1887] Mineralogy and Petrography. a 
included these in its crystallization from a molten magma. Por- 
phyritic biotite crystals were seen to be surrounded by a rim of 
little augite crystals, evidently an alteration product, since in the 
immediate vicinity of the augite the biotite was bleached. In 
the olivine, fluid inclusions containing crystals of salt were 
detected. In some of the hauyne crystals inclusions of pyrrho- 
tite were observed. It was noticed that as decomposition of 
these inclusions proceeded the substance of the hauyne became 
ofa deeper blue color. The inference drawn by the author is to 
the effect that the sulphur freed by this decomposition is the 
agent which produces the blue coloration.’ 
Petrographical News.—About a year ago reference was made 
in these notes to the.work of Hatch? on the andesites of Peru. 
The same author has continued his work, and now appears with 
a paper? on the rocks of the volcanoes in the neighborhood of 
Arequipa, a town in the southern part of Peru, about twenty 
miles from the Pacific coast. These rocks consist of andesites 
in all varieties, from the typical hornblende andesite, through in- 
termediate varieties, to the rock containing augite as its only bi- 
silicate constituent. Hypersthene occurs very widespread in the 
lavas of all the volcanoes in this region. Particular pains were 
taken to identify this mineral in a manner to preclude the possi- 
bility of error, and it was found that the only reliable means of 
distinguishing it from monoclinic augite consisted in the deter- 
mination of the position of the optical axes. In almost every 
case where hornblende was present it was found to be surrounded 
by an opacitic rim, outside of which was occasionally seen a 
second rim of augite microlites. The high percentage of silica 
noticed in certain of the specimens was proven to be due to the 
silicification of the rock by the impregnation of its constituents 
opal.The Ponza Islands, off the west coast of Italy, are 
comprised 4 principally of trachytes, rhyolites, and tufas. An 
interesting point in connection with the trachyte of the island 
of Ponza is the occurrence of olivine in it. Glaucophane is sup- 
posed to occur in that of San Stefano. The tufas contain peb- 
bles and pieces of quartz in addition to the broken crystals of 
various minerals. The ground-mass of the quartz trachyte from 
San Pietro,5 off the southwest coast of Sardinia, consists of chal- 
cedonic substance, in which are grouped little fibres of chalcedony 
in radial apie wae Rhyolite, obsidian, and perlite are also 
found there.——In the diabase porphyrite from Petrosawodsk,® 
in Russia, about = ued miles northeast of St. Ponerinae 
the porphyritic feldspar crystals are composed of parallel growths 
1 E Mi er Ueber natiirliche oo enue ag mn aa 
American N Er February, 1 t. 
i aait u. Petrog., Mittheil. vii., 1886, p. 308. ; 
4 F. Eigel, pi viii., 1886, P 73: s Ib., p. 62. 6 Ç. v. Vogdt, ib., ps tor. 
