1897.] Petrography. 807 
groundmass consisting of diopside-malacolite, augite, aegirin-augite and 
aegirine, amphiboles, related to arvfedsonite and katoforite, ainigma- 
tite, several generations of feldspar and a small quantity of glass. 
Apachite differs from normal phonolite in the great abundance of 
ainigmite and the members of the hornblende group, and in the 
younger age of the latter with respect to the pyroxene. It contains 
also great quantities of microperthitic feldspars. 
An analysis of the rhyolite of Fort Davis is given under II. 
SiOz Al; 203 Fe.03 FeO M gO CaO NaO K H0 TiO P.O; Total 
F: 73.85 14.38 1.96 .34 «6.09 26 4.33 100.37 
SE: 71.10 1139 5.33 1.54 .08 3.95 a 44 .57 = 05 a = 100. 82 
Italian Petrographical Studies.—In a recent paper, Washing- 
ton‘ summarizes the results of his work on the Bolsena-Vesuvius vol- 
canics, and presents some views on the classification of leucite rocks 
and of those intermediate in composition between trachytes and basalts. 
In accordance with the nature of their feldspathic constituent, he 
would divide trachyte-basalts into a trachyte series, embracing those 
rocks containing only an alkali-feldspar, a trachy-andesite series, in- 
cluding those containing an alkali-feldspar and an acid plagioclase, a 
trachy-dolerite series, composed largely of an alkali feldspar and a 
basic plagioclase, an andesite series—acid plagioclase (andesine-oligo- 
clase) rock, and a basalt series, a basic plagioclase series. Among the 
trachy-andesites the author would place the Iceland rhyolites, vulca- 
nite, dornite, the Euganean and the basic auvergne trachytes, an 
among the trachy-dolerite series the toscanites, the vulsinites and the 
Ciminites described by himself, and the banakites, shoshonites and ab- 
sarokites of the western United States. The leucite rocks met with in 
the Italian voleanoes are thought to be best classified as leucitites, 
leucite-basalts, leucite-basanites, leucite-tephrites, leucite-trachytes and 
leucite-phonolites. Upon comparing their analyses the silica contents 
of these rocks are discovered to cluster around 49 per cent and 56 per 
cent, a fact which is regarded as not due to accident. The original 
magma, of which the Italian volcanoes are the differentiated products, 
is thought to have had a composition approximating the following : 
Si0,—57-58 ; Al,O,=17-18; FeO (Fe,0,)=6-7 ; MgO=2-3 ; CaO 
=5-6.5 ; Na,O=2.95 ; K,O=7-8 ; H,O=1-1.5 per cent. 
Rock Differentiation.—Iddings’ devotes a few pages to his theory 
of rock differentiation as applied to the Electric Peak volcanics, reply- 
*Jour. of Geology, Vol. V, p. 349 
ë Quart. Jour. Geol. Soc., Vol: LU, 1896, p. 606. 
