5 54 HENR V S. IVA SHING TON 



(anal. 4, p. 565). It is quite free from olivine. Plagioclase is 

 abundant and basic, giving extinction angles up to 30° on each 

 side of the twinning plane. The groundmass is holocrystalline 

 and composed largely of orthoclase and plagioclase, with augite, 

 biotite and magnetite. In it occur round spots of very feebly 

 doubly refracting substance which closely resemble leucite. 

 Klein comes to the conclusion, however, that these are not leu- 

 cites, since only 0.28 per cent, of KgO is extracted from the 

 rock by HCl, but that they are of glass in a condition of strain. 

 From his description they seem to be the same — or very similar 

 to — certain spots in the groundmass of a leucite phonolite from 

 Lake Bracciano, which will be described in another paper. These 

 are of " pseudo-leucite," a mixture of nepheline and orthoclase 

 probably due to the alteration of leucite crystals. 



The " olivine-bearing andesitic trachytes " of Sassara and 

 Mont' Alfina (Klein, p. 6) belong rather to a type of rock which 

 will be described in the next paper than to the vulsinites. 

 The silica is lower (56.32 per cent.) and magnesia quite 

 high (anal. 6, page 565). Basic plagioclase phenocrysts, with 

 extinction angles up to 30° on each side of the twinning plane 

 are very abundant, more so than orthoclase. Olivine, augite and 

 biotite also occur as phenocrysts. The groundmass contains 

 little glass, and is made up of the same minerals that compose 

 the phenocrysts, except that olivine is wanting. 



Andesite. — An augite-andesite is met with as the last product 

 of eruption at Monte Rado, west of Bagnorea, and is described 

 by Klein (p. 32) . This, it will be remembered, is one of Verri's 

 five centers of activity, and probably poured forth at an earlier 

 stage the leucitic lava streams met with at Sassi Lanciati, Bag- 

 norea and Porano. It is without doubt one of the last eruptions 

 of the Bolsena volcano. Monte Rado is described as a hill 

 covered with scoriae, lapilli and bombs, and the specimen exam- 

 ined by Klein comes from the upper part. As I could not visit 

 the locality I quote from Klein's description. 



The phenocrysts are of plagioclase, which is apparently lab- 

 radorite, and shows zonal structure, augite, brown biotite and 



