolerites. 

 Abich's analyses of these lavas gave the following results — their 

 specific gravity being between 2*86 and 2-96. 



Lava of Stromboli. Lava of Stromboluzzo. 

 53-88 

 12-04 

 9-25 



7-96 

 8-83 

 4-76 

 2-78 



The second of these rocks appears to have undergone a certain 

 amount of alteration. 



These doleritic lavas appear to consist mainly of an aggregation 

 of nearly equal proportions of crystals of Labradorite felspar and 

 augite, to which variable quantities of magnetite and olivine are 

 added in different examples. 



As is usually the case with igneous rocks of basic composition, the 

 lavas of Stromboli only very rarely assume the vitreous condition. 

 The scorias which are ejected from the active crater of Stromboli, at 

 intervals of a few minutes only, sometimes fall so near to the 

 observer that he can approach them while still in a soft and plastic 

 condition, and thrust coins or other hard objects into them. These 

 cinders are found on examination to be perfectly stony in character ; 

 but they are completely full of vesicles, formed by the escape of 

 volatile materials from their midst, and they usually inclose nearly 

 perfect and very beautifully formed crystals of augite — sometimes 

 of considerable size. But besides the scoria?, showers of volcanic 

 sand also fall around the observer standing beside the crater of 

 Stromboli. This volcanic sand proves on examination to be, like 

 the similar materials ejected from Mount Klut in Java in 1864, and 

 from the volcano of Georg in the Gulf of Santorin in 1866, both of 

 which were submitted to microscopical examination by Vogelsang, 

 an aggregate of more or less broken and rubbed crystals of augite, 

 felspar, olivine, and magnetite, with comminuted fragments of scoriae. 



Around the sides of the crater of Stromboli crystals of augite can 

 be collected in great abundance ; they are usually macled, and some- 

 times form beautiful stellar groups and other interesting com- 

 binations. These are doubtless in part ejected directly from the 

 crater, but in other cases result from the breaking up of the light 

 cindery fragments in the midst of which they were inclosed at 

 the time of their ejection. That these crystals were actually formed 

 within the volcanic vent there is not the smallest room for doubt. 



That Stromboli has in comparatively recent times given forth 

 streams of basaltic lava of very considerable magnitude is clear to 

 any geologist who studies the fresh and undecomposed fields of lava 



