1895.] Petrography. 153 
or grains of recrystallized quartz and microlites and bundles of nearly 
` colorless augite. The serpentine on the island is nodular as the result 
of shearing. It was derived in all probability from a rock made up 
almost exclusively of diallage. It contains granules of chromite. This 
serpentine has effected the same alterations in the chert and sandstone 
through which it cuts, as has the fourchite. Some peculiar inclusions 
of a dark rock in the serpentine are supposed to be the remnants of a 
dyke that formerly occupied the fissure, which the serpentine subse- 
quently filled. These fragments now consist of a holocrystalline aggre- 
gate of augite and albite, of which the first mineral is sometimes alter- 
ed to green and brown hornblende. Analyses of the fourchite (I) and 
of a fresh nodule of serpentine (II) follow: 
SiO, Al,O, Fe,O, FeO CaO MgO K,O Na,O P,O, Loss Total 
I. 46.98 17.07 1.85 7.02 1215 829 53 2.54 .09 4.86—101.38 
Il. 42.06 2.72 2.88 39.53 not estimated 12.04— 99.23 
A New Rock-Volcanite.—In an abstract of a paper to appear 
in a German periodical, Hobbs’ gives an account of an anorthoclase- 
augite rock which he calls voleanite. It occurs as bombs projected 
from Volcano in 1888-89. Phenocrysts of anorthoclase, andesine, an 
acmitic augite and olivine are imbedded in a groundmass containing 
two generations of the first named*of these minerals in a glassy base. 
The augite phenocrysts in many instances have been resorbed by the 
rock’s magma and have thus given rise to pseudomorphs of colorless 
pyroxene, ‘magnetite, and plagioclase. The structure of the rock is 
trachytic. Its chemical composition corresponds with that of the 
-dacites, while its mineralogical composition is that of an augite pan- 
tellerite. Analyses of the anorthoclase (II) and of the rock mass (I) 
ollow: 
SiO, Al,O, Fe,O, FeO MnO CaO MgO Na,O K,O H,O P,O, Total 
I. 66.99 17.56 141 3.39 tr 4.25 93 335 34 153 tr—99.75 
TI. 60.01 20.12 2.82 515 23 6433.67 .77 =99.20 
Acmite Trachytes from Montana.—Among the eruptive rocks 
occurring as dykes, sheets and laccolitic masses in the Cretaceous of 
the Crazy Mts. are acmite trachytes and eleolite syenites. The for- 
mer, according to Wolff is present in small sheets and dykes and in 
3 Bull. Geol. Soc. Amer., Vol. 5, p. 598. 
* Bull. Mus. Comp. Zool., xvi, p. 227. 
