ITAIJAX PETROLOGICAL SKETCHES 827 



A few analyses ot" eruptive rocks from this center were pub- 

 blished in 1884 by Ricciardi/ but, as he expressly states that 

 they are of groundmass carefully freed from phenocrysts, they 

 are unfortunately of comparatively little use to us. 



A few years later Bucca^ published some short petrographical 

 descriptions of various rocks from this locality. He concludes 

 that two distinct types are found in the region, "one essentially 

 trachytic, the other leucitic. These two types often appear iso- 

 lated and clearly distinct ; at other times there has been a mix- 

 ture of one with the other." He further thinks that the trachyte 

 is younger than the leucitic rocks and argues from this an 

 increase in acidity during successive eruptions. 



In 1889 appeared the latest works on this region so far as 

 my knowledge extends. The paper by G. Mercallisis a purely 

 petrographical account of the principal rocks with short but useful 

 descriptions. He distinguishes the two types of trachytic and 

 leucitic rocks, and shows that the latter are later than the 

 former. He also gives numerous mineralogical details of a series 

 of ejected blocks, which are also described elsewhere by E. 

 Artini.t 



The other paper of this year is that of Deecke,^ which con- 

 stitutes one of his series of excellent articles on Italian geology. 

 The first part of the article is devoted to a discussion of some 

 of Verri's views and an exposition of his own regarding certain 

 features of the volcano. The second part describes at length 

 the ejected blocks found in the tuffs of Monte Vico, and the 

 third describes various eruptive rocks collected by himself. An 

 almost complete bibliography precedes the paper. Lacroix^ 

 also describes many of the ejected blocks and segregations from 

 this region. 



The best maps are those issued by the Italian government. 



'RicciARDi, Atti Ace. Gioen. Catania, XIX, 1884. 

 =^BuccA, Eoll. Com. Geol. Ital., 18S8, 57-63. 

 3MERCALLI, Rendic. Institut. Lomb., XXII, 1889. 

 •* Artini, Atti Ace. dei Lineei, VI, 1889. 

 sDeecke, Neu. Jahrb., B. Bd. VI, 205-240, 1889. 

 ^Lacroix, Les Enclaves des Roches, Macon, 1893. 



