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CHAP. VII.
UNSTRATIFIED ROCKS.
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C. Basis of hornblende or basalt, with imbedded minerals.
1. Amphibolite.—Basis of hornblende.
2. Basanite.—Basis of compact basalt, with disseminated minerals. (Basalt is viewed as a mixture of augite, olivine, and titaniferous iron.)
3. Trappite.—The basis hard and compact, holds mica, felspar, &c.
4. Melaphyre, or trap porphyry.—The basis is a black petrosiliceous hornblende (by other writers said to be augite), with crystals of felspar.
D. Basis of petrosilex coloured by hornblende.
1. Porphyry.—Basis a paste red or reddish, with crystals of felspar.
2. Ophite.—Basis a paste green, with crystals of felspar.
3. Amygdaloid.—Holds nodules similar (except in colour) to the basis.
4. Euphotide, or diallage rock.—Encloses crystals of diallage.
E. Basis of petrosilex, or compact felspar.
1. Eurite.—The disseminated minerals are mica, felspar, garnets, &c.
2. Leptenite.—Basis of granular felspar with mica and quartz.
3. Trachyte.—Encloses crystals of glassy felspar in a dull (earthy) basis.
F. Basis of claystone (an earthy or granular felspar).
1. Clay porphyry. The enclosed crystals are felspar.
2. Domite porphyry.—The enclosed crystals are mica.
G. Basis of pitchstone or obsidian.
Stigmite.—Encloses crystals of felspar (pitchstone porphyry of authors).
H. Base undetermined.
Many kinds of lava.
Gradations among Igneous Rocks.
The rocks of igneous origin exhibit among one another particular relations and gradations, which it is important to attend to before proceeding to discuss some other
