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make up at least two-thirds of the whole rock. The ground mass between them is dense and of a yellow white color. Under the microscope the phenocrysts are seen to be highly cracked, and, on places where they are crowded, broken in pieces. Surrounded by larger spots of ground mass they show a crystallographic shape often somewhat rounded. The amphibolic mineral is a greenish brown common hornblende; the ground mass is microfelsitic.

Rhyolite from "Muerto Camp."—The rock presents in a dense light grayish brown ground mass phenocrysts of quartz, a glassy sanidine, showing a very distinct blue schillerization, and a somewhat altered biotite. Under the microscope the ground mass consist of microfelsite, forming in part felsospherulites.

A specimen of nepheline tephrite. Grayish brown fine crystalline rock with phenocrysts of biotite, black basaltic hornblende, and some grains of iron ore, probably ilmenite. Under the microscope the rock is very rich in basic components; a green pyroxene, a dark brown basaltic hornblende, and biotite, all in sharp crystals, are bedded in a ground mass made up of some lath-shaped plagioclase and allotriomorphous nepheline.

A series of rocks belonging under the head of syenite porphyries or quartzless porphyries, showing in a fine grained grayish green ground mass phenocrysts of orthoclase. Under the microscope there are, besides, some phenocrysts of green malacolite, and in some specimens irregular patches of brown hornblende. The ground mass is made up of short rectangular orthoclase laths, and some quartz squeezed between them. A specimen nearer to the contact shows a brown colored base with small needles of pyroxene and lath-shaped orthoclase. The latter rock has a hyalopilitic structure resembling that of the "Weisselbergite typus" in the group of augite porphyrites.

There are two specimens of pitchstones. One of them shows in a black glass of somewhat greasy lustre, phenocrysts of a glassy feldspar and quartz, and numerous spherulites of a brown color and 2 to 4 mm. in size. Under the microscope the rock is seen to be made up of a brown glass, with darker streaky spots filled with opaque globulites. The spherulites are pseudospherulites consisting of quartz and feldspar fibres. The other pitchstone is grayish green without microscopical phenocrysts, and looks like the well known green pitchstones of the Isle of Arran. It consists under the microscope of a yellow green entirely isotropic basis, with tender fibrous microlites of a pale green pyroxene (diopside) aggregated