ITALIAN PETROLOGICAL SKETCHES SA7 



examine. This will involve the proposal of some new names, 

 but the baptismal rite will be indulged in as sparingly as may be. 



For the present we must confine ourselves to the Bolsena 

 volcano, and ma}' say that two prominent types exist, the trachy- 

 andcsitic and the leucitic rocks. Even these two prominent 

 types grade into one another to a slight extent, though they can 

 as a rule be readily distinguished. In the following pages I shall 

 describe mv own specimens, turning to Klein and Bucca for 

 descriptions of rocks which I was unable to collect. The tuffs 

 and the metamorphosed ejected blocks will not be touched upon. 

 Ricciardi's analyses cover the ground so completely that only 

 one fresh analysis was made, of the important Bolsena "trach- 

 yte." Vom Rath's analyses and the best of Ricciardi's will be 

 inserted later. 



Vidshiitc. — Vom Rath first called attention to the abnormal 

 chemical character of the "trachyte" of Bolsena, though he 

 speaks of it as containing no plagioclase, probably owing to the 

 rarity of the multiple twinning. As will be seen from Klein's 

 descriptions and my own, and from the analyses, the peculiar 

 "trachytes" of the region are remarkable; mineralogically for 

 their richness in plagioclase and the frequent occurrence of 

 oli\ine as an essential constituent, and chemically for their low 

 silica and high lime and magnesia. Therefore they are not 

 trachytes proper, but correspond to the trachy-dolerites of Abich^ 

 and Hartung,^ and to some of the andesitic-trachytes of Rosen- 

 busch,3 and we shall see that they may be regarded as effusive 

 representatives of Brogger's abyssal monzonites. These olivine- 

 free effusive rocks will be called by the name of Vidsifiite,^ from 

 the Etruscan tribe, Vulsinii, formerly inhabiting this region. 

 Those carrying olivine belong to a peculiar type which will be 

 described in the next paper. 



' Abich, Nat. n. Zusammensetz. d. Vulk. Bild., p. lOl, 1841. 



'Hartung, Azoren, Leipsig, p. 92, i860. Cf. Mugge, Neu. Jahrb., Vol. II, 

 p. 201, 1883. 



3R0SENBUSCH, Mikr. Phys. Vol. II, p. 600, 1S87. 



•• The name Bolsenite has already been used by H. O. Lang (Min. Pet. Mit., XIII, 

 143, 1892) for one of his purely chemical groups, which embraces certain leucitic rocks. 



