454 H. 'S. Washington — Rhyolites of Lipari. 



sions of brown glass, thickly crowded with microlites, 

 are common in them. There are also a few subhedral 

 phenocrysts of what appears to be a somewhat sodic 

 orthoclase, but no pyroxene phenocrysts are visible in 

 my sections. 



The groundmass in which these phenocrysts are im- 

 bedded is very glassy, of a general brownish color, and is 

 hyalopilitic or (as Prof. Zirkel used to say) "a glass- 

 saturated microlite felt." The microlites are very small 

 prisms of alkalic feldspar, numerous still smaller grains 

 and prismoids of pyroxene, and still smaller grains of 

 magnetite. No quartz is visible. 



Chemical composition. — For an analysis of this type 

 there was chosen the specimen just described. For com- 

 parison with it is given an analysis of a cordierite 

 andesite described by Bergeat 12 and Sabatini. 13 This is 

 inserted as being the only published analysis of a rock 

 from Monte Sant' Angelo that I have been able to find; 

 though the presence of cordierite and some of the chemi- 

 cal peculiarities would appear to be caused by assimila- 

 tion of foreign rocks. Bergeat (page 99) also gives two 

 silica determinations of lavas from the same cone, 

 yielding 58.22 and 56.54 per cent. 



TABLE III. 



1 2 



Si0 2 60.57 59.31 



AL0 3 19.47 16.95 



Fe.,0 3 0.94 8.07 



Feb 2.83 



MgO 0.94 1.65 



CaO 6.10 4.30 



NaX) 3.07 1.59 



K,6 3.71 3.42 



H,0-f 0.93 2.64 



H 2 0— 0.11 2.10 



C0 2 none .... 



TiO., 0.71 n.d. 



P 2 5 0.31 0.40 



CI trace n.d. 



MnO 0.06 n.d. 



99.75 100.43 



1. — Hyalodacite, near La Perrera, Monte Sant' Angelo, Lipari. Washing- 

 ton, analyst. 



2. — Cordierite andesite, Varesana, Monte Sant' Angelo, Lipari. Glaser, ana- 

 lyst. Bergeat, op. cit., page 102. 



"Bergeat, Abh. Bayer. Akad. Wiss., 20, 102, 1899; Neues Jahrb., Beil.- 

 Bd. 30, 575, 1910. 



13 Sabatini, in Cortese and Sabatini, Mem. Carta Geol. Ital., VII, 111, 

 1892. 



