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out to contain ninch qnartz. Although acidic hypersthene andesites 

 mark the tirst and thii-d period that Verbeek distinguishes in the 

 history of the volcano, tlie quartz has not been able to develop itself 

 as such, under t!ie circumstances in which these rocks crystallized, 

 and is found in virtual state in the glass of the groundmass. 



The surrounding basalt contains phenocrists of basic plagioclase 

 and a small quantity of olivine in a glassy mass with crystals of 

 more acidic plagioclase, augite and ore. The holocrystalline inclusions 

 of which the largest dimension measures 10 cm. consist of strongly 

 zonair plagioclases, quartz (a good deal of it üne-granophyrically 

 grown together with feldspar), worn dark minei'als and ore. In the 

 fme-granophyrical conglomerations also kali-feldspar may be found. 

 The SiO, percentage varies, the chemical constitution of one of the 

 inclusions appearing from the following analysis (analyst F. G. 

 Mannhardt) : 



Calculating the analyses according to the American system we 

 find a remarkable high percentage of SiO^ that is not bound as a 

 silicate (about 38%). 



It appears from the above-said that the homoeogeneous inclusions 

 of the Kawah Idjen, according to their chemical constitution, show 

 but a few varying types ; in connection with this fact the chemical 

 constitution of the andesites and basalt of the Idjen complex differ 

 but slightly. ') 



1) Loss by ignition. 



') The basalt of the stream of lavas of the Merapi which (lows into the sea 

 near Batoe Dodol on the straits of Bali contains (according to Sïöhr) 540/ o sjq^; 

 two pyroxene andesites of the Kawah Idjen contain 58 "/q and 60o/„ SiO.2 ; and 

 among the rocks that were gathered by me during the eruption of the Raoeng 

 in 1913, on the northern slope of the volcano near the brink of the crater, some 

 amphibole-hypersthene-augite-andesites with 63 °'o SiOj occur. Also the olivine- 

 containing basaltic cinders of the youngest Raoeng-eruption have a high SiOg 

 percentage (54 ''/q)- 



