H. S. Washington — Rhyolites of Lipari. 453 



1 2 



Quartz 31.98 20.70 



Orthoclase 28.91 28.91 



Albite 33.01 34.58 



Anorthite 2.78 3.89 



Diopside ■ 7.23 



Hypersthene 0.20 1.46 



Magnetite 0.70 2.78 



Ilmenite 0.15 0.30 



Apatite 0.34 



From these it appears that both fall in liparose, though 

 No. 2 is almost in dosalane and also is almost domalkalic. 

 The symbols are, for the Giardina rock, I."4.1".3, and 

 for that from Guardia, I(II).4.1(2).3. 



Hyalo-Dacite. 



Although this study was undertaken primarily to ascer- 

 tain the chemical composition of the Lipari rhyolites, 

 yet it has been pushed a step further to include an anal- 

 ysis of a specimen representing the main rock of the 

 central cone of Monte Sant' Angelo. Judging from the 

 descriptions by Sabatini 10 and by Bergeat 11 the rocks of 

 this cone vary considerably, though the specimens that 

 I collected do not show great variety. For special exam- 

 ination there was selected a specimen from near the 

 church of La Perrera to the north of, and above, the 

 town of Lipari. It was taken where the road of Forgia 

 Vecchia makes a sharp bend to the east (right). This 

 specimen was selected from several that resembled it, 

 because it seemed to correspond best with what Bergeat 

 calls the typical lava of Monte Sant' Angelo. 



Megascopic characters. — The rock is dense and com- 

 pact, and of a very dark gray, almost black color. Small 

 (1-2 mm.) phenocrysts of yellowish white feldspar are 

 scattered quite thickly through the dense, almost black, 

 groundmass, which shows a rather dull luster. There 

 are scarcely any phenocrysts of pyroxene. Specimens 

 obtained from the neighborhood of San Calogero and 

 also from near Santa Margherita, greatly resemble this, 

 both megascopically and microscopically. 



Microscopic characters. — In thin section the rock is 

 seen to contain numerous, mostly euhedral, phenocrysts 

 of plagioclase, which is always multiply twinned, and 

 shows extinction angles that indicate a composition of 

 about Ab 2 An 3 . They are not zonally built. Small inclu- 



10 Sabatini, Mem. Carta Geol. Ital., VII, 104, 1892. 



11 Bergeat, Abh. Bayer. Akad. Wiss., 20, 98, 1899. 



