ITALIAN PETROLOGICAL SKETCHES. 



III. THE BRACCIANO, CERVETERI AND TOLFA REGIONS. 



Bibliography. — The modern papers dealing with these three 

 regions petrographically are extremely few, and since some of 

 them are not confined to the description of only one they will be 

 noticed together here. 



We begin, as usual, with vom Rath,' who devotes parts of 

 one Italian " Fragment" to Bracciano and to Tolfa. The descrip- 

 tions are largely topographical, though in the Tolfa paper the 

 "trachyte" is described and an analysis given, and considerable 

 space devoted to the alum mines of the district. With excep- 

 tion of the paper just cited and a few stray notices of rocks in 

 Rosenbusch's " Massige Gesteine," practically all the other 

 articles on the regions are by Italians. Of these the following 

 are the only ones which need be named here. 



Struever^ published in 1885 an account of the ejected blocks 

 and their minerals which are found to the east of Lake Bracciano, 

 but does not touch upon the eruptive rocks proper. Many of 

 the eruptive blocks, and enclosures of Lake Bracciano, are 

 described by Lacroix.^ 



In the same year Tittoni'' describes the so-called Agro Saba- 

 tino, which includes the trachytic. hills immediately to the west 

 of Lake Bracciano, the region southwest of it, and the masses 

 of eruptive rock near Cerveteri.s He gives a good geological 

 map on a scale of i : 50,000. The first half of the paper is 



'Vom Rath, Zeit. d. d. geol. Ges. XVIII, 561-576, 585-607, 1867. 

 = Struever, Atti Ace. dei Lincei, Series 4, I, i, 1885. 

 3Lacroix, Enclaves des Roches, Macon, 189. v 

 *TiTTONi, Boll. Soc. Geol. Ital. IV, 1885, 337-376. 



5 He states that he was the first (in 1879) to discover the eruptive character of 

 these hills. 



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