326 The American Naturalist. [April, 
General Notes. 
PETROGRAPHY:? 
Italian Petrography.—tThe third part of Washington’s’ paper on 
Italian petrography deals with the Bracciano, Cerveteri and Tolfa dis- 
tricts. The products of the Bracciano volcano may be separated into 
a leucitic and a non-leucitic group. The non-leucitic rocks contain or- 
thoclase and basic plagioclase, in this respect resembling the vulsinites 
and the ciminites, but they are more acid than these types, containing 
sometimes as much as 72 per cent. of SiO, a part of which separates as 
quartz. They resemble the quartz-trachytes of Tuscany, and thus oc- 
cupy the position in Brégger’s classification reserved for the quartz- 
trachyte-andesites. The author calls the members of the group toscan- 
ites, he leucite rocks of this voleanic center embrace leucitites, 
leucite-tephrite and leucite-phonolite. 
The rocks of the etek ei are toscanites and leucitites, and 
of the Tolfa district, toscani 
An analysis of the toscanite ee Castle Hill, Tolfa, follows : 
SiO, ALO, Fe,0, FeO MgO CaO NaO KO HO Total 
6019 1604° 116° 248 99 292 226 611 185 = 99.00 
The Quartz-Porphyry in the Ruhr Valley, Westphalia. 
—This rock has been described several times by geologists, but it has 
been reserved for Miigge® to investigate it microscopically. It occurs 
in massive and in schistose phases and in the form of a breccia associ- 
ated with schists. The massive variety resembles, in many respects, a 
gneiss. It is banded in light and dark irregular bands. Spherulites 
united by what was once a glassy matrix marked by perlitie cracks 
constitute the groundmass in which phenocrysts of quartz and ortho- 
clase are imbedded. The rock has suffered profound mechanical and 
chemical alterations. The quartz grains are crossed by fine lamellae 
extinguishing in different positions, and by others extinguishing nearly 
together. The latter are visible in ordinary light. They are phenom- 
ena of translation.* The groundmass is filled with tiny veins of quartz, 
stringers of a sericite-chlorite aggregate and nests of quartz and newly 
1 Edited by Dr. W. S. gl Colby University, Waterville, Me. 
2 Jour. of Geology, Vol. V, p. 34. 
3 Neues Jahrb. f. Min., ete., B. B. X, p. 757 
* Cf. Neues Jahrb. f. Minn., ne 1892, II, p. “95, 98, 1895, p. 213. 
