Volcano üshima, Iilzu. ]5 



Of the above four types of the somma lavas, the first pre- 

 dominates, being exposed almost at every part of the island, 

 while the other types are very much limited in their occurrence, 

 being found only locally and intercalated with lavas of the first 

 type, and even so only on tue soa chfis and never on the ring- 

 wall of tlic somma. This suggests that the lavas of the second 

 to fourth types were discharged as the " effluent " flows in Dana's 

 term. Even the lavas of the first type may perhaps not all have 

 come from the summit crater, but some may have been discharged 

 from flank openings. 



The question as to how these different rock-types were formed 

 will be discussed later (pp. 118 — 120). 



Fragmentai materials are by no means less important than 

 lavas in the building up of the somma. According to their origin 

 they may be divided into two kinds : {a) those originating in 

 the magma itself before its consolidation ^*?«uen/7e éjecta, and {h) 

 those coming from the disturbed and shattered portions of the 

 preexisting rocks. 



Most of the éjecta are juvenile éjecta (a), and are of all 

 grades in size,^ — volcanic ashes, sands, lapiOi, and bombs. 



The blocks belonging to {h) are found imbedded in the layers 

 of volcanic ashes and sands, forming agglomerate beds. Ejecta 

 of various kinds are exposed in alternate layers on the soa cliffs, 

 on the walls of valleys, on road cuttings, and on the crater 

 walls. These appear, so far as observed, to be subaerial deposits, 

 there being no trace of any sortuig acti(3n by the water on the 

 pieces of éjecta. 



Of the various volcanic products, special mention must bo 

 made of scoriae, which are brown to bhtck, consisting almost 

 wholly of glass, and having been formed by the sudden chilling 



