1090 ' The American Naturalist. [December 
formation of the new minerals. Johnston-Lavis ^ gives a description 
of an interesting trachyte from the Bay of Naples. It is of a light gray 
color, and consists of sanidine crystals, fractured and strained by 
pressure, hornblende, in broken, irregular, yellowish green grains, 
small masses of the same substances mixed with grains of pyroxene, and 
with these producing an apparent crystal of hornblende having an ag- 
gregate polarization, and a third variety of the same mineral in dark bluish 
green rods, also composed of an aggregation of grains. This last variety of 
hornblende, together with microlites of sanidine, make up the ground- 
mass. The peculiarity of the rock is the great variety and beauty of the 
minerals implanted on the walls of the vesicles so abundant in it. 
These in the order of their age are : little crystals of sanidine, needles 
of amphibole, a crystallized manganese pyroxene, bunches of hair-like 
chocolate crystals that may be rutile or a titanium breislakite, pseudo- 
hexagonal, colorless, limpid crystals of sodalite, small hexagonal crystals 
of a mineral resembling microsommite, and orange scalenohedra of 
calcite. Miss Raisin ^ gives an account of the perlitic and spherulitic 
felsites of the Lleyn in Wales. These are devitrified lava flows, contain- 
ing concretionary nodules, and other forms produced by secretion. 
The larger spherulites are developed in certain layers. They appear 
to be the most durable portions of the rock, since the pressure that 
modified the matrix in which they lie has not affected them in the 
slightest degree. Some of the nodules are undoubtedly concretionary, 
and others are produced by the filling of vesicles. A few conclusions 
deduced from the facts observed relate to the mode of formation of 
spherulites and lithophysae in rhyolites and andesites. Hutchings ^ 
has discovered an ottrelite schist in Tiatagel, North Cornwall. 
The rock is a hard, lustrous state, composed of sericite, ottrelite and 
ilmenite. The ottrelite is in small flakes, frequently intergrown with 
sericite. Its pleochroism is A=yellowish green, B=blue, C=:green- 
ish yellow, and it is filled with inclusions of rutile. This latter mineral 
is also abundantly scattered through the rest of the rock. An interest- 
ing association of ilmenite and rutile is mentioned, but the manner of 
their combination could not be determined. McMahon' explains the 
polysynthetic structure of porphyritic quartz crystals in a felsite from 
near Delhi, India, by supposing the crystals to have formed at depths, 
and then to have been corroded by the magma after the rock reached 
* Geological Magazine, Feb., 1889, p. 74. 
* Quart. Jour. Geol. Soc, May, 1890. p 247. 
« Geol. Magazine, May, 1889, p. 214. 
1 Micro. Magazine, May, 1888, p 10, 
