ITALIAN PETROLOGICAL SKETCHES 249 



with interstitial prisms of green augite, many magnetite grains, 

 and flakes and laths of alkali feldspar. Some larger crystals of 

 anorthite are also seen. No glass seems to be present. 



To the biotite-leucite-trachytes belong specimens from Tuoro 

 west of Acqua Rotta, and from below Orchi on the northern 

 flank of the volcano. Their groundmass is lighter gray than that 

 of the preceding, small leucite and augite phenocrysts are not 

 very common, but there is an abundance of flakes of biotite of 

 a dark brown color and bronzy luster. In thin section they very 

 much resemble the preceding. Augite phenocrysts are, however, 

 rare, their place being taken by biotite. In the rock from Tuoro 

 its color is of a deep orange red, while in that from Orchi it is 

 much paler. It is much altered at the edges to the usual fine 

 (rrained aggregate. In the groundmass of the former the alkali 

 feldspar is in the form of laths, in the latter it is rather in the 

 form of flakes and interstitial cement. Some basic plagioclase 

 is present, but in small amount. 



A rock which occupies a position between the above and the 

 following group is represented by a specimen also from below 

 Orchi. Megascopically this closely resembles the other, the 

 only important difference being that here leucite phenocrysts 

 are entirely wanting, and replaced by glassy sanidines. There 

 is also considerable augite along with the biotite. The rock in 

 thin section resembles more one of the vulsinites to be described 

 presently than a leucite-trachyte. The sanidine phenocrysts are 

 rarely met with. Large greenish gray augites are not uncommon, 

 which carry inclusions of brown glasS and magnetite and are 

 somewhat corroded. The biotites are all profoundly altered, 

 usually so much so that the crystal is almost completely dis- 

 inteo-rated. The groundmass is made up of flakes and laths of 

 an alkali feldspar, with a considerable number of laths and basic 

 plagioclase which are usually surrounded by mantles of orienta- 

 ted alkali feldspar. Small grayish green irregularly shaped 

 and corroded augite crystals with magnetite grains are common. 

 There are also present many small round spots of leucite, recog- 

 nized by their characteristic inclusions and by their analogies 



