H. 8. Washington — Rhyolites of Lipari. 447 



of Monti S. Angelo, Chirica, Kosa, etc., in the central 

 parts of the island. A pause was followed by the erup- 

 tion of flows of the cordierite andesite of Varesana, and 

 of the rhyolites of Monti Guardia and Giardina in the 

 south end of the island, after which came the eruptions 

 of obsidian and pumice that formed Monte Pelato and 

 the small cones of Forgia Vecchia and Rocche Rosse. 

 These seem to have been the final active phase. The 

 closing of volcanicity is marked by the hot springs of 

 San Calogero and slight fumarolic activity at the present 

 day. 



The order of eruptions, regarded chemically, would 

 seem to have been simple and fairly regular, begin- 

 ning with magmas of about the composition of andose 

 (II.5.3.4), with Si0 2 about 53 per cent, passing to and 

 ending with magmas of the general composition of 

 liparose (1.4.1.3), in which Si0 2 is about 74 per cent. 

 Intermediate magmas are represented by those of the 

 Monte S. Angelo lavas. 



Khyolite Obsidian. Hephaestal 6 Liparose (1.4.1.3). 



The chief specimens examined, which are considered 

 as typical, are from the flows of Forgia Vecchia, above 

 Canneto, and from Rocche Rosse, at the north-east 

 corner. These are small, pumice cones, breached by flows 

 of obsidian running down to the sea. Illustrations of 

 them are to be found in several standard works on vol- 

 canoes, as those of Judd 7 and Mercalli. 8 Similar obsid- 

 ians from Monte della Guardia and elsewhere were also 

 studied. 



Megascopic characters. — The rock is a typical obsid- 

 ian, of a jet-black color, highly vitreous luster, and gen- 

 erally perfect conchoidal fracture. On the thin edges of 

 splinters it is transparent, but gradually becomes gray 

 and dusty with inclusions as the splinter thickens, and 

 here and there small black specks are visible. 



The density of the specimen from Rocche Rosse 

 (analysed) is 2.370, and of that from Forgia Vecchia is 

 2.363, both determined at 18° with the balance. 



Much of this obsidian is banded with gray in various 

 shades, some of the bands being thin and others thick; 



s From Hephaestades, one of the Latin names of the island group. 



7 J. W. Judd, Volcanoes, 1890, Fig-. 41, p. 124. 



8 G. Mercalli, Vulcani Attivi, 1907, Fig. 20, p. 59. 



Am. Jour. Sci.— Fourth Series, Vol. L, No. 300.— December, 1920. 

 33 



