54 The American Naturalist. [January 
quartz, and by the fact that the feldspars of the groundmass are almost — | 
exclusively albites. An analysis of the predominant granite-porphyry i 
yielded : % 
SiO, Al,O, Te,O, FeO MgO CaO Na,O K,O TiO, BaO S,0H,0 Cl Total 
68.65 18.31 .56 .08 .12 1.00 4.86 4.74 .20 .13 .10 1.10 .08=99.88 ~ 
id 
i 
The Volcanic Rocks of Bolsena, Italy.—The volcanic rocks a 
of the Bolsena region in Italy are reported by Washington‘ to comprise 
two distinct types—the trachytie and the leucitic. The former include 
andesite and vulsinite, a rock that differs from normal trachyte in con- 1 
taining a great deal of plagioclase and occasionally some olivine. The — 
plagioclase is anorthite. Both this mineral and the large crystals of | 
orthoclase that occur as phenocrysts are surrounded by mantles of | 
orthoclase in optical continuity with the nuclear grains. An analysis — 
of the rock gave: } 
8:0, TiO, Al,0, Fe,0, FeO MgO CaO Na,O K,O P,O, Ign Total 
58.21 tr 19.90 4.0 Of. -98 -3:58 2.57 . 9,17 —100.09 E 
The vulsinite is ar an effusive rock intermediate in eae be- 
tween trachyte and andesite. 4 
The leucite rocks are leucitites, leucite-phenolites (leucite- orthoclae) 
leucite-tephrite and leucite-basanites. All these rocks are briefly 
scribed by the author. 
The Analcite-bearing Rocks.—Pirsson,’ in a general article om 
the monchiquites and other related rocks gives the results of his study 
of a number of interesting rock types, all of which contain analcite — 
The glassy base of monchiquites is shown to have the properties of this 
mineral. Analcite is also thought to be present in many other rock 
as an original component. The conditions favorable to its production 
are those that obtain in dikes or other small intrusive masses—they 
proa of rocks, Jok as there exists a leucite group. The monchiquites 
are analcite basalts and the fourchites are analcitites. 
Petrographical Notes.—Callaway’ gives a brief account of the 
origin of schists of the MalvernjHills, England. The rocks were orig- 
inally diorites, epidiorites, granites and felsites. They have been chang® 
to schists by the usually processes of dynamic metamorphism. 
5 Jour. Geol., Vol. IV, 1896, p. 542. 
e Jour. Geol., Vol. IV, 1896, p. 679. 
™Proc. Liver. Geol. Society, 1895-96, p. 453. 
